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Showing papers in "Physical Review D in 2009"


Journal ArticleDOI
TL;DR: In this article, a quantum field theory of gravity with dynamical critical exponent equal to $z = 3$ in the UV is presented. But this theory is restricted to satisfy the condition of detailed balance.
Abstract: We present a candidate quantum field theory of gravity with dynamical critical exponent equal to $z=3$ in the UV. (As in condensed-matter systems, $z$ measures the degree of anisotropy between space and time.) This theory, which at short distances describes interacting nonrelativistic gravitons, is power-counting renormalizable in $3+1$ dimensions. When restricted to satisfy the condition of detailed balance, this theory is intimately related to topologically massive gravity in three dimensions, and the geometry of the Cotton tensor. At long distances, this theory flows naturally to the relativistic value $z=1$, and could therefore serve as a possible candidate for a UV completion of Einstein's general relativity or an infrared modification thereof. The effective speed of light, the Newton constant and the cosmological constant all emerge from relevant deformations of the deeply nonrelativistic $z=3$ theory at short distances.

2,816 citations


Journal ArticleDOI
TL;DR: In this article, the authors study the connection between self-acceleration and the presence of ghosts for a quite generic class of theories that modify gravity in the infrared, defined as those that at distances shorter than cosmological, reduce to a certain generalization of the Dvali-Gabadadze-Porrati (DGP) effective theory.
Abstract: In the Dvali-Gabadadze-Porrati (DGP) model, the "self-accelerating" solution is plagued by a ghost instability, which makes the solution untenable. This fact, as well as all interesting departures from general relativity (GR), are fully captured by a four-dimensional effective Lagrangian, valid at distances smaller than the present Hubble scale. The 4D effective theory involves a relativistic scalar pi, universally coupled to matter and with peculiar derivative self-interactions. In this paper, we study the connection between self-acceleration and the presence of ghosts for a quite generic class of theories that modify gravity in the infrared. These theories are defined as those that at distances shorter than cosmological, reduce to a certain generalization of the DGP 4D effective theory. We argue that for infrared modifications of GR locally due to a universally coupled scalar, our generalization is the only one that allows for a robust implementation of the Vainshtein effect-the decoupling of the scalar from matter in gravitationally bound systems-necessary to recover agreement with solar-system tests. Our generalization involves an internal Galilean invariance, under which pi's gradient shifts by a constant. This symmetry constrains the structure of the pi Lagrangian so much so that in 4D there exist only five terms that can yield sizable nonlinearities without introducing ghosts. We show that for such theories in fact there are "self-accelerating" de Sitter solutions with no ghostlike instabilities. In the presence of compact sources, these solutions can support spherically symmetric, Vainshtein-like nonlinear perturbations that are also stable against small fluctuations. We investigate a possible infrared completion of these theories at scales of order of the Hubble horizon, and larger. There are however some features of our theories that may constitute a problem at the theoretical or phenomenological level: the presence of superluminal excitations; the extreme subluminality of other excitations, which makes the quasistatic approximation for certain solar-system observables unreliable due to Cherenkov emission; the very low strong-interaction scale for pi pi scatterings.

2,086 citations


Journal ArticleDOI
TL;DR: In this paper, the authors proposed a light boson invoked by XDM to mediate a large inelastic scattering cross section for the DAMA annual modulation signal at low velocities at redshift, which could produce observable effects on the ionization history of the universe.
Abstract: � > 1GeV 1 . The long range allows a Sommerfeld enhancement to boost the annihilation cross section as required, without altering the weak-scale annihilation cross section during dark matter freeze-out in the early universe. If the dark matter annihilates into the new force carrier φ, its low mass can make hadronic modes kinematically inaccessible, forcing decays dominantly into leptons. If the force carrier is a non-Abelian gauge boson, the dark matter is part of a multiplet of states, and splittings between these states are naturally generated with size αm� � MeV, leading to the eXciting dark matter (XDM) scenario previously proposed to explain the positron annihilation in the galactic center observed by the INTEGRAL satellite; the light boson invoked by XDM to mediate a large inelastic scattering cross section is identified with the φ here. Somewhat smaller splittings would also be expected, providing a natural source for the parameters of the inelastic dark matter (iDM) explanation for the DAMA annual modulation signal. Since the Sommerfeld enhancement is most significant at low velocities, early dark matter halos at redshift � 10 potentially produce observable effects on the ionization history of the universe. Because of the enhanced cross section, detection of substructure is more probable than with a conventional WIMP. Moreover, the low velocity dispersion of dwarf galaxies and Milky Way subhalos can increase the substructure annihilation signal by an additional order of magnitude or more.

