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  • 251. Balazs, Csaba
    et al.
    Li, Tong
    Savage, Chris
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. University of Utah, United States.
    White, Martin
    Interpreting the Fermi-LAT gamma ray excess in the simplified framework2015In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 92, no 12, article id 123520Article in journal (Refereed)
    Abstract [en]

    We test the plausibility of the hypothesis that the annihilation of a Majorana fermion dark matter particle via a scalar mediator explains the gamma ray excess from the Galactic center. Assuming that the mediator couples to all third generation fermions we calculate observables for dark matter abundance and scattering on nuclei, gamma, positron, and antiproton cosmic ray fluxes, radio emission from dark matter annihilation, and the effect of dark matter annihilations on the CMB. After discarding the controversial radio observation, we show that the dark matter model simultaneously fits the observed excesses in the cosmic gamma ray, the positron, and antiproton fluxes, while evading constraints from the CMB and direct detection. The experimental data are consistent with a dark matter (mediator) mass in the 10-100 (3-1000) GeV region and with weakly correlated couplings to bottom quarks and tau leptons with values of 10(-3) - 1 at the 68% credibility level.

  • 252.
    Bale, S. D.
    et al.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA.;Univ Calif Berkeley, Dept Phys, Berkeley, CA 94720 USA..
    Goetz, K.
    Univ Minnesota, Sch Phys & Astron, Minneapolis, MN 55455 USA..
    Harvey, P. R.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Turin, P.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Bonnell, J. W.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Dudok de Wit, T.
    CNRS, LPC2E, 3A Ave Rech Sci, Orleans, France..
    Ergun, R. E.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO USA..
    MacDowall, R. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Pulupa, M.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    André, Mats
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Bolton, M.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO USA..
    Bougeret, J. -L
    Bowen, T. A.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA.;Univ Calif Berkeley, Dept Phys, Berkeley, CA 94720 USA..
    Burgess, D.
    Queen Mary Univ London, Astron Unit, London, England..
    Cattell, C. A.
    Univ Minnesota, Sch Phys & Astron, Minneapolis, MN 55455 USA..
    Chandran, B. D. G.
    Univ New Hampshire, Dept Phys, Durham, NH 03824 USA..
    Chaston, C. C.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Chen, C. H. K.
    Imperial Coll, Dept Phys, London, England..
    Choi, M. K.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Connerney, J. E.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Cranmer, S.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO USA..
    Diaz-Aguado, M.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Donakowski, W.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Drake, J. F.
    Univ Maryland, Dept Phys, College Pk, MD 20742 USA..
    Farrell, W. M.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Fergeau, P.
    CNRS, LPC2E, 3A Ave Rech Sci, Orleans, France..
    Fermin, J.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Fischer, J.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Fox, N.
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA..
    Glaser, D.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Goldstein, M.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Gordon, D.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Hanson, E.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA.;Univ Calif Berkeley, Dept Phys, Berkeley, CA 94720 USA..
    Harris, S. E.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Hayes, L. M.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Hinze, J. J.
    Univ Minnesota, Sch Phys & Astron, Minneapolis, MN 55455 USA..
    Hollweg, J. V.
    Univ New Hampshire, Dept Phys, Durham, NH 03824 USA..
    Horbury, T. S.
    Imperial Coll, Dept Phys, London, England..
    Howard, R. A.
    Naval Res Lab, Washington, DC 20375 USA..
    Hoxie, V.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO USA..
    Jannet, G.
    CNRS, LPC2E, 3A Ave Rech Sci, Orleans, France..
    Karlsson, M.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO USA..
    Kasper, J. C.
    Univ Michigan, Ann Arbor, MI 48109 USA..
    Kellogg, P. J.
    Univ Minnesota, Sch Phys & Astron, Minneapolis, MN 55455 USA..
    Kien, M.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO USA..
    Klimchuk, J. A.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Krasnoselskikh, V. V.
    CNRS, LPC2E, 3A Ave Rech Sci, Orleans, France..
    Krucker, S.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Lynch, J. J.
    Univ Minnesota, Sch Phys & Astron, Minneapolis, MN 55455 USA..
    Maksimovic, M.
    Observ Paris, LESIA, Meudon, France..
    Malaspina, D. M.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO USA..
    Marker, S.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Martin, P.
    CNRS, LPC2E, 3A Ave Rech Sci, Orleans, France..
    Martinez-Oliveros, J.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    McCauley, J.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    McComas, D. J.
    Southwest Res Inst, San Antonio, TX USA..
    McDonald, T.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Meyer-Vernet, N.
    Observ Paris, LESIA, Meudon, France..
    Moncuquet, M.
    Observ Paris, LESIA, Meudon, France..
    Monson, S. J.
    Univ Minnesota, Sch Phys & Astron, Minneapolis, MN 55455 USA..
    Mozer, F. S.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Murphy, S. D.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Odom, J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Oliverson, R.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Olson, J.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Parker, E. N.
    Univ Chicago, Dept Astron & Astrophys, 5640 S Ellis Ave, Chicago, IL 60637 USA..
    Pankow, D.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Phan, T.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Quataert, E.
    Univ Calif Berkeley, Dept Astron, 601 Campbell Hall, Berkeley, CA 94720 USA..
    Quinn, T.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Ruplin, S. W.
    Praxis Studios, Brooklyn, NY USA..
    Salem, C.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Seitz, D.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Sheppard, D. A.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Siy, A.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Stevens, K.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO USA..
    Summers, D.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO USA..
    Szabo, A.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Timofeeva, M.
    CNRS, LPC2E, 3A Ave Rech Sci, Orleans, France..
    Vaivads, Andris
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Velli, M.
    UCLA, Earth Planetary & Space Sci, Los Angeles, CA USA..
    Yehle, A.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO USA..
    Werthimer, D.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Wygant, J. R.
    Univ Minnesota, Sch Phys & Astron, Minneapolis, MN 55455 USA..
    The FIELDS Instrument Suite for Solar Probe Plus2016In: Space Science Reviews, ISSN 0038-6308, E-ISSN 1572-9672, Vol. 204, no 1-4, p. 49-82Article, review/survey (Refereed)
    Abstract [en]

    NASA's Solar Probe Plus (SPP) mission will make the first in situ measurements of the solar corona and the birthplace of the solar wind. The FIELDS instrument suite on SPP will make direct measurements of electric and magnetic fields, the properties of in situ plasma waves, electron density and temperature profiles, and interplanetary radio emissions, amongst other things. Here, we describe the scientific objectives targeted by the SPP/FIELDS instrument, the instrument design itself, and the instrument concept of operations and planned data products.

  • 253. Band, D. L.
    et al.
    Axelsson, Magnus
    Ist Nazl Fis Nucl, Sez Pisa, Pisa, Italy .
    Battelino, Milan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    McGlynn, Sinéad
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Moretti, Elena
    University and INFN of Trieste.
    Ryde, Felix
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Yamazaki, R.
    et al.,
    PROSPECTS FOR GRB SCIENCE WITH THE FERMI LARGE AREA TELESCOPE2009In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 701, no 2, p. 1673-1694Article, review/survey (Refereed)
    Abstract [en]

    The Large Area Telescope (LAT) instrument on the Fermi mission will reveal the rich spectral and temporal gamma-ray burst (GRB) phenomena in the > 100 MeV band. The synergy with Fermi's Gamma-ray Burst Monitor detectors will link these observations to those in the well explored 10-1000 keV range; the addition of the > 100 MeV band observations will resolve theoretical uncertainties about burst emission in both the prompt and afterglow phases. Trigger algorithms will be applied to the LAT data both onboard the spacecraft and on the ground. The sensitivity of these triggers will differ because of the available computing resources onboard and on the ground. Here we present the LAT's burst detection methodologies and the instrument's GRB capabilities.

  • 254. Banerjee, D. P. K.
    et al.
    Varricatt, W. P.
    Mathew, Blesson
    Launila, Olli
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Ashok, N. M.
    THE A-X INFRARED BANDS OF ALUMINUM OXIDE IN STARS: SEARCH AND NEW DETECTIONS2012In: Astrophysical journal Letters, ISSN 2041-8205, Vol. 753, no 1, p. L20-Article in journal (Refereed)
    Abstract [en]

    We describe a search for the A-X infrared bands of AlO with a view toward better understanding the characteristics of this radical. These bands are infrequently encountered in astronomical sources but surprisingly were very prominent in the spectra of two well-known, novalike variables (V838 Mon and V4332 Sgr) thereby motivating us to explore the physical conditions necessary for their excitation. In this study, we present the detection of A-X bands in the spectra of 13 out of 17 stars, selected on the basis of their J-K colors as potential candidates for detection of these bands. The majority of the AlO detections are in asymptotic giant branch (AGB) stars, viz., nine OH/IR stars, two Mira variables, and two bright infrared sources. Our study shows that the A-X bands are fairly prevalent in sources with low temperature and O-rich environments. Interesting variation in the strength of the AlO bands in one of the sources (IRAS 18530+0817) is reported and the cause for this is examined. Possible applications of the present study are discussed in terms of the role of AlO in alumina dust formation, the scope for estimating the radioactive Al-26 content in AGB stars from the A-X bands, and providing possible targets for further mm/radio studies of AlO which has recently been discovered at millimeter wavelengths.

