The detection of GW170817 in gravitational waves provides unprecedented constraints on the equation of state (EOS) of the ultradense matter within the cores of neutron stars (NSs). We extend the nonparametric analysis first introduced by Landry and Essick (2019), and confirm that GW170817 favors soft EOSs. We infer macroscopic observables for a canonical $1.4M_{\odot }$ NS, including the tidal deformability ${\mathrm{\Lambda }}_{1.4}={211}_{-137}^{+312}$ $({491}_{-181}^{+216})$ and radius $R_{1.4}=10.86_{-1.42}^{+2.04}$ $({12.51}_{-0.88}^{+1.00})\mathrm{km}$, as well as the maximum mass for nonrotating NSs $M_{\max }=2.064_{-0.134}^{+0.260}$ $({2.017}_{-0.087}^{+0.238})M_{\odot }$, with nonparametric priors loosely (tightly) constrained to resemble candidate EOSs from the literature. Furthermore, we find weak evidence that GW170817 involved at least one NS based on gravitational-wave data alone ($B_{\mathrm{BBH}}^{\mathrm{NS}}=3.3\pm 1.4$), consistent with the observation of electromagnetic counterparts. We also investigate GW170817’s implications for the maximum spin frequency of millisecond pulsars, and find that the fastest known pulsar is spinning at more than 50% of its breakup frequency at 90% confidence. We additionally find modest evidence in favor of quark matter within NSs, and GW170817 favors the presence of at least one disconnected hybrid star branch in the mass-radius relation over a single stable branch by a factor of 2. Assuming there are multiple stable branches, we find a suggestive posterior preference for a sharp softening around nuclear density followed by stiffening around twice nuclear density, consistent with a strong first-order phase transition. While the statistical evidence in favor of new physics within NS cores remains tenuous with GW170817 alone, these tantalizing hints reemphasize the promise of gravitational waves for constraining the supranuclear EOS.

We consider weakly magnetized hot QED plasma comprising electrons and positrons. There are three distinct dispersive (longitudinal and two transverse) modes of a photon in a thermomagnetic medium. At lowest order in the coupling constant, a photon is damped in this medium via Compton scattering and pair creation process. We evaluate the damping rate of hard photon by calculating the imaginary part of the each transverse dispersive modes in a thermomagnetic QED medium. We note that one of the fermions in the loop of one-loop photon self-energy is considered as soft and the other one is hard. Considering the resummed fermion propagator in a weakly magnetized medium for the soft fermion and the Schwinger propagator for hard fermion, we calculate the soft contribution to the damping rate of hard photon. In weak field approximation the thermal and thermomagnetic contributions to damping rate get separated out for each transverse dispersive mode. The total damping rate for each dispersive mode in presence of magnetic field is found to be reduced than that of the thermal one. This formalism can easily be extended to QCD plasma.

We apply the method proposed by Fröhlich, Morchio, and Strocchi to analyze the bound state spectrum of various gauge theories with a Brout-Englert-Higgs mechanism. These serve as building blocks for theories beyond the standard model but also stress the exceptional role of the standard model weak group. We will show how the Fröhlich-Morchio-Strocchi mechanism relates gauge-invariant bound state operators to invariant objects of the remaining unbroken gauge group after gauge fixing. In particular, this provides a strict gauge-invariant formulation of the latter in terms of the original gauge symmetry without using the terminology of spontaneous gauge symmetry breaking. We also demonstrate that the Fröhlich-Morchio-Strocchi approach allows us to put new constraints on theories beyond the standard model by pure field-theoretical considerations. Particularly the conventional construction of grand unified theories has to be rethought.

We extend a simple and compact method for calculating the three-flavor neutrino oscillation probabilities in uniform matter density to schemes with sterile neutrinos, with favorable features inherited. The only constraint of the extended method is that the scale of the matter potential is not significantly larger than the atmospheric $\mathrm{\Delta }{m}^2$, which is satisfied by all the running and proposed accelerator oscillation experiments. Degeneracies of the zeroth order eigensystem around solar and atmospheric resonances are resolved. Corrections to the zeroth order results are restricted to no larger than the ratio of the solar to the atmospheric $\mathrm{\Delta }{m}^2$. The zeroth order expressions are exact in vacuum because all the higher order corrections vanish when the matter potential equals zero. Also, because all the corrections are continuous functions of matter potential, the zeroth order precision is much better than $\mathrm{\Delta }{m}_{\odot }^2/\mathrm{\Delta }{m}_{\mathrm{atm}}^2$ for the weak matter effect. Numerical tests are presented to verify the theoretical predictions of the exceptional features. Precision and speed comparisons with previous $3+1$ methods are performed. Moreover, possible applications of the method in experiments to check the existence of sterile neutrinos are discussed.

