We investigate how hypothetical particles—sterile neutrinos—can be produced in the interior of exploding supernovae via the resonant conversion of ${\overline{\nu }}_{\mu }$ and ${\overline{\nu }}_{\tau }$. The novelty of our treatment lies in the proper account of the resulting lepton number diffusion. We compute the yield of sterile neutrinos and find that even after taking into account backreaction, sterile neutrinos can carry out a sizeable fraction of the total energy of the explosion comparable to that of active neutrinos. The production is, however, sensitive to the temperature in the inner supernovae regions, making robust predictions of challenging. In order to understand whether this production affects supernova evolution and can therefore be constrained, detailed simulations including the effects of sterile neutrinos are needed.

We explore the potential of the $e^{+}{e}^{-}$ colliders to discover dark matter and determine its properties such as mass and spin. For this purpose we study spin zero and spin one-half cases of dark matter $D$, which belongs to the $SU(2)$ weak doublet and therefore has the charged doublet partner $D^{+}$. For the case of scalar dark matter we chose inert doublet model, while for the case of fermion dark matter we suggest the new minimal fermion dark matter model with only three parameters. We choose two benchmarks for the models under study, which provide the correct amount of observed dark matter (DM) relic density and consistent with the current DM searches. We focus on the particular process $e^{+}{e}^{-}\to D^{+}{D}^{-}\to DD{W}^{+}{W}^{-}\to DD(q\overline{q})({\mu }^{\pm }\nu )$ at the 500 GeV ILC collider that gives rise to the “$\mathrm{dijet}+\mu +{\cancel{E}}_T$” signature and study it at the level of fast detector simulation, taking into account bremsstrahlung and ISR effects. We have found that two kinematical observables—the energy of the muon $E_{\mu }$ and the angular distribution of the $W$ boson, reconstructed from dijet $\cos {\theta }_{jj}$ are very powerful in determination of DM mass and spin, respectively. In particular we have demonstrated that in the case of fermion DM, the masses can be measured with a few percent accuracy already at $500{\mathrm{fb}}^{-1}$ integrated luminosity. At the same time, the scalar DM model which has about an order of magnitude lower signal, requires about a factor of 40 higher luminosity to reach the same accuracy in the mass measurement. We have found that one can distinguish fermion and scalar DM scenarios with about $2{\mathrm{ab}}^{-1}$ total integrated luminosity or less without using the information on the cross sections for benchmarks under study. The methods of the determination of DM properties which we suggest here are generic for the models where DM and its partner belong to the weak multiplet and can be applied to explore various DM models at future $e^{+}{e}^{-}$ colliders.

We advance the threshold resummation formalism for semi-inclusive deep-inelastic scattering (SIDIS) to next-to-next-to-next-to-leading logarithmic ($\mathrm{N}{}^3\mathrm{LL}$) order, including the three-loop hard factor. We expand the results in the strong coupling to obtain approximate next-to-next-to-next-to-leading order (${\mathrm{N}}^3\mathrm{LO}$) corrections for the SIDIS cross section. In Mellin moment space, these corrections include all terms that are logarithmically enhanced at threshold, or that are constant. We also consider a set of corrections that are suppressed near threshold. Our numerical estimates show modest changes of the cross section by the approximate ${\mathrm{N}}^3\mathrm{LO}$ terms, suggesting a very good perturbative stability of the SIDIS process.

Dense compact star matter is studied by using the skyrmion crystal approach. The chiral effective theory used includes the lightest scalar meson, the lowest-lying vector mesons, as well as pions. Consistency with the vector manifestation and the dilaton limit fixed point at high density constrains the anomalous dimension of the gluon field $1.0\lesssim |{\gamma }_{G^2}|\lesssim 2.0$ and leads to the significance of the scale symmetry breaking in the intrinsic parity-odd part of the effective theory. The speed of sound $v_s^2\simeq 1/3$ and the polytropic index $\gamma \simeq 1$—both satisfy the conformal limits—after the dilaton limit fixed point at high density, but the matter is still in the hadronic phase. This means that neither the conformal speed of sound nor the smallness of the polytropic index can be used as a criterion of the onset of quark matter. These conclusions are significant for constructing the equation of state of nuclear matter.

