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  • 101. Abazov, V. M.
    et al.
    Åsman, Barbro
    Clément, Christophe
    Gollub, Nils
    Strandberg, Jonas
    Zverev, E. G.
    et al.,
    Search for excited muons in p(p)over-bar collisions at root s=1.96 TeV2006In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 73, no 11, p. 111102-Article in journal (Refereed)
    Abstract [en]

    We present the results of a search for the production of an excited state of the muon, mu(*), in proton antiproton collisions at root s =1.96 TeV. The data have been collected with the D0 experiment at the Fermilab Tevatron Collider and correspond to an integrated luminosity of approximately 380 pb(-1). We search for mu(*) in the process p (p) over bar ->mu(*)mu, with the mu(*) subsequently decaying to a muon plus photon. No excess above the standard model expectation is observed in data. Interpreting our data in the context of a model that describes mu(*) production by four-fermion contact interactions and mu(*) decay via electroweak processes, we set a 95% confidence level production cross section upper limit ranging from 0.057 to 0.112 pb, depending on the mass of the excited muon. Choosing the scale for contact interactions to be Lambda=1 TeV, excited muon masses below 618 GeV are excluded.

  • 102. Abazov, V. M.
    et al.
    Åsman, Barbro
    Clément, Christophe
    Gollub, Nils
    Strandberg, Jonas
    Zverev, E. G.
    et al.,
    Search for the rare decay B-s(0)->phi mu(+)mu(-) with the D0 detector2006In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 74, no 3, p. 031107-Article in journal (Refereed)
    Abstract [en]

    We present a search for the flavor-changing neutral current decay B-s(0)->phi mu(+)mu(-) using about 0.45 fb(-1) of data collected in p (p) over bar collisions at root s=1.96 TeV with the D0 detector at the Fermilab Tevatron Collider. We find an upper limit on the branching ratio of this decay normalized to B-s(0)-> J/psi phi of B(B-s(0)->phi mu(+)mu(-))/B(B-s(0)-> J/psi phi)< 4.4x10(-3) at the 95% C.L. Using the central value of the world average branching fraction of B-s(0)-> J/psi phi, the limit corresponds to B(B-s(0)->phi mu(+)mu(-))< 4.1x10(-6) at the 95% C.L., the most stringent upper bound to date.

  • 103. Ackermann, M.
    et al.
    Ajello, M.
    Albert, A.
    Anderson, B.
    Atwood, W. B.
    Baldini, L.
    Barbiellini, G.
    Bastieri, D.
    Bellazzini, R.
    Bissaldi, E.
    Blandford, R. D.
    Bloom, E. D.
    Bonino, R.
    Bottacini, E.
    Brandt, T. J.
    Bregeon, J.
    Bruel, P.
    Buehler, R.
    Buson, S.
    Caliandro, G. A.
    Cameron, R. A.
    Caputo, R.
    Caragiulo, M.
    Caraveo, P. A.
    Cecchi, C.
    Charles, E.
    Chekhtman, A.
    Chiang, J.
    Chiaro, G.
    Ciprini, S.
    Claus, R.
    Cohen-Tanugi, J.
    Conrad, J.
    Cuoco, A.
    Cutini, S.
    D'Ammando, F.
    de Angelis, A.
    de Palma, F.
    Desiante, R.
    Digel, S. W.
    Di Venere, L.
    Drell, P. S.
    Drlica-Wagner, A.
    Favuzzi, C.
    Fegan, S. J.
    Franckowiak, A.
    Fukazawa, Y.
    Funk, S.
    Fusco, P.
    Gargano, F.
    Gasparrini, D.
    Giglietto, N.
    Giordano, F.
    Giroletti, M.
    Godfrey, G.
    Gomez-Vargas, G. A.
    Grenier, I. A.
    Grove, J. E.
    Guiriec, S.
    Gustafsson, M.
    Hewitt, J. W.
    Hill, A. B.
    Horan, D.
    Johannesson, G.
    Johnson, R. P.
    Kuss, M.
    Larsson, S.
    Latronico, L.
    Li, J.
    Li, L.
    KTH, School of Engineering Sciences (SCI), Physics.
    Longo, F.
    Loparco, F.
    Lovellette, M. N.
    Lubrano, P.
    Malyshev, D.
    Mayer, M.
    Mazziotta, M. N.
    McEnery, J. E.
    Michelson, P. F.
    Mizuno, T.
    Moiseev, A. A.
    Monzani, M. E.
    Morselli, A.
    Murgia, S.
    Nuss, E.
    Ohsugi, T.
    Orienti, M.
    Orlando, E.
    Ormes, J. F.
    Paneque, D.
    Pesce-Rollins, M.
    Piron, F.
    Pivato, G.
    Raino, S.
    Rando, R.
    Razzano, M.
    Reimer, A.
    Reposeur, T.
    Ritz, S.
    Sanchez-Conde, M.
    Schulz, A.
    Sgro, C.
    Siskind, E. J.
    Spada, F.
    Spandre, G.
    Spinelli, P.
    Tajima, H.
    Takahashi, H.
    Thayer, J. B.
    Tibaldo, L.
    Torres, D. F.
    Tosti, G.
    Troja, E.
    Vianello, G.
    Werner, M.
    Winer, B. L.
    Wood, K. S.
    Wood, M.
    Zaharijas, G.
    Zimmer, S.
    Updated search for spectral lines from Galactic dark matter interactions with pass 8 data from the Fermi Large Area Telescope2015In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 91, no 12, article id 122002Article in journal (Refereed)
    Abstract [en]

    Dark matter in the Milky Way may annihilate directly into. rays, producing a monoenergetic spectral line. Therefore, detecting such a signature would be strong evidence for dark matter annihilation or decay. We search for spectral lines in the Fermi Large Area Telescope observations of the Milky Way halo in the energy range 200 MeV-500 GeV using analysis methods from our most recent line searches. The main improvements relative to previous works are our use of 5.8 years of data reprocessed with the Pass 8 event-level analysis and the additional data resulting from the modified observing strategy designed to increase exposure of the Galactic center region. We search in five sky regions selected to optimize sensitivity to different theoretically motivated dark matter scenarios and find no significant detections. In addition to presenting the results from our search for lines, we also investigate the previously reported tentative detection of a line at 133 GeV using the new Pass 8 data.

