We introduce a convenient formalism to evaluate the phase of a light signal propagating on a general curved background. It allows us to obtain a transparent relation between the frequency-shift and the phase difference in large-scale optical interferometry for a general relativistic setting, as well as to derive compact expressions generalizing the Doppler effect in one-way and two-way schemes. Our recipe is easily applicable to stationary spacetimes, and in particular to the near-Earth experiments where the geometry is described in the parametrized post-Newtonian approximation. As an example, we use it to evaluate the phase difference arising in the optical version of the Colella-Overhauser-Werner experiment.

Einstein’s equations in matter are gravitational analogues of Maxwell’s equations in matter, providing an effective classical description of gravitational fields. We derive Einstein’s equations in matter for relativistic fluids, and use them to illustrate how the Tolman-Oppenheimer-Volkoff equations are modified by the matter’s response to curvature. For a gas of massive fermions, we evaluate how the effective Newton’s constant and other susceptibilities depend on the temperature and density. In anti–de Sitter space, we study the $O(1/(T\ell {)}^2)$ corrections to the geometries sourced by perfect fluids, and illustrate the breakdown of hydrostatics in AdS at small temperatures.

The particle spectrum for collapse to an extremal Reissner-Nordström black hole is solved by use of the corresponding moving mirror model. The amount of particles and energy flux is symmetric in delayed null time as received by an observer at infinity. The star emits a total finite amount of energy carried by particles that are not specified by a temperature. The finite energy limits the evaporation process yet an infinite amount of particles with zero frequency characterize the radiation. At ultralate times the particle emission spectrum is that of a uniformly accelerated mirror.

In the early 1980s, R. Rüdiger published a pair of articles in which the most general conserved charges associated to the motion of particles with spin moving in curved spacetime were found. In particular, it was shown that besides the well-known conserved quantity associated to Killing vectors, it is also possible to have another conserved quantity that is linear in the spin of the particle if the spacetime admits a Killing-Yano tensor. However, in these papers it was proved that in order for this new scalar to be conserved, two obscure conditions involving the Killing-Yano tensor and the curvature must be obeyed. In the present paper we try to shed light over these conditions and end up proving that this conserved quantity is useless for most physically relevant spacetimes. Notably, for particles moving in vacuum (Einstein spacetimes) this conserved scalar constructed with the Killing-Yano tensor will not help on the integration of the equations of motion. Moreover, we prove that, as a consequence of these obscure conditions, the Killing-Yano tensor must be covariantly constant.

We provide detailed analysis of the curvature structure of the spacetime around regular black holes (RBHs) governed by general relativity (GR) combined with nonlinear electrodynamics (NED), characterized by electric charge $Q$, and degree of nonlinearity $n$. We consider special class of the backgrounds introduced by Toshmatov et al. [Phys. Rev. D 98, 028501 (2018)] that have proper Maxwell weak-field limit of the NED sector. We also study the motion of uncharged and charged particles in the RBH background. We determine shadows of such black holes (BHs) using the effective geometry governing motion of photons in the background of NED RBHs. The analysis of circular motion enables to determine innermost stable circular orbits (ISCO) and marginally bound orbits (MBO). We show that the radius of ISCO and MBO for neutral particles decreases as the parameters of the RBH $Q$ and $n$ increase for the fixed value of the BH mass. We demonstrate that for the electrically charged particles properties of the circular orbits strongly depend on their Coulomb interaction with the RBH charge. The dependence of the ISCO radius on the particle specific charge $q$ and the RBH parameters is rather complex, but for the attractive Coulomb interaction there is a general feature (independent of $n$) giving a limiting value of the intensity of this interaction $q{Q}_{\max }$ behind which no stable circular orbits are allowed around the RBH. Comparison of the RBH with Reissner-Nordström black holes (RNBH) shows that for the same electric charges of these backgrounds the location of the relevant orbits is at substantially smaller radii for the RBH, demonstrating thus a strong influence of the NED effects. The analysis of ISCO radius of test particles has shown that the charge of RBH $Q$ can mimic the rotation parameter of Kerr BH up to the value $a=0.8M$. We have also shown that the RN BH charge can mimic the rotation parameter up to $a=0.5M$ and the RBH charge up to $Q=0.2M$. Applications from observational data to the parameters of the supermassive black holes (SMBHs) at the galactic center Messier 87 (M87) and Milky Way so called Sagittarius ${\mathrm{A}}^{*}$ (${\mathrm{Sgr}A}^{*}$) give the mimic value for the RBH charge parameter for the rotation parameter of M87 to be ${10}^{3}Q\approx 277.56_{-1.26}^{+3.82}$, while for ${\mathrm{Sgr}A}^{*}$ there is ${10}^{3}Q\approx 187.33_{-26.4}^{+27.6}$. Moreover, it is shown that the RN BH charge cannot mimic the rotation parameter of the SMBH M87, however, it can mimic the spin parameter of ${\mathrm{Sgr}A}^{*}$ at ${10}^3{Q}_{\mathrm{RN}}/M=828.71_{-60.94}^{+70.58}$.

