We derive, in $d$-dimensional space-time, the effective Lagrangian of static gravitational fields interacting with a QED plasma at high temperature. Using the equivalence between the static hard thermal loops and those with zero external energy-momentum, we compute the effective Lagrangian up to two-loop order. We also obtain a nonperturbative contribution which arises from the sum of all infrared divergent ring diagrams. From the gauge and Weyl symmetries of the theory, we deduce to all orders that this effective Lagrangian is equivalent to the pressure of a QED plasma in Minkowski space-time, with the global temperature replaced by the Tolman local temperature.

We study the Scherk-Schwarz reduction of $D=11$ supergravity with background fluxes in the context of a recently developed framework pertaining to $D=11$ supergravity. We derive the embedding tensor of the associated four-dimensional maximal gauged theories directly from eleven dimensions by exploiting the generalized vielbein postulates, and by analyzing the couplings of the full set of 56 electric and magnetic gauge fields to the generalized vielbeine. The treatment presented here will apply more generally to other reductions of $D=11$ supergravity to maximal gauged theories in four dimensions.

We parametrize a large class of corrections to general relativity which include a long-ranged gravitational scalar field as a dynamical degree of freedom in two ways: parametrizing the structure of the correction to the action, and parametrizing the scalar hair (multipole structure) that compact objects and black holes attain. The presence of this scalar hair violates the no-hair theorems present in general relativity, which leads to several important effects. The effects we consider are (i) the interaction between an isolated body and an external scalar field, (ii) the scalar multipole-multipole interaction between two bodies in a compact binary, (iii) the additional pericenter precession of a binary, (iv) the scalar radiation from a binary, and (v) the modification to the gravitational wave phase from a binary. We apply this framework to example theories including Einstein-dilaton-Gauss-Bonnet gravity and dynamical Chern-Simons gravity, and estimate the size of the effects. Finally, we estimate the bounds that can be placed on parameters of the theories from the precession of pulsar binaries and from gravitational waves.

We present a framework to study generic neutron-star binaries in scalar-tensor theories of gravity. Our formalism achieves this goal by suitably interfacing a post-Newtonian orbital evolution (described by a set of ordinary differential equations) with a set of nonlinear algebraic equations, which provide a description of the scalar charge of each binary’s component along the evolution in terms of isolated-star data. We validate this semianalytical procedure by comparing its results to those of fully general-relativistic simulations, and use it to investigate the behavior of binary systems in large portions of the parameter space of scalar-tensor theories. This allows us to shed further light on the phenomena of “dynamical scalarization,” which we uncovered in [E. Barausse et al., Phys. Rev. D 87, 081506(R) (2013)] and which takes place in tight binaries, even for stars that have exactly zero scalar charge in isolation. We also employ our formalism to study representative binary systems, obtain their gravitational-wave signals and discuss the extent to which deviations from general relativity can be detected. The insights gained by this framework allow us to additionally show that eccentric binaries can undergo scalarization/descalarization phenomena.

We study the linear stability of dynamical, quadratic gravity, focusing on two particular subclasses (the even-parity sector, exemplified by Einstein-Dilaton-Gauss-Bonnet gravity, and the odd-parity sector, exemplified by dynamical Chern-Simons modified gravity) in the high-frequency, geometric optics approximation. This analysis is carried out by studying gravitational and scalar modes propagating on spherically symmetric and axially symmetric, vacuum solutions of the theory and finding the associated dispersion relations. These relations are solved in two separate cases (the scalar regime and the gravitational wave regime, defined by requiring the ratio of the amplitude of the perturbations to be much greater or smaller than unity) and found in both cases to not lead to exponential growth of the propagating modes, suggesting linearly stability. The modes are found to propagate at subluminal and superluminal speeds, depending on the propagating modes’ direction relative to the background geometry, just as in dynamical Chern-Simons gravity.