1,682 citations


Journal ArticleDOI
TL;DR: The existence of axions over a vast mass range from 10-33eV to 10-10eV was investigated in this article, where it was shown that axions in the mass range between 10-28eV and 10-18eV give rise to multiple steps in the matter power spectrum, that will be probed by upcoming galaxy surveys.
Abstract: String theory suggests the simultaneous presence of many ultralight axions possibly populating each decade of mass down to the Hubble scale 10^-33eV Conversely the presence of such a plenitude of axions (an "axiverse") would be evidence for string theory, since it arises due to the topological complexity of the extra-dimensional manifold and is ad hoc in a theory with just the four familiar dimensions We investigate how upcoming astrophysical experiments will explore the existence of such axions over a vast mass range from 10^-33eV to 10^-10eV Axions with masses between 10^-33eV to 10^-28eV cause a rotation of the CMB polarization that is constant throughout the sky The predicted rotation angle is of order \alpha~1/137 Axions in the mass range 10^-28eV to 10^-18eV give rise to multiple steps in the matter power spectrum, that will be probed by upcoming galaxy surveys Axions in the mass range 10^-22eV to 10^-10eV affect the dynamics and gravitational wave emission of rapidly rotating astrophysical black holes through the Penrose superradiance process When the axion Compton wavelength is of order of the black hole size, the axions develop "superradiant" atomic bound states around the black hole "nucleus" Their occupation number grows exponentially by extracting rotational energy from the ergosphere, culminating in a rotating Bose-Einstein axion condensate emitting gravitational waves This mechanism creates mass gaps in the spectrum of rapidly rotating black holes that diagnose the presence of axions The rapidly rotating black hole in the X-ray binary LMC X-1 implies an upper limit on the decay constant of the QCD axion f_a<2*10^17GeV, much below the Planck mass This reach can be improved down to the grand unification scale f_a<2*10^16GeV, by observing smaller stellar mass black holes

1,279 citations


Journal ArticleDOI
TL;DR: In this paper, the authors considered the Galileon field in a dynamical spacetime and showed that a unique nonminimal coupling of the galileon to curvature eliminates all higher derivatives in all field equations, hence yielding second-order equations, without any extra propagating degree of freedom.
Abstract: We consider the recently introduced "galileon" field in a dynamical spacetime When the galileon is assumed to be minimally coupled to the metric, we underline that both field equations of the galileon and the metric involve up to third-order derivatives We show that a unique nonminimal coupling of the galileon to curvature eliminates all higher derivatives in all field equations, hence yielding second-order equations, without any extra propagating degree of freedom The resulting theory breaks the generalized "Galilean" invariance of the original model

1,069 citations


Journal ArticleDOI
TL;DR: In this article, it was shown that the recently detected acceleration of the Uuniverse can be understood by considering a modification of the teleparallel equivalent of general relativity, with no need of dark energy.
Abstract: It is shown that the recently detected acceleration of the Uuniverse can be understood by considering a modification of the teleparallel equivalent of general relativity, with no need of dark energy. The solution also exhibits phases dominated by matter and radiation as expected in the standard cosmological evolution. We perform a joint analysis with measurements of the most recent type Ia supernovae, baryon acoustic oscillation peak, and estimates of the cosmic microwave background shift parameter data to constrain the only new parameter this theory has.

1,030 citations


Journal ArticleDOI
TL;DR: In this paper, it was shown that the near-horizon quantum states can be identified with those of (a chiral half of) a two-dimensional conformal field theory (CFT), and the results apply to any consistent unitary quantum theory of gravity with a Kerr solution.
Abstract: Quantum gravity in the region very near the horizon of an extreme Kerr black hole (whose angular momentum and mass are related by J=GM^2) is considered. It is shown that consistent boundary conditions exist, for which the asymptotic symmetry generators form one copy of the Virasoro algebra with central charge c_L=12J / \hbar. This implies that the near-horizon quantum states can be identified with those of (a chiral half of) a two-dimensional conformal field theory (CFT). Moreover, in the extreme limit, the Frolov-Thorne vacuum state reduces to a thermal density matrix with dimensionless temperature T_L=1/2\pi and conjugate energy given by the zero mode generator, L_0, of the Virasoro algebra. Assuming unitarity, the Cardy formula then gives a microscopic entropy S_{micro}=2\pi J / \hbar for the CFT, which reproduces the macroscopic Bekenstein-Hawking entropy S_{macro}=Area / 4\hbar G. The results apply to any consistent unitary quantum theory of gravity with a Kerr solution. We accordingly conjecture that extreme Kerr black holes are holographically dual to a chiral two-dimensional conformal field theory with central charge c_L=12J / \hbar, and in particular that the near-extreme black hole GRS 1915+105 is approximately dual to a CFT with c_L \sim 2 \times 10^{79}.

