We investigate the presence of vortex configurations in generalized Maxwell-Chern-Simons models with nonminimal coupling, in which we introduce a function that modifies the dynamical term of the scalar field in the Lagrangian. We first follow a route already considered in previous works to develop the Bogomol’nyi procedure, and, in this context, we use the first-order equations to obtain a vortex with a novel behavior at its core. We then go further and introduce a novel procedure to develop the Bogomol’nyi methodology. It supports distinct first-order equations, and we then investigate another model, in which the vortex may engender inversion of the magnetic flux, an effect with no precedents in the study of vortices within the nonminimal context.

If two particles collide near the rotating extremal black hole and one of them is fine-tuned, the energy in the center of mass frame $E_{\mathrm{c}.\mathrm{m}.}$ can grow unbounded. This is the so-called Bañados-Silk-West (BSW) effect. Recently, another type of high energy collisions was considered in which all processes happen in the Schwarzschild background with free falling particles. If the Killing energy $E$ of one of particle is sufficiently small, $E_{\mathrm{c}.\mathrm{m}.}$ grows unbounded. We show that, however, such a particle cannot be created in any precedent collision with finite energies, angular momenta and masses. Therefore, in contrast to the standard BSW effect, this one cannot be realized if initial particles fall from infinity. If the black hole is electrically charged, such a type of collisions is indeed possible, when a particle with very small $E$ collides with one more particle coming from infinity. Thus the BSW effect is achieved due to collisions of neutral particles in the background of a charged black hole. This requires, however, at least a two-step process.

We first study the escape probability of a spinning particle emitted from a Kerr black hole and find that the escape probability increases with the spin of the particle around the extreme Kerr black hole; in contrast, the escape probability decreases at the position near the horizon but increases at the position far from the horizon with the increasing spin of the particle. We then probe the relation between the escape probabilities and the energy extraction efficiencies of collisional Penrose processes for particles with varying spin. For an extreme Kerr black hole, the efficiency increases with the escape probability; for a nonextreme Kerr black hole, the near-horizon efficiency decreases with the escape probability, while the efficiency may increase with the escape probability in the ergosphere. In the event horizon limit, we also find that the average escape probability of the spinning particle produced in the collisional Penrose process decreases with the rotation parameter of the Kerr black hole.

In this paper we study small scalar cosmological perturbations in teleparallel gravity in linear order. We discuss problems which appear in the standard approach to $f(T)$ gravity, and find that these problems may be solved within covariant formulation of teleparallel gravity, which take into account spin connection. We calculate spin connection which symmetrizes the equation for perturbation and split diagonal and nondiagonal parts of the equation of motion. We demonstrate that there is a solution for spin connection, which leads to zero gravitational slip; however, in this case one additional equation appears, so the system may become overdetermined. After that, we show that a more general solution exists, which is incompatible with zero slip, but allows one to write down the equations of motion for cosmological perturbation in a self-consistent way without additional equations to be satisfied.

We investigate the behavior of the Dirac spinor fields in general relativistic high density stellar backgrounds and the possibility of spontaneous spinorization which is analogous to spontaneous scalarization. We consider the model with the modified kinetic term of the Dirac field by the insertion of the fifth gamma matrix ${\widehat{\gamma }}^5$ and the conformal coupling of the Dirac spinor field to the matter sector, which would lead to the tachyonic growth of the Dirac spinor field in the high density compact stellar backgrounds. In order to obtain the static and spherically symmetric solutions, we have to consider the two Dirac fields at the same time. We show that in the constant density stellar backgrounds our model gives rise to the nontrivial solutions of the Dirac spinor fields with any number of nodes, where one mode has one more node than the other. We also show that at the leading order all the components of the effective energy-momentum tensor of the Dirac spinor fields, after the summation over the two fields, vanish for any separable time-dependent ansatz of the Dirac spinor fields in any static and spherically symmetric spacetime backgrounds, indicating that spontaneous spinorization takes place as a stealth process in the static and spherically symmetric spacetime with any number of nodes, which would be quenched by nonlinear effects and leave no observable effects.