  • 104. Agarwal, Abhishek
    et al.
    Lipstein, Arthur E.
    Young, Donovan
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Scattering amplitudes of massive N = 2 gauge theories in three dimensions2014In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 89, no 4, p. 045020-Article in journal (Refereed)
    Abstract [en]

    We study the scattering amplitudes of mass-deformed Chern-Simons theories and Yang-Mills-Chern-Simons theories with N = 2 supersymmetry in three dimensions. In particular, we derive the on-shell supersymmetry algebras which underlie the scattering matrices of these theories. We then compute various 3 and 4-point on-shell tree-level amplitudes in these theories. For the mass-deformed Chern-Simons theory, odd-point amplitudes vanish and we find that all of the 4-point amplitudes can be encoded elegantly in superamplitudes. For the Yang-Mills-Chern-Simons theory, we obtain all of the 4-point tree-level amplitudes using a combination of perturbative techniques and algebraic constraints and we comment on difficulties related to computing amplitudes with external gauge fields using Feynman diagrams. Finally, we propose a Britto-Cachazo-Feng-Witten recursion relation for mass-deformed theories in three dimensions and discuss the applicability of this proposal to mass-deformed N = 2 theories.

  • 105. Antusch, Stefan
    et al.
    Blennow, Mattias
    Fernandez Martinez, Enrique
    Lopez Pavon, Jacobo
    Probing non-unitary mixing and CP-violation at a Neutrino Factory2009In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 80, no 3, p. 033002-Article in journal (Refereed)
    Abstract [en]

    A low-energy nonunitary leptonic mixing matrix is a generic feature of many extensions of the standard model. In such a case, the task of future precision neutrino oscillation experiments is more ambitious than measuring the three mixing angles and the leptonic (Dirac) CP phase, i.e., the accessible parameters of a unitary leptonic mixing matrix. A nonunitary mixing matrix has 13 parameters that affect neutrino oscillations, out of which four are CP violating. In the scheme of minimal unitarity violation we analyze the potential of a neutrino factory for determining or constraining the parameters of the nonunitary leptonic mixing matrix, thereby testing the origin of CP violation in the lepton sector.

  • 106. 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.

  • 107.
    Bergström, Johannes
    et al.
    Universitat de Barcelona.
    Riad, Riad
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Bayesian Model comparison of Higgs couplings2015In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 91, no 7, article id 075008Article in journal (Refereed)
    Abstract [en]

    We investigate the possibility of contributions from physics beyond the Standard Model (SM) to the Higgs couplings, in the light of the LHC data. The work is performed within an interim framework where the magnitude of the Higgs production and decay rates are rescaled through Higgs coupling scale factors. We perform Bayesian parameter inference on these scale factors, concluding that there is good compatibility with the SM. Furthermore, we carry out a Bayesian model comparison on all models where any combination of scale factors can differ from their SM values and find that typically models with fewer free couplings are strongly favored. We consider the evidence that each coupling individually equals the SM value, making the minimal assumptions on the other couplings. Finally, we make a comparison of the SM against a single "not-SM" model and find that there is moderate to strong evidence for the SM.

  • 108. 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.

  • 109. 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.

  • 110. Blennow, Mattias
    Prospects for cosmic neutrino detection in tritium experiments in the case of hierarchical neutrino masses2008In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 77, no 11, p. 113014-Article in journal (Refereed)
    Abstract [en]

    We discuss the effects of neutrino mixing and the neutrino mass hierarchy when considering the capture of the cosmic neutrino background (CNB) on radioactive nuclei. The implications of mixing and hierarchy at future generations of tritium decay experiments are considered. We find that the CNB should be detectable at these experiments provided that the resolution for the kinetic energy of the outgoing electron can be pushed to a few 0.01 eV for the scenario with inverted neutrino mass hierarchy, about an order of magnitude better than that of the upcoming KATRIN experiment. Another order of magnitude improvement is needed in the case of normal neutrino mass hierarchy. We also note that mixing effects generally make the prospects for CNB detection worse due to an increased maximum energy of the normal beta decay background.

  • 111. Blennow, Mattias
    et al.
    Meloni, Davide
    Non-standard interaction effects on astrophysical neutrino fluxes2009In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 80, no 6, p. 065009-Article in journal (Refereed)
    Abstract [en]

    We investigate new physics effects in the production and detection of high-energy neutrinos at neutrino telescopes. Analyzing the flavor ratios ϕμτ and ϕμ/(ϕτe), we find that the standard model predictions for them can be sensibly altered by new physics effects in the case of pion sources. However, the experimental precision required to see the effects would be very difficult to obtain.

  • 112. Blennow, Mattias
    et al.
    Mirizzi, Alessandro
    Serpico, Pasquale
    Nonstandard neutrino-neutrino refractive effects in dense neutrino gases2008In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 78, no 11, p. 113004-Article in journal (Refereed)
    Abstract [en]

     We investigate the effects of nonstandard four-fermion neutrino-neutrino interactions on the flavor evolution of dense neutrino gases. We find that in the regions where the neutrino-neutrino refractive index leads to collective flavor oscillations, the presence of new neutrino interactions can produce flavor equilibration in both normal and inverted neutrino mass hierarchy. In realistic supernova environments, these effects are significant if the nonstandard neutrino-neutrino interaction strength is comparable to the one expected in the standard case, dominating the ordinary matter potential. However, very small nonstandard neutrino-neutrino couplings are enough to trigger the usual collective neutrino flavor transformations in the inverted neutrino mass hierarchy, even if the mixing angle vanishes exactly.