1,011 citations


Journal ArticleDOI
TL;DR: In this paper, the authors extend flat-space scalar field models that obey purely second-order equations, while maintaining their secondorder dependence on both field and metric, and restore to second order the stress tensors as well.
Abstract: We extend to curved backgrounds all flat-space scalar field models that obey purely second-order equations, while maintaining their second-order dependence on both field and metric. This extension simultaneously restores to second order the, originally higher derivative, stress tensors as well. The process is transparent and uniform for all dimensions.

821 citations


Journal ArticleDOI
TL;DR: In this article, it was shown that the anomalous energy distribution of muon pairs is consistent with the hypothesis of the HyperCP Collaboration, without direct contradiction to the existing data on radiative kaon decays.
Abstract: A secluded U(1) sector with weak admixture to photons, $O({10}^{\ensuremath{-}2}\ensuremath{-}{10}^{\ensuremath{-}3})$, and the scale of the breaking below 1 GeV represents a natural yet poorly constrained extension of the standard model. We analyze $g\ensuremath{-}2$ of muons and electrons together with other precision QED data, as well as radiative decays of strange particles to constrain the mass-mixing angle (${m}_{V}\ensuremath{-}\ensuremath{\kappa}$) parameter space. We point out that ${m}_{V}\ensuremath{\simeq}214\text{ }\text{ }\mathrm{MeV}$ and ${\ensuremath{\kappa}}^{2}g3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ can be consistent with the hypothesis of the HyperCP Collaboration, which seeks to explain the anomalous energy distribution of muon pairs in the ${\ensuremath{\Sigma}}^{+}\ensuremath{\rightarrow}p{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ process by a resonance, without direct contradiction to the existing data on radiative kaon decays. The same parameters lead to an $O(\mathrm{\text{few}}\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9})$ upward correction to the anomalous magnetic moment of the muon, possibly relaxing some tension between the experimental value and theoretical determinations of $g\ensuremath{-}2$. The ultrafine energy resolution scan of the ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ cross section and dedicated analysis of lepton spectra from ${K}^{+}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{e}^{+}{e}^{\ensuremath{-}}$ decays should be able to provide a conclusive test of this hypothesis and improve the constraints on the model.

750 citations


Journal ArticleDOI
TL;DR: In this paper, the production and decay properties of new light gauge bosons were identified, and five new experimental approaches were proposed to cover most of the natural parameter space, using currently operating GeV-energy beams and well-established detection methods.
Abstract: Fixed-target experiments are ideally suited for discovering new MeV--GeV mass $U(1)$ gauge bosons through their kinetic mixing with the photon. In this paper, we identify the production and decay properties of new light gauge bosons that dictate fixed-target search strategies. We summarize existing limits and suggest five new experimental approaches that we anticipate can cover most of the natural parameter space, using currently operating GeV-energy beams and well-established detection methods. Such experiments are particularly timely in light of recent terrestrial and astrophysical anomalies (PAMELA, Fermi, DAMA/LIBRA, etc.) consistent with dark matter charged under a new gauge force.

673 citations


Journal ArticleDOI
TL;DR: In this article, the Lyapunov exponent was used to determine the quasinormal modes of black holes in any dimensions, independent of the field equations and only assuming a stationary, spherically symmetric and asymptotically flat line element.
Abstract: Geodesic motion determines important features of spacetimes. Null unstable geodesics are closely related to the appearance of compact objects to external observers and have been associated with the characteristic modes of black holes. By computing the Lyapunov exponent, which is the inverse of the instability time scale associated with this geodesic motion, we show that, in the eikonal limit, quasinormal modes of black holes in any dimensions are determined by the parameters of the circular null geodesics. This result is independent of the field equations and only assumes a stationary, spherically symmetric and asymptotically flat line element, but it does not seem to be easily extendable to anti-de Sitter spacetimes. We further show that (i) in spacetime dimensions greater than four, equatorial circular timelike geodesics in a Myers-Perry black-hole background are unstable, and (ii) the instability time scale of equatorial null geodesics in Myers-Perry spacetimes has a local minimum for spacetimes of dimension d ≥ 6.

Journal ArticleDOI
TL;DR: In this paper, a simple class of models in which the relic density of dark matter is determined by the baryon asymmetry of the Universe was considered, where the interactions that transfer the asymmetry decouple at temperatures above the dark matter mass, freezing in a dark matter asymmetry.
Abstract: We consider a simple class of models in which the relic density of dark matter is determined by the baryon asymmetry of the Universe. In these models a B-L asymmetry generated at high temperatures is transferred to the dark matter, which is charged under B-L. The interactions that transfer the asymmetry decouple at temperatures above the dark matter mass, freezing in a dark matter asymmetry of order the baryon asymmetry. This explains the observed relation between the baryon and dark matter densities for the dark matter mass in the range 5-15 GeV. The symmetric component of the dark matter can annihilate efficiently to light pseudoscalar Higgs particles a or via t-channel exchange of new scalar doublets. The first possibility allows for h{sup 0}{yields}aa decays, while the second predicts a light charged Higgs-like scalar decaying to {tau}{nu}. Direct detection can arise from Higgs exchange in the first model or a nonzero magnetic moment in the second. In supersymmetric models, the would-be lightest supersymmetric partner can decay into pairs of dark matter particles plus standard model particles, possibly with displaced vertices.