The deviation from geodesic motion of the world line of an extended body endowed with multipolar structure up to the mass quadrupole moment is studied in the Kerr background according to the Mathisson-Papapetrou-Dixon model. The properties of the quadrupole tensor are clarified by identifying the relevant components which enter the equations of motion, leading to the definition of an effective quadrupole tensor sharing its own algebraic symmetries, but also obeying those implied by the Mathisson-Papapetrou-Dixon model itself. The equations of motion are then solved analytically in the limit of small values of the characteristic length scales associated with the spin and quadrupole variables in comparison with the one associated with the background curvature and under special assumptions on the body’s structure and motion. The resulting quasicircular orbit is parametrized in a Keplerian-like form, so that temporal, radial, and azimuthal eccentricities as well as semimajor axis, period, and periastron advance are explicitly computed and expressed in terms of gauge-invariant variables in the weak field and slow motion limit. A companion numerical study of the equations of motion is performed too.

In this work we study how nonminimally coupled theories of gravity modify the usual Friedmann equation, and develop two methods to treat these. The ambiguity in the form of the Lagrangian density of a perfect fluid is emphasized, and the impact of different dominant matter species is assessed. The cosmological constant problem is also discussed.

We investigate the implications of dark matter annihilations for cosmological parameter constraints using the causal entropic principle. In this approach cosmologies are weighted by the total entropy production within a causally connected region of spacetime. We calculate the expected entropy from dark matter annihilations within the causal diamond and investigate the preferred values of the cosmological constant and the mass and annihilation cross section of the annihilating dark matter and their dependence on the assumptions in the models. For realistic values of the cross section, we typically find preferred values of $\mathrm{\Lambda }$ on the order of $10^{-5}$ of the present value assuming dark matter annihilations are the primary source of entropy production. The greatest amount of entropy production from dark matter within the causal diamond is likely to occur with light keV scale dark matter with a low annihilation cross section. We also investigate the effect of combining this entropy with the entropy production from stars and show that if the primary source of entropy production is from stars varying the dark matter cross section directly produces a preferred value of ${\mathrm{\Omega }}_m$ in excellent agreement with observations.

We discuss the cosmological consequences of a model based on a nonlocal infrared modification of Einstein equations. We find that the model generates a dynamical dark energy that can account for the presently observed value of ${\mathrm{\Omega }}_{\mathrm{DE}}$, without introducing a cosmological constant. Tuning a free mass parameter $m$ to a value $m\simeq 0.67H_0$, we reproduce the observed value ${\mathrm{\Omega }}_{\mathrm{DE}}\simeq 0.68$. This leaves us with no free parameter, and we then get a pure prediction for the equation of state parameter of dark energy. Writing $w_{\mathrm{DE}}(a)=w_0+(1-a)w_a$, we find $w_0\simeq -1.04$ and $w_a\simeq -0.02$, consistent with the Planck data and on the phantom side. We also argue that nonlocal equations of the type that we propose must be understood as purely classical effective equations, such as those derived in semiclassical gravity for the in-in matrix elements of the metric. As such, any apparent ghost instability in such equations only affects the classical dynamics, but there is no propagating degree of freedom associated to the ghost and no issue of ghost-induced quantum vacuum decay.

In this work we present a nonparametric approach, which works on minimal assumptions, to reconstruct the cosmic expansion of the Universe. We propose to combine a locally weighted scatterplot smoothing method and a simulation-extrapolation method. The first one (LOESS) is a nonparametric approach that allows us to obtain smoothed curves with no prior knowledge of the functional relationship between variables or of the cosmological quantities. The second one (SIMEX) takes into account the effect of measurement errors on a variable via a simulation process. For the reconstructions we use as raw data the Union2.1 type Ia supernovae compilation, as well as recent Hubble parameter measurements. This work aims to illustrate the approach, which turns out to be a self-sufficient technique in the sense that we do not have to choose anything by hand. We examine the details of the method, among them the amount of observational data needed to perform the locally weighted fit which will define the robustness of our reconstruction. In view of our results, we believe that our proposal offers a promising alternative for reconstructing global trends of cosmological data when there is little intuition on the relationship between the variables and we also think it even presents good prospects to generate reliable mock data points where the original sample is poor.

