Simulations of binary neutron stars have seen great advances in terms of physical detail and numerical quality. However, the spin of the neutron stars, one of the simplest global parameters of binaries, remains mostly unstudied. We present the first fully nonlinear general relativistic dynamical evolutions of the last three orbits for constraint-satisfying initial data of spinning neutron star binaries, with astrophysically realistic spins aligned and antialigned to the orbital angular momentum. The initial data are computed with the constant rotational velocity approach. The dynamics of the systems is analyzed in terms of gauge-invariant binding energy vs orbital angular momentum curves. By comparing to a binary black hole configuration, we can estimate the different tidal and spin contributions to the binding energy for the first time. First results on the gravitational waveforms are presented. The phase evolution during the orbital motion is significantly affected by spin-orbit interactions, leading to delayed or early mergers. Furthermore, a frequency shift in the main emission mode of the hypermassive neutron star is observed. Our results suggest that a detailed modeling of merger waveforms requires the inclusion of spin, even for the moderate magnitudes observed in binary neutron star systems.

Accurately modeling an extreme-mass-ratio inspiral requires knowledge of the second-order gravitational self-force on the inspiraling small object. Recently, numerical puncture schemes have been formulated to calculate this force, and their essential analytical ingredients have been derived from first principles. However, the “puncture,” a local representation of the small object’s self-field, in each of these schemes has been presented only in a local coordinate system centered on the small object, while a numerical implementation will require the puncture in coordinates covering the entire numerical domain. In this paper we provide an explicit covariant self-field as a local expansion in terms of Synge’s world function. The self-field is written in the Lorenz gauge, in an arbitrary vacuum background, and in forms suitable for both self-consistent and Gralla-Wald-type representations of the object’s trajectory. We illustrate the local expansion’s utility by sketching the procedure of constructing from it a numerically practical puncture in any chosen coordinate system.

Over the next decade, cosmological measurements of the large-scale structure of the Universe will be sensitive to the combined effects of dynamical dark energy and massive neutrinos. The matter power spectrum is a key repository of this information. We extend higher-order perturbative methods for computing the power spectrum to investigate these effects over quasilinear scales. Through comparison with N-body simulations, we establish the regime of validity of a time-renormalization group perturbative treatment that includes dynamical dark energy and massive neutrinos. We also quantify the accuracy of standard, renormalized and Lagrangian resummation (LPT) perturbation theories without massive neutrinos. We find that an approximation that neglects neutrino clustering as a source for nonlinear matter clustering predicts the baryon acoustic oscillation (BAO) peak position to 0.25% accuracy for redshifts $1\le z\le 3$, justifying the use of LPT for BAO reconstruction in upcoming surveys. We release a modified version of the public Copter code which includes the additional physics discussed in the paper.

The two-parameter charged McVittie solution of the Einstein equations is revisited and its apparent horizons are discussed and located numerically (for the extremal case, analytically). According to the parameter values, this spacetime can be interpreted as a black hole, or a spacelike naked singularity, in a spatially homogeneous and isotropic universe.

In this paper, we scrutinize very closely the cosmology in the proxy theory to massive gravity obtained in de Rham and Heisenberg [Phys. Rev. D 84, 043503 (2011)]. This proxy theory was constructed by covariantizing the decoupling limit Lagrangian of massive gravity, and it represents a subclass of Horndeski scalar-tensor theory. Thus, this covariantization unifies two important classes of modified gravity theories, namely, massive gravity and Horndeski theories. We go beyond the regime which was studied in de Rham and Heisenberg [Phys. Rev. D 84, 043503 (2011)] and show that the theory does not admit any homogeneous and isotropic self-accelerated solutions. We illustrate that the only attractor solution is the flat Minkowski solution; hence, this theory is less appealing as a dark energy model. We also show that the absence of de Sitter solutions is tightly related to the presence of shift symmetry breaking interactions.