  • 113.
    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.

  • 114. Caldarelli, Marco M.
    et al.
    Camps, Joan
    Goutéraux, Blaise
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Skenderis, Kostas
    AdS/Ricci-flat correspondence and the Gregory-Laflamme instability2013In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 87, no 6, p. 061502-Article in journal (Refereed)
    Abstract [en]

    We show that for every asymptotically anti-de Sitter (AdS) solution compactified on a torus there is a corresponding Ricci-flat solution obtained by replacing the torus by a sphere, performing a Weyl rescaling of the metric and appropriately analytically continuing the dimension of the torus/sphere (as in generalized dimensional reduction). In particular, it maps Minkowski spacetime to AdS on a torus, the holographic stress energy tensor of AdS to the stress energy tensor due to a brane localized in the interior of spacetime and AdS black branes to (asymptotically flat) Schwarzschild black branes. Applying it to the known solutions describing the hydrodynamic regime in AdS/CFT, we derive the hydrodynamic stress tensor of asymptotically flat black branes to second order, which is constrained by the parent conformal symmetry. We compute the dispersion relation of the Gregory-Laflamme unstable modes through cubic order in the wave number, finding remarkable agreement with numerical data. In the case of no transverse sphere, AdS black branes are mapped to Rindler spacetime and the second-order transport coefficients of the fluid dual to Rindler spacetime are recovered.

  • 115.
    Caputa, Pawel
    et al.
    KTH. Stockholm Univ, Sweden.
    Veliz-Osorio, Alvaro
    Entanglement constant for conformal families2015In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 92, no 6, article id 065010Article in journal (Refereed)
    Abstract [en]

    We show that in 1 + 1 dimensional conformal field theories, exciting a state with a local operator increases the Renyi entanglement entropies by a constant which is the same for every member of the conformal family. Hence, it is an intrinsic parameter that characterizes local operators from the perspective of quantum entanglement. In rational conformal field theories this constant corresponds to the logarithm of the quantum dimension of the primary operator. We provide several detailed examples for the second Renyi entropies and a general derivation.

  • 116. Carloni, Sante
    et al.
    Koivisto, Tomi Sebastian
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Lobo, Francisco S. N.
    Dynamical system analysis of hybrid metric-Palatini cosmologies2015In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 92, no 6, article id 064035Article in journal (Refereed)
    Abstract [en]

    The so-called f(X) hybrid metric-Palatini gravity, where X = R + T, with T the stress-energy trace and R the Ricci scalar, presents a unique viable generalization of the f(R) theories within the metric-affine formalism. In this paper, the cosmology of the f(X) theories is studied using the dynamical system approach. The method consists of formulating the propagation equation in terms of suitable (expansion-normalized) variables as an autonomous system. The fixed points of the system then represent exact cosmological solutions described by power law or de Sitter expansion. The formalism is applied to two classes of f(X) models, revealing both standard cosmological fixed points and new accelerating solutions that can be attractors in the phase space. In addition, the fixed point with vanishing expansion rate is considered with special care in order to characterize the stability of Einstein static spaces and bouncing solutions.

  • 117. Cetoli, A.
    et al.
    Pethick, C. J.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Interaction of gravitational waves with matter2012In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 85, no 6, p. 064036-Article in journal (Refereed)
    Abstract [en]

    We develop a unified formalism for describing the interaction of gravitational waves with matter that clearly separates the effects of general relativity from those due to interactions in the matter. Using it, we derive a general expression for the dispersion of gravitational waves in matter in terms of correlation functions for the matter in flat spacetime. The self energy of a gravitational wave is shown to have contributions analogous to the paramagnetic and diamagnetic contributions to the self energy of an electromagnetic wave. We apply the formalism to some simple systems: free particles, an interacting scalar field, and a fermionic superfluid.

  • 118. Chen, Pisin
    et al.
    Izumi, Keisuke
    Nester, James M.
    Ong, Yen Chin
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Remnant symmetry, propagation, and evolution in f(T) gravity2015In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 91, no 6, article id 064003Article in journal (Refereed)
    Abstract [en]

    It was recently argued that f(T) gravity could inherit "remnant symmetry" from the full Lorentz group, despite the fact that the theory is not locally Lorentz invariant. Confusion has arisen regarding the implication of this result for the previous works, which established that f(T) gravity is pathological due to superluminal propagation, local acausality, and nonunique time evolution. We clarify that the existence of the "remnant group" does not rid the theory of these various problems but, instead, strongly supports it.

  • 119. de Rham, Claudia
    et al.
    Heisenberg, Lavinia
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm University, Sweden.
    Ribeiro, Raquel H.
    Ghosts and matter couplings in massive gravity, bigravity and multigravity2014In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 90, no 12, p. 124042-Article in journal (Refereed)
    Abstract [en]

    Recently, several works have investigated the coupling to matter in ghost-free massive bigravity and multigravity and a new effective coupling to matter has been proposed. In this paper we clarify some confusion on the existence and the implications of a ghost above the strong coupling scale. We confirm that the standard constraint which is otherwise typically present in this type of theories disappears on generic backgrounds as soon as this new coupling is considered. This implies the reemergence of the BoulwareDeser ghost. Nevertheless the absence of ghost in the decoupling limit implies that the cutoff scale (if identified with the scale at which the ghost enters) is higher than the strong coupling scale. Therefore there is a valid interesting region of applicability for these couplings at scales below the cutoff.

