Neutrino-matter interactions play an important role in the postmerger evolution of neutron star-neutron star and black hole-neutron star mergers. Most notably, they determine the properties of the bright optical/infrared transients observable after a merger. Unfortunately, Boltzmann’s equations of radiation transport remain too costly to be evolved directly in merger simulations. Simulations rely instead on approximate transport algorithms with unquantified modeling errors. In this paper, we use for the first time a time-dependent general relativistic Monte Carlo (MC) algorithm to solve Boltzmann’s equations and estimate important properties of the neutrino distribution function $\sim 10\mathrm{ms}$ after a neutron star merger that resulted in the formation of a massive neutron star surrounded by an accretion disk. We do not fully couple the MC algorithm to the fluid evolution, but use a short evolution of the merger remnant to critically assess errors in our approximate gray two-moment transport scheme. We demonstrate that the analytical closure used by the moment scheme is highly inaccurate in the polar regions, but performs well elsewhere. While the average energy of polar neutrinos is reasonably well captured by the two-moment scheme, estimates for the neutrino energy become less accurate at lower latitudes. The two-moment formalism also overestimates the density of neutrinos in the polar regions by $\sim 50\%$, and underestimates the neutrino pair-annihilation rate at the poles by factors of 2–3. Although the latter is significantly more accurate than one might have expected before this study, our results indicate that predictions for the properties of polar outflows and for the creation of a baryon-free region at the poles are likely to be affected by errors in the two-moment scheme, thus limiting our ability to reliably model kilonovae and gamma-ray bursts.

Many galaxy clusters have giant halos of nonthermal radio emission, indicating the presence of relativistic electrons in the clusters. Relativistic protons may also be accelerated by merger and/or accretion shocks in galaxy clusters. These cosmic-ray (CR) electrons and/or protons are expected to produce gamma rays through inverse-Compton scatterings or inelastic $pp$ collisions respectively. Despite of intense efforts in searching for high-energy gamma-ray emission from galaxy clusters, conclusive evidence is still missing so far. Here we report the discovery of $\ge 200\mathrm{MeV}$ gamma-ray emission from the Coma cluster direction with an unbinned likelihood analysis of the 9 years of Fermi-LAT Pass 8 data. The gamma-ray emission shows a spatial morphology roughly coincident with the giant radio halo, with an apparent excess at the southwest of the cluster. Using the test statistic analysis, we further find tentative evidence that the gamma-ray emission at the Coma center is spatially extended. The extended component has an integral energy flux of $\sim 2\times {10}^{-12}\mathrm{erg}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$ in the energy range of 0.2–300 GeV and the spectrum is soft with a photon index of $\simeq -2.7$. Interpreting the gamma-ray emission as arising from CR proton interaction, we find that the volume-averaged value of the CR to thermal pressure ratio in the Coma cluster is about $\sim 2\%$. Our results show that galaxy clusters are likely a new type of GeV gamma-ray sources, and they are probably also giant reservoirs of CR protons.

We critically reexamine two possible dark matter candidates within the Standard Model. First, we consider the $uuddss$ hexaquark. Its QCD binding energy could be large enough to make it (quasi)stable. We show that the cosmological dark matter abundance is reproduced thermally if its mass is 1.2 GeV. However, we also find that such a mass is excluded by the stability of oxygen nuclei. Second, we consider the possibility that the instability in the Higgs potential leads to the formation of primordial black holes while avoiding vacuum decay during inflation. We show that the nonminimal Higgs coupling to gravity must be as small as allowed by quantum corrections, $|{\xi }_H|<0.01$. Even so, one must assume that the Universe survived in $e^{120}$ independent regions to fluctuations that lead to vacuum decay with probability $1/2$ each.

Observations of gravitational-wave signals from binary neutron-star mergers, like GW170817, can be used to constrain the neutron-star equation of state (EoS). One method involves modeling the EoS and measuring the model parameters through Bayesian inference. A previous study [B. D. Lackey and L. Wade, Phys. Rev. D 91, 043002 (2015)] has demonstrated the effectiveness of using a phenomenologically parameterized piecewise polytrope to extract constraining information from a simulated population of binary neutron-star mergers. Despite its advantages compared to more traditional methods of measuring the tidal deformability of neutron stars, notable deficiencies arise when using this EoS model. In this work, we describe in detail the implementation of a model built from a spectral decomposition of the adiabatic index that was used by the LIGO-Virgo Collaboration [arXiv:1805.11581] to constrain the neutron-star EoS from GW170817. We demonstrate its overall consistency in recovering the neutron-star EoS from a simulated signal to the piecewise-polytropic implementation used by Lackey and Wade and explain any differences that arise. We find that both models recover consistent tidal information from the simulate signals with tightest constraints on the EoS around twice nuclear saturation density. As expected, the statistical error that arises in the piecewise-polytropic representation near the fixed joining densities is greatly reduced by using the spectral model. In addition, we find that our choice of prior can have a dominant effect on EoS constraints.

