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  • 151. Meloni, Davide
    et al.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Leptonic CP violation at neutrino telescopes2012In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 86, no 6, p. 067701-Article in journal (Refereed)
    Abstract [en]

    With the advent of the recent measurements in neutrino physics, we investigate the role of high-energy neutrino flux ratios at neutrino telescopes for the possibility of determining the leptonic CP-violating phase delta and the underlying pattern of the leptonic mixing matrix. We find that the flux ratios show a dependence of O(10%) on the CP-violating phase, and for optimistic uncertainties on the flux ratios less than 10%, they can be used to distinguish between CP-conserving and CP-violating values of the phase at 2 sigma in a nonvanishing interval around the maximal value vertical bar delta vertical bar = pi/2.

  • 152.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Cutting with Occam's razor2012In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 86, no 9, p. 097301-Article in journal (Refereed)
    Abstract [en]

    We comment positively on the recent article "Seesaw mechanism with Occam's razor" [K. Harigaya et al. Phys. Rev. D 86, 013002 (2012).] by Harigaya, Ibe, and Yanagida. In this article, the authors are using the principle of Occam's razor in neutrino physics-a principle that should be applied more often in science in general. At the end, we also discuss the Bayesian method in statistics, in which Occam's razor is naturally built in.

  • 153.
    Ohlsson, Tommy
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Zhang, He
    Zhou, Shun
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Effects of nonstandard neutrino interactions at PINGU2013In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 88, no 1, p. 013001-Article in journal (Refereed)
    Abstract [en]

    Neutrino oscillation experiments in the past decades have greatly improved our knowledge on neutrinos by measuring the fundamental neutrino parameters. The ongoing and upcoming neutrino oscillation experiments are intended to pin down the neutrino mass hierarchy and to discover the leptonic CP violation. By means of neutrino oscillograms, we analyze the impact of nonstandard neutrino interactions on neutrino oscillations in Earth matter. The standard neutrino oscillation probabilities may be significantly changed by nonstandard interaction parameters, and, in particular, the CP-violating effects in the energy range E = 1-20 GeV are greatly enhanced. In addition, the event rates of muon neutrinos in the proposed huge atmospheric neutrino experiment, PINGU at the South Pole, have been estimated in the presence of nonstandard neutrino interactions. It has been found that the PINGU experiment has very good sensitivities to the nonstandard neutrino interaction parameters.

  • 154.
    Ohlsson, Tommy
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Zhang, He
    Zhou, Shun
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Probing the leptonic Dirac CP-violating phase in neutrino oscillation experiments2013In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 87, no 5, p. 053006-Article in journal (Refereed)
    Abstract [en]

    The discovery of leptonic CP violation is one of the primary goals of next-generation neutrino oscillation experiments, which is feasible due to the recent measurement of a relatively large leptonic mixing angle theta(13). We suggest two new working observables Delta A(alpha beta)(m) equivalent to max[A(alpha beta)(CP)(delta) - min[A(alpha beta)(CP)(delta)] and Delta A(alpha beta)(CP)(delta) equivalent to A(alpha beta)(CP)(delta) - A(alpha beta)(CP)(0) to describe the CP-violating effects in long-baseline and atmospheric neutrino oscillation experiments. The former signifies the experimental sensitivity to the leptonic Dirac CP-violating phase delta and can be used to optimize the experimental setup, while the latter measures the intrinsic leptonic CP violation and can be used to extract delta directly from the experimental observations. Both analytical and numerical analyses are carried out to illustrate their main features. It turns out that an intense neutrino beam with sub-GeV energies and a baseline of a few 100 km may serve as an optimal experimental setup for probing leptonic CP violation.

  • 155.
    Ohlsson, Tommy
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Zhang, He
    Zhou, Shun
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Radiative corrections to the leptonic Dirac CP-violating phase2013In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 87, no 1, p. 013012-Article in journal (Refereed)
    Abstract [en]

    Since the smallest leptonic mixing angle theta(13) has been measured to be relatively large, it is quite promising to constrain or determine the leptonic Dirac CP-violating phase delta in future neutrino oscillation experiments. Given some typical values of delta = pi/2, pi, and 3 pi/2 at the low energy scale, as well as current experimental results of the other neutrino parameters, we perform a systematic study of radiative corrections to delta by using the one-loop renormalization group equations in the minimal supersymmetric standard model and the universal extra-dimensional model. It turns out that delta is rather stable against radiative corrections in both models, except for the minimal supersymmetric standard model with a very large value of tan beta. Both cases of Majorana and Dirac neutrinos are discussed. In addition, we use the preliminary indication of delta = (1.08(-0.31)(+0.28))pi or delta = (1.67(-0.77)(+0.37))pi from the latest global-fit analyses of data from neutrino oscillation experiments to illustrate how it will be modified by radiative corrections.