We study the Vainshtein mechanism in the context of slowly rotating stars in scalar-tensor theories. While the Vainshtein screening is well established for spherically symmetric spacetimes, we examine its validity in the axisymmetric case for slowly rotating sources. We show that the deviations from the general relativity solution are small in the weak-field approximation outside the star: the solution for the frame-dragging function is the same as in general relativity at leading order. Moreover, in most cases the corrections are suppressed by powers of the Vainshtein radius provided that the screening operates in spherical symmetry. Outside the Vainshtein radius, the frame dragging function receives corrections that are not suppressed by the Vainshtein radius, but which are still subleading. This suggests that the Vainshtein mechanism in general can be extended to slowly rotating stars and that it works analogously to the static case inside the Vainshtein radius. We also study relativistic stars and show that for some theories the frame-dragging function in vacuum does not receive corrections at all, meaning that the screening is perfect outside the star.

We show that a nonminimal coupling to gravity can not only make some inflationary models consistent with cosmological data, similar to the case of Higgs inflation, but can also invoke slow-roll violation to realize a graceful exit from inflation. In particular, this is the case in models where a destabilizing mechanism that ends inflation should be assumed when the model is minimally coupled to gravity. As explicit examples, we consider the power-law and inverse monomial inflation models with a nonminimal coupling to gravity. While these models are excluded in the minimally coupled case, we show that they can become viable again in nonminimally coupled scenarios. In most scenario we considered, reheating can be naturally realized via gravitational particle production but this depends on the underlying theory of gravity in a nontrivial way reheating can be naturally realized via gravitational particle production but that this depends on the underlying theory of gravity in a nontrivial way.

After the discovery of gravitational waves from binary black holes (BBHs) and binary neutron stars (BNSs) with the LIGO and Virgo detectors, neutron-star black holes (NSBHs) are the natural next class of binary systems to be observed. In this work, we develop a waveform model for aligned-spin NSBHs combining a BBH baseline waveform (available in the effective-one-body approach) with a phenomenological description of tidal effects (extracted from numerical-relativity simulations) and correcting the amplitude during the late inspiral, merger and ringdown to account for the NS tidal disruption. In particular, we calibrate the amplitude corrections using NSBH waveforms obtained with the numerical-relativity spectral Einstein code (spec) and the sacra code. The model was calibrated using simulations with NS masses in the range $1.2–1.4M_{\odot }$, tidal deformabilities up to 4200 (for a $1.2M_{\odot }$ NS), and dimensionless BH spin magnitude up to 0.9. Based on the simulations used and on checking that sensible waveforms are produced, we recommend our model to be employed with a NS mass in the range $1–3M_{\odot }$, tidal deformability 0–5000, and (dimensionless) BH spin magnitude up to 0.9. We also validate our model against two new, highly accurate NSBH waveforms with BH spin 0.9 and mass ratios 3 and 4, characterized by tidal disruption, produced with SpEC, and find very good agreement. Furthermore, we compute the unfaithfulness between waveforms from NSBH, BBH, and BNS systems, finding that it will be challenging for the Advanced LIGO-Virgo detector network at design sensitivity to distinguish different source classes. We perform a Bayesian parameter-estimation analysis on a synthetic numerical-relativity signal in zero noise to study parameter biases. Finally, we reanalyze GW170817, with the hypothesis that it is a NSBH. We do not find evidence to distinguish the BNS and NSBH hypotheses; however, the posterior for the mass ratio is shifted to less equal masses under the NSBH hypothesis.

We demonstrate the application of a convolutional neural network to the gravitational wave signals from core collapse supernovae. Using simulated time series of gravitational wave detectors, we show that, based on the explosion mechanisms, a convolutional neural network can be used to detect and classify the gravitational wave signals buried in noise. For the waveforms used in the training of the convolutional neural network, our results suggest that a network of advanced LIGO, advanced VIRGO and KAGRA (HLVK), or a network of LIGO A+, advanced VIRGO and KAGRA ($\mathrm{H}+\mathrm{L}+\mathrm{VL}$) is likely to detect a magnetorotational core collapse supernova out to the large or even small Magellanic clouds. A neutrino-driven event is likely to be detectable with a network of $\mathrm{H}+\mathrm{L}+\mathrm{VK}$ and HLVK if the distance is within 5 and 3 kpc respectively. By testing the convolutional neural network with waveforms not used for training, we show that the true alarm probability is 66% at 60 kpc for waveforms R3E1AC and R4E1FC_L with a network of $\mathrm{H}+\mathrm{L}+\mathrm{VK}$. For waveforms s20 and SFHx, the true alarm probabilities are 56% for $\mathrm{H}+\mathrm{L}+\mathrm{VK}$ at 7 kpc and 50% for HLVK at 5 kpc respectively. All are at false alarm probability equal to 0.1%.