Decays of radioisotopes on inner detector surfaces can pose a major background concern for the direct detection of dark matter. While these backgrounds are conventionally mitigated with position cuts, these cuts reduce the exposure of the detector by decreasing the sensitive mass, and uncertainty in position determination may make it impossible to adequately remove such events in certain detectors. In this paper, we provide a new technique for substantially reducing these surface backgrounds in liquid argon (LAr) detectors, independent of position cuts. These detectors typically use a coating of tetraphenyl-butadiene (TPB) on the inner surfaces as a wavelength shifter to convert vacuum ultraviolet (VUV) LAr scintillation light to the visible spectrum. We find that TPB scintillation contains a component with a previously unreported exceptionally long lifetime ($\sim \mathrm{ms}$). We discovered that this component differs significantly in magnitude between alpha, beta, and VUV excitation, which enables the use of pulse shape discrimination to suppress surface backgrounds by more than a factor of $10^3$ with negligible loss of dark matter sensitivity. We also discuss how this technique can be extended beyond just LAr experiments.

The LISA Pathfinder charge management device was responsible for neutralizing the cosmic-ray-induced electric charge that inevitably accumulated on the free-falling test masses at the heart of the experiment. We present measurements made on ground and in flight that quantify the performance of this contactless discharge system which was based on photoemission under UV illumination. In addition, a two-part simulation is described that was developed alongside the hardware. Modeling of the absorbed UV light within the Pathfinder sensor was carried out with the Geant4 software toolkit and a separate Matlab charge transfer model calculated the net photocurrent between the test masses and surrounding housing in the presence of AC and DC electric fields. We confront the results of these models with observations and draw conclusions for the design of discharge systems for future experiments like LISA that will also employ free-falling test masses.

We consider a scenario with only one sterile neutrino $N$ and negligible mixing with the active neutrinos ${\nu }_L$, where its interactions with ordinary particles could be described in a model-independent approach based on an effective theory. Under such a framework, we consider the contributions of the sterile neutrino $N$ to the pure leptonic decays $M\to l\nu$ and $\nu \overline{\nu }$, and the radiative leptonic decays $M\to l\nu \gamma$ with $M$ denoting the pseudoscalar mesons $B$, $D$, and $K$. We find that it can produce significant effects on some of these rare decay processes.

Gauge coupling unification and the stability of the Higgs vacuum are among two of the cherished features of low-energy supersymmetric models. Putting aside questions of naturalness, supersymmetry might only be realized in nature at very high energy scales. If this is the case, the preservation of gauge coupling unification and the stability of the Higgs vacuum would certainly require new physics, but it need not necessarily be at weak scale energies. New physics near the unification scale could, in principle, ensure grand unification, while new physics below ${10}^{10}\mathrm{GeV}$ could ensure the stability of the Higgs vacuum. Surprisingly however, we find that in the context of a supersymmetric SO(10) grand unified theory, gauge coupling unification and the Higgs vacuum stability, when taken in conjunction with existing phenomenological constraints, require the presence of $\mathcal{O}(\mathrm{TeV})$-scale physics. This weak-scale physics takes the form of a complex scalar ${\mathrm{SU}(2)}_L$ triplet with zero hypercharge, originating from the $\mathbf{210}$ of SO(10).

We calculate the finite-temperature density and polarization equations of state of one-dimensional fermions with a zero-range interaction, considering both attractive and repulsive regimes. In the path-integral formulation of the grand-canonical ensemble, a finite chemical potential asymmetry makes these systems intractable for standard Monte Carlo approaches due to the sign problem. Although the latter can be removed in one spatial dimension, we consider the one-dimensional situation in the present work to provide an efficient test for studies of the higher-dimensional counterparts. To that end, we use the complex Langevin approach, which we compare here with other approaches: imaginary-polarization studies, third-order perturbation theory, and the third-order virial expansion. We find very good qualitative and quantitative agreement across all methods in the regimes studied, which supports their validity.