Recently, a novel kind of scalar wigs around Schwarzschild black holes—scalar dynamical resonance states—was introduced in [Phys. Rev. D 84, 083008 (2011)] and [Phys. Rev. Lett. 109, 081102 (2012)]. In this paper, we investigate the existence and evolution of Dirac dynamical resonance states. First, we look for stationary resonance states of a Dirac field around a Schwarzchild black hole by using the Schrödinger-like equations reduced from the Dirac equation in Schwarzschild spacetime. Then Dirac pseudostationary configurations are constructed from the stationary resonance states. We use these configurations as initial data and investigate their numerical evolutions and energy decay. These dynamical solutions are the so-called “Dirac dynamical resonance states.” It is found that the energy of the Dirac dynamical resonance states shows an exponential decay. The decay rate of energy is affected by the resonant frequency, the mass of the Dirac field, the total angular momentum, and the spin-orbit interaction. In particular, for an ultralight Dirac field, the corresponding particles can stay around a Schwarzschild black hole for a very long time, even for cosmological time scales.

Recent years have seen a burgeoning interest in using pulsar timing arrays (PTAs) as gravitational-wave (GW) detectors. To date, that interest has focused mainly on three particularly promising source types: supermassive black hole binaries, cosmic strings, and the stochastic background from early-Universe phase transitions. In this paper, by contrast, our aim is to investigate the PTA potential for discovering unanticipated sources. We derive significant constraints on the available discovery space based solely on energetic and statistical considerations: we show that a PTA detection of GWs at frequencies above $\sim {10}^{-5}\mathrm{Hz}$ would either be an extraordinary coincidence or violate “cherished beliefs;” we show that for PTAs GW memory can be more detectable than direct GWs, and that, as we consider events at ever higher redshift, the memory effect increasingly dominates an event’s total signal-to-noise ratio. The paper includes also a simple analysis of the effects of pulsar red noise in PTA searches, and a demonstration that the effects of periodic GWs in the $\sim {10}^{-7}–{10}^{-4.5}\mathrm{Hz}$ band would not be degenerate with small errors in standard pulsar parameters (except in a few narrow bands).

Gravitational waves from coalescing stellar-mass black hole binaries (BBHs) are expected to be detected by the Advanced Laser Interferometer gravitational-wave observatory and Advanced Virgo. Detection searches operate by matched filtering the detector data using a bank of waveform templates. Traditionally, template banks for BBHs are constructed from intermediary analytical waveform models which are calibrated against numerical relativity simulations and which can be evaluated for any choice of BBH parameters. This paper explores an alternative to the traditional approach, namely, the construction of template banks directly from numerical BBH simulations. Using nonspinning BBH systems as an example, we demonstrate which regions of the mass-parameter plane can be covered with existing numerical BBH waveforms. We estimate the required number and required length of BBH simulations to cover the entire nonspinning BBH parameter plane up to mass ratio 10, thus illustrating that our approach can be used to guide parameter placement of future numerical simulations. We derive error bounds which are independent of analytical waveform models; therefore, our formalism can be used to independently test the accuracy of such waveform models. The resulting template banks are suitable for advanced LIGO searches.

Motivated by the current observation of a 125 GeV Higgs boson, we calculate $t\to cH$ and $t\to cg(\gamma )H$ in the unitary gauge in the littlest Higgs model with $T$ parity (LHT). Because of the large contribution from the new mirror fermions, we find that the branching ratios of $t\to cH$ and $t\to cgH$ can be greatly enhanced in the LHT model and maximally reach $O({10}^{-5})$ in the allowed parameter space. When the mirror fermion mass $M_3>2(1.5)\mathrm{TeV}$ and the cutoff scale $f=500\mathrm{GeV}$, the process of $pp\to t\overline{t}\to 3b+c+\ell +{\cancel{E}}_T^{\text{miss}}$ can reach $3\sigma$ ($5\sigma$) sensitivity at 8(14) TeV LHC with luminosity $\mathcal{L}=20(300){\mathrm{fb}}^{-1}$.

In the present work the $Y(4260)$ resonance is considered as a weakly bound state of a pseudoscalar $D$ and an axial $D_1$ charm meson. We consider the two-body decay $Y(4260)\to Z_c(3900{)}^{\pm }+{\pi }^{\mp }$, where $Z_c(3900{)}^{\pm }$ is treated as hadron molecule as well. Moreover we compute the $Y(4260)$ decay modes $J/\psi {\pi }^{+}{\pi }^{-}$, recently observed by the BESIII Collaboration, and $\psi (2S){\pi }^{+}{\pi }^{-}$. In the last process both the contact diagram with $D{D}_1\to \psi (nS){\pi }^{+}{\pi }^{-}$ and the resonance diagram with $D{D}_1\to Z_c(3900{)}^{\pm }+{\pi }^{\mp }\to \psi (nS){\pi }^{+}{\pi }^{-}$ are taken into account.