A new theoretical framework, based on the quantum field theory of open systems applied to neutrinos, has been developed to describe the neutrino evolution in external environments accounting for the effect of the neutrino quantum decoherence. The developed new approach enables one to obtain the explicit expressions of the decoherence and relaxation parameters that account for a particular process, in which the neutrino participates, and also for the characteristics of an external environment and of the neutrino itself, including the neutrino energy. We have used this approach to consider a new mechanism of the neutrino quantum decoherence engendered by the neutrino radiative decay to photons and dark photons in an astrophysical environment. The importance of the performed studies is highlighted by the prospects of the forthcoming new large volume neutrino detectors that will provide new frontier in high-statistics measurements of neutrino fluxes from supernovae.

Quantum mechanics predicts that the decay rate of unstable systems could be effectively modified by the process of the measurement of the survival probability. Depending on the intrinsic properties of the unstable system and the experimental setup for the observation, one could obtain the so called (direct) quantum Zeno and inverse quantum Zeno effects corresponding to a slowing down or a speeding up of the decay, respectively. We argue that the inverse quantum Zeno effect is in principle detectable at a percent level for the neutron decay in experiments with trapped ultracold neutrons. Conversely, this effect is basically undetectable in experiments in which the neutron lifetime is measured by measuring the decays of beams of neutrons. As a test of our claim, we propose a simple qualitative correlation between the number of neutrons in the trap and the neutron lifetime: the larger the number, the faster the decay. Finally we discuss also the presently available measurements of the neutron lifetime and address the issue of the possible discrepancy that has been reported among the results obtained by the different experimental techniques.

The next-to minimal supersymmetric Standard Model (NMSSM) with a Type-I seesaw mechanism extends the NMSSM by three generations of right-handed neutrino fields to generate neutrino mass. As a byproduct, it renders the lightest sneutrino as a viable dark matter (DM) candidate. Due to the gauge singlet nature of the DM, its scattering with nucleon is suppressed in most cases to coincide spontaneously with the latest XENON-1T results. Consequently, broad parameter spaces in the Higgs sector, especially a light Higgsino mass, are resurrected as experimentally allowed, which makes the theory well suited to explain the long-standing $b\overline{b}$ excess at LEP-II and the continuously observed $\gamma \gamma$ excess by CMS Collaboration. We show by both analytic formulas and numerical results that the theory can naturally predict the central values of the excesses in its broad parameter space, and the explanations are consistent with the Higgs data of the discovered Higgs boson, $B$-physics, and DM physics measurements, the electroweak precision data, as well as the LHC search for sparticles. Part of the explanations may be tested by future DM experiments and the supersymmetry (SUSY) search at the LHC.

We discuss the different Kimber-Martin-Ryskin (KMR) prescriptions for unintegrated parton distribution functions (uPDFs). We show that the strong-ordering (SO) and the angular-ordering (AO) cutoffs lead to strong discrepancies between the obtained cross sections. While the result obtained with the AO cutoff overestimates the heavy-flavor cross section by about a factor of 3, the SO cutoff gives the correct answer. We also solve the issue of the KMR uPDF definitions mentioned by Golec-Biernat and Staśto [Phys. Lett. B 781, 633 (2018)] and show that, in the case of the AO cutoff, the KMR uPDFs are ill defined.

Color charge correlations in the proton at moderately small $x\sim 0.1$ are extracted from its light-cone wave function. The charge fluctuations are far from Gaussian and they exhibit interesting dependence on the impact parameter and on the relative transverse momentum (or distance) of the gluon probes. We provide initial conditions for small-$x$ Balitsky-Kovchegov evolution of the dipole scattering amplitude with impact parameter and $\widehat{r}·\widehat{b}$ dependence, and with a nonzero $C$-odd component due to three-gluon exchange. Lastly, we compute the (forward) Weizsäcker-Williams gluon distributions, including the distribution of linearly polarized gluons, up to fourth order in $A^{+}$. The correction due to the quartic correlator provides a transverse momentum scale, $q\gtrsim 0.5\mathrm{GeV}$, for nearly maximal polarization.

