We investigate the Unruh-Fulling effect in a class of nonlocal field theories by examining both the number operator and Unruh-DeWitt detector methods. Unlike in previous literature, we use Unruh quantization to quantize the matter field. Such choice, as oppose to standard Minkowski decomposition, naturally incorporates the time translational invariance in the positive frequency Wightman function and thus captures the thermal equilibrium of the system. We analyze the Unruh-Fulling effect for a massless real scalar field in both the Lorentz noninvariant and Lorentz invariant nonlocal theories. In Lorentz noninvariant nonlocal theory, the expectation value of number operator and the response function of the detector are modified by an overall multiplicative factor. Whereas in Lorentz invariant nonlocal theory these quantities remain identical to those of the standard Unruh-Fulling effect. The temperature of the thermal bath remains unaltered for both the Lorentz noninvariant and Lorentz invariant nonlocal theories. Therefore, in terms of temperature, the nonlocal Unruh-Fulling effect is universal while it is derived via Unruh quantization, whereas the transition rate may be modified.

We discuss the conditions under which static, finite-energy, configurations of a complex scalar field $\varphi$ with constant phase and spherically-symmetric norm exist in a potential of the form $V({\varphi }^{*}\varphi ,{\varphi }^N+{\varphi }^{*N})$ with $N\in \mathbb{N}$ and $N\ge 2$, i.e., a potential with a $Z_N$-symmetry. Such configurations are called $Z_N$-balls. We build explicit solutions in ($3+1$)-dimensions from a model mimicking effective field theories based on the Polyakov loop in finite-temperature $\mathrm{SU}(N)$ Yang-Mills theory. We find $Z_N$-balls for $N=3$, 4, 6, 8, 10, and show that only static solutions with zero radial nodes exist for $N$ odd, while solutions with radial nodes may exist for $N$ even.

It is demonstrated that it is possible to find a field theory containing massless scalar particles which has infrared structure closely resembling that of quantum electrodynamics and perturbative quantum gravity but exhibiting no gauge invariance or internal symmetries at all, and in particular, no apparent asymptotic symmetry. It is shown that, unlike soft photons and gravitons, the soft scalars do not decouple from dressed states, and they are generically produced when hard dressed particles interact. However, the entanglement of the hard and resulting soft particles is vanishingly small.

Every 4D $\mathcal{N}=2$ superconformal field theory $\mathcal{T}$ corresponds to an associated vertex operator algebra $\mathbb{V}(\mathcal{T})$, which is in general nonrational with a more involved representation theory. Null states in $\mathbb{V}(\mathcal{T})$ can give rise to nontrivial flavored modular differential equations, which must be satisfied by the refined/flavored character of all the $\mathbb{V}(\mathcal{T})$ modules. Taking some $A_1$ theories ${\mathcal{T}}_{g,n}$ of class $\mathcal{S}$ as examples, we construct the flavored modular differential equations satisfied by the Schur index. We show that three types of surface defect indices give rise to common solutions to these differential equations and therefore are sources of $\mathbb{V}(\mathcal{T})$-module characters. These equations transform almost covariantly under modular transformations, ensuring the presence of logarithmic solutions which may correspond to characters of logarithmic modules.

We study charged and radially excited boson stars in both asymptotically flat as well as asymptotically anti–de Sitter spacetime. We demonstrate that two different types of radially excited solutions exist: one that persists in the linear limit of small scalar fields, in which analytical arguments suggest the existence of these solutions, and one that appears only in the highly nonlinear regime of the model. We also demonstrate that the formation of wavy scalar hair discussed previously for black holes and boson stars in asymptotically flat spacetime persists for asymptotically anti–de Sitter spacetime.

Gravitational wave (GW) memory is studied in the context of a certain class of braneworld wormholes. Unlike other wormhole geometries, this novel class of wormholes do not require any exotic matter fields for its traversability. First, we study geodesics in this wormhole spacetime, in the presence of a GW pulse. The resulting evolution of the geodesic separation shows the presence of displacement and velocity memory effects. Motivated by the same, we study the memory effects at null infinity using the Bondi-Sachs formalism, adapted for a braneworld wormhole. Our analysis provides a nontrivial change of the Bondi mass after the passage of a burst of gravitational radiation and hence manifests the memory effect at null infinity. In both of these exercises, the presence of extra dimension and the wormhole nature of the spacetime geometry gets imprinted in the memory effect. Since future GW detectors will be able to probe the memory effect, the present work provides another avenue to search for compact objects other than black holes.

We investigate stationary accretion of the collisionless Vlasov gas onto the Kerr black hole, occurring in the equatorial plane. The solution is specified by imposing asymptotic boundary conditions: at infinity the gas obeys the Maxwell-Jüttner distribution, restricted to the equatorial plane (both in positions and momenta). In the vicinity of the black hole, the motion of the gas is governed by the spacetime geometry. We compute accretion rates of the rest-mass, the energy, and the angular momentum, as well as the particle number surface density, focusing on the dependence of these quantities on the asymptotic temperature of the gas and the black hole spin. The rest-mass and energy-accretion rates, normalized by the black hole mass and appropriate asymptotic surface densities of the gas, increase with increasing asymptotic temperature. The accretion slows down the rotation of the black hole.