  • 255. Barbiellini, G.
    et al.
    Bastieri, D.
    Bechtol, K.
    Bellazzini, R.
    Blandford, R. D.
    Borgland, A. W.
    Bregeon, J.
    Bruel, P.
    Buehler, R.
    Buson, S.
    Caliandro, G. A.
    Cameron, R. A.
    Caraveo, P. A.
    Cavazzuti, E.
    Cecchi, C.
    Chaves, R. C. G.
    Chekhtman, A.
    Cheung, C. C.
    Chiang, J.
    Ciprini, S.
    Claus, R.
    Cohen-Tanugi, J.
    D'Ammando, F.
    de Angelis, A.
    Dermer, C. D.
    Digel, S. W.
    do Couto e Silva, E.
    Drell, P. S.
    Drlica-Wagner, A.
    Favuzzi, C.
    Focke, W. B.
    Franckowiak, A.
    Fukazawa, Y.
    Fusco, P.
    Gargano, F.
    Gasparrini, D.
    Germani, S.
    Giglietto, N.
    Giommi, P.
    Giordano, F.
    Giroletti, M.
    Glanzman, T.
    Godfrey, G.
    Grenier, I. A.
    Grove, J. E.
    Guiriec, S.
    Hadasch, D.
    Hayashida, M.
    Hays, E.
    Hughes, R. E.
    Jackson, Miranda S.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Jogler, T.
    Knoedlseder, J.
    Kuss, M.
    Lande, J.
    Larsson, S.
    Longo, F.
    Loparco, F.
    Lovellette, M. N.
    Lubrano, P.
    Mazziotta, M. N.
    Mehault, J.
    Michelson, P. F.
    Mizuno, T.
    Moiseev, A. A.
    Monte, C.
    Monzani, M. E.
    Morselli, A.
    Moskalenko, I. V.
    Murgia, S.
    Nemmen, R.
    Nuss, E.
    Ohsugi, T.
    Omodei, N.
    Orienti, M.
    Orlando, E.
    Paneque, D.
    Perkins, J. S.
    Piron, F.
    Pivato, G.
    Prokhorov, D.
    Raino, S.
    Razzano, M.
    Razzaque, S.
    Reimer, A.
    Reimer, O.
    Ritz, S.
    Romoli, C.
    Sanchez-Conde, M.
    Sanchez, D. A.
    Sgro, C.
    Siskind, E. J.
    Spandre, G.
    Spinelli, P.
    Takahashi, H.
    Tanaka, T.
    Tibaldo, L.
    Tinivella, M.
    Tosti, G.
    Troja, E.
    Usher, T. L.
    Vandenbroucke, J.
    Vasileiou, V.
    Vianello, G.
    Vitale, V.
    Waite, A. P.
    Winer, B. L.
    Wood, K. S.
    Yang, Z.
    Fermi large area telescope observations of blazar 3C 279 occultations by the sun2014In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 784, no 2, p. 118-Article in journal (Refereed)
    Abstract [en]

    Observations of occultations of bright. gamma-ray sources by the Sun may reveal predicted pair halos around blazars and/or new physics, such as, e.g., hypothetical light dark matter particles-axions. We use Fermi Gamma-Ray Space Telescope (Fermi) data to analyze four occultations of blazar 3C 279 by the Sun on October 8 each year from 2008 to 2011. A combined analysis of the observations of these occultations allows a point-like source at the position of 3C 279 to be detected with significance of approximate to 3 sigma, but does not reveal any significant excess over the flux expected from the quiescent Sun. The likelihood ratio test rules out complete transparency of the Sun to the blazar. gamma-ray emission at a 3s confidence level.

  • 256.
    Barekat, Atefeh
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Department of Astronomy, AlbaNova University Center, Stockholm University, Stockholm, Sweden .
    Brandenburg, A.
    Near-polytropic stellar simulations with a radiative surface2014In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 571, p. A68-Article in journal (Refereed)
    Abstract [en]

    Context. Studies of solar and stellar convection often employ simple polytropic setups using the diffusion approximation instead of solving the proper radiative transfer equation. This allows one to control separately the polytropic index of the hydrostatic reference solution, the temperature contrast between top and bottom, and the Rayleigh and Peclet numbers. Aims. Here we extend such studies by including radiative transfer in the gray approximation using a Kramers-like opacity with freely adjustable coefficients. We study the properties of such models and compare them with results from the diffusion approximation. Methods. We use the Pencil code, which is a high-order finite difference code where radiation is treated using the method of long characteristics. The source function is given by the Planck function. The opacity is written as kappa = kappa(0)rho T-a(b), where a = 1 in most cases, b is varied from -3.5 to +5, and kappa(0) is varied by four orders of magnitude. We adopt a perfect monatomic gas. We consider sets of one-dimensional models and perform a comparison with the diffusion approximation in one-and two-dimensional models. Results. Except for the case where b = 5, we find one-dimensional hydrostatic equilibria with a nearly polytropic stratification and a polytropic index close to n = (3 -b)/(1 + a), covering both convectively stable (n > 3/2) and unstable (n < 3/2) cases. For b = 3 and a = -1, the value of n is undefined a priori and the actual value of n depends then on the depth of the domain. For large values of kappa(0), the thermal adjustment time becomes long, the Peclet and Rayleigh numbers become large, and the temperature contrast increases and is thus no longer an independent input parameter, unless the Stefan-Boltzmann constant is considered adjustable. Conclusions. Proper radiative transfer with Kramers-like opacities provides a useful tool for studying stratified layers with a radiative surface in ways that are more physical than what is possible with polytropic models using the diffusion approximation.

  • 257.
    Basak, Rupal
    et al.
    KTH, School of Engineering Sciences (SCI), Physics. Polish Academy of Sciences, Poland.
    Zdziarski, Andrzej A.
    Parker, Michael
    Islam, Nazma
    Analysis of NuSTAR and Suzaku observations of Cyg X-1 in the hard state: evidence for a truncated disc geometry2017In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 472, no 4, p. 4220-4232Article in journal (Refereed)
    Abstract [en]

    The geometry of the accretion flow in black hole X-ray binaries in the hard state, in particular the position of the disc inner edge, has been a subject of intense debate in recent years. We address this issue by performing a spectral study of simultaneous observations of Cyg X-1 in the hard state by NuSTAR and Suzaku. The same data were analysed before, and modelled by a lamppost containing hybrid electrons and located very close to the horizon, whose emission was incident on a surrounding disc extending almost to the innermost stable circular orbit. We re-analyse the incident continuum model and show that it suffers from the lack of physical self-consistency. Still, the good fit to the data provided by this model indicates that the real continuum has a similar shape. We find it features a strong soft X-ray excess below a few keV, which we model as a soft thermal-Comptonization component, in addition to the main hard thermal-Compton component. This continuum model with reflection of both components yields the overall lowest chi(2) and has a geometry with a hot inner accretion flow and a disc truncated at similar or equal to 13-20 gravitational radii. On the other hand, we have also found spectral solution with a lamppost at a large height and a disc that can extend to the innermost stable circular orbit, though somewhat statistically worse. Overall, we find that the fitted truncation radius depends on the assumed continuum and geometry.

  • 258. Battelino, M.
    et al.
    Ryde, Felix
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Omodei, N.
    Longo, F.
    Simulation of Prompt Emission from GRBs with a Photospheric Component and its Detectability by GLAST2007In: Gamma-Ray Bursts: Prospects for GLAST / [ed] Axelsson and Ryde, 2007, Vol. 906, p. 28-39Conference paper (Other academic)
    Abstract [en]

    The prompt emission from gamma-ray bursts (GRBs) still requires a physical explanation. Studies of time-resolved GRB spectra, observed in the keV-MeV range, show that a hybrid model consisting of two components, a photospheric and a non-thermal component, in many cases fits bright, single-pulsed bursts as well as, and in some instances even better than, the Band function. With an energy coverage from 8 keV up to 300 GeV, GLAST will give us an unprecedented opportunity to further investigate the nature of the prompt emission. In particular, it will give us the possibility to determine whether a photospheric component is the determining feature of the spectrum or not. Here we present a short study of the ability of GLAST to detect such a photospheric component in the sub-MeV range for typical bursts, using simulation tools developed within the GLAST science collaboration.

  • 259.
    Baum, Sebastian
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Visinelli, Luca
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Freese, Katherine
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Stengel, Patrick
    Dark matter capture, subdominant WIMPs, and neutrino observatories2017In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 95, no 4, article id 043007Article in journal (Refereed)
    Abstract [en]

    Weakly interacting massive particles (WIMPs), which are among the best motivated dark matter (DM) candidates, could make up all or only a fraction of the total DM budget. We consider a scenario in which WIMPs are a subdominant DM component; such a scenario would affect both current direct and indirect bounds on the WIMP-nucleon scattering cross section. In this paper we focus on indirect searches for the neutrino flux produced by annihilation of subdominant WIMPs captured by the Sun or the Earth via either spin-dependent or spin-independent scattering. We derive the annihilation rate and the expected neutrino flux at neutrino observatories. In our computation, we include an updated chemical composition of the Earth with respect to the previous literature, leading to an increase of the Earth's capture rate for spin-dependent scattering by a factor of 3. Results are compared with current bounds from Super-Kamiokande and IceCube. We discuss the scaling of bounds from both direct and indirect detection methods with the WIMP abundance.

  • 260. Bavarsad, Ehsan
    et al.
    Stahl, Clement
    KTH.
    Xue, She-Sheng
    Scalar current of created pairs by Schwinger mechanism in de Sitter spacetime2016In: PHYSICAL REVIEW D, ISSN 2470-0010, Vol. 94, no 10, article id 104011Article in journal (Refereed)
    Abstract [en]

    We consider a charged scalar field in a D-dimensional de Sitter spacetime and investigate pair creation by a Schwinger mechanism in a constant electric field background. Using a semiclassical approximation the current of the created pairs has been estimated. We find that the semiclassical current of the created pairs in the strong electric field limit responds as E-D/2. Going further but restricting to D = 3 dimensional de Sitter spacetime, the quantum expectation value of the spacelike component of the induced current has been computed in the in-vacuum state by applying an adiabatic subtraction scheme. We find that, in the strong electric field limit, the current responds as E-3/2. In the weak electric field limit the current has a linear response in E and an inverse dependence on the mass of the scalar field. In the case of a massless scalar field, the current varies with E-1 which leads to a phenomenon of infrared hyperconductivity. A new relation between infrared hyperconductivity, tachyons, and conformality is discussed, and a scheme to avoid an infrared hyperconductivity regime is proposed. In D dimension, we eventually presented some first estimates of the backreaction of the Schwinger pairs to the gravitational field, and we find a decrease of the Hubble constant due to the pair creation.