We present the improved constraints on couplings of solar axions and more generic bosonic dark matter particles using 737.1 kg days of data from the CDEX-1B experiment. The CDEX-1B experiment, located at the China Jinping Underground Laboratory, primarily aims at the direct detection of weakly interacting massive particles using a p-type point-contact germanium detector. We adopt the profile likelihood ratio method for analysis of data in the presence of backgrounds. An energy threshold of 160 eV was achieved, much better than the 475 eV of CDEX-1A with an exposure of 335.6 kg days. This significantly improves the sensitivity for the bosonic dark matter below 0.8 keV among germanium detectors. Limits are also placed on the coupling $g_{Ae}<2.48\times {10}^{-11}$ from Compton, bremsstrahlung, atomic-recombination, and deexcitation channels and $g_{AN}^{\mathrm{eff}}\times g_{Ae}<4.14\times {10}^{-17}$ from a ${}^{57}\mathrm{Fe}$ M1 transition at 90% confidence level.

A key ingredient in the evaluation of hadronic light-by-light (HLBL) scattering in the anomalous magnetic moment of the muon $(g-2{)}_{\mu }$ concerns short-distance constraints that follow from QCD by means of the operator product expansion. Here we concentrate on the most important such constraint, in the longitudinal amplitudes, and show that it can be implemented efficiently in terms of a Regge sum over excited-pseudoscalar states, constrained by phenomenological input on masses, two-photon couplings, as well as short-distance constraints on HLBL scattering and the pseudoscalar transition form factors. Our estimate of the effect of the longitudinal short-distance constraints on the HLBL contribution is $\mathrm{\Delta }{a}_{\mu }^{\mathrm{LSDC}}=13(6)\times {10}^{-11}$. This is significantly smaller than previous estimates, which mostly relied on an ad-hoc modification of the pseudoscalar poles and led to up to a 40% increase with respect to the nominal pseudoscalar-pole contributions, when evaluated with modern input for the relevant transition form factors. We also comment on the status of the transversal short-distance constraints and, by matching to perturbative QCD, argue that the corresponding correction will be significantly smaller than its longitudinal counterpart.

We investigate the gauge symmetry and gauge-fixing dependence properties of the effective average action for quantum gravity models of general form. Using the background field formalism and the standard Becchi-Rouet-Stora-Tyutin (BRST)-based arguments, one can establish the special class of regulator functions that preserves the background field symmetry of the effective average action. Unfortunately, regardless if the gauge symmetry is preserved at the quantum level, the noninvariance of the regulator action under the global BRST transformations leads to the gauge-fixing dependence even under the use of the on-shell conditions.

We semianalytically investigate the scalar self-force experienced in the final stages of extreme mass ratio inspirals of nonspinning scalar particles into supermassive nearly extremal Kerr black holes. We exploit the near-horizon conformal symmetry to find the self-force for general corotating equatorial geodesics. The angular component of the self-force is shown to be universal at leading order in the high spin limit. We verify that the energy and angular momentum losses of the scalar particle match with the asymptotic fluxes of scalar radiation. In particular, we relate the previously described persistent oscillations in the asymptotic energy and angular momentum fluxes with the local self-force. Such oscillations arise from traveling waves that prevent the near-horizon and the asymptotic region to fully decouple in the extremal limit. Conformal invariance is therefore reduced to discrete scale invariance with associated logarithmic periodicity.

Using a novel and self-consistent approach that avoids the scalar-tensor identification in the Einstein frame, we reanalyze the viability of $f(R)$ gravity within the context of solar-system tests. In order to do so, we depart from a simple but fully relativistic system of differential equations that describe a compact object in a static and spherically symmetric spacetime, and then we make suitable linearizations that apply to nonrelativistic objects such as the Sun. We then show clearly under which conditions the emerging chameleonlike mechanism can lead to a post-Newtonian parameter $\gamma$ compatible with the observational bounds. To illustrate this method, we use several specific $f(R)$ models proposed to explain the current acceleration of the Universe, and we show which of them are able to satisfy those bounds.

Echoes are known as modifications of the usual quasinormal ringing of a black hole at late times because of the deviation of space-time from the initial black hole geometry in a small region near its event horizon. We consider a class of brane-world model solutions of the Shiromizu-Maeda-Sasaki equations, which describe both black holes and wormholes and interpolate between them via a continuous parameter. In this way the brane-world scenario provides a natural model for wormholes mimicking the black hole behavior if the continuous parameter is chosen near the threshold with a black hole solution. We show that in the vicinity of this threshold interpolating between black holes and wormholes, quasinormal ringing of the wormholes at the initial stage is indistinguishable from that of the black holes with nearby values of the above parameter, but at later times the signal is modified by intensive echoes. We notice that the black hole mimickers that are wormholes near the threshold have the largest quality factor and are therefore the best oscillators among the considered examples.