We examine the possibility of spontaneous vectorization in the vector-tensor theories with the vector conformal and disformal couplings to matter. We study the static and spherically symmetric solutions of the relativistic stars with the nontrivial profile of the vector field satisfying the boundary conditions $A_{\mu }\to 0$ at the spatial infinity, where $A_{\mu }$ represents the vector field. First, we study the linear perturbations about the general relativistic (GR) stellar solutions with the vanishing vector field $A_{\mu }=0$. We show that the pure vector disformal coupling causes the ghost or gradient instability of the GR stars, indicating the breakdown of the hyperbolicity on the GR stellar backgrounds. On the other hand, the pure conformal coupling causes the tachyonic instability of the GR solutions and would lead to the spontaneous growth of the vector field toward the nontrivial solutions as in the manner of spontaneous scalarization in the scalar-tensor theories. We then construct the static and spherically symmetric solutions of the relativistic stars with 0 and 1 nodes of the vector field in the presence of the pure disformal coupling. We find that the properties of the solutions with the nontrivial vector field are similar to those of the generalized Proca theories. As in the mass-radius diagram the branches of the 0 and 1 node solutions are disconnected to that of the GR solutions in the lower density regimes, they may be formed from the selected choice of the initial conditions. We also construct the 0 node solutions in the case of the pure conformal coupling, and show that the branch of these solutions is connected to that of the GR solutions in both the low and high density regions and hence would arise spontaneously via the continuous evolution from the GR solutions. Finally, we briefly discuss the combined effects of the conformal and disformal couplings on the nontrivial solutions.

We find a (quasi)local first law of thermodynamics, $\mathrm{\Delta }E=T\mathrm{\Delta }S-W$, connecting gravitational entropy, $S$, with matter energy and work. For Einstein gravity, $S$ is the Bekenstein-Hawking entropy, while for general theories of gravity, $S$ is the Wald entropy, evaluated on the stretched future light cone of any point in an arbitrary spacetime, not necessarily containing a black hole. The equation can be written as $\rho \mathrm{\Delta }V=T\mathrm{\Delta }S-p\mathrm{\Delta }V$ by regarding the energy-momentum tensor as that of a fluid.

The paper studies the physical characteristics for the extended $f(P)$ cubic gravity from a transitive perspective based on dynamical system analysis, by considering the linear stability theory in two specific cases, corresponding to power–law $f(P)=f_0{P}^{\alpha }$ and exponential $f(P)=f_0{e}^{\alpha P}$ gravity types, where $f_0$ and $\alpha$ are constant parameters. In these cases we have analyzed the effects in the phase space complexity, revealing the cosmological solutions attached to the critical points. For the power–law and exponential gravity types, we have noticed the presence of two cosmological epochs associated to the critical points involved, corresponding to de Sitter eras and quintessencelike epochs, described by a constant effective equation of state. For all of these solutions we have studied the dynamical characteristics which are associated to the stability properties, determining possible constraints to various parameters from a transient perspective. The dynamical prospects asserted that the extended $f(P)$ cubic gravity can represent a promising modified theory of gravitation, leading to the manifestation of the accelerated expansion at late time evolution.

