We propose a model for short duration gamma-ray bursts (sGRBs) based on the formation of a quark star after the merger of two neutron stars. We assume that the sGRB central engine is a proto-magnetar, which has been previously invoked to explain the plateaulike X-ray emission observed following both long and short GRBs. Here, we show that: (i) a few milliseconds after the merger it is possible to form a stable and massive star made in part of quarks; (ii) during the early cooling phase of the incompletely formed quark star, the flux of baryons ablated from the surface by neutrinos is large and it does not allow the outflow to achieve a bulk Lorentz factor high enough to produce a GRB; (iii) after the quark burning front reaches the stellar surface, baryon ablation ceases and the jet becomes too baryon poor to produce a GRB; (iv) however, between these two phases a GRB can be produced over the finite time scale required for the baryon pollution to cease; a characteristic time scale of the order of $\sim 0.1\mathrm{s}$ naturally results from the time the conversion front needs to cover the distance between the rotational pole and the latitude of the last closed magnetic field line; (v) we predict a correlation between the luminosity of the sGRB and its duration, consistent with the data; (vi) our model also predicts a delay of the order of ten seconds between the time of the merger event and the sGRB, allowing for the possibility of precursor emission and implying that the jet will encounter the dense cocoon formed immediately after the merger.

For application in future cryogenically cooled gravitational wave detectors, the thermal noise of low absorbing mirror coatings has to be reduced. The development of low mechanical and optical loss materials is challenging, but thermal noise reduction can be significantly supported by using a multimaterial coating design. We analyze the possible improvement of the total (optical and mechanical) loss of a three-material based coating obtained by optimizing the properties of the top layer of the coating stack. A top-layer material with sufficiently high refractive index could have a significantly higher optical and mechanical loss than currently used tantala, while still enabling reduction of the total coating loss. Restrictions on possible top-layer material properties are made, and the option of a crystalline top layer is discussed.

With proper profiles of the scalar potential and the dilaton field, for the first time, the spontaneous chiral symmetry breaking in the vacuum and its restoration at finite temperature are correctly realized in the holographic QCD framework. In the chiral limit, a nonzero chiral condensate develops in the vacuum and decreases with temperature, and the phase transition is of the second order for a two-flavor case and of the first order for a three-flavor case. In the case of explicit chiral symmetry breaking, in the two-flavor case, the second-order phase transition turns into a crossover with any nonzero current quark mass, and in the three-flavor case, the first-order phase transition turns into a crossover at a finite current quark mass. The correct description of chiral symmetry breaking and restoration makes the holographic QCD models more powerful in dealing with nonperturbative QCD phenomena. This framework can be regarded as a general setup in an application of AdS/CFT to describe conventional Ginzburg-Landau-Wilson–type phase transitions, e.g. in condensed matter and cosmology systems.

We analyze the sensitivity of next-generation tonne-scale neutrinoless double-$\beta$ decay ($0\nu \beta \beta$) experiments and searches for same-sign di-electrons plus jets at the Large Hadron Collider to TeV scale lepton number violating interactions. Taking into account previously unaccounted for physics and detector backgrounds at the LHC, renormalization group evolution, and long-range contributions to $0\nu \beta \beta$ nuclear matrix elements, we find that the reach of tonne-scale $0\nu \beta \beta$ generally exceeds that of the LHC for a class of simplified models. However, for a range of heavy particle masses near the TeV scale, the high luminosity LHC and tonne-scale $0\nu \beta \beta$ may provide complementary probes.

A lepto-baryonic left-right symmetric theory is considered along with pointing out stable dark matter candidates whose stability is ensured automatically where leptons and baryons are defined as local gauge symmetries. These theories are generally anomalous, and the possible gauge anomaly free solutions for these theories are presented. It is found that the neutral component of fermion triplets can be a viable dark matter candidate originally introduced for gauge anomaly cancellation. The other dark matter possibilities within this lepto-baryonic left-right symmetric theory are also presented.