  • 261. Baym, Gordon
    et al.
    Patil, Subodh P.
    Pethick, Christopher
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. University of Copenhagen, Denmark.
    Damping of gravitational waves by matter2017In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 96, no 8, article id 084033Article in journal (Refereed)
    Abstract [en]

    We develop a unified description, via the Boltzmann equation, of damping of gravitational waves by matter, incorporating collisions. We identify two physically distinct damping mechanisms-collisional and Landau damping. We first consider damping in flat spacetime, and then generalize the results to allow for cosmological expansion. In the first regime, maximal collisional damping of a gravitational wave, independent of the details of the collisions in the matter is, as we show, significant only when its wavelength is comparable to the size of the horizon. Thus damping by intergalactic or interstellar matter for all but primordial gravitational radiation can be neglected. Although collisions in matter lead to a shear viscosity, they also act to erase anisotropic stresses, thus suppressing the damping of gravitational waves. Damping of primordial gravitational waves remains possible. We generalize Weinberg's calculation of gravitational wave damping, now including collisions and particles of finite mass, and interpret the collisionless limit in terms of Landau damping. While Landau damping of gravitational waves cannot occur in flat spacetime, the expansion of the universe allows such damping by spreading the frequency of a gravitational wave of given wave vector.

  • 262. Bazilevskaya, G. A.
    et al.
    Mayorov, A. G.
    Malakhov, V. V.
    Mikhailov, V. V.
    Adriani,
    Barbarino, G. C.
    Bellotti, R.
    Boezio, M.
    Bogomolov, E. A.
    Bonechi, L.
    Bongi, M.
    Bonvicini, V.
    Bottai, S.
    Bruno, A.
    Cafagna, F.
    Campana, D.
    Carbone, R.
    Carlson, Per
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Casolino, M.
    Castellini, G.
    Consiglio, L.
    De Pascale, M. P.
    De Santis, C.
    De Simone, N.
    Di Felice, V.
    Galper, A. M.
    Gillard, William
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Jerse, G.
    Karelin, A. V.
    Koldashov, S. V.
    Krutkov, S. Y.
    Kvashnin, A. N.
    Leonov, A.
    Marcelli, L.
    Menn, W.
    Mocchiutti, E.
    Monaco, A.
    Mori, N.
    Osteria, G.
    Palma, F.
    Papini, P.
    Pearce, Mark
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Picozza, P.
    Pizzolotto, C.
    Ricci, M.
    Ricciarini, S. B.
    Sarkar, R.
    Rossetto, Laura
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Simon, M.
    Sparvoli, R.
    Spillantini, P.
    Stozhkov, Y. I.
    Vacchi, A.
    Vannuccini, E.
    Vasilyev, G.
    Voronov, S. A.
    Wu, J.
    Yurkin, Y. T.
    Zampa, G.
    Zampa, N.
    Zverev, V. G.
    Solar energetic particle events in 2006-2012 in the PAMELA experiment data2013In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 409, no 1Article in journal (Refereed)
    Abstract [en]

    The PAMELA magnetic spectrometer launched in June 2006 has observed the last strong energetic solar particle event of the 23rd solar cycle in December 2006. Subsequent long minimum of solar activity and weak development of the 24th solar cycle led to a deficit in the solar energetic particle events on the Earth orbit. As a result, only few events with protons accelerated above 100 MeV occurred in 2010-2012. The paper gives the preliminary results on energetic solar particles in the beginning of the 24th solar circle as measured with the PAMELA instrument.

  • 263.
    Begue, Dereli
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Boer, M.
    Gendre, B.
    Amati, L.
    Dichiara, S.
    Orange, N. B.
    A Study of GRBs with Low-luminosity Afterglows2017In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 850, no 2, article id 117Article in journal (Refereed)
    Abstract [en]

    We present a sample composed of the 41 faintest X-ray afterglows of the population of long gamma-ray bursts (lGRBs) with known redshift. We study their intrinsic properties (spectral index, decay index, distance, luminosity, isotropic radiated energy, and peak energy) and their luminosity distribution functions to assess whether they belong to the same population as the brighter afterglow events. We find that these events belong to a population of nearby ones, different from the general population of lGRBs. In addition, these events are faint during their prompt phase, and include the few possible outliers of the Amati relation.

  • 264.
    Begué, Damien
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Oskar Klein Centre for Cosmoparticle Physics, AlbaNova, Stockholm, Sweden.
    Poynting flux dominated jets challenged by their photospheric emission2015In: SECOND ICRANET CESAR LATTES MEETING: SUPERNOVAE, NEUTRON STARS AND BLACK HOLES, American Institute of Physics (AIP), 2015, article id UNSP 070003Conference paper (Refereed)
    Abstract [en]

    One of the key open question for gamma-ray bursts (GRBs) jets, is the magnetization of the outflow. Here we consider the photospheric emission of Poynting flux dominated outflows, when the dynamics is mediated by magnetic reconnection. We show that thermal three-particle processes, responsible for the thermalization of the plasma, become inefficient far below the photosphere. Conservation of the total photon number above this radius, combined with Compton scattering below the photosphere enforces kinetic equilibrium between electrons and photons. This, in turn, leads to an increase in the observed photon temperature, which reaches greater than or similar to 8 MeV (observed energy) when decoupling the plasma at the photosphere. This result is weakly dependent on the free model parameters. The predicted peak energy is more than an order of magnitude higher than the observed peak energy of most GRBs, which puts strong constraints on the magnetization of these outflows.

  • 265. Belov, A.
    et al.
    Klimov, P.
    Capel, Francesca
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Bertaina, M.
    Fausti, F.
    Mignone, M.
    Mini-EUSO photodetector module data processing system2017In: Proceedings of Science, Sissa Medialab Srl , 2017Conference paper (Refereed)
    Abstract [en]

    Mini-EUSO is a UV telescope which is developed by the JEM-EUSO collaboration to be placed on board the International Space Station (ISS) to carry out measurements of UV atmosphere airglow and transient luminous events (TLEs) in a wide field of view (>40°) and high temporal resolution (2.5 μs). Mini-EUSO is developed to be a space qualified pathfinder of future JEMEUSO missions. Optical system of the detector consists of two Fresnel lenses of 25 cm diameter. The focal surface is composed of 36 produced by Hamamatsu multi anode photomultiplier tubes (MAPMT), each with 64 pixels. The output signal of all 2304 pixels is digitized and then passed to the data processing system that was specially developed for the experiment and is being discussed in this work. Data processing system is based on produced by Xilinx ZYNQ chip that contains both programmable part (FPGA) and processor. Such combination in a single chip gives a big advantage for processing a data gathered from focal surface including fast multi-level trigger algorithms, data buffering, MAPMTs high voltage control algorithms, interfaces with front-end electronics and with the separate central processor unit for data storage. The multi-level trigger was developed for the mini-EUSO instrument to perform measurements in various time scales (temporal resolutions 2.5 μs, 320 μs, 40 ms). This trigger was successfully implemented and tested. 

  • 266. Beniwal, Ankit
    et al.
    Rajec, Filip
    Savage, Christopher
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Scott, Pat
    Weniger, Christoph
    White, Martin
    Williams, Anthony G.
    Combined analysis of effective Higgs portal dark matter models2016In: Physical Review D, ISSN 2470-0010, Vol. 93, no 11, article id 115016Article in journal (Refereed)
    Abstract [en]

    We combine and extend the analyses of effective scalar, vector, Majorana and Dirac fermion Higgs portal models of dark matter (DM), in which DM couples to the Standard Model (SM) Higgs boson via an operator of the form (ODMHH)-H-dagger. For the fermion models, we take an admixture of scalar.. and pseudoscalar (psi) over bari gamma(5)psi interaction terms. For each model, we apply constraints on the parameter space based on the Planck measured DM relic density and the LHC limits on the Higgs invisible branching ratio. For the first time, we perform a consistent study of the indirect detection prospects for these models based on the WMAP7/Planck observations of the cosmic microwave background, a combined analysis of 15 dwarf spheroidal galaxies by Fermi-LAT and the upcoming Cherenkov Telescope Array (CTA). We also perform a correct treatment of the momentum-dependent direct search cross section that arises from the pseudoscalar interaction term in the fermionic DM theories. We find, in line with previous studies, that current and future direct search experiments such as LUX and XENON1T can exclude much of the parameter space, and we demonstrate that a joint observation in both indirect and direct searches is possible for high mass weakly interacting massive particles. In the case of a pure pseudoscalar interaction of a fermionic DM candidate, future gamma-ray searches are the only class of experiment capable of probing the high mass range of the theory.

  • 267.
    Beresnyak, Andrey
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    On the Parallel Spectrum and Anisotropy in MHD Turbulence2015In: NUMERICAL MODELING OF SPACE PLASMA FLOWS: ASTRONUM-2014 / [ed] Pogorelov, NV Audit, E Zank, GP, ASTRONOMICAL SOC PACIFIC , 2015, Vol. 498, p. 3-9Conference paper (Refereed)
    Abstract [en]

    MHD turbulence is anisotropic and shows different spectral slopes measured parallel and perpendicular to the local magnetic field. Solar wind observations typically show a k(-2) power law scaling, which is much steeper than the perpendicular scaling, typically k(-5/3). In this paper I show that this scaling could be interpreted as the Lagrangian frequency spectrum omega(-2) of the evolving Afven perturbations. As Alfven waves propagate exactly along magnetic field lines, the measurement of the spectrum along the field line is equivalent to the measurement of the frequency spectrum. This was tested using high-resolution simulations of MHD turbulence, e.g., I verified that the cutoff of the parallel spectrum scales as Kolmogorov timescale, not lengthscale.