We analyze the dynamics of a Taub cosmological model in the presence of a massless minimally coupled scalar field and a cosmological constant, in the limit when both the universe volume and the scalar field live in a quasiclassical approximation. In other words, we study the dynamics of a quantum small anisotropy evolving on a de Sitter background and in the presence of a kinetic term of the inflaton field. We demonstrate that the quantum anisotropy exponentially decays during the universe expansion, approaching a finite and small value. This result suggests that the quantum isotropization of the universe during a de Sitter phase is much weaker than the corresponding classical evolution, favoring the survival of certain degree of anisotropy to the de Sitter phase. Finally we analyze the case when also the scalar field is considered as quantum variable, by showing how its variance naturally spreads because of no potential term significantly affects its dynamics. This behavior results to be different from the anisotropy which is subjected to the potential coming out from the spatial curvature.

The significant increase in precision that will be achieved by Stage IV cosmic shear surveys means that several currently used theoretical approximations may cease to be valid. An additional layer of complexity arises from the fact that many of these approximations are interdependent; the procedure to correct for one involves making another. Two such approximations that must be relaxed for upcoming experiments are the reduced shear approximation and the effect of neglecting magnification bias. Accomplishing this involves the calculation of the convergence bispectrum; typically subject to the Limber approximation. In this work, we compute the post-Limber convergence bispectrum, and the post-Limber reduced shear and magnification bias corrections to the angular power spectrum for a Euclid-like survey. We find that the Limber approximation significantly overestimates the bispectrum when any side of the bispectrum triangle, ${\ell }_i<60$. However, the resulting changes in the reduced shear and magnification bias corrections are well below the sample variance for $\ell \le 5000$. We also compute a worst-case scenario for the additional biases on $w_0{w}_a\mathrm{CDM}$ cosmological parameters that result from the difference between the post-Limber and Limber approximated forms of the corrections. These further demonstrate that the reduced shear and magnification bias corrections can safely be treated under the Limber approximation for upcoming surveys.

Observations recently suggest $4.4\sigma$ discrepancy between Hubble constant measured locally and that inferred from cosmic microwave background in standard cosmology. Either standard cosmology or local measurement might expect something new. We investigate the possibility that the value of Hubble constants might be affected by the observers’ motional status in the local measurement. Using adapted coordinates for geodesic observers in Friedmann-Lemaitre-Robertson-Walker space-time and constraints inferred from observation of cosmic shear, we find that the motional status of the reference frame could contribute to about $1.1\pm 0.3\%$ discrepancy of these Hubble constants. Namely, the difference is $\mathrm{\Delta }{H}_0=0.81\pm 0.22\mathrm{km}{\mathrm{s}}^{-1}{\mathrm{Mpc}}^{-1}$, if the locally measured Hubble constant is $74\mathrm{km}{\mathrm{s}}^{-1}{\mathrm{Mpc}}^{-1}$. This effect seems not negligible as an uncertainty for local measurement of Hubble constant.

Binary neutron-star mergers will predominantly produce black-hole remnants of mass $\sim 3–4M_{\odot }$, thus populating the putative low-mass gap between neutron stars and stellar-mass black holes. If these low-mass black holes are in dense astrophysical environments, mass segregation could lead to “second-generation” compact binaries merging within a Hubble time. In this paper, we investigate possible signatures of such low-mass compact binary mergers in gravitational-wave observations. We show that this unique population of objects, if present, will be uncovered by the third-generation gravitational-wave detectors, such as Cosmic Explorer and Einstein Telescope. Future joint measurements of chirp mass $\mathcal{M}$ and effective spin ${\chi }_{\mathrm{eff}}$ could clarify the formation scenario of compact objects in the low-mass gap. As a case study, we show that the recent detection of GW190425 (along with GW170817) favors a double Gaussian mass model for neutron stars, under the assumption that the primary in GW190425 is a black hole formed from a previous binary neutron-star merger.