  • 120.
    Di Bari, Pasquale
    et al.
    University of Southampton.
    King, Stephen
    University of Southampton.
    Luhn, Christoph
    University of Southampton.
    Merle, Alexander
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Schmidt-May, Angnis
    Max-Planck-Institut fuer Kernphysik.
    Radiative Inflation and Dark Energy2011In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 84, no 8Article in journal (Refereed)
    Abstract [en]

    We propose a model based on radiative symmetry breaking that combines inflation with dark energy and is consistent with the Wilkinson Microwave Anisotropy Probe 7-year regions. The radiative inflationary potential leads to the prediction of a spectral index 0.955 less than or similar to n(S) less than or similar to 0.967 and a tensor to scalar ratio 0.142 less than or similar to r less than or similar to 0.186, both consistent with current data but testable by the Planck experiment. The radiative symmetry breaking close to the Planck scale gives rise to a pseudo Nambu-Goldstone boson with a gravitationally suppressed mass which can naturally play the role of a quintessence field responsible for dark energy. Finally, we present a possible extra dimensional scenario in which our model could be realized.

  • 121.
    Ezquiaga, J. M.
    et al.
    nstituto de Física Teórica UAM/CSIC, Universidad Autónoma de Madrid.
    García-Bellido, J.
    nstituto de Física Teórica UAM/CSIC, Universidad Autónoma de Madrid.
    Zumalacárregui, Miguel
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Towards the most general scalar-tensor theories of gravity: A unified approach in the language of differential forms2016In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 94, no 2, article id 024005Article in journal (Refereed)
    Abstract [en]

    We use a description based on differential forms to systematically explore the space of scalar-tensor theories of gravity. Within this formalism, we propose a basis for the scalar sector at the lowest order in derivatives of the field and in any number of dimensions. This minimal basis is used to construct a finite and closed set of Lagrangians describing general scalar-tensor theories invariant under local Lorentz transformations in a pseudo-Riemannian manifold, which contains ten physically distinct elements in four spacetime dimensions. Subsequently, we compute their corresponding equations of motion and find which combinations are at most second order in derivatives in four as well as an arbitrary number of dimensions. By studying the possible exact forms (total derivatives) and algebraic relations between the basis components, we discover that there are only four Lagrangian combinations producing second-order equations, which can be associated with Horndeski's theory. In this process, we identify a new second-order Lagrangian, named kinetic Gauss-Bonnet, that was not previously considered in the literature. However, we show that its dynamics is already contained in Horndeski's theory. Finally, we provide a full classification of the relations between different second-order theories. This allows us to clarify, for instance, the connection between different covariantizations of Galileons theory. In conclusion, our formulation affords great computational simplicity with a systematic structure. As a first step, we focus on theories with second-order equations of motion. However, this new formalism aims to facilitate advances towards unveiling the most general scalar-tensor theories.

  • 122. Ghosh, Monojit
    et al.
    Ghoshal, Pomita
    Goswami, Srubabati
    Nath, Newton
    Raut, Sushant K.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    New look at the degeneracies in the neutrino oscillation parameters, and their resolution by T2K, NO nu A and ICAL2016In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 93, no 1, article id 013013Article in journal (Refereed)
    Abstract [en]

    The three major unknown neutrino oscillation parameters at the present juncture are the mass hierarchy, the octant of the mixing angle theta(23) and the CP phase delta(CP). It is well known that the presence of hierarchy-delta(CP) and octant degeneracies affects the unambiguous determination of these parameters. In this paper, we show that a comprehensive way to study the remaining parameter degeneracies is in the form of a generalized hierarchy -theta(23) - delta(CP) degeneracy. This is best depicted as contours in the test (theta(23) - delta(CP)) plane for different representative true values of parameters. We show that the wrong-hierarchy and/or wrong-octant solutions can be further classified into eight different solutions depending on whether they occur with the wrong or right value of delta(CP). These eight solutions are different from the original eightfold degenerate solutions and can exist, in principle, even if theta(13) is known. These multiple solutions, apart from affecting the determination of the true hierarchy and octant, also affect the accurate estimation of delta(CP). We identify which of these eight different degenerate solutions can occur in the test (theta(23) - delta(CP)) parameter space, taking the long-baseline experiment NO nu A running in the neutrino mode as an example. The inclusion of the NO nu A antineutrino run removes the wrong-octant solutions appearing with both right and wrong hierarchy. Adding T2K data to this resolves the wrong hierarchy-right octant solutions to a large extent. The remaining wrong-hierarchy solutions can be removed by combining NO nu A + T2K with atmospheric neutrino data. We demonstrate this using ICAL@INO as the prototype atmospheric neutrino detector. We find that the degeneracies can be resolved at the 2 sigma level by the combined data set, for the true parameter space considered in the study.

  • 123. Good, Michael R. R.
    et al.
    Ong, Yen Chin
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm University, Sweden.
    Are black holes springlike?2015In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 91, no 4, article id 044031Article in journal (Refereed)
    Abstract [en]

    A (3 + 1)-dimensional asymptotically flat Kerr black hole angular speed Omega(+) can be used to define an effective spring constant, k = m Omega(2)(+). Its maximum value is the Schwarzschild surface gravity, k = kappa, which rapidly weakens as the black hole spins down and the temperature increases. The Hawking temperature is expressed in terms of the spring constant: 2 pi T = kappa - k. Hooke's law, in the extremal limit, provides the force F = 1/4, which is consistent with the conjecture of maximum force in general relativity.

  • 124. Gorsky, Alexander
    et al.
    Gudnason, Sven Bjarke
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Krikun, Alexander
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Baryon and chiral symmetry breaking in holographic QCD2015In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 91, no 12, article id 126008Article in journal (Refereed)
    Abstract [en]

    We study the relationship between chiral symmetry breaking and baryons in holographic QCD. We construct a soliton with unit baryon charge in the presence of a nonzero mean value of the scalar bifundamental field, which is dual to the chiral condensate. We obtain a relation between the chiral condensate and the mass of the baryon and find in a clear-cut way that at large values of the condensate the holographic soliton is no longer located on the IR wall. Instead it is split into two halves, which are symmetrically located on the left and right flavor branes. On the other hand we find that the local value of the quark condensate is suppressed in the core of the soliton, which is evidence for a partial chiral symmetry restoration inside the baryon.