  • 268.
    Beresnyak, Andrey
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Los Alamos National Laboratory, United States .
    On the parallel spectrum in magnetohydrodynamic turbulence2015In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 801, no 1, article id L9Article in journal (Refereed)
    Abstract [en]

    Anisotropy of MHD turbulence has been studied extensively for many years, most prominently by measurements in the solar wind and high-resolution simulations. The spectrum parallel to the local magnetic field was observed to be steeper than the perpendicular spectrum, typically k(-2), consistent with the widely accepted Goldreich & Sridhar model. In this Letter, I looked deeper into the nature of the relation between parallel and perpendicular spectra and argue that this k(-2) scaling has the same origin as the omega(-2) scaling of the Lagrangian frequency spectrum in strong hydrodynamic turbulence. This follows from the fact that Alfven waves propagate along magnetic field lines. It has now became clear that the observed anisotropy can be argued without invocation of the "critical balance" argument and is more robust that was previously thought. The relation between parallel (Lagrangian) and perpendicular (Eulerian) spectra is an inevitable consequence of strong turbulence of Alfven waves, rather than a conjecture based on the uncertainty relation. I tested this using high-resolution simulations of MHD turbulence, in particular, I verified that the cutoff of the parallel spectrum scales as a Kolmogorov timescale, not lengthscale.

  • 269.
    Beresnyak, Andrey
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Los Alamos National Laboratory, United States.
    THE FLOW AROUND A COSMIC STRING. I. HYDRODYNAMIC SOLUTION2015In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 804, no 2, article id 121Article in journal (Refereed)
    Abstract [en]

    Cosmic strings are linear topological defects which are hypothesized to be produced during inflation. Most searches for strings have relied on the string's lensing of background galaxies or the cosmic microwave background. In this paper, I obtained a solution for the supersonic flow of collisional gas past the cosmic string which has two planar shocks with a shock compression ratio that depends on the angle defect of the string and its speed. The shocks result in the compression and heating of the gas and, given favorable conditions, particle acceleration. Gas heating and over-density in an unusual wedge shape can be detected by observing the HI line at high redshifts. Particle acceleration can occur in the present-day universe when the string crosses the hot gas contained in galaxy clusters and, since the consequences of such a collision persist for cosmological timescales, could be located by looking at unusual large-scale radio sources situated on a single spatial plane.

  • 270.
    Beresnyak, Andrey
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm University, Sweden.
    Miniati, Francesco
    TURBULENT AMPLIFICATION AND STRUCTURE OF THE INTRACLUSTER MAGNETIC FIELD2016In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 817, no 2, article id 127Article in journal (Refereed)
    Abstract [en]

    We compare DNS calculations of homogeneous isotropic turbulence with the statistical properties of intracluster turbulence from the Matryoshka Run and find remarkable similarities between their inertial ranges. This allowed us to use the time-dependent statistical properties of intracluster turbulence to evaluate dynamo action in the intracluster medium, based on earlier results from a numerically resolved nonlinear magneto- hydrodynamic turbulent dynamo. We argue that this approach is necessary (a) to properly normalize dynamo action to the available intracluster turbulent energy and (b) to overcome the limitations of low Re affecting current numerical models of the intracluster medium. We find that while the properties of intracluster magnetic field are largely insensitive to the value and origin of the seed field, the resulting values for the Alfven speed and the outer scale of the magnetic field are consistent with current observational estimates, basically confirming the idea that the magnetic field in today's galaxy clusters is a record of its past turbulent activity.

  • 271. Bergenius, S.
    et al.
    Pearce, Mark
    KTH, Superseded Departments, Physics.
    Proton irradiation response of CsI(Tl) crystals for the GLAST calorimeter2004Conference paper (Other academic)
  • 272. Bergström, L.
    et al.
    Edlund, C.
    KTH, School of Computer Science and Communication (CSC), Numerical Analysis and Computer Science, NADA. Stockholm University, Sweden.
    Fairbairn, M.
    Järemo, Anna Karin
    KTH, School of Computer Science and Communication (CSC), Numerical Analysis and Computer Science, NADA.
    Kreiss, Gunilla
    KTH, School of Computer Science and Communication (CSC), Numerical Analysis and Computer Science, NADA.
    Pieri, L.
    Signals of WIMP annihilation into electrons at the galactic center2005In: Proceedings of the 29th International Cosmic Ray Conference, Vol 4: OG 2.1, 2.2 & 2.3, Tata Institute of Fundamental Research , 2005, p. 57-60Conference paper (Refereed)
    Abstract [en]

    Photons from the annihilation of dark matter in the center of our Galaxy are expected to provide a promising way to find out the nature and distribution of the dark matter itself. These photons can be either produced directly and/or through successive decays of annihilation products, or radiated from electrons and positrons. This ends up in a multi-wavelength production of photons whose expected intensity can be compared to observational data. Assuming that the Lightest Supersymmetric Particle makes the dark matter, we derive the expected photon signal from a given dark matter model and compare it with present available data.

  • 273. Bern, Zvi
    et al.
    Davies, Scott
    Di Vecchia, Paolo
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. University of Copenhagen, Denmark .
    Nohle, Josh
    Low-energy behavior of gluons and gravitons from gauge invariance2014In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 90, no 8, p. 084035-Article in journal (Refereed)
    Abstract [en]

    We show that at tree level, on-shell gauge invariance can be used to fully determine the first subleading soft-gluon behavior and the first two subleading soft-graviton behaviors. Our proofs of the behaviors for n-gluon and n-graviton tree amplitudes are valid in D dimensions and are similar to Low's proof of universality of the first subleading behavior of photons. In contrast to photons coupling to massive particles, in four dimensions the soft behaviors of gluons and gravitons are corrected by loop effects. We comment on how such corrections arise from this perspective. We also show that loop corrections in graviton amplitudes arising from scalar loops appear only at the second soft subleading order. This case is particularly transparent because it is not entangled with graviton infrared singularities. Our result suggests that if we set aside the issue of infrared singularities, soft-graviton Ward identities of extended Bondi, van der Burg, Metzner and Sachs symmetry are not anomalous through the first subleading order.

  • 274. Bern, Zvi
    et al.
    Davies, Scott
    Nohle, Josh
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm University, Sweden.
    Double-copy constructions and unitarity cuts2016In: PHYSICAL REVIEW D, ISSN 2470-0010, Vol. 93, no 10, article id 105015Article in journal (Refereed)
    Abstract [en]

    The duality between color and kinematics enables the construction of multiloop gravity integrands directly from corresponding gauge-theory integrands. This has led to new nontrivial insights into the structure of gravity theories, including the discovery of enhanced ultraviolet cancellations. To continue to gain deeper understandings and probe these new properties, it is crucial to further improve techniques for constructing multiloop gravity integrands. In this paper, we show by example how one can alleviate difficulties encountered at the multiloop level by relaxing the color-kinematics duality conditions to hold manifestly only on unitarity cuts instead of globally on loop integrands. As an example, we use a minimal Ansatz to construct an integrand for the two-loop four-point nonsupersymmetric pure Yang-Mills amplitude in D dimensions that is compatible with these relaxed color-kinematics duality constraints. We then immediately obtain a corresponding gravity integrand through the double-copy procedure. Comments on ultraviolet divergences are also included.

  • 275. Berthomier, M.
    et al.
    Fazakerley, A. N.
    Forsyth, C.
    Pottelette, R.
    Alexandrova, O.
    Anastasiadis, A.
    Aruliah, A.
    Blelly, P. -L
    Briand, C.
    Bruno, R.
    Canu, P.
    Cecconi, B.
    Chust, T.
    Daglis, I.
    Davies, J.
    Dunlop, M.
    Fontaine, D.
    Genot, V.
    Gustavsson, B.
    Haerendel, G.
    Hamrin, M.
    Hapgood, M.
    Hess, S.
    Kataria, D.
    Kauristie, K.
    Kemble, S.
    Khotyaintsev, Y.
    Koskinen, H.
    Lamy, L.
    Lanchester, B.
    Louarn, P.
    Lucek, E.
    Lundin, R.
    Maksimovic, M.
    Manninen, J.
    Marchaudon, A.
    Marghitu, O.
    Marklund, Göran T.
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Milan, S.
    Moen, J.
    Mottez, F.
    Nilsson, H.
    Ostgaard, N.
    Owen, C. J.
    Parrot, M.
    Pedersen, A.
    Perry, C.
    Pincon, J. -L
    Pitout, F.
    Pulkkinen, T.
    Rae, I. J.
    Rezeau, L.
    Roux, A.
    Sandahl, I.
    Sandberg, I.
    Turunen, E.
    Vogt, J.
    Walsh, A.
    Watt, C. E. J.
    Wild, J. A.
    Yamauchi, M.
    Zarka, P.
    Zouganelis, I.
    Alfvén: magnetosphere-ionosphere connection explorers2012In: Experimental astronomy (Print), ISSN 0922-6435, E-ISSN 1572-9508, Vol. 33, no 2-3, p. 445-489Article in journal (Refereed)
    Abstract [en]

    The aurorae are dynamic, luminous displays that grace the night skies of Earth's high latitude regions. The solar wind emanating from the Sun is their ultimate energy source, but the chain of plasma physical processes leading to auroral displays is complex. The special conditions at the interface between the solar wind-driven magnetosphere and the ionospheric environment at the top of Earth's atmosphere play a central role. In this Auroral Acceleration Region (AAR) persistent electric fields directed along the magnetic field accelerate magnetospheric electrons to the high energies needed to excite luminosity when they hit the atmosphere. The "ideal magnetohydrodynamics" description of space plasmas which is useful in much of the magnetosphere cannot be used to understand the AAR. The AAR has been studied by a small number of single spacecraft missions which revealed an environment rich in wave-particle interactions, plasma turbulence, and nonlinear acceleration processes, acting on a variety of spatio-temporal scales. The pioneering 4-spacecraft Cluster magnetospheric research mission is now fortuitously visiting the AAR, but its particle instruments are too slow to allow resolve many of the key plasma physics phenomena. The Alfv,n concept is designed specifically to take the next step in studying the aurora, by making the crucial high-time resolution, multi-scale measurements in the AAR, needed to address the key science questions of auroral plasma physics. The new knowledge that the mission will produce will find application in studies of the Sun, the processes that accelerate the solar wind and that produce aurora on other planets.