Bulk matter produced in heavy ion collisions can have multiple conserved quantum numbers like baryon number, strangeness and electric charge. The diffusion process of these charges can be described by a diffusion matrix describing the interdependence of diffusion of different charges. The diffusion coefficient matrix is estimated here from the Boltzmann kinetic theory for the hadronic phase within relaxation time approximation. In the derivation for the same, we impose the Landau-Lifshitz conditions of fit. This leads to, e.g., the diagonal diffusion coefficients to be manifestly positive definite. The explicit calculations are performed within the ambit of hadron resonance gas model with and without excluded volume corrections. It is seen that the off-diagonal components can be significant to affect the charge diffusion in a fluid with multiple conserved charges. The excluded volume correction effects is seen to be not significant in the estimation of the elements of the diffusion matrix.

We show that recent improvements in the $O(\alpha )$ long-distance quantum electrodynamics (QED) corrections to the radiative inclusive $K_{e3}$ decay rate using the Sirlin representation are free from infrared divergences and collinear electron mass singularities in the limit $m_e\to 0$, as predicted by the Kinoshita-Lee-Nauenberg theorem. We also verify that in massless QED with the simultaneous dimensional regularization of QED photon infrared divergences and electron mass singularities leads to the same result for the inclusive rate in the limit of four space-time dimensions. The equivalence of the two approaches results in part from an interesting interplay between a small chirality-breaking effect in the massless electron limit and the generalization of space-time algebra and phase space integrals to $d>4$ dimensions. Our finding supports the small theoretical uncertainty claimed for $K_{e3}$ radiative inclusive rates and reaffirms its utility in precision unitarity tests of the quark mixing matrix.

We construct an infinite class of new ultraviolet-complete four-graviton scattering amplitudes that reduce to Einstein gravity at low energies, vanish at high energies, are meromorphic, and exhibit a triple-product structure $\mathcal{A}(s)\mathcal{A}(t)\mathcal{A}(u)$. The spectrum invariantly exhibits accumulation points in the form of infinite towers of states on each mass pole, whose residue can be positively expanded on tree-level exchanges of irreducible representations of the Lorentz group.

We tackle the question of whether regular black holes or other alternatives to the Schwarzschild solution can arise from an action principle in quantum gravity. Focusing on an asymptotic expansion of such solutions and inspecting the corresponding field equations, we demonstrate that their realization within a principle of stationary action would require either fine-tuning, or strong infrared nonlocalities in the gravitational effective action. This points to an incompatibility between large-distance locality and many of the proposed alternatives to classical black holes.

In this paper we have considered the thermodynamics of a Born-Infeld AdS black hole using inputs from the dual boundary field theory. Here, we have varied the cosmological constant $\mathrm{\Lambda }$ and Newton’s gravitational constant $G$ along with the Born-Infeld parameter $b$ in the bulk. A novel universal critical behavior of the central charge (occurring in the boundary conformal field theory) in extended black hole thermodynamics for charged black holes has been recently observed [Cong et al.,Phys. Rev. Lett. 127, 091301 (2021).], and we have extended this study to Born-Infeld AdS black holes. The Born-Infeld parameter has the dimension of inverse length, therefore, when considered in the first law of thermodynamics of the bulk in the mixed form, which includes the central charge of the boundary conformal field theory, it modifies the thermodynamic volume and the chemical potential (which are conjugate to pressure and central charge, respectively). We observe that due to this inclusion of the Born-Infeld nonlinearity in this analysis, the universal nature of the critical value of the central charge observed in [Cong et al., Phys. Rev. Lett. 127, 091301 (2021)] breaks down. We also observe an interesting behavior of the free energy of the black hole with Hawking temperature due to the variations in both the central charge and the Born-Infeld parameter. It is also observed in our analysis that for a sufficiently small value of the Born-Infeld parameter (a small value of this parameter has more prominent nonlinear effects), there exists a critical value of the temperature below which no black hole can exist.