  • 156. Plimak, L. I.
    et al.
    Stenholm, Stig
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Quantum Electronics and Quantum Optics, QEO (moved to SCI 2011-07-01).
    Causal signal transmission by quantum fields. IV. The causal Wick theorem2011In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 84, no 6, p. 065025-Article in journal (Refereed)
    Abstract [en]

    Wick's theorem in the Schwinger-Perel-Keldysh closed-time-loop formalism is written in a form where the place of contractions is taken by the linear response function of the field. This result demonstrates that the physical information supplied by Wick's theorem for operators is propagation of the free field in space and time.

  • 157.
    Savage, Christopher
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. University of Utah, United States.
    Scaffidi, Andre
    White, Martin
    Williams, Anthony G.
    LUX likelihood and limits on spin-independent and spin-dependent WIMP couplings with LUXCalc2015In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 92, no 10, article id 103519Article in journal (Refereed)
    Abstract [en]

    We present LUXCalc, a new utility for calculating likelihoods and deriving weakly interacting massive particle (WIMP)-nucleon coupling limits from the recent results of the LUX direct search dark matter experiment. After a brief review of WIMP-nucleon scattering, we derive LUX limits on the spin-dependent WIMP-nucleon couplings over a broad range of WIMP masses, under standard assumptions on the relevant astrophysical parameters. We find that, under these and other common assumptions, LUX excludes the entire spin-dependent parameter space consistent with a dark matter interpretation of DAMA's anomalous signal, the first time a single experiment has been able to do so. We also revisit the case of spin-independent couplings, and demonstrate good agreement between our results and the published LUX results. Finally, we derive constraints on the parameters of an effective dark matter theory in which a spin-1 mediator interacts with a fermionic WIMP and Standard Model fermions via axial-vector couplings. A detailed appendix describes the use of LUXCalc with standard codes to place constraints on generic dark matter theories.

  • 158. Sierra, D. Aristizabal
    et al.
    Herrero-Garcia, Juan
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Restrepo, D.
    Vicente, A.
    Diboson anomaly: Heavy Higgs resonance and QCD vectorlike exotics2016In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 93, no 1, article id 015012Article in journal (Refereed)
    Abstract [en]

    The ATLAS Collaboration (and also CMS) has recently reported an excess over Standard Model expectations for gauge boson pair production in the invariant mass region 1.8-2.2 TeV. In light of these results, we argue that such a signal might be the first manifestation of the production and further decay of a heavy CP-even Higgs resulting from a type-I two Higgs doublet model. We demonstrate that in the presence of colored vectorlike fermions, its gluon fusion production cross section is strongly enhanced, with the enhancement depending on the color representation of the new fermion states. Our findings show that barring the color triplet case, any QCD "exotic" representation can fit the ATLAS result in fairly large portions of the parameter space. We have found that if the diboson excess is confirmed and this mechanism is indeed responsible for it, then the LHC Run-2 should find (i) a CP-odd scalar with mass below similar to 2.3 TeV, (ii) new colored states with masses below similar to 2 TeV, (iii) no statistically significant diboson events in the W(+/-)Z channel, (iv) events in the triboson channels W(+/-)W(-/+)Z and ZZZ with invariant mass amounting to the mass of the CP-odd scalar.

  • 159.
    Sivertsson, Sofia
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Edsjö, Joakim
    Accurate calculations of the WIMP halo around the Sun and prospects for its gamma-ray detection2010In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 81, no 6, p. 063502-1-063502-14Article in journal (Refereed)
    Abstract [en]

    Galactic weakly interacting massive particles (WIMPs) may scatter off solar nuclei to orbits gravitationally bound to the Sun. Once bound, the WIMPs continue to lose energy by repeated scatters in the Sun, eventually leading to complete entrapment in the solar interior. While the density of the bound population is highest at the center of the Sun, the only observable signature of WIMP annihilations inside the Sun is neutrinos. It has been previously suggested that although the density of WIMPs just outside the Sun is lower than deep inside, gamma rays from WIMP annihilation just outside the surface of the Sun, in the so-called WIMP halo around the Sun, may be more easily detected. We here revisit this problem using detailed Monte Carlo simulations and detailed composition and structure information about the Sun to estimate the size of the gamma-ray flux. Compared to earlier simpler estimates, we find that the gamma-ray flux from WIMP annihilations in the solar WIMP halo would be negligible; no current or planned detectors would be able to detect this flux.

