We study the influence of higher curvature effects on stellar structure and conclude that the properties of stars are greatly impacted when such terms are dynamic. In particular, the surface gravitational redshift, which is connected to the equation of state and also the mass-radius ratio, differs greatly from the corresponding values in general relativity as evidenced through our empirical comparisons. A model of a superdense star with strange star equation of state is constructed within the framework of the Einstein-Gauss-Bonnet theory. Under these assumptions large classes of solutions are admitted by the field equations. We isolate a particular class with the ansatz of the Vaidya-Tikekar superdense star spatial gravitational potential. The model is found to satisfy elementary requirements for physical applicability and stability. The parameter values chosen are consistent with observed star models. A significant effect of the higher curvature terms is to reduce the speed of sound and to drastically reduce the values of the surface gravitational redshift compared to the Einstein counterpart. These latter results have implications for interpretations of observations in relativistic astrophysics which are often made against the background of the standard general theory of relativity. Additionally, our results suggest a value for the Gauss-Bonnet coupling of the order of ${10}^3$ in the context of strange stars.

Searches for gravitational-wave signals are often based on maximizing a detection statistic over a bank of waveform templates, covering a given parameter space with a variable level of correlation. Results are often evaluated using a noise-hypothesis test, where the background is characterized by the sampling distribution of the loudest template. In the context of continuous gravitational-wave searches, properly describing said distribution is an open problem: current approaches focus on a particular detection statistic and neglect template-bank correlations. We introduce a new approach using extreme value theory to describe the distribution of the loudest template’s detection statistic in an arbitrary template bank. Our new proposal automatically generalizes to a wider class of detection statistics, including (but not limited to) line-robust statistics and transient continuous-wave signal hypotheses, and improves the estimation of the expected maximum detection statistic at a negligible computing cost. The performance of our proposal is demonstrated on simulated data as well as by applying it to different kinds of (transient) continuous-wave searches using O2 Advanced LIGO data. We release an accompanying python software package, distromax, implementing our new developments.

We study the quasinormal modes (QNMs) of a charged scalar field on a Reissner-Nordström-anti-de Sitter (RN-${\mathrm{AdS}}_5$) black hole in the small radius limit by using the isomonodromic method. We also derive the low-temperature expansion of the fundamental QNM frequency. Finally, we provide numerical evidence that instabilities appear in the small radius limit for large values of the charge of the scalar field.

Using asymptotic characterization results of spacetimes at conformal infinity, we prove that Kerr-Schild–de Sitter spacetimes are in one-to-one correspondence with spacetimes in the Kerr–de Sitter-like class with conformally flat $\mathcal{I}$. Kerr-Schild–de Sitter are spacetimes of Kerr-Schild form with de Sitter background that solve the $(\mathrm{\Lambda }>0)$-vacuum Einstein equations and admit a smooth conformal compactification sharing $\mathcal{I}$ with the background metric. Kerr–de Sitter-like metrics with conformally flat $\mathcal{I}$ are a generalization of the Kerr–de Sitter metrics, defined originally in four spacetime dimensions and extended here to all dimensions in terms of their initial data at $\mathcal{I}$. We explicitly construct all metrics in this class as limits or analytic extensions of Kerr–de Sitter. The structure of limits is inferred from corresponding limits of the asymptotic data, which appear to be hard to guess from the spacetime metrics.

Motion of a test particle plays an important role in understanding the properties of a spacetime. As a new type of the strong gravity system, boson stars could mimic black holes located at the center of galaxies. Studying the motion of a test particle in the spacetime of a rotating boson star will provide the astrophysical observable effects if a boson star is located at the center of a galaxy. In this paper, we investigate the timelike geodesic of a test particle in the background of a rotating boson star with angular number $m=(1,2,3)$. With the change of angular number and frequency, a rotating boson star will transform from the low rotating state to the highly relativistic rapidly rotating state, the corresponding Lense-Thirring effects will be more and more significant and it should be studied in detail. By solving the four-velocity of a test particle and integrating the geodesics, we investigate the bound orbits with a zero and nonzero angular momentum. We find that a test particle can stay a longer time in the central region of a boson star when the boson star becomes from low rotating state to highly relativistic rotating state. Comparing the periapse values of the orbits obtained in rotating boson stars and the corresponding orbits of the observed stars orbiting Sagittarius $A^{*}$, we discuss the possible observable effects of the astrophysical boson star in the Galactic center.