Recently, a few-degrees extended $\gamma$-ray halo in the direction of the Geminga pulsar has been detected by HAWC, Milagro and Fermi-LAT. These observations can be interpreted with positrons ($e^{+}$) and electrons ($e^{-}$) accelerated by the Geminga pulsar wind nebula (PWN), released in a Galactic environment with a low diffusion coefficient ($D_0$), and inverse Compton scattering (ICS) with the interstellar radiation fields. We inspect here how the morphology of the ICS $\gamma$-ray flux depends on the energy, the pulsar age and distance, and the strength and extension of the low-diffusion bubble. In particular we show that $\gamma$-ray experiments with a peak of sensitivity at TeV energies are the most promising ones to detect ICS halos. We perform a study of the sensitivity of HAWC, HESS and the future CTA experiment finding that, with efficiencies of the order of a few %, the first two experiments should have already detected a few tens of ICS halos while the latter will increase the number of detections by a factor of 4. We then consider a sample of sources associated to PWNe and detected in the HESS Galactic plane survey and in the second HAWC catalog. We use the information available in these catalogs for the $\gamma$-ray spatial morphology and flux of these sources to inspect the value of $D_0$ around them and the $e^{\pm }$ injection spectrum. All sources are detected as extended with a $\gamma$-ray emission extended about 15–80 pc. Assuming that most of the $e^{\pm }$ accelerated by these sources have been released in the interstellar medium, the diffusion coefficient is $2–30\times {10}^{26}{\mathrm{cm}}^2/\mathrm{s}$ at 1 TeV, i.e., 2 orders of magnitude smaller than the value considered to be the average in the Galaxy. These observations imply that Galactic PWNe have low-diffusion bubbles with a size of at least 80 pc.

We study collective oscillations of Majorana neutrinos in some of the most extreme astrophysical sites such as neutron star merger remnants and magneto-rotational core-collapse supernovae which include dense neutrino media in the presence of strong magnetic fields. We show that neutrinos can reach flavor equilibrium if neutrino transition magnetic moment ${\mu }_{\nu }$ is strong enough, namely when ${\mu }_{\nu }/{\mu }_{\mathrm{B}}\gtrsim {10}^{-14}–{10}^{-15}$ with ${\mu }_{\mathrm{B}}$ being the Bohr magneton. This sort of flavor equilibrium, which is not necessarily flavor equipartition, can occur on (short) scales determined by the strength of the magnetic term in the Hamiltonian. Our findings can have interesting implications for the physics of such violent astrophysical environments.

Longitudinal control signals used to keep gravitational wave detectors at a stable operating point are often affected by modulations from test mass misalignments leading to an elevated noise floor ranging from 50 to 500 Hz. Nonstationary noise of this kind results in modulation sidebands and increases the number of glitches observed in the calibrated strain data. These artifacts ultimately affect the data quality and decrease the efficiency of the data analysis pipelines looking for astrophysical signals from continuous waves as well as the transient events. In this work, we develop a scheme to subtract one such bilinear noise from the gravitational wave strain data and demonstrate it at the GEO 600 observatory. We estimate the coupling by making use of narrow-band signal injections that are already in place for noise projection purposes and construct a coherent bilinear signal by a two-stage system identification process. We improve upon the existing filter design techniques by employing a Bayesian adaptive directed search strategy that optimizes across the several key parameters that affect the accuracy of the estimated model. The scheme takes into account the possible nonstationarities in the coupling by periodically updating the involved filter coefficients. The resulting postoffline subtraction leads to a suppression of modulation sidebands around the calibration lines along with a broadband reduction of the midfrequency noise floor. The observed increase in the astrophysical range and a reduction in the occurrence of nonastrophysical transients suggest that the above method is a viable data cleaning technique for current and future generation gravitational wave observatories.

The sensitivity of ground-based gravitational-wave (GW) detectors will be improved in the future via the injection of frequency-dependent squeezed vacuum. The achievable improvement is ultimately limited by losses of the interferometer electromagnetic field that carries the GW signal. The analysis and reduction of optical loss in the GW signal chain will be critical for optimal squeezed light-enhanced interferometry. In this work, we analyze a strategy for reducing output-side losses due to spatial mode mismatch between optical cavities with the use of adaptive optics. Our goal is not to design a detector from the top down, but rather to minimize losses within the current design. Accordingly, we consider actuation on optics already present and one transmissive optic to be added between the signal recycling mirror and the output mode cleaner. The results of our calculation show that adaptive mode-matching with the current Advanced LIGO design is a suitable strategy for loss reduction that provides less than 2% mean output mode-matching loss. The range of actuation required is $+47\mu \mathrm{D}$ on SR3, $+140\mathrm{mD}$ on OM1 and OM2, $+50\mathrm{mD}$ on the SRM substrate, and $-50\mathrm{mD}$ on the added new transmissive optic. These requirements are within the demonstrated ranges of real actuators in similar or identical configurations to the proposed implementation. We also present a novel technique that graphically illustrates the matching of interferometer modes and allows for a quantitative comparison of different combinations of actuators.