We investigate how the resolution of the singularity problem for the Schwarzschild black hole could be related to the presence of quantum gravity effects at horizon scales. Motivated by the analogy with the cosmological Schwarzschild-de Sitter solution, we construct a broad class of nonsingular, static, asymptotically flat black-hole solutions with a de Sitter (dS) core, sourced by an anisotropic fluid, which effectively encodes the quantum corrections. The latter are parametrized by a single length-scale $\ell$, which has a dual interpretation as an effective “quantum hair” and as the length-scale resolving the classical singularity. Depending on the value of $\ell$, these solutions can have two horizons, be extremal (when the two horizons merge) or be horizonless exotic stars. We also investigate the thermodynamic behavior of our black-hole solutions and propose a generalization of the area law in order to account for their entropy. We find a second-order phase transition near extremality, when $\ell$ is of order of the classical Schwarzschild radius $R_{\mathrm{S}}$. Black holes with $\ell \sim R_{\mathrm{S}}$ are thermodynamically preferred with respect to those with $\ell \ll R_{\mathrm{S}}$, supporting the relevance of quantum corrections at horizon scales. We also find that the extremal configuration is a zero-temperature, zero-entropy state with its near-horizon geometry factorizing as ${\mathrm{AdS}}_2\times {\mathrm{S}}^2$, signalizing the possible relevance of these models for the information paradox. Finally, we show that the presence of quantum corrections with $\ell \sim R_{\mathrm{S}}$ have observable phenomenological signatures in the photon orbits and in the quasinormal modes (QNMs) spectrum. In particular, in the near-extremal regime, the imaginary part of the QNMs spectrum scales with the temperature as $c_1/\ell +c_2\ell T_{\mathrm{H}}^2$, while it goes to zero linearly in the near-horizon limit. Our general findings are confirmed by revisiting two already known models, which are particular cases of our general class of models, namely the Hayward and Gaussian-core black holes.

It has been shown that the synergy of a scalar field coupling with both the Ricci scalar and the Gauss-Bonnet invariant significantly affects the properties of scalarized black holes and neutron stars, including their domain of existence and the amount of scalar hair they carry. Here we study the radial stability of scalarized black-hole solutions. We demonstrate that they are stable against radial perturbations for Ricci couplings consistent with both a late-time cosmological attractor and the evasion of binary pulsar constraints. In addition, we investigate the effect of the Ricci coupling on the hyperbolicity of the equation governing linear, radial perturbations and show that it significantly reduces the region over which hyperbolicity is lost.

We investigate two Type-IIa minimally modified gravity theories, namely V $(\phi )$ Cold Dark Matter (VCDM) and Cuscuton theories. We confirm that all acceptable Cuscuton solutions are always solutions for VCDM theory. However, the inverse does not hold. We find that VCDM allows for the existence of exact general relativity (GR) solutions with or without the presence of matter fields and a cosmological constant. We determine the conditions of existence for such GR-VCDM solutions in terms of the trace of the extrinsic curvature and on the fields which define the VCDM theory. On the other hand, for the Cuscuton theory, we find that the same set of exact GR solutions (such as Schwarzschild and Kerr spacetimes) is not compatible with timelike configurations of the Cuscuton field and therefore cannot be considered as acceptable solutions. Nonetheless, in Cuscuton theory, there could exist solutions which are not the same but close enough to GR solutions. We also show the conditions to determine intrinsic-VCDM solutions, i.e., solutions which differ from GR and do not belong to the Cuscuton model. We finally show that in cosmology a mapping between VCDM and the Cuscuton is possible, for a generic form of the VCDM potential. In particular, we find that for a quadratic potential in VCDM theory, this mapping is well defined giving an effective redefinition of the Planck mass for the cosmological background solutions of both theories.

In this paper, we study the dynamics of scalar hair around a Schwarzchild black hole. The scalar hair is sourced by the Gauss-Bonnet invariant with a linear coupling. We work perturbatively in the coupling constant and ignore the backreaction of the scalar hair and the Gauss-Bonnet invariant. We evolve the scalar field in the background of a Schwarzchild black hole and study the dynamical formation of scalar hair with different self-interactions. We integrate the energy and compute the energy flux of the scalar hair in terms of the canonical energy-momentum tensor and give the corresponding dependence on the self-interactions. Our results allow us to estimate the radiation and the condensation of scalar field with different self-interactions; these would improve our understanding for the dynamical scalarization of black holes and the possible configuration of the scalar hair in scalar Gauss-Bonnet gravity.