Large dark matter overdensities can form around black holes of astrophysical and primordial origin as they form and grow. This “dark dress” inevitably affects the dynamical evolution of binary systems and induces a dephasing in the gravitational waveform that can be probed with future interferometers. In this paper, we introduce a new analytical model to rapidly compute gravitational waveforms in the presence of an evolving dark matter distribution. We then present a Bayesian analysis determining when dressed black hole binaries can be distinguished from GR-in-vacuum ones and how well their parameters can be measured, along with how close they must be to be detectable by the planned Laser Interferometer Space Antenna (LISA). We show that LISA can definitively distinguish dark dresses from standard binaries and characterize the dark matter environments around astrophysical and primordial black holes for a wide range of model parameters. Our approach can be generalized to assess the prospects for detecting, classifying, and characterizing other environmental effects in gravitational wave physics.

Fully understanding the average core-collapse supernova requires detecting the diffuse supernova neutrino background (DSNB) in all flavors. While the DSNB ${\overline{\nu }}_e$ flux is near detection, and the DSNB ${\nu }_e$ flux has a good upper limit and prospects for improvement, the DSNB ${\nu }_x$ (each of ${\nu }_{\mu }$, ${\nu }_{\tau }$, ${\overline{\nu }}_{\mu }$, ${\overline{\nu }}_{\tau }$) flux has a poor limit and heretofore had no clear path for improved sensitivity. We show that a succession of xenon-based dark matter detectors—XENON1T (completed), XENONnT/LUX-ZEPLIN (running), and DARWIN (proposed)—can dramatically improve sensitivity to DSNB ${\nu }_x$ the neutrino-nucleus coherent scattering channel. XENON1T could match the present sensitivity of $\sim {10}^3{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$ per ${\nu }_x$ flavor, XENONnT/LUX-ZEPLIN would have linear improvement of sensitivity with exposure, and a long run of DARWIN could reach a flux sensitivity of $\sim 10{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$. Together, these would also contribute to greatly improve bounds on nonstandard scenarios. Ultimately, to reach the standard flux range of $\sim 1{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$, even larger exposures will be needed, which we show may be possible with the series of proposed lead-based RES-NOVA detectors.

We discuss a simple renormalizable, gauge invariant model with a fermiophobic $Z^{\prime }$ boson: it has no couplings to the three Standard Model (SM) chiral families, but does couple to a fourth vectorlike (VL) family. The SM Higgs couples to the fourth VL lepton, leading to an enhanced contribution to the muon anomalous magnetic moment ${(g-2)}_{\mu }$. The latter contribution requires a nonvanishing coupling of $Z^{\prime }$ to right-handed muons, which arises within this model due to mixing effects between the SM and VL fermions, along with $Z^{\prime }$ couplings to the second generation SM lepton doublet and third generation SM quark doublet. This model can simultaneously account for the measured $B$-decay ratios $R_{K^{(*)}}$ and ${(g-2)}_{\mu }$. We identify the parameter space where this explanation is consistent with existing experimental constraints coming from $B_s-{\overline{B}}_s$ mixing, neutrino trident production and collider searches. We also check that the SM Higgs coupling to the fourth VL lepton does not produce a dangerous contribution to the Higgs diphoton decay.

We introduce an effort to catalog the gauge-invariant interactions of Standard Model (SM) particles and new fields in a variety of representations of the SM color gauge group $\mathrm{SU}(3{)}_{\mathrm{c}}$. In this first installment, we direct this effort toward fields in the six-dimensional (sextet, $\mathbf{6}$) representation. We consider effective operators of mass dimension up to seven (comprehensively up to dimension six), featuring both scalar and fermionic color sextets. We use an iterative tensor-product method to identify the color invariants underpinning such operators, emphasizing structures that have received little attention to date. In order to demonstrate the utility of our approach, we study a simple but novel model of color-sextet fields at the Large Hadron Collider (LHC). We compute cross sections for an array of new production channels enabled by our operators, including single-sextet production and sextet production in association with photons or leptons. We also discuss dijet-resonance constraints on a sextet fermion. This example shows that there remains a wide array of fairly minimal but well motivated and unexplored models with extended strong sectors as we await the high-luminosity LHC.

We present a determination of the nonsinglet transversity parton distribution function (PDF) of the nucleon, normalized with respect to the tensor charge at ${\mu }^2=2{\mathrm{GeV}}^2$ from lattice quantum chromodynamics. We apply the pseudodistribution approach, using a gauge ensemble with a lattice spacing of 0.094 fm and the light quark mass tuned to a pion mass of 358 MeV. We extract the transversity PDF from the analysis of the short-distance behavior of the Ioffe-time pseudodistribution using the leading-twist next-to-leading order (NLO) matching coefficients calculated for transversity. We reconstruct the $x$-dependence of the transversity PDF through an expansion in a basis of Jacobi polynomials in order to reduce the PDF ansatz dependence. Within the limitations imposed by a heavier-than-physical pion mass and a fixed lattice spacing, we present a comparison of our estimate for the valence transversity PDF with the recent global fit results based on single transverse spin asymmetry. We find the intrinsic nucleon sea to be isospin symmetric with respect to transversity.