The Askaryan Radio Array (ARA) is an ultrahigh energy (UHE, $>{10}^{17}\mathrm{eV}$) neutrino detector designed to observe neutrinos by searching for the radio waves emitted by the relativistic products of neutrino-nucleon interactions in Antarctic ice. In this paper, we present constraints on the diffuse flux of ultrahigh energy neutrinos between ${10}^{16}$ and ${10}^{21}\mathrm{eV}$ resulting from a search for neutrinos in two complementary analyses, both analyzing four years of data (2013–2016) from the two deep stations (A2, A3) operating at that time. We place a 90% CL upper limit on the diffuse all flavor neutrino flux at ${10}^{18}\mathrm{eV}$ of $EF(E)=5.6\times {10}^{-16}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}{\mathrm{sr}}^{-1}$. This analysis includes four times the exposure of the previous ARA result and represents approximately $1/5$th the exposure expected from operating ARA until the end of 2022.

After eleven gravitational-wave detections from compact-binary mergers, we are yet to observe the striking general-relativistic phenomenon of orbital precession. Measurements of precession would provide valuable insights into the distribution of black-hole spins, and therefore into astrophysical binary formation mechanisms. Using our recent two-harmonic approximation of precessing-binary signals [S. Fairhurst et al., Phys. Rev. D 102, 024055 (2020)], we introduce the “precession signal-to-noise ratio”, ${\rho }_p$. We demonstrate that this can be used to clearly identify whether precession was measured in an observation (by comparison with both current detections and simulated signals), and can immediately quantify the measurability of precession in a given signal, which currently requires computationally expensive parameter-estimation studies. ${\rho }_p$ has numerous potential applications to signal searches, source-property measurements, and population studies. We give one example: assuming one possible astrophysical spin distribution, we predict that precession has a one in $\sim 25$ chance of being observed in any detection.

We derive the fragmentation function (FF), which describes the probability for a charm quark to emit a $D$ meson with a certain momentum fraction, in the Nambu–Jona-Lasinio model. The corresponding elementary FF is calculated with the quark-meson coupling determined in the Nambu–Jona-Lasinio model involving charm quarks. The FF in the infinite momentum frame is constructed through the jet process governed by the elementary FF, and then evolved to the charm scale, at which it is defined. To prepare the FF suitable for an analysis of $D$ meson production at CLEO, we further match the above FF to that in the finite momentum frame at one loop in QCD. It is shown that the charm quark FF, including the finite momentum effects, leads to theoretical results in agreement with the CLEO data.

We examined the effects of the weak magnetic field on the properties of heavy quarkonia immersed in a thermal medium of quarks and gluons and studied how the magnetic field affects the quasifree dissociation of quarkonia in the aforementioned medium. For that purpose, we have revisited the general structure of gluon self-energy tensor in the presence of a weak magnetic field in thermal medium and obtained the relevant structure functions using the imaginary-time formalism. The structure functions give rise to the real and imaginary parts of the resummed gluon propagator, which further give the real and imaginary parts of the dielectric permittivity. The real and imaginary parts of the dielectric permittivity will be used to evaluate the real and imaginary parts of the complex heavy quark potential. We have observed that the real part of the potential is found to be more screened, whereas the magnitude of the imaginary part of the potential gets increased on increasing the value of both temperature and magnetic field. In addition to this, we have observed that the real part gets slightly more screened while the imaginary part gets increased in the presence of a weak magnetic field as compared to their counterparts in the absence of a magnetic field (pure thermal). The increase in the screening of the real part of the potential leads to the decrease of binding energies of $J/\mathrm{\Psi }$ and $\mathrm{\Upsilon }$, whereas the increase in the magnitude of the imaginary part leads to the increase of thermal width with the temperature and magnetic field both. Also the binding energy and thermal width in the presence of a weak magnetic field become smaller and larger, respectively, as compared to that in the pure thermal case. With the observations of binding energy and thermal width in hand, we have finally obtained the dissociation temperatures for $J/\mathrm{\Psi }$ and $\mathrm{\Upsilon }$, which become slightly lower in the presence of a weak magnetic field. For example, with $eB=0m_{\pi }^2$ the $J/\psi$ and $\mathrm{\Upsilon }$ are dissociated at $1.80T_c$ and $3.50T_c$, respectively, whereas with $eB=0.5m_{\pi }^2$ they dissociated at slightly lower values $1.74T_c$ and $3.43T_c$, respectively. This observation leads to the slightly early dissociation of quarkonia because of the presence of a weak magnetic field.