  • 125. Greenwald, J.
    et al.
    Lenells, Jonatan
    Lu, J. X.
    Satheeshkumar, V. H.
    Wang, A.
    Black holes and global structures of spherical spacetimes in Horava-Lifshitz theory2011In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 84, no 8, article id 084040Article in journal (Refereed)
    Abstract [en]

    We systematically study black holes in the Horava-Lifshitz theory by following the kinematic approach, in which a horizon is defined as the surface at which massless test particles are infinitely redshifted. Because of the nonrelativistic dispersion relations, the speed of light is unlimited, and test particles do not follow geodesics. As a result, there are significant differences in causal structures and black holes between general relativity (GR) and the Horava-Lifshitz theory. In particular, the horizon radii generically depend on the energies of test particles. Applying them to the spherical static vacuum solutions found recently in the nonrelativistic general covariant theory of gravity, we find that, for test particles with sufficiently high energy, the radius of the horizon can be made as small as desired, although the singularities can be seen, in principle, only by observers with infinitely high energy. In these studies, we pay particular attention to the global structure of the solutions, and find that, because of the foliation-preserving- diffeomorphism symmetry, Diff(M,F), they are quite different from the corresponding ones given in GR, even though the solutions are the same. In particular, the Diff(M,F) does not allow Penrose diagrams. Among the vacuum solutions, some give rise to the structure of the Einstein-Rosen bridge, in which two asymptotically flat regions are connected by a throat with a finite nonzero radius. We also study slowly rotating solutions in such a setup, and obtain all the solutions characterized by an arbitrary function A 0(r). The case A0=0 reduces to the slowly rotating Kerr solution obtained in GR.

  • 126. Greenwald, J.
    et al.
    Lenells, Jonatan
    Satheeshkumar, V. H.
    Wang, A.
    Gravitational collapse in Hořava-Lifshitz theory2013In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 88, no 2, article id 024044Article in journal (Refereed)
    Abstract [en]

    We study gravitational collapse of a spherical fluid in nonrelativistic general covariant theory of the Hořava-Lifshitz gravity with the projectability condition and an arbitrary coupling constant λ, where |λ-1| characterizes the deviation of the theory from general relativity in the infrared limit. The junction conditions across the surface of a collapsing star are derived under the (minimal) assumption that the junctions be mathematically meaningful in terms of distribution theory. When the collapsing star is made of a homogeneous and isotropic perfect fluid, and the external region is described by a stationary spacetime, the problem reduces to the matching of six independent conditions. If the perfect fluid is pressureless (a dust fluid), it is found that the matching is also possible. In particular, in the case λ=1, the external spacetime is described by the Sch-(anti-)de Sitter solution written in Painlevé-Gullstrand coordinates. In the case λ≠1, the external spacetime is static but not asymptotically flat. Our treatment can be easily generalized to other versions of Hořava-Lifshitz gravity or, more generally, to any theory of higher-order derivative gravity.

  • 127.
    Gudnason, Sven Bjarke
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Nitta, Muneto
    Baryonic sphere: A spherical domain wall carrying baryon number2014In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 89, no 2, p. 025012-Article in journal (Refereed)
    Abstract [en]

    We construct a spherical domain wall which has baryon charge distributed on a sphere of finite radius in a Skyrme model with a sixth-order derivative term and a modified mass term. Its distribution of energy density likewise takes the form of a sphere. In order to localize the domain wall at a finite radius we need a negative coefficient in front of the Skyrme term and a positive coefficient of the sixth order derivative term to stabilize the soliton. Increasing the pion mass pronounces the shell-like structure of the configuration.

  • 128.
    Gudnason, Sven Bjarke
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, Sweden.
    Nitta, Muneto
    Baryonic torii: Toroidal baryons in a generalized Skyrme model2015In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 91, no 4, article id 045027Article in journal (Refereed)
    Abstract [en]

    We study a Skyrme-type model with a potential term motivated by Bose-Einstein condensates (BECs), which we call the BEC Skyrme model. We consider two flavors of the model: the first is the Skyrme model, and the second has a sixth-order derivative term instead of the Skyrme term, both with the added BEC-motivated potential. The model contains toroidally shaped Skyrmions, and they are characterized by two integers P and Q, representing the winding numbers of two complex scalar fields along the toroidal and poloidal cycles of the torus, respectively. The baryon number is B = PQ. We find stable Skyrmion solutions for P = 1, 2, 3, 4, 5 with Q = 1, while for P = 6 and Q = 1, it is only metastable. We further find that configurations with higher Q > 1 are all unstable and split into Q configurations with Q = 1. Finally we discover a phase transition, possibly of first order, in the mass parameter of the potential under study.

  • 129.
    Gudnason, Sven Bjarke
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Nitta, Muneto
    D-brane solitons in various dimensions2015In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 91, no 4, article id 045018Article in journal (Refereed)
    Abstract [en]

    We construct a D-brane soliton, a composite topological soliton sharing some properties with a D-brane, in a Skyrme model in 4 + 1 dimensions, in which Skyrmions are strings ending on a domain wall. We further generalize this D-brane soliton to diverse dimensions. A string, carrying the pi(N-1) topological charge, ends on a domain wall in an O(N) model with higher-derivative terms in N + 1 dimensions.

  • 130.
    Gudnason, Sven Bjarke
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Nitta, Muneto
    Domain wall Skyrmions2014In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 89, no 8, p. 085022-Article in journal (Refereed)
    Abstract [en]

    Skyrmions of different dimensions are related by domain walls. We obtain explicit full numerical solutions of various Skyrmion configurations trapped inside a domain wall. We find for the quadratic mass term that multi-Skyrmions are ring shaped and conjecture for the linear mass term, that the lowest-energy state of multi-Skyrmions will consist of charge-2 rings accommodated in a lattice.