In this work, we predict the spectroscopy behavior of these light unflavored vector mesons with masses at the range of $2.4\sim 3\mathrm{GeV}$, which are still missing in the experiment. By presenting their mass spectrum and studying their two-body Okubo-Zweig-lizuka allowed decay widths, we discuss the possible experimental evidences of these discussed states combining with the present experimental data. Especially, we strongly suggest that our experimental colleagues carry out the exploration of these higher states via the $e^{+}{e}^{-}$ annihilation into light mesons. It is obvious that BESIII and Belle II will be potential experiments to achieve this target.

We consider massive higher-spin multiplets coupled to quantum gravity and compute their contributions to the gravitational beta functions at one loop. Such theories, if quantized with the Feynman prescription, would contain ghosts. Instead, those degrees of freedom are turned into purely virtual particles by means of the fakeon prescription and the resulting theories are both renormalizable and unitary. We extract the necessary number of fields to obtain asymptotic freedom by solving the relevant renormalization-group equations in the ultraviolet limit. We show that in the case of irreducible rank-$s$ bosons with minimal kinetic term only a certain number of fields with $0\le s\le 3$ is compatible with asymptotic freedom. No solution involving fermionic rank-$s$ fields are found. We also consider the cases of rank-1 and symmetric rank-2 tensor fields with nonminimal kinetic terms and repeat the analysis, finding that the allowed number of fields is enlarged. Possible implications for metric affine theories of gravity are pointed out.

It is well known that extremal black holes do not Hawking radiate, which is usually realized by taking an extremal limit from the nonextremal case. However, one cannot perceive the same phenomenon using the Bogoliubov transformation method starting from an extremal black hole itself, i.e., without the limiting case consideration. In that case, the Bogoliubov coefficients do not satisfy the required normalization condition. In canonical formulation, which closely mimics the Bogoliubov transformation method, one can consistently reproduce the vanishing number density of Hawking quanta for an extremal Kerr black hole. In this method, the relation between the spatial near-null coordinates, imperative in understanding the Hawking effect, was approximated into a sum of linear and inverse terms only. In the present work, we first show that one can reach the same conclusion in canonical formulation even with the complete relationship between the near-null coordinates, which contains an additional logarithmic term. It is worth mentioning that in the nonextremal case, a similar logarithmic term alone leads to the thermal Hawking radiation. Secondly, we study the case with only the inverse term in the relation (i.e., when the spatial near-null coordinates associated to the past and future observers are inversely related to each other) to understand whether it is the main contributing term in vanishing number density. Third, for a qualitative realization, we consider a simple thought experiment to understand the corresponding Hawking temperature and conclude that the inverse term indeed plays a crucial role in the vanishing number density.

The response of black holes to companions is of fundamental importance in the context of their dynamics and of gravitational-wave emission. Here, we explore the effect of charge on the static response of black holes. With a view to constraining broader setups, we consider charged geometries in an arbitrary number of spacetime dimensions $D\ge 4$. Tensor tidal Love numbers are shown to follow a power law in the black hole temperature $\sim T_H^{2l+1}$, and thus vanish at extremality. In contrast, the black hole charge $Q$ excites new modes of polarization in the vector sector that are otherwise not responsive in the neutral limit. In four dimensions, Love numbers and magnetic susceptibilities vanish for all values of the charge that respect the extremality bound. Using the theory of Fuchsian equations we are able to obtain analytical results in most cases, even beyond the hypergeometric instances.

We introduce a rigorous and general framework to study systematically self-gravitating elastic materials within general relativity, and apply it to investigate the existence and viability, including radial stability, of spherically symmetric elastic stars. We present the mass-radius ($M-R$) diagram for various families of models, showing that elasticity contributes to increasing the maximum mass and the compactness up to $\approx 22\%$, thus supporting compact stars with mass well above two solar masses. Some of these elastic stars can reach compactness as high as $GM/(c^{2}R)\approx 0.35$ while remaining stable under radial perturbations and satisfying all energy conditions and subluminal wave propagation, thus being physically realizable models of stars with a light ring. We provide numerical evidence that radial instability occurs for central densities larger than that corresponding to the maximum mass, as in the perfect-fluid case. Elasticity may be a key ingredient to building consistent models of exotic ultracompact objects and black hole mimickers, and can also be relevant for a more accurate modeling of the interior of neutron stars.