We investigate constraints on the new $B-L$ gauge boson ($Z_{BL}$) mass and coupling ($g_{BL}$) in a $U(1{)}_{B-L}$ extension of the standard model (SM) with an SM singlet Dirac fermion ($\zeta$) as dark matter (DM). The DM particle $\zeta$ has an arbitrary $B-L$ charge $Q$ chosen to guarantee its stability. We focus on the small $Z_{BL}$ mass and small $g_{BL}$ regions of the model, and find new constraints for the cases where the DM relic abundance arises from thermal freeze-out as well as freeze-in mechanisms. In the thermal freeze-out case, the dark matter coupling is given by $g_{\zeta }\equiv g_{BL}Q\simeq 0.016\sqrt{m_{\zeta }[\mathrm{GeV}]}$ to reproduce the observed DM relic density and $g_{BL}\ge 2.7\times {10}^{-8}\sqrt{m_{\zeta }[\mathrm{GeV}]}$ for the DM particle to be in thermal equilibrium prior to freeze-out. Combined with the direct dark matter detection constraints and the indirect constraints from cosmic microwave background and AMS-02 measurements, discussed in earlier papers, we find that the allowed mass regions are limited to be $m_{\zeta }\gtrsim 200\mathrm{GeV}$ and $M_{Z_{BL}}\gtrsim 10\mathrm{GeV}$. We then discuss the lower $g_{BL}$ values where the freeze-in scenario operates and find the following relic density constraints on parameters depending on the $g_{BL}$ range and dark matter mass: Case (A): for $g_{BL}\ge 2.7\times {10}^{-8}\sqrt{m_{\zeta }[\mathrm{GeV}]}$, one has $g_{\zeta }^2{g}_{BL}^2+\frac{0.82}{1.2}{g}_{\zeta }^4\simeq 8.2\times {10}^{-24}$; and Case (B): for $g_{BL}<2.7\times {10}^{-8}\sqrt{m_{\zeta }[\mathrm{GeV}]}$, there are two separate constraints depending on $m_{\zeta }$. Case (B1): for $m_{\zeta }\lesssim 2.5\mathrm{TeV}$, we find $g_{\zeta }^2{g}_{BL}^2\simeq 8.2\times {10}^{-24}(\frac{m_{\zeta }}{2.5\mathrm{TeV}})$; and Case (B2): for $m_{\zeta }\gtrsim 2.5\mathrm{TeV}$, we have $g_{\zeta }^2{g}_{BL}^2\simeq 8.2\times {10}^{-24}$. For this case, we display the various parameter regions of the model that can be probed by a variety of “Lifetime Frontier” experiments such as FASER, FASER2, Belle II, SHiP, and LDMX.

We study the decay of the $Z$ vector boson into a photon and a massless (invisible) dark photon in high-energy collisions. The photon can be used as a trigger for the event, while the dark photon is detected indirectly as missing momentum in the event final state. We investigate the possibility of searching for such a dark photon at the LHC, HL-LHC, and future lepton colliders, and compare the respective sensitivities. As expected, the best result is found for the lepton colliders running at the $Z$ mass, FCC-ee and CEPC, with a final sensitivity to branching ratios of order $O({10}^{-11})$. We also discuss how to use the photon angular distribution of the events in lepton collisions to discriminate between the dark photon and a pseudoscalar state like the axion.