Recent gravitational wave observations show evidence for the presence of higher harmonics, thus possibly indicating that these waves were generated in the inspiral of compact objects with asymmetric mass ratios. Signals with higher harmonics contain a trove of information that can lead to a better estimation of system parameters and possibly to more stringent tests of general relativity. Gravitational wave models that include higher harmonics, however, have only been developed within general relativity, while models to test theory-agnostic deviations from general relativity have been purely based on the signal’s dominant mode. We here extend the parametrized post-Einsteinian framework to include the $\ell =2$, 3, and 4 harmonics, thereby providing a ready-to-use Fourier-domain waveform model for tests of general relativity with higher harmonics. We find that the deformations to the higher harmonics of the Fourier phase can be easily mapped to the deformation of the dominant harmonic, while the deformations to the higher harmonics of the Fourier amplitude in general cannot in a theory-agnostic way. Nonetheless, we develop a simple ansatz for the deformations of the waveform amplitude (through a rescaling deformation of the time-domain amplitude) that both minimizes the number of independent amplitude deformations parameters and captures the predictions of all known modified theories to date.

We present a convolutional neural network that is capable of searching for continuous gravitational waves, quasimonochromatic, persistent signals arising from asymmetrically rotating neutron stars, in approximately one year of simulated data that is plagued by nonstationary, narrow-band disturbances, i.e., lines. Our network has learned to classify the input strain data into four categories: (1) only Gaussian noise, (2) an astrophysical signal injected into Gaussian noise, (3) a line embedded in Gaussian noise, and (4) an astrophysical signal contaminated by both Gaussian noise and line noise. In our algorithm, different frequencies are treated independently; therefore, our network is robust against sets of evenly spaced lines, i.e., combs, and we only need to consider a perfectly sinusoidal line in this work. We find that our neural network can distinguish between astrophysical signals and lines with high accuracy. In a frequency band without line noise, the sensitivity depth of our network is about ${\mathcal{D}}^{95\%}\simeq 43.9$ with a false alarm probability of $\sim 0.5\%$, while in the presence of line noise, we can maintain a false alarm probability of $\sim 10\%$ and achieve ${\mathcal{D}}^{95\%}\simeq 3.62$ when the line noise amplitude is $h_0^{\mathrm{line}}/\sqrt{S_{\mathrm{n}}(f_k)}=1.0$. The network is robust against the time derivative of the frequency $\dot{f}$ of a gravitational-wave signal, i.e., the spin-down, and can handle $|\dot{f}|\lesssim {10}^{-12}\mathrm{Hz}/\mathrm{s}$, even though our training sets only include signals with $\dot{f}=0$. We evaluate the computational cost of our method to be $\mathcal{O}({10}^{19})$ floating point operations, and compare it to those from standard all-sky searches, putting aside differences between covered parameter spaces. Our results show that our method is more efficient by 1 or 2 orders of magnitude than standard searches. Although our neural network takes about $\mathcal{O}({10}^8)\sec$ to employ using our current facilities [a single graphics processing unit (GPU) of GTX1080Ti], we expect that it can be reduced to an acceptable level by utilizing a larger number of improved GPUs.

We calculate the self-force acting on a charged particle on a circular geodesic orbit in the equatorial plane of a rotating black hole. We show by direct calculation that the dissipative self-force balances with the sum of the flux radiated to infinity and through the black hole horizon. Prograde orbits are found to stimulate black hole superradiance, though we confirm that the condition for floating orbits cannot be met. We calculate the conservative component of the self-force by application of the mode sum regularization method, and we present a selection of numerical results. We obtain the leading-order coefficients in post-Newtonian expansions of the dissipative and conservative components of the self-force, using an analytical method and numerical fitting, respectively. The self-force on the innermost stable circular orbits of the Kerr spacetime is calculated, and comparisons are drawn between the electromagnetic and gravitational self forces.