The process $e^{+}{e}^{-}\to {\pi }^0\gamma$ is studied with the SND detector at the VEPP-2M $e^{+}{e}^{-}$ collider. The $e^{+}{e}^{-}\to {\pi }^0\gamma$ cross section is measured in the center-of-mass energy range from 0.60 to 1.38 GeV. The cross section is well described by the vector meson dominance model. From the fit to the cross-section data we determine the branching fractions $B(\rho \to {\pi }^0\gamma )=(4.20\pm 0.52)\times {10}^{-4}$, $B(\omega \to {\pi }^0\gamma )=(8.88\pm 0.18)\%$, and $B(\varphi \to {\pi }^0\gamma )=(1.367\pm 0.072)\times {10}^{-3}$, and the relative phase between the $\rho$ and $\omega$ amplitudes ${\phi }_{\rho }=(-12.7\pm 4.5)°$. Our data on the process $e^{+}{e}^{-}\to {\pi }^0\gamma$ are the most accurate to date.

For black-hole binaries whose spins are (anti-) aligned with respect to the orbital angular momentum of the binary, we compute the frequency-domain phasing coefficients including the quadratic-in-spin terms up to the third post-Newtonian (3PN) order, the cubic-in-spin terms at the leading order, 3.5PN, and the spin-orbit effects up to the 4PN order. In addition, we obtain the 2PN spin contributions to the amplitude of the frequency-domain gravitational waveforms for nonprecessing binaries, using recently derived expressions for the time-domain polarization amplitudes of binaries with generic spins, complete at that accuracy level. These two results are updates to [K. G. Arun, A. Buonanno, G. Faye, and E. Ochsner, Phys. Rev. D 79, 104023 (2009).] for amplitude and [M. Wade, J. D. E. Creighton, E. Ochsner, and A. B. Nielsen, Phys. Rev. D 88, 083002 (2013).] for phasing. They should be useful for constructing banks of templates that accurately model nonprecessing inspiraling binaries, for parameter estimation studies, and for constructing analytical template families that account for the inspiral-merger-ringdown phases of the binary.

It is well known that the Fock quantization of field theories in general spacetimes suffers from an infinite ambiguity, owing to the inequivalent possibilities in the selection of a representation of the canonical commutation or anticommutation relations, but also owing to the freedom in the choice of variables to describe the field among all those related by linear time-dependent transformations, including the dependence through functions of the background. In this work we remove this ambiguity (up to unitary equivalence) in the case of a massive Dirac free field propagating in a spacetime with homogeneous and isotropic spatial sections of spherical topology. Two physically reasonable conditions are imposed in order to arrive at this result: (a) The invariance of the vacuum under the spatial isometries of the background, and (b) the unitary implementability of the dynamical evolution that dictates the Dirac equation. We characterize the Fock quantizations with a nontrivial fermion dynamics that satisfy these two conditions. Then, we provide a complete proof of the unitary equivalence of the representations in this class under very mild requirements on the time variation of the background, once a criterion to discern between particles and antiparticles has been set.

In the present paper, we revisit gravitational theories which are invariant under TDiffs—transverse (volume-preserving) diffeomorphisms and global scale transformations. It is known that these theories can be rewritten in an equivalent diffeomorphism-invariant form with an action including an integration constant (cosmological constant for the particular case of non-scale-invariant unimodular gravity). The presence of this integration constant, in general, breaks explicitly scale invariance and induces a runaway potential for the (otherwise massless) dilaton, associated with the determinant of the metric tensor. We show, however, that if the metric carries mass dimension ${[\mathrm{GeV}]}^{-2}$, the scale invariance of the system is preserved, unlike the situation in theories in which the metric has mass dimension different from $-2$. The dilaton remains massless and couples to other fields only through derivatives, without any conflict with observations. We observe that one can define a specific limit for fields and their derivatives (in particular, the dilaton goes to zero, potentially related to the small distance domain of the theory) in which the only singular terms in the action correspond to the Higgs mass and the cosmological constant. We speculate that the self-consistency of the theory may require the regularity of the action, leading to the absence of the bare Higgs mass and cosmological constant, whereas their small finite values may be generated by nonperturbative effects.