We consider the extension of the Standard Model (SM) with a strongly interacting QCD-like hidden sector, at least two generations of right-handed neutrinos, and one scalar singlet. Once the scalar singlet obtains a nonzero vacuum expectation value, active neutrino masses are generated through a type-I seesaw mechanism. Simultaneously, the electroweak scale is generated through the radiative corrections involving these massive fermions. This is the essence of the scenario that is known as the “neutrino option” for which the successful masses of right-handed neutrinos are in the range ${10}^7–{10}^8\mathrm{GeV}$. The main goal of this work is to scrutinize the potential to accommodate dark matter in such a realization. The dark matter candidates are Nambu-Goldstone bosons which appear due to the dynamical breaking of the hidden chiral symmetry. The mass spectrum studied in this work is such that masses of Nambu-Goldstone bosons and the singlet scalar exceed those of right-handed neutrinos. Having the masses of all relevant particles several orders of magnitude above $\mathcal{O}(\mathrm{TeV})$, the freeze-out of dark matter is not achievable, and, hence, we turn to alternative scenarios, namely, freeze-in. The Nambu-Goldstone bosons can interact with particles that are not in the SM but, however, have non-negligible abundance through their not-too-small couplings with the SM. Utilizing this, we demonstrate that the dark matter in the model is successfully produced at a temperature scale where the right-handed neutrinos are still stable. We note that the lepton number asymmetry sufficient for the generation of observable baryon asymmetry of the Universe can be produced in right-handed neutrino decays. Hence, we infer that the model has the potential to simultaneously address several of the most relevant puzzles in contemporary high-energy physics.

We compute boundary correlation functions for scalar fields on tessellations of two- and three-dimensional hyperbolic geometries. We present evidence that the continuum relation between the scalar bulk mass and the scaling dimension associated with boundary-to-boundary correlation functions survives the truncation of approximating the continuum hyperbolic space with a lattice.

The properties of electrically charged strange quark stars predicted by an interacting quark matter equation of state (EoS) based on cold and dense perturbative quantum chromodynamics (pQCD) are investigated. The stability of strange stars is analyzed considering different models for the electric charge distribution inside the star as well as for distinct values for the total electric charge. A comparison with the predictions derived using the MIT bag model is also presented. We show that the presence of a net electric charge inside strange stars is implied in a larger maximum mass in comparison to their neutral counterparts. Moreover, we demonstrate that the pQCD EoS implies larger values for the maximum mass of charged strange stars, with very heavy charged stars being stable systems against radial oscillations. For an electric charge distribution given by $q(r)=\beta r^3$, the pQCD EoS implies unstable configurations for large values of the renormalization scale as well as for large values of $\beta$, in contrast to the MIT bag model predictions.

Bramante, Delgado, and Martin [Phys. Rev. D 96, 063002 (2017), hereafter BDM17] extended the analytical formalism of dark matter (DM) capture in a very important way, which allows, in principle, the use of compact astrophysical objects, such as neutron stars (NSs), as dark matter detectors. In this comment, we point out the existence of a region in the dark matter neutron scattering cross section $({\sigma }_{nX})$ vs dark matter mass $(m_X)$ where the constraining power of this method is lost. This corresponds to a maximal temperature ($T_{\mathrm{crit}}$) the NS has to have, in order to serve as a dark matter detector. In addition, we point out several typos and errors in BDM17 that do not affect drastically their conclusions. Moreover, we provide analytical approximations for the total capture rates of dark matter particle of arbitrary mass for various limiting regimes.

The first and second swampland conjectures (FSC & SSC) are substantially modified in noncritical string cosmology, in which cosmic time is identified with the timelike Liouville mode of the supercritical string. In this scenario the Friedmann equation receives additional contributions due to the noncriticality of the string. These are potentially important when one seeks to apply the Bousso bound for the entropy of states that may become light as the dilaton takes on trans-Planckian values, as in a de Sitter phase, and restore consistency with the FSC and in at least some cases also the SSC. The weak gravity conjecture (WGC) for scalar potentials is saturated in the supercritical string scenarios discussed in this work, but only if one uses the dilaton as appears in the string effective action, with a kinetic term that is not canonically normalized. In the case of a noncritical Starobinsky potential, the WGC is satisfied by both the canonically normalized dilaton and the dilaton used in the string effective action.