We have developed an inversion method for determination of the characteristics of the acceleration mechanism directly and nonparametrically from observations, in contrast to the usual forward fitting of parametric model variables to observations. In two recent papers [V. Petrosian and Q. Chen, Astrophys. J. 712, L131 (2010); Q. Chen and V. Petrosian, Astrophys. J. 777, 33 (2013)], we demonstrated the efficacy of this inversion method by its application to acceleration of electrons in solar flares based on stochastic acceleration by turbulence. Here we explore its application for determining the characteristics of shock acceleration in supernova remnants (SNRs) based on the electron spectra deduced from the observed nonthermal radiation from SNRs and the spectrum of the cosmic ray electrons observed near the Earth. These spectra are related by the process of escape of the electrons from SNRs and energy loss during their transport in the Galaxy. Thus, these observations allow us to determine spectral characteristics of the momentum and pitch angle diffusion coefficients, which play crucial roles in both direct acceleration by turbulence and in high Mach number shocks. Assuming that the average electron spectrum deduced from a few well-known SNRs is representative of those in the solar neighborhood, we find interesting discrepancies between our deduced forms for these coefficients and those expected from well-known wave-particle interactions. This may indicate that the standard assumptions made in the treatment of shock acceleration need revision. In particular, the escape of particles from SNRs may be more complex than generally assumed.

The first year of observations by the Planck satellite mission shows that the cosmic microwave background fluctuations are consistent with Gaussian statistics in the primordial perturbations, a key prediction of the simplest models of inflation. However, there are hints of anomalies in the cosmic microwave background power spectrum and bispectrum. We check for the possibility that some of these anomalous features have a common physical origin in a transient reduction of the inflaton speed of sound. We do this by exploiting predicted correlations between the power spectrum and bispectrum. Our results suggest that current data might already be sensitive enough to detect transient reductions in the speed of sound as mild as a few percent. Since this is a signature of interactions, it opens a new window for the detection of extra degrees of freedom during inflation.

The modified Newtonian dynamics (MOND) is an attempt to modify the gravitation theory to solve the dark matter problem. This phenomenology is very successful at the galactic level. The main effect produced by MOND in the Solar System is called the external field effect parametrized by the parameter $Q_2$. We have used nine years of Cassini range and Doppler measurements to constrain $Q_2$. Our estimate of this parameter based on Cassini data is given by $Q_2=(3\pm 3)\times 10^{-27}{\mathrm{s}}^{-2}$, which shows no deviation from General Relativity and excludes a large part of the relativistic MOND theories. This limit can also be interpreted as a limit on an external tidal potential acting on the Solar System coming from the internal mass of our Galaxy (including dark matter) or from a new hypothetical body.

Charged-pion decay offers many opportunities to study Lorentz violation. Using an effective field theory approach, we study Lorentz violation in the lepton, $W$ boson, and quark sectors and derive the differential pion-decay rate, including muon polarization. Using coordinate redefinitions we are able to relate the first-generation quark sector, in which no bounds were previously reported, to the lepton and $W$-boson sector. This facilitates a tractable calculation, enabling us to place bounds on the level of $10^{-4}$ on first-generation quark parameters. Our expression for the pion-decay rate can be used to constrain Lorentz violation in future experiments.

We consider a system of unstable Dirac fermions in a general parity-nonconserving theory with intergeneration mixing and explain how to renormalize its propagator matrix to all orders in perturbation theory. We work in the pole scheme, in which the squares of the renormalized masses are identified with the complex pole positions and the wave-function renormalization (WFR) matrices are adjusted according to the Lehmann-Symanzik-Zimmermann reduction formalism. The unit-residue property is explicitly verified for the renormalized dressed propagator matrix. Closed analytic expressions for the pole-mass counterterms and WFR matrices in terms of the self-energy functions are presented. We identify residual degrees of freedom in the WFR matrices and propose an additional renormalization condition to exploit them. We demonstrate that, in the presence of instability, the WFR matrices of the in and out states bifurcate in the sense that they are no longer related by pseudo-Hermitian conjugation. The well-known one- and two-loop results for stable fermions are recovered. The all-order renormalized propagator of a single unstable fermion takes a particularly compact form. We also briefly discuss Dirac spinors for unstable fermions.

We investigate a Randall-Sundrum (RS) model with an SU(2) doublet propagating in the bulk. Upon calculating its gravitational effect we find that a stabilized radius can be generated without the use of an additional scalar, as needed for example in the Goldberger-Wise (GW) mechanism, and with no additional fine-tuning other than the inescapable one due to the cosmological constant; similar tuning is also present in the GW mechanism. The lowest scalar excitation in this scenario, the counterpart of the radion of the GW mechanism, has both radionlike and Higgs-like couplings to the Standard Model fields. It, thus, plays a dual role and we, therefore, denote it as the “Higgs radion” ($h_r$). As opposed to the GW radion case, our Higgs radion is found to be compatible with the 126 GeV scalar recently discovered at the LHC, at the level of $1\sigma$, with a resulting 95% C.L. bound on the KK-gluon mass of $4.48\mathrm{TeV}<M_{\mathrm{KKG}}<5.44\mathrm{TeV}$. An important consequence of our setup should be accentuated: the radion of the traditional RS scenarios simply does not exist, so that our Higgs radion is not the conventional mixed state between the GW radion and the Higgs.