We report on a two-flavor lattice QCD study of the $D_s$ and $D_s^{*}$ leptonic decays parametrized by the decay constants $f_{D_s}$ and $f_{D_s^{*}}$. As the phenomenology in the $D_s$ sector seems very promising in the next years with the experiments LHCb and Belle II, it is worth putting a big effort in lattice computations regarding its nonperturbative QCD contributions. Before examining more challenging processes such as hadron-hadron transitions, a natural first step is to address some basic aspects in the context of leptonic decays, where systematic uncertainties from excited state contaminations and cut-off effects in the computation of charmed meson decay matrix elements can be investigated in a more straightforward setting.

A theoretical model of the reactions $e^{+}{e}^{-}\to K^{+}{K}^{-}\gamma$ and $e^{+}{e}^{-}\to K^0\overline{K^0}\gamma$ has been derived. The strong interaction between kaons is taken into account using a general form of the $K\overline{K}$ scattering amplitude. It is shown that some models formulated in the past are particular cases of the present approach. The formulas for the $K\overline{K}$ effective mass dependence of the differential cross section as well as for the angular kaon and photon distributions and for the branching fractions of the $\varphi (1020)\to K^{+}{K}^{-}\gamma$ and $\varphi (1020)\to K^0\overline{K^0}\gamma$ decays have been obtained. We present numerical results for the functions entering into transition amplitudes, $K\overline{K}$ effective mass distributions, total cross sections, and branching fractions. Finally, the model is generalized to treat other reactions with two pseudoscalar mesons accompanying a photon in the final state.

We consider the chiral Lagrangian for charmed baryon fields with $J^P={\frac{1}{2}}^{+}$ or $J^P={\frac{3}{2}}^{+}$ quantum numbers. A chiral expansion framework for the baryon ground state masses is worked out to ${\mathrm{N}}^3\mathrm{LO}$ as to compute their dependence on the up, down and strange quark masses for finite box QCD lattice simulations. It is formulated in terms of on-shell meson and baryon masses. The convergence of such a scheme is illustrated with physical masses as taken from the Particle Data Group (PDG). The counter terms relevant at ${\mathrm{N}}^3\mathrm{LO}$ are correlated systematically by large-$N_c$ sum rules to leading and subleading order in a manner that keeps the renormalization scale invariance of the approach.

Transverse momentum dependent (TMD) parton distributions in a proton are important in high-energy physics from both theoretical and phenomenological points of view. Using the latest RHIC and LHC data on the inclusive soft hadron production in $pp$ and $AA$ collisions at small transverse momenta, we determine the parameters of the initial TMD gluon density derived in the framework of a quark-gluon string model at the low scale ${\mu }_0\sim 1–2\mathrm{GeV}$ and refine its large-$x$ behavior using the LHC data on the $t\overline{t}$ production at $\sqrt{s}=13\mathrm{TeV}$. Then, we apply the Catani-Ciafaloni-Fiorani-Marchesini evolution equation to extend the obtained TMD gluon density to the whole kinematical region. In addition, the complementary TMD valence and sea quark distributions are generated. The latter are evaluated in the approximation where the gluon-to-quark splitting occurs at the last evolution step using the TMD gluon-to-quark splitting function. Several phenomenological applications of the proposed TMD quark and gluon densities to the LHC processes are discussed.

Lepton flavor universality can be tested in the semileptonic decays ${\mathrm{\Lambda }}_b\to {\mathrm{\Lambda }}_c^{(*)}$, where ${\mathrm{\Lambda }}_c^{(*)}$ denotes either the ground state ${\mathrm{\Lambda }}_c(2286)$ (with $J^P=1/2^{+}$) or its orbital excitations ${\mathrm{\Lambda }}_c(2595)$ (with $J^P=1/2^{-}$) and ${\mathrm{\Lambda }}_c(2625)$ (with $J^P=3/2^{-}$). We calculate the differential decay rates as well as the branching fractions of these decays for both tauonic and muonic modes with form factors obtained from a covariant confined quark model previously developed by us. We present results for the rate ratios of the tauonic and muonic modes which provide important tests of lepton flavor universality in forthcoming experiments.

We report on the first cross section measurement of charged-current single charged pion production by neutrinos and antineutrinos on argon. This analysis was performed using the ArgoNeuT detector exposed to the NuMI beam at Fermilab. The measurements are presented as functions of muon momentum, muon angle, pion angle, and angle between muon and pion. The flux-averaged cross sections are measured to be $2.7\pm 0.5(\mathrm{stat})\pm 0.5(\mathrm{syst})\times {10}^{-37}{\mathrm{cm}}^2/\mathrm{Ar}$ for neutrinos at a mean energy of 9.6 GeV and $8.4\pm 0.9(\mathrm{stat}{)}_{-0.8}^{+1.0}(\mathrm{syst})\times {10}^{-38}{\mathrm{cm}}^2/\mathrm{Ar}$ for antineutrinos at a mean energy of 3.6 GeV with the charged pion momentum above $100\mathrm{MeV}/c$. The results are compared with several model predictions.