Journal ArticleDOI
TL;DR: In this paper, the authors study the various linear responses of neutron stars to external relativistic tidal fields and find that the Love number of a star decreases with the radius of the star.
Abstract: We study the various linear responses of neutron stars to external relativistic tidal fields. We focus on three different tidal responses, associated to three different tidal coefficients: (i) a gravito-electric-type coefficient $G{\ensuremath{\mu}}_{\ensuremath{\ell}}=[\mathrm{\text{length}}{]}^{2\ensuremath{\ell}+1}$ measuring the $\ensuremath{\ell}$th-order mass multipolar moment $G{M}_{{a}_{1}\dots{}{a}_{\ensuremath{\ell}}}$ induced in a star by an external $\ensuremath{\ell}$th-order gravito-electric tidal field ${G}_{{a}_{1}\dots{}{a}_{\ensuremath{\ell}}}$; (ii) a gravito-magnetic-type coefficient $G{\ensuremath{\sigma}}_{\ensuremath{\ell}}=[\mathrm{\text{length}}{]}^{2\ensuremath{\ell}+1}$ measuring the $\ensuremath{\ell}$th spin multipole moment $G{S}_{{a}_{1}\dots{}{a}_{\ensuremath{\ell}}}$ induced in a star by an external $\ensuremath{\ell}$th-order gravito-magnetic tidal field ${H}_{{a}_{1}\dots{}{a}_{\ensuremath{\ell}}}$; and (iii) a dimensionless ``shape'' Love number ${h}_{\ensuremath{\ell}}$ measuring the distortion of the shape of the surface of a star by an external $\ensuremath{\ell}$th-order gravito-electric tidal field. All the dimensionless tidal coefficients $G{\ensuremath{\mu}}_{\ensuremath{\ell}}/{R}^{2\ensuremath{\ell}+1}$, $G{\ensuremath{\sigma}}_{\ensuremath{\ell}}/{R}^{2\ensuremath{\ell}+1}$, and ${h}_{\ensuremath{\ell}}$ (where $R$ is the radius of the star) are found to have a strong sensitivity to the value of the star's ``compactness'' $c\ensuremath{\equiv}GM/({c}_{0}^{2}R)$ (where we indicate by ${c}_{0}$ the speed of light). In particular, $G{\ensuremath{\mu}}_{\ensuremath{\ell}}/{R}^{2\ensuremath{\ell}+1}\ensuremath{\sim}{k}_{\ensuremath{\ell}}$ is found to strongly decrease, as $c$ increases, down to a zero value as $c$ is formally extended to the ``black hole (BH) limit'' ${c}^{\mathrm{BH}}=1/2$. The shape Love number ${h}_{\ensuremath{\ell}}$ is also found to significantly decrease as $c$ increases, though it does not vanish in the formal limit $c\ensuremath{\rightarrow}{c}^{\mathrm{BH}}$, but is rather found to agree with the recently determined shape Love numbers of black holes. The formal vanishing of ${\ensuremath{\mu}}_{\ensuremath{\ell}}$ and ${\ensuremath{\sigma}}_{\ensuremath{\ell}}$ as $c\ensuremath{\rightarrow}{c}^{\mathrm{BH}}$ is a consequence of the no-hair properties of black holes. This vanishing suggests, but in no way proves, that the effective action describing the gravitational interactions of black holes may not need to be augmented by nonminimal worldline couplings.

Journal ArticleDOI
TL;DR: In this article, a parametrized high-density equation of state (EOS) based on piecewise polytropes with 3 free parameters was introduced to systematize the study of constraints placed by astrophysical observations on the nature of neutron-star matter.
Abstract: We introduce a parametrized high-density equation of state (EOS) in order to systematize the study of constraints placed by astrophysical observations on the nature of neutron-star matter To obtain useful constraints, the number of parameters must be smaller than the number of EOS-related neutron-star properties measured, but large enough to accurately approximate the large set of candidate EOSs We find that a parametrized EOS based on piecewise polytropes with 3 free parameters matches, to about 4% rms error, an extensive set of candidate EOSs at densities below the central density of $14{M}_{\ensuremath{\bigodot}}$ stars Adding observations of more massive stars constrains the higher-density part of the EOS and requires an additional parameter We obtain constraints on the allowed parameter space set by causality and by present and near-future astronomical observations with the least model dependence Stringent constraints on the EOS parameter space are associated with the future measurement of the moment of inertia of PSR J0737-3039A combined with the maximum known neutron-star mass We also present in an appendix a more efficient algorithm than has previously been used for finding points of marginal stability and the maximum angular velocity of stable stars