Within an effective field theory framework, we discuss the possibility to discriminate among different operators that contribute to lepton flavor violating (LFV) $\tau$ decays. Correlations among decay rates in different channels are shown to provide a basic handle to unravel the origin of LFV in these processes. More information about the underlying dynamics responsible for LFV can be gathered from differential distributions in three-body decays like $\tau \to \mu \pi \pi$ or $\tau \to 3\mu$: these are considered in some detail. We incorporate in our analysis recent developments in the determination of the hadronic form factors for $\tau \to \mu \pi \pi$. Future prospects for the observation of LFV $\tau$ decays and its interpretation are also discussed.

In the next-to-minimal supersymmetric standard model (NMSSM) a variety of parameter configurations yields a Higgs boson consistent with the one observed at the LHC. Additionally, the Higgs sector of the model can contain explicit charge parity ($CP$)-violating phases even at the tree level, in contrast with the minimal supersymmetric standard model (MSSM). In this article we present the one-loop Higgs boson mass matrix of the complex NMSSM in the renormalization-group-improved effective potential approach. We also present the trilinear Higgs boson self couplings as well as various partial decay widths of a generic $CP$-mixed Higgs boson in the model. We then analyze a very interesting phenomenological scenario wherein the decay of a relatively light pseudoscalar-like Higgs boson into $\sim 125\mathrm{GeV}$ standard model-like Higgs boson(s) is induced by nonzero $CP$-violating phases. We discuss in detail a few benchmark cases in which such a decay can contribute significantly to the production of SM-like Higgs bosons at the LHC on top of the gluon fusion process. It can thus be partially responsible for the $\gamma \gamma$ excess near 125 GeV due to the subsequent decay of the SM-like Higgs boson. Such a scenario is extremely difficult to realize in the complex MSSM and, if probed at the LHC, it could provide an indication of the nonminimal nature of supersymmetry.

Recent results from the cryogenic dark matter search experiment have renewed interest in light (5–15 GeV) dark matter with a large spin-independent neutralino-nucleon scattering cross section, ${\sigma }_{\mathrm{SI}}\gtrsim 10^{-42}{\mathrm{cm}}^2$. Previous work had suggested that the lightest neutralino in the next-to-MSSM can fall in this mass range and achieve both the correct thermal relic abundance and the desired level for the scattering cross section, provided light Higgs bosons to mediate the pair annihilation and neutralino-nucleon scattering. However, the requirement of a 126 GeV standard model (SM)-like Higgs boson significantly impacts the allowed parameter space. Here, we examine the regions of the NMSSM capable of producing a light neutralino with ${\sigma }_{\mathrm{SI}}\sim 10^{-42}–{10}^{-41}{\mathrm{cm}}^2$, with the scattering mediated by a very light singlet-like scalar, and a 126 GeV standard model-like Higgs consistent with the LHC results, while satisfying other relevant cosmological, flavor and collider constraints. We focus on two different scenarios for annihilation in the early Universe, namely annihilation mediated by (1) a light scalar or by (2) a light pseudoscalar. As expected, both cases are highly constrained. Nevertheless, we find that there persists potentially viable parameter space to accommodate either scenario. In the first, accidental cancellations in the couplings allow for a SM-like Higgs with a total width and invisible branching fraction compatible with the observed Higgs boson. Alternatively, the second scenario can occur in regions featuring smaller branching fractions of the SM-like Higgs to pairs of light scalars, pseudoscalars, and neutralinos without cancellations. The strongest constraints in both cases come from rare meson decays and exotic decays of the SM-like Higgs boson into neutralinos and light, charge parity even Higgs pairs. We outline the relevant parameter space for both scenarios and comment on prospects for future discovery with various experiments.

The Dalitz decay $H\to f\overline{f}\gamma$ is calculated for very small $f\overline{f}$ invariant masses where the $f\overline{f}$ pair could be mistaken for a photon in the analysis of $H\to \gamma \gamma$ decays. Using the ATLAS cuts and the full Dalitz decay amplitude, we estimate this fraction to be 7.06%.