Fast radio bursts (FRBs) can be used in cosmology by studying the dispersion measure (DM) as a function of redshift. The large-scale structure of matter distribution is regarded as a major error budget for such applications. Using optical galaxy and dispersion measure mocks built from $N$-body simulations, we have shown that the galaxy number density can be used as a tracer for large-scale electron density and help improve the measurement of DM as a function of redshift. We have shown that, using the line-of-sight galaxy number counts within 1 arcmin around the given localized FRB source can help improve the cosmological parameter constraints by more than 20% if the DM uncertainty caused by large-scale structure only is taken into account. However, the improvement will drop to about 15% if large DM uncertainty caused by the other origin is considered.

We numerically and analytically explore the background cosmological dynamics of multifield dark energy with highly nongeodesic or “spinning” field-space trajectories. These extensions of standard single-field quintessence possess appealing theoretical features and observable differences from the cosmological standard model. At the level of the cosmological background, we perform a phase-space analysis and identify approximate attractors with late-time acceleration for a wide range of initial conditions. Focusing on two classes of field-space geometry, we derive bounds on parameter space by demanding viable late-time acceleration and the absence of gradient instabilities, as well as from the de Sitter swampland conjecture.

The LIGO–Virgo–KAGRA collaborations (LVK) produced a catalog containing gravitational-wave (GW) observations from the first half of the third GW observing run (O3a). This catalog, GWTC-2.1, includes for the first time a number of exceptional GW candidates produced from merging black-hole-binaries with unequivocally unequal component masses. Since subdominant multipole moments and spin-induced orbital precession are more likely to leave measurable imprints on the emitted GW from unequal component mass binaries, these general relativistic phenomena may now be measurable. Indeed, both GW190412 and GW190814 have already shown conclusive evidence for subdominant multipole moments. This provides valuable insights into the dynamics of the binary. We calculate the evidence for subdominant multipole moments and spin-induced orbital precession for all merging black-hole-binaries in GWTC-2.1 that were observed during O3a and show that (a) no gravitational-wave candidate has measurable higher order multipole content beyond $\ell =3$, (b) in addition to the confident subdominant multipole measurements in GW190412 and GW190814, GW190519_153544 and GW190929_012149 show marginal evidence for the $(\ell ,|m|)=(3,3)$ subdominant multipole, (c) GW190521 shows no evidence for precession but it may have measurable subdominant multipole content and (d) GW190412 may show evidence for spin-induced orbital precession and (e) we observe no significant evidence for precession in the current population of binary black hole mergers.

Dark matter (DM) occupies the majority of matter content in the universe and is probably cold (CDM). However, modifications to the standard CDM model may be required by the small-scale observations, and DM may be self-interacting (SIDM) or warm (WDM). Here we show that the diffractive lensing of gravitational waves (GWs) from binary black hole mergers by small halos ($\sim {10}^3–{10}^6{M}_{\odot }$; minihalos) may serve as a clean probe to the nature of DM, free from the contamination of baryonic processes in the DM studies based on dwarf/satellite galaxies. The expected lensed GW signals and event rates resulting from CDM, WDM, and SIDM models are significantly different from each other, because of the differences in halo density profiles and abundances predicted by these models. We estimate the detection rates of such lensed GW events for a number of current and future GW detectors, such as the Laser Interferometer Gravitational Observatories (LIGO), the Einstein Telescope (ET), the Cosmic Explorer (CE), Gravitational-wave Lunar Observatory for Cosmology (GLOC), the Deci-Hertz Interferometer Gravitational Wave Observatory (DECIGO), and the Big Bang Observer (BBO). We find that GLOC may detect one such event per year assuming the CDM model, DECIGO (BBO) may detect more than several (hundreds of) such events per year, by assuming the CDM, WDM (with mass $>30\mathrm{keV}$) or SIDM model, suggesting that the DM nature may be strongly constrained by DECIGO and BBO via the detection of diffractive lensed GW events by minihalos. Other GW detectors are unlikely to detect a significant number of such events within a limited observational time period. However, if the inner slope of the minihalo density profile is sufficiently steeper than the Navarro-Frenk-White profile, e.g., the pseudo-Jaffe profile, one may be able to detect one to more than 100 such GW events by ET and CE.