  • 276. Bertolini, Stefano
    et al.
    Di Luzio, Luca
    Malinsky, Michal
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Intermediate mass scales in the nonsupersymmetric SO(10) grand unification: A reappraisal2009In: PHYSICAL REVIEW D, ISSN 1550-7998, Vol. 80, no 1, p. 015013-Article in journal (Refereed)
    Abstract [en]

    The constraints of gauge unification on intermediate mass scales in nonsupersymmetric SO(10) scenarios are systematically discussed. With respect to the existing reference studies we include the U(1) gauge mixing renormalization at the one- and two-loop level, and reassess the two-loop beta coefficients. We evaluate the effects of additional Higgs multiplets required at intermediate stages by a realistic mass spectrum and update the discussion to the present day data. On the basis of the obtained results, SO(10) breaking patterns with up to two intermediate mass scales are discussed for potential relevance and model predictivity.

  • 277.
    Bettoni, Dario
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, Sweden.
    Ezquiaga, Jose Maria
    Hinterbichler, Kurt
    Zumalacarregui, Miguel
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, Sweden; Univ Calif Berkeley, USA.
    Speed of gravitational waves and the fate of scalar-tensor gravity2017In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 95, no 8, article id 084029Article in journal (Refereed)
    Abstract [en]

    The direct detection of gravitational waves (GWs) is an invaluable new tool to probe gravity and the nature of cosmic acceleration. A large class of scalar-tensor theories predicts that GWs propagate with velocity different than the speed of light, a difference that can be O(1) for many models of dark energy. We determine the conditions behind the anomalous GW speed, namely, that the scalar field spontaneously breaks Lorentz invariance and couples to the metric perturbations via the Weyl tensor. If these conditions are realized in nature, the delay between GW and electromagnetic signals from distant events will run beyond human time scales, making it impossible to measure the speed of GWs using neutron star mergers or other violent events. We present a robust strategy to exclude or confirm an anomalous speed of GWs using eclipsing binary systems, the electromagnetic phase of which can be exquisitely determined. The white dwarf binary J0651 + 2844 is a known example of such a system that can be used to probe deviations in the GW speed as small as cg/ c - 1 greater than or similar to 2 x 10(-12) when LISA comes online. This test will either eliminate many contender models for cosmic acceleration or wreck a fundamental pillar of general relativity.

  • 278.
    Bhat, P.
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Brandenburg, Axel
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Hydraulic effects in a radiative atmosphere with ionization2016In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 587, article id A90Article in journal (Refereed)
    Abstract [en]

    Context. In his 1978 paper, Eugene Parker postulated the need for hydraulic downward motion to explain magnetic flux concentrations at the solar surface. A similar process has also recently been seen in simplified (e.g., isothermal) models of flux concentrations from the negative effective magnetic pressure instability (NEMPI). Aims. We study the effects of partial ionization near the radiative surface on the formation of these magnetic flux concentrations. Methods. We first obtain one-dimensional (1D) equilibrium solutions using either a Kramers-like opacity or the H-opacity. The resulting atmospheres are then used as initial conditions in two-dimensional (2D) models where flows are driven by an imposed gradient force that resembles a localized negative pressure in the form of a blob. To isolate the effects of partial ionization and radiation, we ignore turbulence and convection. Results. Because of partial ionization, an unstable stratification always forms near the surface. We show that the extrema in the specific entropy profiles correspond to the extrema in the degree of ionization. In the 2D models without partial ionization, strong flux concentrations form just above the height where the blob is placed. Interestingly, in models with partial ionization, such flux concentrations always form at the surface well above the blob. This is due to the corresponding negative gradient in specific entropy. Owing to the absence of turbulence, the downflows reach transonic speeds. Conclusions. We demonstrate that, together with density stratification, the imposed source of negative pressure drives the formation of flux concentrations. We find that the inclusion of partial ionization affects the entropy profile dramatically, causing strong flux concentrations to form closer to the surface. We speculate that turbulence effects are needed to limit the strength of flux concentrations and homogenize the specific entropy to a stratification that is close to marginal.

  • 279. Bhat, P. Narayana
    et al.
    Meegan, Charles A.
    von Kienlin, Andreas
    Paciesas, William S.
    Briggs, Michael S.
    Burgess, J. Michael
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Burns, Eric
    Chaplin, Vandiver
    Cleveland, William H.
    Collazzi, Andrew C.
    Connaughton, Valerie
    Diekmann, Anne M.
    Fitzpatrick, Gerard
    Gibby, Melissa H.
    Giles, Misty M.
    Goldstein, Adam M.
    Greiner, Jochen
    Jenke, Peter A.
    Kippen, R. Marc
    Kouveliotou, Chryssa
    Mailyan, Bagrat
    McBreen, Sheila
    Pelassa, Veronique
    Preece, Robert D.
    Roberts, Oliver J.
    Sparke, Linda S.
    Stanbro, Matthew
    Veres, Peter
    Wilson-Hodge, Colleen A.
    Xiong, Shaolin
    Younes, George
    Yu, Hoi-Fung
    Zhang, Binbin
    THE THIRD FERMI GBM GAMMA-RAY BURST CATALOG: THE FIRST SIX YEARS2016In: Astrophysical Journal Supplement Series, ISSN 0067-0049, E-ISSN 1538-4365, Vol. 223, no 2, article id 28Article in journal (Refereed)
    Abstract [en]

    Since its launch in 2008, the Fermi Gamma-ray Burst Monitor (GBM) has triggered and located on average approximately two.-ray bursts (GRBs) every three days. Here, we present the third of a series of catalogs of GRBs detected by GBM, extending the second catalog by two more years through the middle of 2014 July. The resulting list includes 1405 triggers identified as GRBs. The intention of the GBM GRB catalog is to provide information to the community on the most important observables of the GBM-detected GRBs. For each GRB, the location and main characteristics of the prompt emission, the duration, peak flux, and fluence are derived. The latter two quantities are calculated for the 50-300 keV energy band where the maximum energy release of GRBs in the instrument reference system is observed, and also for a broader energy band from 10 to 1000 keV, exploiting the full energy range of GBM's low-energy [NaI[Tl)] detectors. Using statistical methods to assess clustering, we find that the hardness and duration of GRBs are better fit by a two-component model with short-hard and long-soft bursts than by a model with three components. Furthermore, information is provided on the settings and modifications of the triggering criteria and exceptional operational conditions during years five and six in the mission. This third catalog is an official product of the Fermi GBM science team, and the data files containing the complete results are available from the High-Energy Astrophysics Science Archive Research Center.

  • 280. Bi, Huan-Yu
    et al.
    Wu, Xing-Gang
    Ma, Yang
    Ma, Hong-Hao
    Brodsky, Stanley J.
    Mojaza, Matin
    Degeneracy relations in QCD and the equivalence of two systematic all-orders methods for setting the renormalization scale2015In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 748, p. 13-18Article in journal (Refereed)
    Abstract [en]

    The Principle of Maximum Conformality (PMC) eliminates QCD renormalization scale-setting uncertainties using fundamental renormalization group methods. The resulting scale-fixed pQCD predictions are independent of the choice of renormalization scheme and show rapid convergence. The coefficients of the scale-fixed couplings are identical to the corresponding conformal series with zero beta-function. Two all-orders methods for systematically implementing the PMC-scale setting procedure for existing high order calculations are discussed in this article. One implementation is based on the PMC-BLM correspondence (PMC-I); the other, more recent, method (PMC-II) uses the R-delta-scheme, a systematic generalization of the minimal subtraction renormalization scheme. Both approaches satisfy all of the principles of the renormalization group and lead to scale-fixed and scheme-independent predictions at each finite order. In this work, we show that PMC-I and PMC-II scale-setting methods are in practice equivalent to each other. We illustrate this equivalence for the four-loop calculations of the annihilation ratio Re+e- and the Higgs partial width Gamma(H -> b (b) over bar). Both methods lead to the same resummed ('conformal') series up to all orders. The small scale differences between the two approaches are reduced as additional renormalization group {beta(i)}-terms in the pQCD expansion are taken into account. We also show that special degeneracy relations, which underly the equivalence of the two PMC approaches and the resulting conformal features of the pQCD series, are in fact general properties of non-Abelian gauge theory. (C) 2015 The Authors. Published by Elsevier B.V.

  • 281.
    Bisbas, Thomas G.
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. University College London, UK; Max-Planck-Institut für Extraterrestrische Physik, Germany; University of Florida, USA.
    Haworth, Thomas J.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. University of Cambridge, UK.
    Barlow, M. J.
    Viti, S.
    Harries, T. J.
    Bell, T.
    Yates, J. A.
    TORUS-3DPDR: a self-consistent code treating three-dimensional photoionization and photodissociation regions2015In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 454, no 3, p. 2828-2843Article in journal (Refereed)
    Abstract [en]

    The interaction of ionizing and far-ultraviolet radiation with the interstellar medium is of great importance. It results in the formation of regions in which the gas is ionized, beyond which are photodissociation regions (PDRs) in which the gas transitions to its atomic and molecular form. Several numerical codes have been implemented to study these two main phases of the interstellar medium either dynamically or chemically. In this paper we present TORUS-3DPDR, a new self-consistent code for treating the chemistry of three-dimensional photoionization and photodissociation regions. It is an integrated code coupling the two codes TORUS, a hydrodynamics and Monte Carlo radiation transport code, and 3D-PDR, a PDRs code. The new code uses a Monte Carlo radiative transfer scheme to account for the propagation of the ionizing radiation including the diffusive component as well as a ray-tracing scheme based on the HEALPIX package in order to account for the escape probability and column density calculations. Here, we present the numerical techniques we followed and we show the capabilities of the new code in modelling three-dimensional objects including single or multiple sources. We discuss the effects introduced by the diffusive component of the ultraviolet field in determining the thermal balance of PDRs as well as the effects introduced by a multiple sources treatment of the radiation field. With this new code, three-dimensional synthetic observations for the major cooling lines are possible, for making feasible a detailed comparison between hydrodynamical simulations and observations.