We revisit the four-dimensional theory of gravity that arises from string theory with higher-derivative corrections. By compactifying and truncating the ten-dimensional effective action of heterotic string theory at first order in ${\alpha }^{\prime }$, and carefully dealing with field redefinitions, we show that the four-dimensional theory takes the form of an axidilaton model where the scalars couple to the Gauss-Bonnet and Pontryagin densities. Thus, the actual string gravity is a generalization of the well-studied Einstein-dilaton-Gauss-Bonnet and dynamical Chern-Simons models. Using this action we compute the stringy corrections to the Kerr geometry, and we obtain, for the first time to our knowledge, the corrections to the entropy of the Kerr black hole at order ${\alpha }^{\prime 2}$. We check that the first law of black hole mechanics is satisfied and discuss several properties of the solution. Our results suggest that there exist black hole solutions with $J>M^2$ and therefore the extremal ratio $J/M^2$ must be modified positively.

We study solutions describing spinning null sources called gyratons in generic theories of gravity with terms that are quadratic in curvature and contain an arbitrary number of covariant derivatives. In particular, we show that the properties of $pp$ waves of the algebraic type III allow for extreme simplification of the field equations. It turns out that the resulting differential equations are exactly solvable due to partial decoupling and linearity of the equations. This is demonstrated explicitly by finding axially symmetric gyraton solutions in Stelle’s fourth derivative gravity and the nonlocal gravity with an infinite number of derivatives.

We revisit the possibility that the stochastic common-spectrum process recently detected by the NANOGrav pulsar timing array experiment could be due to primordial gravitational waves (GWs). A naïve extrapolation down to interferometer scales of the blue GW spectrum required to explain NANOGrav consistently with cosmic microwave background (CMB) observations would strongly violate upper limits on the stochastic GW background (SGWB) amplitude from Laser Interferometer Gravitational Wave Observatory/Virgo. In combination with the fact that there are over 19 decades in frequency between CMB and interferometer scales, this motivates us to move beyond the commonly adopted approximation of a pure power-law GW spectrum. We consider a broken power-law parametrization for the SGWB spectrum, which turns from blue to red above the break frequency: while phenomenological, this choice maps to various well-motivated early-Universe models, including scenarios featuring noninstantaneous reheating or a nonstandard background expansion following reheating. After a detailed discussion of the contribution of the resulting SGWB to the early-Universe radiation energy density, we constrain the broken power-law model against a wide variety of multifrequency cosmological and GW observations. We find that this phenomenological model is able to explain the NANOGrav signal while remaining in agreement with upper limits on the tensor-to-scalar ratio on CMB scales, big bang nucleosynthesis constraints on the early-Universe radiation energy density, and upper limits on the SGWB amplitude on interferometer scales. We briefly discuss the very bright prospects for testing this model with next-generation probes across the GW frequency landscape, which motivate further exploring connections to specific well-motivated early-Universe models.

Due to the nonlinearity of the Euler–Poisson equations, it is possible that the nonlinear Jeans instability may lead to a faster density growing rate than the rate in the standard theory of linearized Jeans instability, which motivates us to study the nonlinear Jeans instability. The aim of this article is to develop a method proving the Jeans instability for slightly nonlinear Euler–Poisson equations in the expanding Newtonian universe. The standard proofs of the Jeans instability rely on the Fourier analysis. However, it is difficult to generalize Fourier method to a nonlinear setting, and thus there is no result in the nonlinear analysis of Jeans instability. We firstly develop a non-Fourier-based method to reprove the linearized Jeans instability in the expanding Newtonian universe. Secondly, we generalize this idea to a slightly nonlinear case. This method relies on the Cauchy problem of the Fuchsian system due to the recent developments of this system in mathematics. The fully nonlinear Jeans instability for the Euler–Poisson and Einstein–Euler equations are in progress.

Observations of high-redshift galaxies have provided us with a rich tool to study the physics at play during the epoch of reionization. The luminosity function (LF) of these objects is an indirect tracer of the complex processes that govern galaxy formation, including those of the first dark-matter structures. In this work, we present an extensive analysis of the UV galaxy LF at high redshifts to extract cosmological and astrophysical parameters. We provide a number of phenomenological approaches in modeling the UV LF and take into account various sources of uncertainties and systematics in our analysis, including cosmic variance, dust extinction, scattering in the halo-galaxy connection, and the Alcock-Paczyński effect. Using UV LF measurements from the Hubble Space Telescope together with external data on the matter density, we derive the large-scale matter clustering amplitude to be ${\sigma }_8={0.76}_{-0.14}^{+0.12}$, after marginalizing over the unknown astrophysical parameters. We find that with current data this result is only weakly sensitive to our choice of astrophysical modeling, as well as the calibration of the underlying halo mass function. As a cross check, we run our analysis pipeline with mock data from the IllustrisTNG hydrodynamical simulations and find consistent results with their input cosmology. In addition, we perform a simple forecast for future space telescopes, where an improvement of roughly 30% upon our current result is expected. Finally, we obtain constraints on astrophysical parameters and the halo-galaxy connection for the models considered here. All methods discussed in this work are implemented in the form of a versatile likelihood code, gallumi, which we make public.