We present a new effective-one-body (EOB) model for eccentric binary coalescences. The model stems from the state-of-the-art model TEOBiResumS_SM for circularized coalescing black-hole binaries, that is modified to explicitly incorporate eccentricity effects both in the radiation reaction and in the waveform. Using Regge-Wheeler-Zerilli-type calculations of the gravitational wave losses as benchmarks, we find that a rather accurate ($\sim 1\%$) expression for the radiation reaction along mildly eccentric orbits ($e\sim 0.3$) is given by dressing the current, EOB-resummed, circularized angular momentum flux, with a leading-order (Newtonian-like) prefactor valid along general orbits. An analogous approach is implemented for the waveform multipoles. The model is then completed by the usual merger-ringdown part informed by circularized numerical relativity (NR) simulations. The model is validated against the 22, publicly available, NR simulations calculated by the Simulating eXtreme Spacetime (SXS) Collaboration, with mild eccentricities, mass ratios between 1 and 3, and up to rather large dimensionless spin values ($\pm 0.7$). The maximum EOB/NR unfaithfulness, calculated with Advanced LIGO noise, is at most of order 3%. The analytical framework presented here should be seen as a promising starting point for developing highly faithful waveform templates driven by eccentric dynamics for present, and possibly future, gravitational wave detectors.

In the paper we propose and solve analytically the nonlinear evolution equation in the leading twist approximation for the odderon contribution. We found three qualitative features of this solution, which differs the odderon contribution from the Pomeron one: (i) the behavior in the vicinity of the saturation scale cannot be derived from the linear evolution in a dramatic difference with the Pomeron case; (ii) a substantial decrease of the odderon contribution with the energy; and (iii) the lack of geometric scaling behavior. The two last features have been seen in numerical attempts to solve the odderon equation.

The structure of the three-boson bound state in Minkowski space is studied for a model with contact interaction. The Faddeev-Bethe-Salpeter equation is solved both in Minkowski and Euclidean spaces. The results are in fair agreement for comparable quantities, like the transverse amplitude obtained when the longitudinal constituent momenta of the light-front valence wave function are integrated out. The Minkowski space solution is obtained numerically by using a recently proposed method based on the direct integration over the singularities of the propagators and interaction kernel of the four-dimensional integral equation. The complex singular structure of the Faddeev components of the Bethe-Salpeter vertex function for space and timelike momenta in an example of a Borromean system is investigated in detail. Furthermore, the transverse amplitude is studied as a mean to access the double-parton transverse momentum distribution. Following that, we show that the two-body short-range correlation contained in the valence wave function is evidenced when the pair has a large relative momentum in a back-to-back configuration, where one of the Faddeev components of the Bethe-Salpeter amplitude dominates over the others. In this situation a power-law behavior is derived and confirmed numerically.

We present a systematic calculation of the current jet production semi-inclusive deeply inelastic scattering process at the electron-ion collider energy. Contributions from weak interactions are considered which give rise to parity-violating effects. We consider the general form of the polarized electron beam scattering off the polarized target which has spin 1. The calculations are carried out up to twist-3 level in the quantum chromodynamics parton model by applying the collinear expansion where multiple gluon scattering is taken into account and gauge links are obtained automatically. We present complete results for structure functions and spin/azimuthal asymmetries in terms of the gauge-invariant transverse momentum dependent parton distribution functions. Both the unpolarized and the polarized electron beam cases correspond to 24 azimuthal asymmetries, in which 6 of them appear at the leading twist, while 18 of them contribute at twist-3 level. In addition, we also calculate the parity-violating asymmetries which arise from the interference of the electromagnetic and weak interactions.