  • 282. Biswas, A.
    et al.
    Choubey, S.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Khan, S.
    Galactic gamma ray excess and dark matter phenomenology in a U(1)B−L model2016In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2016, no 8, article id 114Article in journal (Refereed)
    Abstract [en]

    In this work, we have considered a gauged U(1)B−L extension of the Standard Model (SM) with three right handed neutrinos for anomaly cancellation and two additional SM singlet complex scalars with nontrivial B-L charges. One of these is used to spontaneously break the U(1)B−L gauge symmetry, leading to Majorana masses for the neutrinos through the standard Type I seesaw mechanism, while the other becomes the dark matter (DM) candidate in the model. We test the viability of the model to simultaneously explain the DM relic density observed in the CMB data as well as the Galactic Centre (GC) γ-ray excess seen by Fermi-LAT. We show that for DM masses in the range 40-55 GeV and for a wide range of U(1)B−L gauge boson masses, one can satisfy both these constraints if the additional neutral Higgs scalar has a mass around the resonance region. In studying the dark matter phenomenology and GC excess, we have taken into account theoretical as well as experimental constraints coming from vacuum stability condition, Planck bound on DM relic density, LHC and LUX and present allowed areas in the model parameter space consistent with all relevant data, calculate the predicted gamma ray flux from the GC and discuss the related phenomenology.

  • 283. Biswas, Anirban
    et al.
    Choubey, Sandhya
    KTH, School of Engineering Sciences (SCI), Physics. Harish-Chandra Research Institute, India.
    Covi, Laura
    Khan, Sarif
    Explaining the 3.5 keV X-ray line in a L mu - L-tau extension of the inert doublet model2018In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, no 2, article id 002Article in journal (Refereed)
    Abstract [en]

    We explain the existence of neutrino masses and their flavour structure, dark matter relic abundance and the observed 3.5 keV X-ray line within the framework of a gauged U(1) L-mu-L-tau extension of the "scotogenic" model. In the U(1) L-mu-L-tau symmetric limit, two of the RH neutrinos are degenerate in mass, while the third is heavier. The U(1) L-mu-L-tau symmetry is broken spontaneously. Firstly, this breaks the mu-tau symmetry in the light neutrino sector. Secondly, this results in mild splitting of the two degenerate RH neutrinos, with their mass difference given in terms of the U(1) L-mu-L-tau breaking parameter. Finally, we get a massive Z(mu tau) gauge boson. Due to the added Z(2) symmetry under which the RH neutrinos and the inert doublet are odd, the canonical Type-I seesaw is forbidden and the tiny neutrino masses are generated radiatively at one loop. The same Z(2) symmetry also ensures that the lightest RH neutrino is stable and the other two can only decay into the lightest one. This makes the two nearly-degenerate lighter neutrinos a two-component dark matter, which in our model are produced by the freeze-in mechanism via the decay of the Z(mu tau) gauge boson in the early universe. We show that the next-to-lightest RH neutrino has a very long lifetime and decays into the lightest one at the present epoch explaining the observed 3.5 keV line.

  • 284. Blanchet, L.
    et al.
    Heisenberg, Lavinia
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm University, Sweden.
    Dipolar dark matter with massive bigravity2015In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, Vol. 2015, no 12Article in journal (Refereed)
    Abstract [en]

    Massive gravity theories have been developed as viable IR modifications of gravity motivated by dark energy and the problem of the cosmological constant. On the other hand, modified gravity and modified dark matter theories were developed with the aim of solving the problems of standard cold dark matter at galactic scales. Here we propose to adapt the framework of ghost-free massive bigravity theories to reformulate the problem of dark matter at galactic scales. We investigate a promising alternative to dark matter called dipolar dark matter (DDM) in which two different species of dark matter are separately coupled to the two metrics of bigravity and are linked together by an internal vector field. We show that this model successfully reproduces the phenomenology of dark matter at galactic scales (i.e. MOND) as a result of a mechanism of gravitational polarisation. The model is safe in the gravitational sector, but because of the particular couplings of the matter fields and vector field to the metrics, a ghost in the decoupling limit is present in the dark matter sector. However, it might be possible to push the mass of the ghost beyond the strong coupling scale by an appropriate choice of the parameters of the model. Crucial questions to address in future work are the exact mass of the ghost, and the cosmological implications of the model.

  • 285. Blanchet, Luc
    et al.
    Heisenberg, Lavinia
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm University, Sweden.
    Dark matter via massive bigravity2015In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 91, no 10, article id 103518Article in journal (Refereed)
    Abstract [en]

    In this work we investigate the existence of relativistic models for dark matter in the context of bimetric gravity, used here to reproduce the modified Newtonian dynamics (MOND) at galactic scales. For this purpose we consider two different species of dark matter particles that separately couple to the two metrics of bigravity. These two sectors are linked together via an internal U(1) vector field, and some effective composite metric built out of the two metrics. Among possible models only certain classes of kinetic and interaction terms are allowed without invoking ghost degrees of freedom. Along these lines we explore the number of allowed kinetic terms in the theory and point out the presence of ghosts in a previous model. Finally, we propose a promising class of ghost-free candidate theories that could provide the MOND phenomenology at galactic scales while reproducing the standard cold dark matter model at cosmological scales.

  • 286.
    Blennow, Mattias
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Fernandez-Martinez, Enrique
    Zaldivar, Bryan
    Freeze-in through portals2014In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, no 1, p. 003-Article in journal (Refereed)
    Abstract [en]

    The popular freeze-out paradigm for Dark Matter (DM) production, relies on DM-baryon couplings of the order of the weak interactions. However, different search strategies for DM have failed to provide a conclusive evidence of such (non-gravitational) interactions, while greatly reducing the parameter space of many representative models. This motivates the study of alternative mechanisms for DM genesis. In the freeze-in framework, the DM is slowly populated from the thermal bath while never reaching equilibrium. In this work, we analyse in detail the possibility of producing a frozen-in DM via a mediator particle which acts as a portal. We give analytical estimates of different freeze-in regimes and support them with full numerical analyses, taking into account the proper distribution functions of bath particles. Finally, we constrain the parameter space of generic models by requiring agreement with DM relic abundance observations.

  • 287.
    Blennow, Mattias
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Herrero Garcia, Juan
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Schwetz, Thomas
    A halo-independent lower bound on the dark matter capture rate in the Sun from a direct detection signal2015In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, no 5, article id 036Article in journal (Refereed)
    Abstract [en]

    We show that a positive signal in a dark matter (DM) direct detection experiment can be used to place a lower bound on the DM capture rate in the Sun, independent of the DM halo. For a given particle physics model and DM mass we obtain a lower bound on the capture rate independent of the local DM density, velocity distribution, galactic escape velocity, as well as the scattering cross section. We illustrate this lower bound on the capture rate by assuming that upcoming direct detection experiments will soon obtain a significant signal. When comparing the lower bound on the capture rate with limits on the high-energy neutrino flux from the Sun from neutrino telescopes, we can place upper limits on the branching fraction of DM annihilation channels leading to neutrinos. With current data from IceCube and Super-Kamiokande non-trivial limits can be obtained for spin-dependent interactions and direct annihilations into neutrinos. In some cases also annihilations into tau tau or bb start getting constrained. For spin-independent interactions current constraints are weak, but they may become interesting for data from future neutrino telescopes.

  • 288. Boezio, M.
    et al.
    Carlson, Per
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Casolino, M.
    Castellini, G.
    Consiglio, L.
    de Pascale, M. P.
    de Santis, C.
    de Simone, N.
    Di Felice, V.
    Galper, A. M.
    Gillard, William
    KTH, School of Engineering Sciences (SCI), Physics.
    Grishantseva, L.
    Jerse, G.
    Karelin, A. V.
    Kheymits, M. D.
    Koldashov, S. V.
    Krutkov, S. Y.
    Kvashnin, A. N.
    Leonov, A.
    Malakhov, V.
    Marcelli, L.
    Mayorov, A. G.
    Menn, W.
    Mikhailov, V. V.
    Mocchiutti, E.
    Monaco, A.
    Mori, N.
    Nikonov, N.
    Osteria, G.
    Palma, F.
    Papini, P.
    Pearce, Mark
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Picozza, P.
    Pizzolotto, C.
    Ricci, M.
    Ricciarini, S. B.
    Rossetto, Laura
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Sarkar, R.
    Simon, M.
    Sparvoli, R.
    Spillantini, P.
    Stozhkov, Y. I.
    Vacchi, A.
    Vannuccini, E.
    Vasilyev, G.
    Voronov, S. A.
    Yurkin, Y. T.
    Wu, Juan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zampa, G.
    Zampa, N.
    Zverev, V. G.
    The PAMELA space mission for antimatter and dark matter searches in space2012In: Hyperfine Interactions, ISSN 0304-3843, E-ISSN 1572-9540, Vol. 213, no 1-3, p. 147-158Article in journal (Refereed)
    Abstract [en]

    The PAMELA satellite-borne experiment has presented new results on cosmic-ray antiparticles that can be interpreted in terms of DM annihilation or pulsar contribution. The instrument was launched from the Baikonur cosmodrome and it has been collecting data since July 2006. The combination of a permanent magnet silicon strip spectrometer and a silicon-tungsten imaging calorimeter allows precision studies of the charged cosmic radiation to be conducted over a wide energy range with high statistics. The primary scientific goal is the measurement of the antiproton and positron energy spectrum in order to search for exotic sources. PAMELA is also searching for primordial antinuclei (anti-helium), and testing cosmic-ray propagation models through precise measurements of the antiparticle energy spectrum and precision studies of light nuclei and their isotopes. This talk illustrates the most recent scientific results obtained by the PAMELA experiment.