Gravitational waves emitted by coalescing binary systems containing neutron stars (or other compact objects) carry signatures of the stars’ internal equation of state, notably, through the influence of tidal deformations during the binary’s inspiral stage. While the leading-order tidal effects for post-Newtonian binaries of compact bodies in general relativity are due to the bodies’ mass-quadrupole moments induced by gravitoelectric tidal fields, we consider here the leading effects due to current-quadrupole moments induced by gravitomagnetic tidal fields. We employ an effective action approach to determine the near-zone gravitational field and the conservative orbital dynamics, initially allowing for arbitrary (not just tidally induced) current quadrupoles; our approach significantly reduces the complexity of the calculation compared to previous derivations of the conservative dynamics for arbitrary multipoles. We finally compute the leading contributions from gravitomagnetic tides to the phase and (for the first time) the mode amplitudes of the gravitational waves from a quasicircular binary inspiral, given in terms of the bodies’ quadrupolar gravitomagnetic tidal Love numbers (tidal linear response coefficients in an adiabatic approximation). In the phase, gravitomagnetic tides are suppressed by one post-Newtonian order relative to gravitoelectric ones, but this is not always the case for the mode amplitudes. In the $(\ell ,|m|)=(2,1)$ and (3,2) modes, for example, they appear at the same leading orders.

Freeze-out or freeze-in during a period of early matter domination can yield the correct dark matter abundance for small values of the velocity-averaged annihilation cross section, $⟨{\sigma }_{\mathrm{ann}}v{⟩}_{\mathrm{f}}<3\times {10}^{-26}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$. However, in a generic nonstandard thermal history, such a period is typically preceded by other phases. Here, we study production of dark matter in a simple postinflationary history where a radiation-dominated phase after reheating is followed by an epoch of early matter domination. Focusing on the freeze-in regime, we show that dark matter production prior to early matter domination can dominate the relic abundance in large parts of the parameter space, including weak scale dark matter masses, and the allowed regions are highly dependent on the entire postinflationary history. Moreover, for a very broad range of $⟨{\sigma }_{\mathrm{ann}}v{⟩}_{\mathrm{f}}$ spanning over several decades, dark matter particles can start in chemical equilibrium early on and decouple during early matter domination, thereby rendering the relic abundance essentially independent of $⟨{\sigma }_{\mathrm{ann}}v{⟩}_{\mathrm{f}}$. We briefly discuss connections to different observables as a possible means to test the elusive freeze-in scenario in this case.

We offer a standing wave explanation for the rising proper motions of stars at the center of the globular cluster 47-Tucanae, amounting to $\simeq 0.44\%$ of the total mass. We show that this can be explained as a solitonic core of dark matter composed of light bosons, $m\ge {10}^{-18}\mathrm{eV}$, corresponding to $\le 0.27\mathrm{pc}$, as an alternative to a single black hole (BH) or a concentration of stellar BH remnants proposed recently. This is particularly important because having a concentrated stellar BH remnant with the above radii is very challenging without the heavy core since the three-body encounters would prevent the BHs from being that concentrated. We propose that this core develops from dark matter captured in the deep gravitational potential of this globular cluster as it orbits the dark halo of our Galaxy. This boson may be evidence for a second light axion, additional to a lighter boson of ${10}^{-22}\mathrm{eV}$, favored for the dominant dark matter implied by the large dark cores of dwarf spheroidal galaxies. The identification of two such light bosonic mass scales favors the generic string theory prediction of a wide, discrete mass spectrum of axionic scalar fields.

Microlensing of stars places significant constraints on subplanetary-mass compact objects, including primordial black holes, as dark matter candidates. As the lens’ Einstein radius in the source plane becomes comparable to the size of the light source, however, source amplification is strongly suppressed, making it challenging to constrain lenses with a mass at or below ${10}^{-10}$ solar masses, i.e., asteroid-mass objects. Current constraints, using Subaru Hyper Suprime Cam (HSC) observations of M31, assume a fixed source size of one solar radius. However, the actual stars in M31 bright enough to be used for microlensing are typically much larger. We correct the HSC constraints by constructing a source size distribution based on the M31 PHAT survey and on a synthetic stellar catalog and by correspondingly weighting the finite-size source effects. We find that the actual HSC constraints are weaker by up to almost 3 orders of magnitude in some cases, broadening the range of masses for which primordial black holes can be the totality of the cosmological dark matter by almost 1 order of magnitude.