Journal ArticleDOI
TL;DR: In this article, the equation of state in $2+1$ flavor QCD at finite temperature with physical strange quark mass and almost physical light quark masses using lattices with temporal extent was calculated.
Abstract: We calculate the equation of state in $2+1$ flavor QCD at finite temperature with physical strange quark mass and almost physical light quark masses using lattices with temporal extent ${N}_{\ensuremath{\tau}}=8$. Calculations have been performed with two different improved staggered fermion actions, the asqtad and p4 actions. Overall, we find good agreement between results obtained with these two $O({a}^{2})$ improved staggered fermion discretization schemes. A comparison with earlier calculations on coarser lattices is performed to quantify systematic errors in current studies of the equation of state. We also present results for observables that are sensitive to deconfining and chiral aspects of the QCD transition on ${N}_{\ensuremath{\tau}}=6$ and 8 lattices. We find that deconfinement and chiral symmetry restoration happen in the same narrow temperature interval. In an appendix we present a simple parametrization of the equation of state that can easily be used in hydrodynamic model calculations. In this parametrization we include an estimate of current uncertainties in the lattice calculations which arise from cutoff and quark mass effects.

Journal ArticleDOI
TL;DR: In this article, the authors proposed to replace the future event horizon area with the inverse of the Ricci scalar curvature, which is phenomenologically viable and naturally solves the coincidence problem of dark energy.
Abstract: Motivated by the holographic principle, it has been suggested that the dark energy density may be inversely proportional to the area of the event horizon of the Universe. However, such a model would have a causality problem. In this paper, we propose to replace the future event horizon area with the inverse of the Ricci scalar curvature. We show that this model does not only avoid the causality problem and is phenomenologically viable, but also naturally solves the coincidence problem of dark energy. Our analysis of the evolution of density perturbations show that the matter power spectra and cosmic microwave background temperature anisotropy is only slightly affected by such modification.

Journal ArticleDOI
TL;DR: In this article, it was shown that the effective-theory approach upon which that claim is based ceases to be valid beyond a cutoff scale, and that the extrapolation of the pure SM potential beyond this cutoff scale is unwarranted and the scenario is akin to other ad hoc inflaton potentials afflicted with significant fine-tuning.
Abstract: We critically examine the recent claim that the standard model (SM) Higgs boson $\mathcal{H}$ could drive inflation in agreement with observations if $|\mathcal{H}{|}^{2}$ has a strong coupling $\ensuremath{\xi}\ensuremath{\sim}{10}^{4}$ to the Ricci curvature scalar. We first show that the effective-theory approach upon which that claim is based ceases to be valid beyond a cutoff scale $\ensuremath{\Lambda}={m}_{p}/\ensuremath{\xi}$, where ${m}_{p}$ is the reduced Planck mass. We then argue that knowing the Higgs potential profile for the field values relevant for inflation ($|\mathcal{H}|g{m}_{p}/\sqrt{\ensuremath{\xi}}\ensuremath{\gg}\ensuremath{\Lambda}$) requires knowledge of the ultraviolet completion of the SM beyond $\ensuremath{\Lambda}$. In absence of such microscopic theory, the extrapolation of the pure SM potential beyond $\ensuremath{\Lambda}$ is unwarranted and the scenario is akin to other ad hoc inflaton potentials afflicted with significant fine-tuning. The appealing naturalness of this minimal proposal is therefore lost.

Journal ArticleDOI
TL;DR: In this article, a relativistic theory of Love numbers is presented for compact bodies with strong internal gravities. But the theory is not applicable to non-rotating black holes.
Abstract: In Newtonian gravitational theory, a tidal Love number relates the mass multipole moment created by tidal forces on a spherical body to the applied tidal field. The Love number is dimensionless, and it encodes information about the body's internal structure. We present a relativistic theory of Love numbers, which applies to compact bodies with strong internal gravities; the theory extends and completes a recent work by Flanagan and Hinderer, which revealed that the tidal Love number of a neutron star can be measured by Earth-based gravitational-wave detectors. We consider a spherical body deformed by an external tidal field, and provide precise and meaningful definitions for electric-type and magnetic-type Love numbers; and these are computed for polytropic equations of state. The theory applies to black holes as well, and we find that the relativistic Love numbers of a nonrotating black hole are all zero.