  • 160.
    Sivertsson, Sofia
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Edsjö, Joakim
    Stockholm University.
    WIMP diffusion in the Solar System including solar WIMP-nucleon scattering2012In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 85, no 12, p. 123514-Article in journal (Refereed)
    Abstract [en]

    Dark matter in the form of Weakly Interacting Massive Particles (WIMPs) can be captured by the Sun and the Earth, sink to their cores, annihilate and produce neutrinos that can be searched for with neutrino telescopes. The calculation of the capture rates of WIMPs in the Sun and especially the Earth are affected by large uncertainties coming mainly from effects of the planets in the Solar System, reducing the capture rates by up to an order of magnitude (or even more in some cases). We show that the WIMPs captured by weak scatterings in the Sun also constitute an important bound WIMP population in the Solar System. Taking this population and its interplay with the population bound through gravitational diffusion into account cancel the planetary effects on the capture rates, and the capture essentially proceeds as if the Sun and the Earth were free in the galactic halo. The neutrino signals from the Sun and the Earth are thus significantly higher than claimed in the scenarios with reduced capture rates.

  • 161.
    Sundell, Peter
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Turku Center for Quantum Physics, Department of Physics and Astronomy, University of Turku, Turku, Finland.
    Koivisto, Tomi Sebastian
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Anisotropic cosmology and inflation from a tilted Bianchi IX model2015In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 92, no 12, article id 123529Article in journal (Refereed)
    Abstract [en]

    The dynamics of the tilted axisymmetric Bianchi IX cosmological models are explored allowing energy flux in the source fluid. The Einstein equations and the continuity equation are presented treating the equation of state w and the tilt angle of the fluid lambda as time-dependent functions, but when analyzing the phase space w and lambda are considered free parameters and the shear, the vorticity and the curvature of the spacetime span a three-dimensional phase space that contains seven fixed points. One of them is an attractor that inflates the universe anisotropically, thus providing a counterexample to the cosmic no-hair conjecture. Also, examples of realistic though fine-tuned cosmologies are presented wherein the rotation can become significant towards the present epoch but the shear stays within the observational bounds. The examples suggest that the model used here can explain the parity-violating anomalies of the cosmic microwave background. The result significantly differs from an earlier study, where a nonaxisymmetric Bianchi IX type model with a tilted perfect dust source was found to induce too much shear for observationally significant vorticity.

  • 162. Szilagyi, B.
    et al.
    Kreiss, Heinz-Otto
    KTH, School of Computer Science and Communication (CSC), Numerical Analysis and Computer Science, NADA.
    Winicour, J.
    Modeling the black hole excision problem2005In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 71, no 10, p. 104035-Article in journal (Refereed)
    Abstract [en]

    We analyze the excision strategy for simulating black holes. The problem is modeled by the propagation of quasilinear waves in a 1-dimensional spatial region with timelike outer boundary, spacelike inner boundary and a horizon in between. Proofs of well-posed evolution and boundary algorithms for a second differential order treatment of the system are given for the separate pieces underlying the finite-difference problem. These are implemented in a numerical code which gives accurate long term simulations of the quasilinear excision problem. Excitation of long wavelength exponential modes, which are latent in the problem, are suppressed using conservation laws for the discretized system. The techniques are designed to apply directly to recent codes for the Einstein equations based upon the harmonic formulation.

  • 163.
    Wagstaff, Jacques M.
    et al.
    Hamburger Sternwarte, Germany.
    Banerjee, Robi
    Hamburger Sternwarte, Germany.
    CMB spectral distortions from the decay of causally generated magnetic fields2015In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 92, no 12, article id 123004Article in journal (Refereed)
    Abstract [en]

    We improve previous calculations of the cosmic microwave background spectral distortions due to the decay of primordial magnetic fields. We focus our studies on causally generated magnetic fields at the electroweak and QCD phase transitions. We also consider the decay of helical magnetic fields. We show that the decay of nonhelical magnetic fields generated at either the electroweak or QCD scale produce mu-and y-type distortions below 10(-8) which are probably not detectable by a future PIXIE-like experiment. We show that magnetic fields generated at the electroweak scale must have a helicity fraction f(*) > 10(-4) in order to produce detectable mu-type distortions. Hence, a positive detection coming from the decay of magnetic fields would rule out nonhelical primordial magnetic fields and provide a lower bound on the magnetic helicity.

1234 151 - 163 of 163
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