  • 289. Boezio, M.
    et al.
    Munini, R.
    Adriani, O.
    Barbarino, G. C.
    Bazilevskaya, G. A.
    Bellotti, R.
    Bogomolov, E. A.
    Bongi, M.
    Bonvicini, V.
    Bottai, S.
    Bruno, A.
    Cafagna, F.
    Campana, D.
    Carlson, Per
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Casolino, M.
    Castellini, G.
    De Santis, C.
    Di Felice, V.
    Galper, A. M.
    Karelin, A. V.
    Koldashov, S. V.
    Koldobskiy, S.
    Krutkov, S. Y.
    Kvashnin, A. N.
    Leonov, A.
    Malakhov, V.
    Marcelli, L.
    Martucci, M.
    Mayorov, A. G.
    Menn, W.
    Mergé, M.
    Mikhailov, V. V.
    Mocchiutti, E.
    Monaco, A.
    Mori, N.
    Osteria, G.
    Panico, B.
    Papini, P.
    Pearce, Mark
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Picozza, P.
    Ricci, M.
    Ricciarini, S. B.
    Simon, M.
    Sparvoli, R.
    Spillantini, P.
    Stozhkov, Y. I.
    Vacchi, A.
    Vannuccini, E.
    Vasilyev, G.
    Voronov, S. A.
    Yurkin, Y. T.
    Zampa, G.
    Zampa, N.
    The PAMELA experiment: A cosmic ray experiment deep inside the heliosphere2017In: Proceedings of Science, Sissa Medialab Srl , 2017Conference paper (Refereed)
    Abstract [en]

    It was the 15th of June of 2006 when the PAMELA satellite-borne experiment was launched from the Baikonur cosmodrome in Kazakstan. Then, for nearly ten years, PAMELA has been making high-precision measurements of the charged component of the cosmic radiation opening a new era of precision studies in cosmic rays and challenging our basic vision of the mechanisms of production, acceleration and propagation of cosmic rays in the galaxy and in the heliosphere. The study of the time dependence of the various components of the cosmic radiation from the unusual 23rd solar minimum through the maximum of solar cycle 24 clearly shows solar modulation effects as well as charge sign dependence. PAMELA measurement of the energy spectra during solar energetic particle events fills the existing energy gap between the highest energy particles measured in space and the ground-based domain. Finally, by sampling the particle radiation in different regions of the magnetosphere, PAMELA data provide a detailed study of the Earth s magnetosphere. In this highlight paper, PAMELA main results as well as recent progress about solar and heliospheric physics with PAMELA will be presented. 

  • 290. Boezio, Mirko
    et al.
    Pearce, Mark
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Albi, M.
    Bonvicini, V.
    Lund, Jens
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Lundquist, J.
    Mocchiutti, Emiliano
    INFN Sezione di Trieste, Padriciano 99, 34012 Trieste, Italy.
    Vacchi, A.
    Zampa, G.
    Zampa, N.
    The electron-hadron separation performance of the PAMELA electromagnetic calorimeter2006Conference paper (Refereed)
    Abstract [en]

    A silicon-tungsten sampling imaging calorimeter has been designed and built for thePAMELA satellite-borne experiment. The main physics goals of the experiment are themeasurement of the flux of antiprotons (80 MeV-190 GeV) and positrons (50 MeV-270 GeV) in the cosmic radiation. The calorimeter has been designed to identify antiprotons from an electron background and positrons in a background of protons with a high efficiency and rejection power. This work presents the electron-hadron separationcapabilities of the calorimeter as obtained using both Monte Carlo and test beam data.The calorimeter is found to have sufficient performance to reach the primary scientific objectives of PAMELA, providing a proton rejection factor of ∼105 while keeping a ∼90% efficiency in selecting electrons and positrons. From simulations, an electron rejection factor of ∼105 in antiproton measurements (∼90% antiproton identification efficiency) is demonstrated. 

  • 291. Boezio, Mirko
    et al.
    Pearce, Mark
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Albi, M.
    Bonvicini, V.
    Lund, Jens
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Lundquist, J.
    Mocchiutti, Emiliano
    INFN Sezione di Trieste, Padriciano 99, 34012 Trieste, Italy.
    Vacchi, A.
    Zampa, G.
    Zampa, N.
    The electron-hadron separation performance of the PAMELA electromagnetic calorimeter2006In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 26, no 2, p. 111-118Article in journal (Refereed)
    Abstract [en]

    A silicon-tungsten sampling imaging calorimeter has been designed and built for thePAMELA satellite-borne experiment. The main physics goals of the experiment are themeasurement of the flux of antiprotons (80 MeV-190 GeV) and positrons (50 MeV-270 GeV) in the cosmic radiation. The calorimeter has been designed to identify antiprotons from an electron background and positrons in a background of protons with a high efficiency and rejection power. This work presents the electron-hadron separationcapabilities of the calorimeter as obtained using both Monte Carlo and test beam data.The calorimeter is found to have sufficient performance to reach the primary scientific objectives of PAMELA, providing a proton rejection factor of ∼105 while keeping a ∼90% efficiency in selecting electrons and positrons. From simulations, an electron rejection factor of ∼105 in antiproton measurements (∼90% antiproton identification efficiency) is demonstrated. 

  • 292.
    Bonnevier, Johan
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Melbéus, Henrik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Merle, Alexander
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Monoenergetic gamma rays from nonminimal Kaluza-Klein dark matter annihilations2012In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 85, no 4, p. 043524-Article in journal (Refereed)
    Abstract [en]

    We investigate monoenergetic gamma-ray signatures from annihilations of dark matter comprised of Z(1), the first Kaluza-Klein (KK) excitation of the Z boson in a nonminimal universal extra dimensions (UED) model. The self interactions of the non-Abelian Z(1) gauge boson give rise to a large number of contributing Feynman diagrams that do not exist for annihilations of the Abelian gauge boson B-1, which is the standard Kaluza-Klein dark matter (KKDM) candidate. We find that the annihilation rate is indeed considerably larger for the Z(1) than for the B-1. Even though relic density calculations indicate that the mass of the Z(1) should be larger than the mass of the B-1, the predicted monoenergetic gamma fluxes are of the same order of magnitude. We compare our results to existing experimental limits, as well as to future sensitivities, for image air Cherenkov telescopes, and we find that the limits are reached already with a moderately large boost factor. The realistic prospects for detection depend on the experimental energy resolution.

  • 293. Bouchet, L.
    et al.
    Chauvin, Maxime
    KTH, School of Engineering Sciences (SCI), Physics.
    Amestoy, P. R.
    Rouet, F. -H
    Buttari, A.
    Tools for analyzing large data-set and handling intensity variations of sources with INTEGRAL/SPI2014In: Proceedings of Science, Sissa Medialab Srl , 2014Conference paper (Refereed)
    Abstract [en]

    The INTEGRAL/SPI X/gamma-ray spectrometer (20 keV-8 MeV) is an instrument for which it is essential to process many exposures at the same time to increase the low signal-to-noise ratio of the weakest sources and/or low-surface brightness extended emission. The processing of several years of data simultaneously (10 years actually) with traditional methods of data reduction is ineffective and sometimes not possible at all. Thanks to the newly developed tools, processing large data-sets from SPI is possible with both a reasonable turnaround time and low memory usage. We present also techniques that we have developed to overcome difficulties related to the intensity variation of sources/background between sources between consecutive exposures.

  • 294.
    Bracco, Andrea
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Candelaresi, S.
    Univ Dundee, Div Math, Dundee DD1 4HN, Scotland..
    Del Sordo, F.
    Univ Crete, FORTH, Phys Dept, Iraklion, Greece..
    Brandenburg, Axel
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Is there a left-handed magnetic field in the solar neighborhood?: Exploring helical magnetic fields in the interstellar medium through dust polarization power spectra2019In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 621, article id A97Article in journal (Refereed)
    Abstract [en]

    Context. The analysis of the full-sky Planck polarization data at 850 mu m revealed unexpected properties of the E- and B-mode power spectra of dust emission in the interstellar medium (ISM). The positive cross-correlations over a wide range of angular scales between the total dust intensity, T, and both E and (most of all) B modes has raised new questions about the physical mechanisms that affect dust polarization, such as the Galactic magnetic field structure. This is key both to better understanding ISM dynamics and to accurately describing Galactic foregrounds to the polarization of the cosmic microwave background (CMB). In particular, in the quest to find primordial B modes of the CMB, the observed positive cross-correlation between T and B for interstellar dust requires further investigation towards parity-violating processes in the ISM. Aims. In this theoretical paper we investigate the possibility that the observed cross-correlations in the dust polarization power spectra, and specifically the one between T and B, can be related to a parity-odd quantity in the ISM such as the magnetic helicity. Methods. We produce synthetic dust polarization data, derived from 3D analytical toy models of density structures and helical magnetic fields, to compare with the E and B modes of observations. We present several models. The first is an ideal fully helical isotropic case, such as the Arnold-Beltrami-Childress field. Second, following the nowadays favored interpretation of the T-E signal in terms of the observed alignment between the magnetic field morphology and the filamentary density structure of the diffuse ISM, we design models for helical magnetic fields wrapped around cylindrical interstellar filaments. Lastly, focusing on the observed T-B correlation, we propose a new line of interpretation of the Planck observations advocating the presence of a large-scale helical component of the Galactic magnetic field in the solar neighborhood. Results. Our analysis shows that: I) the sign of magnetic helicity does not affect E and B modes for isotropic magnetic-field configurations; II) helical magnetic fields threading interstellar filaments cannot reproduce the Planck results; and III) a weak helical left-handed magnetic field structure in the solar neighborhood may explain the T-B correlation seen in the Planck data. Such a magnetic-field configuration would also account for the observed large-scale T-E correlation. Conclusions. This work suggests a new perspective for the interpretation of the dust polarization power spectra that supports the imprint of a large-scale structure of the Galactic magnetic field in the solar neighborhood.