Journal ArticleDOI
TL;DR: In this paper, the rate at which energy injected by dark matter (DM) annihilation heats and ionizes the photon-baryon plasma at z{approx}1000, and provides accurate fitting functions over the relevant redshift range for a broad array of annihilation channels and DM masses.
Abstract: We compute in detail the rate at which energy injected by dark matter (DM) annihilation heats and ionizes the photon-baryon plasma at z{approx}1000, and provide accurate fitting functions over the relevant redshift range for a broad array of annihilation channels and DM masses. The resulting perturbations to the ionization history can be constrained by measurements of the CMB temperature and polarization angular power spectra. We show that models which fit recently measured excesses in 10-1000 GeV electron and positron cosmic rays are already close to the 95% confidence limits from WMAP. The recently launched Planck satellite will be capable of ruling out a wide range of DM explanations for these excesses. In models of dark matter with Sommerfeld-enhanced annihilation, where rises with decreasing WIMP velocity until some saturation point, the WMAP5 constraints imply that the enhancement must be close to saturation in the neighborhood of the Earth.

Journal ArticleDOI
Sung-Sik Lee1
TL;DR: Using the anti-de Sitter/conformal field theory correspondence, this article calculated a fermionic spectral function in a $2+1$ dimensional nonrelativistic quantum field theory which is dual to a gravitational theory in the ${\mathrm{AdS}}_{4}$ background with a charged black hole.
Abstract: Using the anti-de Sitter/conformal field theory correspondence, we calculate a fermionic spectral function in a $2+1$ dimensional nonrelativistic quantum field theory which is dual to a gravitational theory in the ${\mathrm{AdS}}_{4}$ background with a charged black hole. The spectral function shows no quasiparticle peak but the Fermi surface is still well-defined. Interestingly, all momentum points inside the Fermi surface are critical and the gapless modes are defined in a critical Fermi ball in the momentum space.

Journal ArticleDOI
TL;DR: In this article, the effect of soft gluon emission in the hadroproduction of gluino-gluino and squark-antisquark pairs at the next-to-leading logarithmic accuracy within the framework of the minimal supersymmetric model was studied.
Abstract: We study the effect of soft gluon emission in the hadroproduction of gluino-gluino and squark-antisquark pairs at the next-to-leading logarithmic accuracy within the framework of the minimal supersymmetric model. We present the calculation of the one-loop soft anomalous dimension matrices controlling the color evolution of the underlying hard-scattering processes. The numerical results for resummed cross sections for proton-proton collisions at the Large Hadron Collider are discussed in detail.

Journal ArticleDOI
TL;DR: In this paper, it was shown that at the level of linear response the low-frequency limit of a strongly coupled field theory at finite temperature is determined by the horizon geometry of its gravity dual, i.e., by the ''membrane paradigm'' fluid of classical black hole mechanics.
Abstract: We show that at the level of linear response the low-frequency limit of a strongly coupled field theory at finite temperature is determined by the horizon geometry of its gravity dual, i.e., by the ``membrane paradigm'' fluid of classical black hole mechanics. Thus, generic boundary theory transport coefficients can be expressed in terms of geometric quantities evaluated at the horizon. When applied to the stress tensor this gives a simple, general proof of the universality of the shear viscosity in terms of the universality of gravitational couplings, and when applied to a conserved current it gives a new general formula for the conductivity. Away from the low-frequency limit the behavior of the boundary theory fluid is no longer fully captured by the horizon fluid even within the derivative expansion; instead, we find a nontrivial evolution from the horizon to the boundary. We derive flow equations governing this evolution and apply them to the simple examples of charge and momentum diffusion.

Journal ArticleDOI
TL;DR: In this article, the authors compared the performance of different PN waveform families in the context of initial and advanced LIGO detectors and concluded that as long as the total mass remains less than a certain upper limit, all template families at 3.5PN TaylorT3 and TaylorEt are equally good for the purpose of detection.
Abstract: The two-body dynamics in general relativity has been solved perturbatively using the post-Newtonian (PN) approximation. The evolution of the orbital phase and the emitted gravitational radiation are now known to a rather high order up to $\mathcal{O}({v}^{8})$, $v$ being the characteristic velocity of the binary. The orbital evolution, however, cannot be specified uniquely due to the inherent freedom in the choice of parameter used in the PN expansion, as well as the method pursued in solving the relevant differential equations. The goal of this paper is to determine the (dis)agreement between different PN waveform families in the context of initial and advanced gravitational-wave detectors. The waveforms employed in our analysis are those that are currently used by Initial LIGO/Virgo, that is, the time-domain PN models TaylorT1, TaylorT2, TaylorT3, the Fourier-domain representation TaylorF2 (or stationary phase approximant), and the effective-one-body model, and two more recent models, TaylorT4 and TaylorEt. For these models we examine their overlaps with one another for a number of different binaries at 2PN, 3PN, and 3.5PN orders to quantify their differences. We then study the overlaps of these families with the prototype effective-one-body family, currently used by Initial LIGO, calibrated to numerical-relativity simulations to help us decide whether there exist preferred families, in terms of detectability and computational cost, that are the most appropriate as search templates. We conclude that as long as the total mass remains less than a certain upper limit ${M}_{\mathrm{crit}}$, all template families at 3.5PN order (except TaylorT3 and TaylorEt) are equally good for the purpose of detection. The value of ${M}_{\mathrm{crit}}$ is found to be $\ensuremath{\sim}12{M}_{\ensuremath{\bigodot}}$ for Initial, Enhanced, and Advanced LIGO. From a purely computational point of view, we recommend that 3.5PN TaylorF2 be used below ${M}_{\mathrm{crit}}$ and that the effective-one-body model calibrated to numerical-relativity simulations be used for total binary mass $Mg{M}_{\mathrm{crit}}$.