  • 131.
    Gudnason, Sven Bjarke
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Chinese Acad Sci, Peoples R China.
    Nitta, Muneto
    Fractional Skyrmions and their molecules2015In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 91, no 8, article id 085040Article in journal (Refereed)
    Abstract [en]

    We study a Skyrme-type model with a quadratic potential for a field with S-2 vacua. We consider two flavors of the model, the first is the Skyrme model and the second has a sixth-order derivative term instead of the Skyrme term; both with the added quadratic potential. The model contains molecules of half Skyrmions, each of them is a global (anti)monopole with baryon number 1/2. We numerically construct solutions with baryon numbers one through six, and find stable solutions which look like beads on rings. We also construct a molecule with fractional Skyrmions having the baryon numbers 1/3 + 2/3, by adding a linear potential term.

  • 132.
    Gudnason, Sven Bjarke
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, Sweden.
    Nitta, Muneto
    Incarnations of Skyrmions2014In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 90, no 8, p. 085007-Article in journal (Refereed)
    Abstract [en]

    Skyrmions can be transformed into lumps or baby Skyrmions by being trapped inside a domain wall. Here we find that they can also be transformed into sine-Gordon kinks when confined by vortices, resulting in confined Skyrmions. We show this both by an effective field theory approach and by direct numerical calculations. The existence of these trapped and confined Skyrmions does not rely on higher-derivative terms when the host solitons are flat or straight. We also construct a Skyrmion as a twisted vortex ring in a model with a sixth-order derivative term.

  • 133.
    Heisenberg, Lavinia
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm University, Sweden..
    More on effective composite metrics2015In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 92, no 2, article id 023525Article in journal (Refereed)
    Abstract [en]

    In this work we study different classes of effective composite metrics proposed in the context of one-loop quantum corrections in bimetric gravity. For this purpose we consider contributions of the matter loops in the form of cosmological constants and potential terms yielding two types of effective composite metrics. This guarantees a nice behavior at the quantum level. However, the theoretical consistency at the classical level needs to be ensured additionally. It turns out that among all these possible couplings, only one unique effective metric survives these criteria at the classical level.

  • 134.
    Hossenfelder, Sabine
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Analog systems for gravity duals2015In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 91, no 12, article id 124064Article in journal (Refereed)
    Abstract [en]

    We show that analog gravity systems exist for charged, planar black holes in asymptotic anti-de Sitter space. These black holes have been employed to describe, via the gauge-gravity duality, strongly coupled condensed matter systems on the boundary of anti-de Sitter (AdS) space. The analog gravity system is a different condensed matter system that, in a suitable limit, describes the same bulk physics as the theory on the AdS boundary. This combination of the gauge-gravity duality and analog gravity therefore suggests a duality between different condensed matter systems.

  • 135.
    Hossenfelder, Sabine
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Comment on "Relative locality and the soccer ball problem"2013In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 88, no 2, p. 028701-Article in journal (Other academic)
    Abstract [en]

    It is explained why the argument by Amelino-Camelia et al. [Phys. Rev. D 84, 087702 (2011)] does not answer the question how to describe multiparticle states in models with a deformed Lorentz symmetry in momentum space.

  • 136.
    Hossenfelder, Sabine
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Disentangling the black hole vacuum2015In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 91, no 4, article id 044015Article in journal (Refereed)
    Abstract [en]

    We study the question of whether disentanglement of Hawking radiation can be achieved with any local operation. We assume that the operation we look for is unitary, from which follow restrictions on its action on basis vectors. This allows us to formulate requirements on the operation of disentanglement. We then show that these requirements can be fulfilled by a timelike boundary condition in the near-horizon area and that the local observer does not notice the presence of the boundary and does not encounter a firewall.

  • 137.
    Hossenfelder, Sabine
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Phenomenology of space-time imperfection. I. Nonlocal defects2013In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 88, no 12, p. 124030-Article in journal (Refereed)
    Abstract [en]

    If space-time is emergent from a fundamentally nongeometric theory it will generically be left with defects. Such defects need not respect the locality that emerges with the background. Here, we develop a phenomenological model that parametrizes the effects of nonlocal defects on the propagation of particles. In this model, Lorentz invariance is preserved on the average. We derive constraints on the density of defects from various experiments.

  • 138.
    Hossenfelder, Sabine
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Phenomenology of space-time imperfection. II. Local defects2013In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 88, no 12, p. 124031-Article in journal (Refereed)
    Abstract [en]

    We propose a phenomenological model for the scattering of particles on space-time defects in a treatment that maintains Lorentz invariance on the average. The local defects considered here cause a stochastic violation of momentum conservation. The scattering probability is parametrized in the density of defects and the distribution of the momentum that a particle can obtain when scattering on the defect. We identify the most promising observable consequences and derive constraints from existing data.

  • 139.
    Johansson, Henrik
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. CERN, Dept Phys, Theory Grp, CH-1211 Geneva 23, Switzerland.
    Kosower, David A.
    Larsen, Kasper J.
    Sogaard, Mads
    Cross-order integral relations from maximal cuts2015In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 92, no 2, article id 025015Article in journal (Refereed)
    Abstract [en]

    We study the Anastasiou-Bern-Dixon-Kosower relation using maximal cuts of one-and two-loop integrals with up to five external legs. We show how to find a special combination of integrals that allows the relation to exist, and how to reconstruct the terms with one-loop integrals squared. The reconstruction relies on the observation that integrals across different loop orders can have support on the same generalized unitarity cuts and can share global poles. We discuss the appearance of nonhomologous integration contours in multivariate residues. Their origin can be understood in simple terms, and their existence enables us to distinguish contributions from different integrals. Our analysis suggests that maximal and near-maximal cuts can be used to infer the existence of integral identities more generally.