As a possible method to detect gravastars (gravitational-vacuum-star), which was originally proposed by Mazur and Mottola, we study their gravitational lensing effects. Specifically, we adopt a spherical thin-shell model of a gravastar developed by Visser and Wiltshire, which connects interior de Sitter geometry and exterior Schwarzschild geometry, and assume that its surface is optically transparent. We calculate the image of a companion which rotates around the gravastar; we find that some characteristic images appear, depending on whether the gravastar possess unstable circular orbits of photons (Model 1) or not (Model 2). For Model 2, we calculate the total luminosity change, which is called microlensing effects; the maximal luminosity could be considerably larger than the black hole with the same mass.

Recent cosmic microwave background (CMB) temperature and polarization anisotropy measurements from the Planck mission have significantly improved previous constraints on the neutrino masses as well as the bounds on extended models with massless or massive sterile neutrino states. However, due to parameter degeneracies, additional low redshift priors are mandatory in order to sharpen the CMB neutrino bounds. We explore here the role of different priors on low redshift quantities, such as the Hubble constant, the cluster mass bias, and the reionization optical depth $\tau$. Concerning current priors on the Hubble constant and the cluster mass bias, the bounds on the neutrino parameters may differ appreciably depending on the choices adopted in the analyses. With regard to future improvements in the priors on the reionization optical depth, a value of $\tau =0.05\pm 0.01$, motivated by astrophysical estimates of the reionization redshift, would lead to $\sum m_{\nu }<0.0926\mathrm{eV}$ at 90% C.L., when combining the full Planck measurements, baryon acoustic oscillation, and Planck clusters data, thereby opening the window to unravel the neutrino mass hierarchy with existing cosmological probes.

We investigate the cosmology of massive electrodynamics and explore the possibility whether the massive photon could provide an explanation of dark energy. The action is given by the scalar-vector-tensor theory of gravity, which is obtained by nonminimal coupling of the massive Stueckelberg QED with gravity; its cosmological consequences are studied by paying particular attention to the role of photon mass. We find that the theory allows for cosmological evolution where the radiation- and matter-dominated epochs are followed by a long period of virtually constant dark energy that closely mimics a $\mathrm{\Lambda }\mathrm{CDM}$ model. We also find that the main source of the current acceleration is provided by the nonvanishing photon mass governed by the relation $\mathrm{\Lambda }\sim m^2$. A detailed numerical analysis shows that the nonvanishing photon mass on the order of $\sim 10^{-34}\mathrm{eV}$ is consistent with current observations. This magnitude is far less than the most stringent limit on the photon mass available so far, which is on the order of $m\le 10^{-27}\mathrm{eV}$.

We consider search strategies for an extended Higgs sector at the high-luminosity LHC14 utilizing multitop final states. In the framework of a two Higgs doublet model, the purely top final states ($t\overline{t}$, $4t$) are important channels for heavy Higgs bosons with masses in the wedge above $2m_t$ and at low values of $\tan \beta$, while a $2b2t$ final state is most relevant at moderate values of $\tan \beta$. We find, in the $t\overline{t}H$ channel, with $H\to t\overline{t}$, that both single and three lepton final states can provide statistically significant constraints at low values of $\tan \beta$ for $m_A$ as high as $\sim 750\mathrm{GeV}$. When systematics on the $t\overline{t}$ background are taken into account, however, the three lepton final state is more powerful, though the precise constraint depends fairly sensitively on lepton fake rates. We also find that neither $2b2t$ nor $t\overline{t}$ final states provide constraints on additional heavy Higgs bosons with couplings to tops smaller than the top Yukawa due to expected systematic uncertainties in the $t\overline{t}$ background.