Journal ArticleDOI
TL;DR: In this paper, the authors propose a basis of four simplified models, each specified by only 2-3 masses and 4-5 branching ratios, for use in a first characterization of data.
Abstract: Low-energy SUSY and several other theories that address the hierarchy problem predict pair-production at the LHC of particles with Standard Model quantum numbers that decay to jets, missing energy, and possibly leptons. If an excess of such events is seen in LHC data, a theoretical framework in which to describe it will be essential to constraining the structure of the new physics. We propose a basis of four deliberately simplified models, each specified by only 2-3 masses and 4-5 branching ratios, for use in a first characterization of data. Fits of these simplified models to the data furnish a quantitative presentation of the jet structure, electroweak decays, and heavy-flavor content of the data, independent of detector effects. These fits, together with plots comparing their predictions to distributions in data, can be used as targets for describing the data within any full theoretical model.

Journal ArticleDOI
TL;DR: This work imposes that the matter threading the wormhole satisfies the energy conditions, so that it is the effective stress-energy tensor containing higher order curvature derivatives that is responsible for the null energy condition violation.
Abstract: In this work, we construct traversable wormhole geometries in the context of f (R) modified theories of gravity. We impose that the matter threading the wormhole satisfies the energy conditions, so that it is the effective stress-energy tensor containing higher order curvature derivatives that is responsible for the null energy condition violation. Thus, the higher order curvature terms, interpreted as a gravitational fluid, sustain these nonstandard wormhole geometries, fundamentally different from their counterparts in general relativity. In particular, by considering specific shape functions and several equations of state, exact solutions for f(R) are found.

Journal ArticleDOI
TL;DR: In this article, the sensitivity of neutrino experiments at the luminosity frontier to generic hidden sectors containing new (sub)-GeV neutral states was discussed, and it was shown that the LSND electron recoil event sample currently provides the most stringent direct constraint on MeV-scale dark matter models.
Abstract: We discuss the sensitivity of neutrino experiments at the luminosity frontier to generic hidden sectors containing new (sub)-GeV neutral states. The weak interaction of these states with the standard model can be efficiently probed through all of the allowed renormalizable ``portals'' (in the Higgs, vector, and neutrino sectors) at fixed target proton beam facilities, with complementary sensitivity to colliders. We concentrate on the kinetic-mixing vector portal, and show that certain regions of the parameter space for a new $\mathrm{U}(1{)}_{S}$ gauge sector with long-lived sub-GeV mass states decaying to standard model leptons are already severely constrained by the data sets at LSND, MiniBooNE, and NuMI/MINOS. Furthermore, scenarios in which portals allow access to stable neutral particles, such as MeV-scale dark matter, generally predict that the neutrino beam is accompanied by a ``dark matter beam,'' observable through neutral-current-like interactions in the detector. As a consequence, we show that the LSND electron recoil event sample currently provides the most stringent direct constraint on MeV-scale dark matter models.

Journal ArticleDOI
TL;DR: In this paper, the authors studied the details of preheating in an inflationary scenario in which the standard model Higgs, strongly nonminimally coupled to gravity, plays the role of the inflaton.
Abstract: We study the details of preheating in an inflationary scenario in which the standard model Higgs, strongly nonminimally coupled to gravity, plays the role of the inflaton. We find that the Universe does not reheat immediately through perturbative decays, but rather initiates a complex process in which perturbative and nonperturbative effects are mixed. The Higgs condensate starts oscillating around the minimum of its potential, producing W and Z gauge bosons nonperturbatively, due to violation of the so-called adiabaticity condition. However, during each semioscillation, the created gauge bosons partially decay (perturbatively) into fermions. The decay of the gauge bosons prevents the development of parametric resonance, since bosons cannot accumulate significantly at the beginning. However, the energy transferred to the decay products of the bosons is not enough to reheat the Universe, so after about a hundred oscillations, the resonance effects will eventually dominate over the perturbative decays. Around the same time (or slightly earlier), backreaction from the gauge bosons into the Higgs condensate will also start to be significant. Soon afterwards, the Universe is filled with the remnant condensate of the Higgs and a nonthermal distribution of fermions and bosons (those of the standard model), which redshift as radiation and matter,more » respectively. We compute the distribution of the energy budget among all the species present at the time of backreaction. From there until thermalization, the evolution of the system is highly nonlinear and nonperturbative, and will require a careful study via numerical simulations.« less