We revisit the Coleman-Hill theorem in the context of reduced planar QED. Using the global U(1) Ward identity for this nonlocal but still gauge-invariant theory, we can confirm that the topological piece of the photon self-energy at zero momentum does not receive further quantum corrections apart from the potential one-loop contribution, even when considering the Lorentz-noninvariant case due to the Fermi velocity $v_F<c$. This is of relevance to probe possible time parity odd dynamics in a planar sheet of graphene which has an effective description in terms of ($2+1$)-dimensional planar reduced QED.

We analyze two-dimensional nonlinear sigma models at nonzero chemical potentials, which are governed by a complex action. In the spirit of contour deformations (thimbles), we extend the fields into the complex plane, which allows us to incorporate the chemical potentials $\mu$ as twisted boundary conditions. We write down the equations of motion and find exact BPS-like solutions in terms of pairs of (anti)holomorphic functions, in particular generalizations of unit charge and fractional instantons to generic $\mu$. The decay of these solutions is controlled by the imaginary part of $\mu$ and a vanishing imaginary part causes jumps in the action. We analyze how the total charge is distributed into localized objects and to what extent these are characterized by topology.

A significant fraction of stars are members of gravitationally bound hierarchies containing three or more components. Almost all low-mass stars in binaries with periods shorter than three days are part of a hierarchical system. We therefore anticipate that a large fraction of compact galactic binaries detected by the Laser Interferometer Space Antenna will be members of hierarchical triple or quadruple system. The acceleration imparted by the hierarchical companions can be detected in the gravitational wave signal for outer periods as large as 100 years. For systems with periods that are shorter than, or comparable to, the mission lifetime, it will be possible to measure the period and eccentricity of the outer orbit. Laser Interferometer Space Antenna observations of hierarchical stellar systems will provide insight into stellar evolution, including the role that Lidov-Kozai oscillations play in driving systems toward merger.

The pure $R^2$ gravity is equivalent to Einstein gravity with cosmological constant and a massless scalar field, and it further possesses the so-called restricted Weyl symmetry, which is a symmetry larger than scale symmetry. To incorporate matter, we consider a restricted Weyl invariant action composed of pure $R^2$ gravity, SU(2) Yang-Mills fields, and a nonminimally coupled massless Higgs field (a triplet of scalars). When the restricted Weyl symmetry is spontaneously broken, it is equivalent to an Einstein-Yang-Mills-Higgs (EYMH) action with a cosmological constant and a massive Higgs nonminimally coupled to gravity, i.e., via a term $\tilde{\xi }R|\overrightarrow{\mathrm{\Phi }}{|}^2$. When the restricted Weyl symmetry is not spontaneously broken, linearizations about Minkowski spacetime do not yield gravitons in the original $R^2$ gravity and hence it does not gravitate. However, we show that in the broken gauge sector of our theory, where the Higgs field acquires a nonzero vacuum expectation value, Minkowski spacetime is a viable gravitating background solution. We then obtain numerically gravitating magnetic monopole solutions for nonzero coupling constant $\tilde{\xi }=1/6$ in three different backgrounds: Minkowski, anti–de Sitter (AdS), and de Sitter (dS), all of which are realized in our restricted Weyl invariant theory.

There is a viable vector-tensor gravity (VTG) theory, the vector field of which produces repulsive forces leading to important effects. In the background universe, the effect of these forces is an accelerated expansion identical to that produced by vacuum energy (cosmological constant). Here, we prove that another of these effects arises for great enough collapsing masses which lead to Schwarzschild black holes and singularities in general relativity. For these masses, pressure becomes negligible against gravitational attraction, and the complete collapse cannot be stopped in the context of general relativity; however, in VTG, a strong gravitational repulsion could stop the falling of the shells toward the symmetry center. A certain study of a collapsing dust cloud is then developed, and in order to undertake this task, the VTG equations in comoving coordinates are written. In this sense, as it happens in general relativity for a pressureless dust ball, three different solutions are found. These three situations are analyzed, and the problem of the shell crossings is approached. The apparent horizons and trapped surfaces, the analysis of which will lead to diverse situations, depending on a certain theory characteristic parameter value, are also examined.