The strange magnetic form factor of the nucleon is studied in a chiral effective model motivated by the heavy baryon formalism at next-to-leading order. The one-loop contributions from kaon and intermediate octet and decuplet hyperons are included, using finite-range regularization to deal with the ultraviolet divergences. Drawing on an established connection between quenched and full QCD, this model makes it possible to predict the strange magnetic form factor under the hypothesis that for a dipole regulator mass $\mathrm{\Lambda }$ around 0.8 GeV, strangeness in the core is negligible. The strange magnetic form factor is found to be small and negative over a range of momentum transfer, while the strange magnetic moment is consistent with the best lattice QCD determinations.

In coming years, gravitational-wave detectors should find black hole–neutron star (BH-NS) binaries, potentially coincident with astronomical phenomena like short gamma ray bursts. These binaries are expected to precess. Gravitational-wave science requires a tractable model for precessing binaries, to disentangle precession physics from other phenomena like modified strong field gravity, tidal deformability, or Hubble flow; and to measure compact object masses, spins, and alignments. Moreover, current searches for gravitational waves from compact binaries use templates where the binary does not precess and are ill-suited for detection of generic precessing sources. In this paper we provide a closed-form representation of the single-spin precessing waveform in the frequency domain by reorganizing the signal as a sum over harmonics, each of which resembles a nonprecessing waveform. This form enables simple analytic calculations of the Fisher matrix for use in template bank generation and coincidence metrics, and jump proposals to improve the efficiency of Markov chain Monte Carlo sampling. We have verified that for generic BH-NS binaries, our model agrees with the time-domain waveform to 2%. Straightforward extensions of the derivations outlined here (and provided in full online) allow higher accuracy and error estimates.

We complete the analysis of part I in this series [S. Stotyn et. al.,Phys. Rev. D 89, 044017 (2014)] by numerically constructing boson stars in $2+1$ dimensional Einstein gravity with negative cosmological constant, minimally coupled to a complex scalar field. These lower dimensional boson stars have strikingly different properties than their higher dimensional counterparts, most noticeably that there exists a finite central energy density, above which an extremal Bañados-Teitelboim-Zanelli (BTZ) black hole forms. In this limit, all of the scalar field becomes enclosed by the horizon; it does not contract to a singularity, but rather the origin remains smooth and regular and the solution represents a spinning boson star trapped inside a degenerate horizon. Additionally, whereas in higher dimensions the mass, angular momentum, and angular velocity all display damped harmonic oscillations as functions of the central energy density, in $D=3$ these quantities change monotonically up to the bound on the central energy density. Some implications for the holographic dual of these objects are discussed and it is argued that the boson star and extremal BTZ black hole phases are dual to a spontaneous symmetry breaking at zero temperature but finite energy scale.

We numerically construct asymptotically anti–de Sitter boson star solutions using a minimally coupled $\frac{D-1}{2}$-tuplet complex scalar field in $D=5$, 7, 9, 11 dimensions. The metric admits multiple Killing vector fields in general, however the scalar fields are only invariant under a particular combination, leading to such boson star solutions possessing just a single helical Killing symmetry. These boson stars form a one parameter family of solutions, which can be parametrized by the energy density at their center. As the central energy density tends to infinity, the angular velocity, mass, and angular momentum of the boson star exhibit damped harmonic oscillations about finite central values, while the Kretschmann invariant diverges, signaling the formation of a black hole in this limit.

Introducing heavy particles with strong couplings to the Higgs field can strengthen electroweak phase transition through the entropy release mechanism from both bosons and fermions. We analyze the possibility of electroweak baryogenesis in the minimal supersymmetric Standard Model (MSSM) with new vectorlike superfields. The new vectorlike particles belong to the representation $5+\overline{5}+10+\overline{10}$ of $SU(5)$. By analyzing in detail the effective potential at finite temperature, we show that a strongly first-order electroweak phase transition in this model is ruled out by a combination of the 125 GeV Higgs requirement, the bound for exotic quarks, the gluon fusion Higgs production rate, and the Higgs diphoton decay rate, as well as the electroweak precision measurement.