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TL;DR: In this paper, the authors derived the general form for a three-dimensional scale-invariant field theory with supersymmetry, SU(4) symmetry, and a U(1) symmetry.
Abstract: We derive the general form for a three-dimensional scale-invariant field theory with $\mathcal{N}=6$ supersymmetry, $SU(4)$ R-symmetry and a $U(1)$ global symmetry. The results can be written in terms of a 3-algebra in which the triple product is not antisymmetric. For a specific choice of 3-algebra we obtain the $\mathcal{N}=6$ theories that have been recently proposed as models for M2-branes in an ${\mathbb{R}}^{8}/{\mathbb{Z}}_{k}$ orbifold background.

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TL;DR: In this article, the behavior of photons in the presence of Lorentz and CPT violation is studied, and a complete characterization of the coefficients for all mass dimensions via a decomposition using spin-weighted spherical harmonics.
Abstract: The behavior of photons in the presence of Lorentz and CPT violation is studied. Allowing for operators of arbitrary mass dimension, we classify all gauge-invariant Lorentz- and CPT-violating terms in the quadratic Lagrange density associated with the effective photon propagator. The covariant dispersion relation is obtained, and conditions for birefringence are discussed. We provide a complete characterization of the coefficients for Lorentz violation for all mass dimensions via a decomposition using spin-weighted spherical harmonics. The resulting nine independent sets of spherical coefficients control birefringence, dispersion, and anisotropy in the photon propagator. We discuss the restriction of the general theory to various special models, including among others the minimal standard-model extension, the isotropic limit, the case of vacuum propagation, the nonbirefringent limit, and the vacuum-orthogonal model. The transformation of the spherical coefficients for Lorentz violation between the laboratory frame and the standard Sun-centered frame is provided. We apply the results to various astrophysical observations and laboratory experiments. Astrophysical searches of relevance include studies of birefringence and of dispersion. We use polarimetric and dispersive data from gamma-ray bursts to set constraints on coefficients for Lorentz violation involving operators of dimensions four through nine, and we describe the mixing of polarizations induced by Lorentz and CPT violation in the cosmic-microwave background. Laboratory searches of interest include cavity experiments. We present the general theory for searches with cavities, derive the experiment-dependent factors for coefficients in the vacuum-orthogonal model, and predict the corresponding frequency shift for a circular-cylindrical cavity.

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TL;DR: In this article, the PACS-CS project presented the first results of a simulation of a 2+1$ flavor lattice QCD on the physical point with the nonperturbatively improved Wilson quark action and the Iwasaki gauge action.
Abstract: We present the first results of the PACS-CS project which aims to simulate $2+1$ flavor lattice QCD on the physical point with the nonperturbatively $O(a)$-improved Wilson quark action and the Iwasaki gauge action. Numerical simulations are carried out at $\ensuremath{\beta}=1.9$, corresponding to the lattice spacing of $a=0.0907(13)\text{ }\text{ }\mathrm{fm}$, on a ${32}^{3}\ifmmode\times\else\texttimes\fi{}64$ lattice with the use of the domain-decomposed HMC algorithm to reduce the up-down quark mass. Further algorithmic improvements make possible the simulation whose up-down quark mass is as light as the physical value. The resulting pseudoscalar meson masses range from 702 MeV down to 156 MeV, which clearly exhibit the presence of chiral logarithms. An analysis of the pseudoscalar meson sector with SU(3) chiral perturbation theory reveals that the next-to-leading order corrections are large at the physical strange quark mass. In order to estimate the physical up-down quark mass, we employ the SU(2) chiral analysis expanding the strange quark contributions analytically around the physical strange quark mass. The SU(2) low energy constants ${\overline{l}}_{3}$ and ${\overline{l}}_{4}$ are comparable with the recent estimates by other lattice QCD calculations. We determine the physical point together with the lattice spacing employing ${m}_{\ensuremath{\pi}}$, ${m}_{K}$ and ${m}_{\ensuremath{\Omega}}$ as input. The hadron spectrum extrapolated to the physical point shows an agreement with the experimental values at a few % level of statistical errors, albeit there remain possible cutoff effects. We also find that our results of ${f}_{\ensuremath{\pi}}$, ${f}_{K}$ and their ratio, where renormalization is carries out perturbatively at one loop, are compatible with the experimental values. For the physical quark masses we obtain ${m}_{ud}^{\overline{\mathrm{MS}}}$ and ${m}_{s}^{\overline{\mathrm{MS}}}$ extracted from the axial-vector Ward-Takahashi identity with the perturbative renormalization factors. We also briefly discuss the results for the static quark potential.