The quark-line disconnected diagram is a potentially important ingredient in lattice QCD calculations of the hadronic vacuum polarization contribution to the anomalous magnetic moment of the muon. It is also a notoriously difficult one to evaluate. Here, for the first time, we give an estimate of this contribution based on lattice QCD results that have a statistically significant signal, albeit at one value of the lattice spacing and an unphysically heavy value of the $u/d$ quark mass. We use HPQCD’s method of determining the anomalous magnetic moment by reconstructing the Adler function from time moments of the current-current correlator at zero spatial momentum. Our results lead to a total (including $u$, $d$ and $s$ quarks) quark-line disconnected contribution to $a_{\mu }$ of $-0.15\%$ of the $u/d$ hadronic vacuum polarization contribution with an uncertainty which is 1% of that contribution.

Recent anomalies in the decays of $B$ mesons and the Higgs boson provide hints towards lepton flavor (universality) violating physics beyond the Standard Model. We observe that four-fermion operators which can explain the $B$-physics anomalies have corresponding analogs in the kaon sector, and we analyze their impact on $K\to \pi \ell {\ell }^{\prime }$ and $K\to \ell {\ell }^{\prime }$ decays $(\ell =\mu ,e)$. For these processes, we note the corresponding physics opportunities at the NA62 experiment. In particular, assuming minimal flavor violation, we comment on the required improvements in sensitivity necessary to test the $B$-physics anomalies in the kaon sector.

We present the new nCTEQ15 set of nuclear parton distribution functions (PDFs) with uncertainties. This fit extends the CTEQ proton PDFs to include the nuclear dependence using data on nuclei all the way up to ${}^{208}\mathrm{Pb}$. The uncertainties are determined using the Hessian method with an optimal rescaling of the eigenvectors to accurately represent the uncertainties for the chosen tolerance criteria. In addition to the deep inelastic scattering and Drell-Yan processes, we also include inclusive pion production data from the Relativistic Heavy Ion Collider to help constrain the nuclear gluon PDF. Furthermore, we investigate the correlation of the data sets with specific nuclear PDF flavor components and asses the impact of individual experiments. We also provide comparisons of the nCTEQ15 set with recent fits from other groups.

We argue that the effective theory for electromagnetic fields in spatially varying meson condensations in dense nuclear and quark matter is given by the axion electrodynamics. We show that one of the helicity states of photons there has the nonrelativistic gapless dispersion relation $\omega \sim k^2$ at small momentum, while the other is gapped. This “nonrelativistic photon” may also be realized at the interface between topological and trivial insulators in condensed matter systems.

In this paper we investigate how to realize various quite well-known cosmological bouncing models in the context of the recently developed unimodular $F(R)$ gravity. Particularly, we shall study the matter bounce scenario, the singular bounce, the superbounce and a symmetric bounce scenario. We present the behavior of the Hubble radius for each of the bouncing models we shall take into account, and we investigate which era of the bouncing model is responsible for the cosmological perturbations. As we shall demonstrate, the various bouncing models do not behave in the same way, so the cosmological perturbations for each model may correspond to a different era, in comparison to other models. Also we present which unimodular $F(R)$ gravity realizes each model. We also show that Newton’s law is not modified in the unimodular $F(R)$ gravity, which also is proven to be a ghost-free theory, and in addition we discuss the matter stability issue. Finally, we demonstrate how it is possible to solve a cosmological constant problem in the context of unimodular $F(R)$ gravity.

We revisit the “state-dependence” of the map that we proposed recently between bulk operators in the interior of a large anti–de Sitter black hole and operators in the boundary CFT. By refining recent versions of the information paradox, we show that this feature is necessary for the CFT to successfully describe local physics behind the horizon—not only for single-sided black holes but even in the eternal black hole. We show that state-dependence is invisible to an infalling observer who cannot differentiate these operators from those of ordinary quantum effective field theory. Therefore the infalling observer does not observe any violations of quantum mechanics. We successfully resolve a large class of potential ambiguities in our construction. We analyze states where the CFT is entangled with another system and show that the $\mathrm{ER}=\mathrm{EPR}$ conjecture emerges from our construction in a natural and precise form. We comment on the possible semiclassical origins of state-dependence.