  • 140. Kahniashvili, Tina
    et al.
    Brandenburg, Axel
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Campanelli, Leonardo
    Ratra, Bharat
    Tevzadze, Alexander G.
    Evolution of inflation-generated magnetic field through phase transitions2012In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 86, no 10, p. 103005-Article in journal (Refereed)
    Abstract [en]

    We study the evolution of an inflation-generated magnetic field, due to its coupling to fluid motions, during cosmological phase transitions. We find that the magnetic field stays almost unchanged on large scales, while on small scales, the spectrum is modified in such a way that power at small scales becomes progressively suppressed. We also show that the magnetic field generates turbulent motions in the initially turbulence-free plasma. On large scales, the slope of the resulting kinetic energy spectrum is consistent with that of white noise.

  • 141. Kahniashvili, Tina
    et al.
    Kar, Arjun
    Lavrelashvili, George
    Agarwal, Nishant
    Heisenberg, Lavinia
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm University, Sweden.
    Kosowsky, Arthur
    Cosmic expansion in extended quasidilaton massive gravity2015In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 91, no 4, article id 041301Article in journal (Refereed)
    Abstract [en]

    Quasidilaton massive gravity offers a physically well-defined gravitational theory with nonzero graviton mass. We present the full set of dynamical equations governing the expansion history of the Universe, valid during radiation domination, matter domination, and a late-time self-accelerating epoch related to the graviton mass. The existence of self-consistent solutions constrains the amplitude of the quasidilaton field and the graviton mass, as well as other model parameters. We point out that the effective mass of gravitational waves can be significantly larger than the graviton mass, opening the possibility that a single theory can explain both the late-time acceleration of cosmic expansion and modifications of structure growth leading to the suppression of large-angle correlations observed in the cosmic microwave background.

  • 142. Kahniashvili, Tina
    et al.
    Tevzadze, Alexander G.
    Brandenburg, Axel
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Neronov, Andrii
    Evolution of primordial magnetic fields from phase transitions2013In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 87, no 8, p. 083007-Article in journal (Refereed)
    Abstract [en]

    We consider the evolution of primordial magnetic fields generated during cosmological, electroweak, or QCD phase transitions. We assume that the magnetic field generation can be described as an injection of magnetic energy to cosmological plasma at a given scale determined by the moment of magnetic field generation. A high Reynolds number ensures strong coupling between the magnetic field and fluid motions. The subsequent evolution of the magnetic field is governed by decaying hydromagnetic turbulence. Both our numerical simulations and a phenomenological description allow us to recover "universal'' laws for the decay of magnetic energy and the growth of magnetic correlation length in the turbulent (low-viscosity) regime. In particular, we show that during the radiation-dominated epoch, the energy and correlation length of nonhelical magnetic fields scale as conformal time to the powers -1/2 and +1/2, respectively. For helical magnetic fields, the energy and correlation length scale as conformal time to the powers -1/3 and +2/3, respectively. The universal decay law of the magnetic field implies that the strength of the magnetic field generated during the QCD phase transition could reach similar to 10(-9) G with the present-day correlation length similar to 50 kpc. The fields generated at the electroweak phase transition could be as strong as similar to 10(-10) G with correlation lengths reaching similar to 0.3 kpc. These values of the magnetic fields are consistent with the lower bounds of the extragalactic magnetic fields.

  • 143.
    Keränen, Ville
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Nonequilibrium Wilson loops in N=4 super Yang-Mills theory2013In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 88, no 10, p. 105022-Article in journal (Refereed)
    Abstract [en]

    We consider rectangular Wilson loops in certain nonequilibrium quantum states in N = 4 super Yang-Mills theory at weak coupling, prepared with a quantum quench. We find that in the ladder approximation, the Bethe-Salpeter equation can be reduced to solving a massive 1 + 1 dimensional wave equation with a leaking boundary condition leading to a quasinormal behavior analogous to what is found in studying dynamics of fields in black hole backgrounds. Furthermore, we find that the Wilson loops with size L approach a thermal form after time T approximate to L/2. The thermal form found in the current paper follows from the particular initial state chosen.

  • 144. Krog, Jens
    et al.
    Mojaza, Matin
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Sannino, Francesco
    Four-fermion limit of gauge-Yukawa theories2015In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 92, no 8, article id 085043Article in journal (Refereed)
    Abstract [en]

    We elucidate and extend the conditions that map gauge-Yukawa theories at low energies into time-honored gauged four-fermion interactions at high energies. These compositeness conditions permit us to investigate theories of composite dynamics through gauge-Yukawa theories. Here we investigate whether perturbative gauge-Yukawa theories can have a strongly coupled limit at high energy that can be mapped into a four-fermion theory. Interestingly, we are able to precisely carve out a region of the perturbative parameter space supporting such a composite limit. This has interesting implications on our current view on models of particle physics. As a template model we use an SU(N-C) gauge theory with N-F Dirac fermions transforming according to the fundamental representation of the gauge group. The fermions further interact with a gauge singlet complex N-F x N-F Higgs boson that ceases to be a physical degree of freedom at the ultraviolet composite scale, where it gives away to the four-fermion interactions. We compute the hierarchy between the ultraviolet and infrared composite scales of the theory and show that they are naturally large and well separated. Our results show that some weakly coupled gauge-Yukawa theories can be viewed, in fact, as composite theories. It is therefore tantalizing to speculate that the standard model, with its phenomenological perturbative Higgs sector, could hide, in plain sight, a composite theory.