We study the $CP$ violation in lepton-number-violating meson decays $M^{\pm }\to {\ell }_1^{\pm }{\ell }_2^{\pm }{M}^{\prime \mp }$, where $M$ and $M^{\prime }$ are pseudoscalar mesons, $M=K,D,D_s,B,B_c$ and $M^{\prime }=\pi ,K,D,D_s$, and the charged leptons are ${\ell }_1,{\ell }_2=e,\mu$. It turns out that the $CP$-violating difference $S_{-}(M)\equiv [\mathrm{\Gamma }(M^{-}\to {\ell }_1^{-}{\ell }_2^{-}{M}^{\prime +})-\mathrm{\Gamma }(M^{+}\to {\ell }_1^{+}{\ell }_2^{+}{M}^{\prime -})]$ can become appreciable when two intermediate on-shell Majorana neutrinos $N_j$ ($j=1,2$) participate in these decays. Our calculations show that the asymmetry becomes largest when the masses of $N_1$ and $N_2$ are almost degenerate, i.e., when the mass difference $\mathrm{\Delta }{M}_N$ becomes comparable with the (small) decay widths ${\mathrm{\Gamma }}_N$ of these neutrinos: $\mathrm{\Delta }{M}_N\cancel{\gg }{\mathrm{\Gamma }}_N$. We show that in such a case, the $CP$ ratio ${\mathcal{A}}_{CP}(M)\equiv [\mathrm{\Gamma }(M^{-}\to {\ell }_1^{-}{\ell }_2^{-}{M}^{\prime +})-\mathrm{\Gamma }(M^{+}\to {\ell }_1^{+}{\ell }_2^{+}{M}^{\prime -})]/[\mathrm{\Gamma }(M^{-}\to {\ell }_1^{-}{\ell }_2^{-}{M}^{\prime +})+\mathrm{\Gamma }(M^{+}\to {\ell }_1^{+}{\ell }_2^{+}{M}^{\prime -})]$ becomes a quantity $\sim 1$. The observation of $CP$ violation in these decays would be consistent with the existence of the well-motivated $\nu \mathrm{MSM}$ model with two almost degenerate heavy neutrinos in the mass range $M_N\sim 0.1–{10}^1\mathrm{GeV}$.

In the quantum kinetic framework, we investigate the momentum spectrum and the number density of created electron-positron pairs from vacuum in the combined electric fields composed of two sets of alternating-sign electric field pulse trains, a strong but slowly varying one and a weak but rapidly changing one. It is found that the pair production can be strongly enhanced by combining the multiple-slit interference effect with the dynamically assisted Schwinger mechanism. By considering the contribution of the transverse momentum, we find that the number density of created particles depends linearly on the electric field pulse number, i.e., a power law with index 1. Moreover, we study the effect of interpulse time delay on pair production and find that the number density is very sensitive to the interpulse time delay. The symmetry of the momentum spectrum for an $N$-pulse electric field and the difference of the multiple-slit interference effect between the nonperturbative Schwinger mechanism and the perturbative multiphoton electron-positron pair creation are also studied. Some possible explanations for observed results of momentum spectrum and number density are also given and discussed.

Elementary processes capable of producing neutrons in thunderstorms are analyzed. Efficiency is evaluated of nuclear fusion, photonuclear reaction, electrodisintegration, and reaction inverse to the $\mathrm{\beta }$-decay . An extraordinary strong electric field is required for nuclear fusion to occur in a lightning channel. The inverse to $\mathrm{\beta }$-decay reactions are too weak. The generation of neutrons in a thunderstorm is connected with photonuclear and, to a lesser degree, with electrodisintegration reactions.

Measurements of $W\gamma$ and $Z\gamma$ production in proton-proton collisions at $\sqrt{s}=7\mathrm{TeV}$ are used to extract limits on anomalous triple gauge couplings. The results are based on data recorded by the CMS experiment at the LHC that correspond to an integrated luminosity of $5.0{\mathrm{fb}}^{-1}$. The cross sections are measured for photon transverse momenta $p_{\mathrm{T}}^{\gamma }>15\mathrm{GeV}$, and for separations between photons and final-state charged leptons in the pseudorapidity-azimuthal plane of $\mathrm{\Delta }R(\ell ,\gamma )>0.7$ in $\ell \nu \gamma$ and $\ell \ell \gamma$ final states, where $\ell$ refers either to an electron or a muon. A dilepton invariant mass requirement of $m_{\ell \ell }>50\mathrm{GeV}$ is imposed for the $Z\gamma$ process. No deviations are observed relative to predictions from the standard model, and limits are set on anomalous $WW\gamma$, $ZZ\gamma$, and $Z\gamma \gamma$ triple gauge couplings.