  • 295. Bradač, M.
    et al.
    Garcia-Appadoo, D.
    Huang, K. -H
    Vallini, Livia
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Dipartimento di Fisica e Astronomia, Italy.
    Finney, E. Q.
    Hoag, A.
    Lemaux, B. C.
    Schmidt, K. B.
    Treu, T.
    Carilli, C.
    Dijkstra, M.
    Ferrara, A.
    Fontana, A.
    Jones, T.
    Ryan, R.
    Wagg, J.
    Gonzalez, A. H.
    ALMA [C II] 158 μm Detection of a Redshift 7 Lensed Galaxy behind RX J1347.1-11452017In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 836, no 1, article id L2Article in journal (Refereed)
    Abstract [en]

    We present the results of ALMA spectroscopic follow-up of a z =6.766 Lyα emitting galaxy behind the cluster RX J1347.1-1145. We report the detection of [C ii] 158 μm line fully consistent with the Lyα redshift and with the peak of the optical emission. Given the magnification of μ =5.0 ±0.3, the intrinsic (corrected for lensing) luminosity of the [C ii] line is L [C ii] = 1.4+0.2-0.3 × 107 L⊙, roughly ∼5 times fainter than other detections of z ∼ 7 galaxies. The result indicates that low L [C ii] in z ∼ 7 galaxies compared to the local counterparts might be caused by their low metallicities and/or feedback. The small velocity offset (δv = 20+140-40 Km s-1) between the Lyα and [C ii] line is unusual, and may be indicative of ionizing photons escaping.

  • 296.
    Brandenburg, Axel
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm University, Sweden.
    Magnetic Prandtl number dependence of the kinetic-to-magnetic dissipation ratio2014In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 791, no 1, article id 12Article in journal (Refereed)
    Abstract [en]

    Using direct numerical simulations of three-dimensional hydromagnetic turbulence, either with helical or non-helical forcing, we show that the kinetic-to-magnetic energy dissipation ratio always increases with the magnetic Prandtl number, i.e., the ratio of kinematic viscosity to magnetic diffusivity. This dependence can always be approximated by a power law, but the exponent is not the same in all cases. For non-helical turbulence, the exponent is around 1/3, while for helical turbulence it is between 0.6 and 2/3. In the statistically steady state, the rate of energy conversion from kinetic into magnetic by the dynamo must be equal to the Joule dissipation rate. We emphasize that for both small-scale and large-scale dynamos, the efficiency of the energy conversion depends sensitively on the magnetic Prandtl number, and thus on the microphysical dissipation process. To understand this behavior, we also study shell models of turbulence and one-dimensional passive and active scalar models. We conclude that the magnetic Prandtl number dependence is qualitatively best reproduced in the one-dimensional model as a result of dissipation via localized Alfvén kinks.

  • 297.
    Brandenburg, Axel
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Bracco, Andrea
    Kahniashvili, Tina
    Carnegie Mellon Univ, McWilliams Ctr Cosmol, 5000 Forbes Ave, Pittsburgh, PA 15213 USA.;Carnegie Mellon Univ, Dept Phys, 5000 Forbes Ave, Pittsburgh, PA 15213 USA.;Ilia State Univ, Abastumani Astrophys Observ, 3-5 Cholokashvili St, GE-0194 Tbilisi, Rep of Georgia..
    Mandal, Sayan
    Carnegie Mellon Univ, McWilliams Ctr Cosmol, 5000 Forbes Ave, Pittsburgh, PA 15213 USA.;Carnegie Mellon Univ, Dept Phys, 5000 Forbes Ave, Pittsburgh, PA 15213 USA..
    Pol, Alberto Roper
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80303 USA.;Univ Colorado, Dept Aerosp Engn Sci, Boulder, CO 80303 USA..
    Petrie, Gordon J. D.
    Natl Solar Observ, 3665 Discovery Dr, Boulder, CO 80303 USA..
    Singh, Nishant K.
    Max Planck Inst Sonnensystemforsch, Justus von Liebig Weg 3, D-37077 Gottingen, Germany..
    E and B Polarizations from Inhomogeneous and Solar Surface Turbulence2019In: Astrophysical Journal, ISSN 0004-637X, Vol. 870, no 2, article id 87Article in journal (Refereed)
    Abstract [en]

    Gradient- and curl-type or E- and B-type polarizations have been routinely analyzed to study the physics contributing to the cosmic microwave background polarization and galactic foregrounds. They characterize the parity-even and parity-odd properties of the underlying physical mechanisms, such as, for example, hydromagnetic turbulence in the case of dust polarization. Here, we study spectral correlation functions characterizing the parity-even and parity-odd parts of linear polarization for homogeneous and inhomogeneous turbulence to show that only the inhomogeneous helical case can give rise to a parity-odd polarization signal. We also study nonhelical turbulence and suggest that a strong non-vanishing (here negative) skewness of the E polarization is responsible for an enhanced ratio of the EE to the BB (quadratic) correlation in both the helical and nonhelical cases. This could explain the enhanced EE/BB ratio observed recently for dust polarization. We close with a preliminary assessment of using the linear polarization of the Sun to characterize its helical turbulence without being subjected to the pi ambiguity that magnetic inversion techniques have to address.

  • 298.
    Brandenburg, Axel
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm University, Sweden.
    Giampapa, Mark S.
    Enhanced Stellar Activity for Slow Antisolar Differential Rotation2018In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 855, no 2, article id L22Article in journal (Refereed)
    Abstract [en]

    High-precision photometry of solar-like members of the open cluster M67 with Kepler/K2 data has recently revealed enhanced activity for stars with a large Rossby number, which is the ratio of rotation period to the convective turnover time. Contrary to the well established behavior for shorter rotation periods and smaller Rossby numbers, the chromospheric activity of the more slowly rotating stars of M67 was found to increase with increasing Rossby number. Such behavior has never been reported before, although it was theoretically predicted to emerge as a consequence of antisolar differential rotation (DR) for stars with Rossby numbers larger than that of the Sun, because in those models the absolute value of the DR was found to exceed that for solar-like DR. Using gyrochronological relations and an approximate age of 4 Gyr for the members of M67, we compare with computed rotation rates using just the B - V color. The resulting rotation-activity relation is found to be compatible with that obtained by employing the measured rotation rate. This provides additional support for the unconventional enhancement of activity at comparatively low rotation rates and the possible presence of antisolar differential rotation.

  • 299.
    Brandenburg, Axel
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Gressel, Oliver
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Jabbari, Sarah
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Kleeorin, Nathan
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Rogachevskii, Igor
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Mean-field and direct numerical simulations of magnetic flux concentrations from vertical field2014In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 562, p. A53-Article in journal (Refereed)
    Abstract [en]

    Context. Strongly stratified hydromagnetic turbulence has previously been found to produce magnetic flux concentrations if the domain is large enough compared with the size of turbulent eddies. Mean-field simulations (MFS) using parameterizations of the Reynolds and Maxwell stresses show a large-scale negative effective magnetic pressure instability and have been able to reproduce many aspects of direct numerical simulations (DNS) regarding growth rate, shape of the resulting magnetic structures, and their height as a function of magnetic field strength. Unlike the case of an imposed horizontal field, for a vertical one, magnetic flux concentrations of equipartition strength with the turbulence can be reached, resulting in magnetic spots that are reminiscent of sunspots. Aims. We determine under what conditions magnetic flux concentrations with vertical field occur and what their internal structure is. Methods. We use a combination of MFS, DNS, and implicit large-eddy simulations (ILES) to characterize the resulting magnetic flux concentrations in forced isothermal turbulence with an imposed vertical magnetic field. Results. Using DNS, we confirm earlier results that in the kinematic stage of the large-scale instability the horizontal wavelength of structures is about 10 times the density scale height. At later times, even larger structures are being produced in a fashion similar to inverse spectral transfer in helically driven turbulence. Using ILES, we find that magnetic flux concentrations occur for Mach numbers between 0.1 and 0.7. They occur also for weaker stratification and larger turbulent eddies if the domain is wide enough. Using MFS, the size and aspect ratio of magnetic structures are determined as functions of two input parameters characterizing the parameterization of the effective magnetic pressure. DNS, ILES, and MFS show magnetic flux tubes with mean-field energies comparable to the turbulent kinetic energy. These tubes can reach a length of about eight density scale heights. Despite being ≤1% equipartition strength, it is important that their lower part is included within the computational domain to achieve the full strength of the instability. Conclusions. The resulting vertical magnetic flux tubes are being confined by downflows along the tubes and corresponding inflow from the sides, which keep the field concentrated. Application to sunspots remains a viable possibility.

  • 300.
    Brandenburg, Axel
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Hubbard, Alexander
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Käpylä, Petri
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Dynamical quenching with non-local alpha and downward pumping2015In: Astronomical Notes - Astronomische Nachrichten, ISSN 0004-6337, E-ISSN 1521-3994, Vol. 336, no 1, p. 91-96Article in journal (Refereed)
    Abstract [en]

    In light of new results, the one-dimensional mean-field dynamo model of Brandenburg & Kapyla (2007) with dynamical quenching and a nonlocal Babcock-Leighton a effect is re-examined for the solar dynamo. We extend the one-dimensional model to include the effects of turbulent downward pumping (Kitchatinov & Olemskoy 2011), and to combine dynamical quenching with shear. We use both the conventional dynamical quenching model of Kleeorin & Ruzmaikin (1982) and the alternate one of Hubbard & Brandenburg (2011), and confirm that with varying levels of non-locality in the a effect, and possibly shear as well, the saturation field strength can be independent of the magnetic Reynolds number.

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