  • 145.
    Könnig, F.
    KTH. Ruprecht-Karls-Universität Heidelberg, Germany.
    Higuchi ghosts and gradient instabilities in bimetric gravity2015In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 91, no 10, article id 104019Article in journal (Refereed)
    Abstract [en]

    Bimetric gravity theories allow for many different types of cosmological solutions, but not all of them are theoretically allowed. In this work we discuss the conditions to satisfy the Higuchi bound and to avoid gradient instabilities in the scalar sector at the linear level. We find that in expanding universes the ratio of the scale factors of the reference and observable metric has to increase at all times. This automatically implies a ghost-free helicity-2 and helicity-0 sector and enforces a phantom dark energy. Furthermore, the condition for the absence of gradient instabilities in the scalar sector will be analyzed. Finally, we discuss whether cosmological solutions can exist, including exotic evolutions like bouncing cosmologies, in which both the Higuchi ghost and scalar instabilities are absent at all times.

  • 146. Larjo, Klaus
    et al.
    Lowe, David A.
    Thorlacius, Larus
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Black holes without firewalls2013In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 87, no 10, p. 104018-Article in journal (Refereed)
    Abstract [en]

    The postulates of black hole complementarity do not imply a firewall for infalling observers at a black hole horizon. The dynamics of the stretched horizon, that scrambles and reemits information, determines whether infalling observers experience anything out of the ordinary when entering a large black hole. In particular, there is no firewall if the stretched horizon degrees of freedom retain information for a time of the order of the black hole scrambling time.

  • 147. Lindner, M.
    et al.
    Merle, Alexander
    Max-Planck-Institut für Kernphysik, Heidelberg, Germany.
    Niro, V.
    Enhancing dark matter annihilation into neutrinos2010In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 82, no 12, p. 123529-Article in journal (Refereed)
    Abstract [en]

    We perform a detailed and quasi model-independent analysis of direct annihilation of dark matter into neutrinos. Considering different cases for scalar and fermionic dark matter, we identify several settings in which this annihilation is enhanced, contrary to some statements in the literature. The key point is that several restrictions of, e.g., a supersymmetric framework do not hold in general. The mass generation mechanism of the neutrinos plays an important role, too. We illustrate our considerations by two examples that are not (as usually) suppressed by the smallness of the neutrino mass, for which we also present a numerical analysis. Our results can be easily used as guidelines for model building.

  • 148. Liu, Ji-Yuan
    et al.
    Zhou, Shun
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Hybrid textures of Majorana neutrino mass matrix and current experimental tests2013In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 87, no 9, p. 093010-Article in journal (Refereed)
    Abstract [en]

    Motivated by recent measurements of a relatively large theta(13) in the Daya Bay and RENO reactor neutrino experiments, we carry out a systematic analysis of the hybrid textures of Majorana neutrino mass matrix M-v, which contain one texture zero and two equal nonzero matrix elements. We show that three neutrino masses (m(1).m(2).m(3)) and three leptonic CP-violating phases (delta, rho, sigma) can fully be determined from two neutrino mass-squared differences (delta m(2), Delta m(2)) and three flavor mixing angles (theta(12), theta(23), theta(13)). Out of sixty logically possible patterns of M-v, thirty-nine are found to be compatible with current experimental data at the 3 sigma level. We demonstrate that the texture zero of M-v is stable against one-loop quantum corrections, while the equality between two independent elements not. Phenomenological implications of M-v for the neutrinoless double-beta decay and leptonic CP violation are discussed, and a realization of the texture zero and equality by means of discrete flavor symmetries is illustrated.

  • 149. Lowe, David A.
    et al.
    Thorlacius, Larus
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Pure states and black hole complementarity2013In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 88, no 4, p. 044012-Article in journal (Refereed)
    Abstract [en]

    The future apparent horizon of a black hole develops large stress energy due to quantum effects, unless the outgoing modes are in a thermal density matrix at the local Hawking temperature. It is shown for generic pure states that the deviation from thermality is so small that infalling observers will see no drama on their way to the stretched horizon, providing a derivation of black hole complementarity after the Page time. Atypical pure states, and atypical observers, may of course see surprises, but that is not surprising.

  • 150. Ma, H. -H
    et al.
    Wu, X. -G
    Ma, Y.
    Brodsky, S. J.
    Mojaza, Matin
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Setting the renormalization scale in perturbative QCD: Comparisons of the principle of maximum conformality with the sequential extended Brodsky-Lepage-Mackenzie approach2015In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 91, no 9, article id 094028Article in journal (Refereed)
    Abstract [en]

    A key problem in making precise perturbative QCD (pQCD) predictions is how to set the renormalization scale of the running coupling unambiguously at each finite order. The elimination of the uncertainty in setting the renormalization scale in pQCD will greatly increase the precision of collider tests of the Standard Model and the sensitivity to new phenomena. Renormalization group invariance requires that predictions for observables must also be independent on the choice of the renormalization scheme. The well-known Brodsky-Lepage-Mackenzie (BLM) approach cannot be easily extended beyond next-to-next-to-leading order of pQCD. Several suggestions have been proposed to extend the BLM approach to all orders. In this paper we discuss two distinct methods. One is based on the "Principle of Maximum Conformality" (PMC), which provides a systematic all-orders method to eliminate the scale and scheme ambiguities of pQCD. The PMC extends the BLM procedure to all orders using renormalization group methods; as an outcome, it significantly improves the pQCD convergence by eliminating renormalon divergences. An alternative method is the "sequential extended BLM" (seBLM) approach, which has been primarily designed to improve the convergence of pQCD series. The seBLM, as originally proposed, introduces auxiliary fields and follows the pattern of the β0-expansion to fix the renormalization scale. However, the seBLM requires a recomputation of pQCD amplitudes including the auxiliary fields; due to the limited availability of calculations using these auxiliary fields, the seBLM has only been applied to a few processes at low orders. In order to avoid the complications of adding extra fields, we propose a modified version of seBLM which allows us to apply this method to higher orders. We then perform detailed numerical comparisons of the two alternative scale-setting approaches by investigating their predictions for the annihilation cross section ratio Re+e- at four-loop order in pQCD.

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