Binary neutron star mergers, which can lead to less massive black holes relative to other known astrophysical channels, have the potential to probe modifications to general relativity that arise at smaller curvature scales compared to more massive compact object binaries. As a representative example of this, here we study binary neutron star mergers in shift-symmetric Einstein-scalar-Gauss-Bonnet gravity using evolutions of the full, nonperturbative evolution equations. We find that the impact on the inspiral is small, even at large values of the modified gravity coupling (as expected, as neutron stars do not have scalar charge in this theory). However, postmerger there can be strong scalar effects, including radiation. When a black hole forms, it develops scalar charge, impacting the ringdown gravitational wave signal. In cases where a longer-lived remnant star persists postmerger, we find that the oscillations of the star source levels of scalar radiation similar to the black hole formation cases. In remnant stars, we further find that at coupling values comparable to the maximum value for which black hole solutions of the same mass exist, there is significant nonlinear enhancement in the scalar field, which if sufficiently large lead to a breakdown in the evolution, seemingly due to loss of hyperbolicity of the underlying equations.

The detection of gravitational waves from compact binary coalescence (CBC) has allowed us to probe the strong-field dynamics of general relativity (GR). Among various tests performed by the LIGO-Virgo-KAGRA Collaboration are parametrized tests, where parametrized modifications to GR waveforms are introduced and constrained. This analysis typically requires the generation of more than millions of computationally expensive waveforms. The computational cost is higher for a longer signal, and current analyses take weeks to years to complete for a binary neutron star (BNS) signal. We present a technique to accelerate the parametrized tests using a multiband decomposition of likelihood, which was originally proposed by one of the authors to accelerate parameter estimation analyses of CBC signals assuming GR. We show that our technique speeds up the parametrized tests of a $1.4M_{\odot }–1.4M_{\odot }$ BNS signal by a factor of $\mathcal{O}(10)$ for a low-frequency cutoff of 20 Hz. We also verify the accuracy of our method using simulated signals and real data.

The time delay of a light signal in the quadrupole field of a body at rest is determined in the second post-Newtonian (2PN) approximation in harmonic coordinates. For grazing light rays at the Sun, Jupiter, and Saturn the 2PN quadrupole effect in time delay amounts up to 0.004, 0.14, and 0.04 picosecond, respectively. These values are compared with the time delay in the first post-Newtonian (1PN and 1.5PN) approximation, where it turns out that only the first eight mass multipoles and the spin dipole of these massive bodies are required for a given goal accuracy of 0.001 picosecond in time delay measurements in the solar system. In addition, the spin-hexapole of Jupiter is required on that scale of accuracy.

I define here a novel function on a modeled space of gravitational-wave signals, before studying its properties as a statistic for detection, as an objective function for identification, and as an effective likelihood function for inference. The main motivation behind this work is the open data-analysis problem for signals from extreme-mass-ratio inspirals, which is severely hindered by the presence of strong nonlocal parameter degeneracy in the signal space. I demonstrate the utility of the proposed function for the analysis of such signals, and suggest various possible directions for future research.

Thanks to unparalleled near-horizon images of the shadows of Messier 87* (M87*) and Sagittarius A* (Sgr A*) delivered by the Event Horizon Telescope (EHT), two amazing windows opened up to us for the strong-field test of the gravity theories as well as fundamental physics. Information recently published from EHT about the Sgr A*’s shadow lets us have a novel possibility of exploration of Lorentz symmetry violation (LSV) within the Standard-Model extension (SME) framework. Despite the agreement between the shadow image of Sgr A* and the prediction of the general theory of relativity, there is still a slight difference which is expected to be fixed by taking some fundamental corrections into account. We bring up the idea that the recent inferred shadow image of Sgr A* is explicable by a minimal SME-inspired Schwarzschild metric containing the Lorentz-violating (LV) terms obtained from the post-Newtonian approximation. The LV terms embedded in Schwarzschild metric are dimensionless spatial coefficients ${\overline{s}}^{jk}$ associated with the field responsible for LSV in the gravitational sector of the minimal SME theory. In this way, one can control Lorentz invariance violation in the allowed sensitivity level of the first shadow image of Sgr A*. Actually, using the bounds released within $1\sigma$ uncertainty for the shadow size of Sgr A* and whose fractional deviation from standard Schwarzschild, we set upper limits for the two different combinations of spatial diagonal coefficients and the time-time coefficient of the SME, as well. The best upper bound is at the ${10}^{-2}$ level, which should be interpreted differently from those constraints previously extracted from well-known frameworks since unlike standard SME studies it is not obtained from a Sun-centered celestial frame but comes from probing the black hole horizon scale.

We study effects of the particles coupling with scalar field (SF) on the distribution of stable circular orbits (SCO) around the naked singularity described by the well-known Fisher-Janis-Newman-Winicour solution (F/JNW). The power-law and exponential models of the particle–SF interaction are analyzed. The focus is on the nonconnected SCO distributions. A method is used that facilitates numerical studies of the SCO regions in the case of the general static spherically symmetric metric. In case of F/JNW, we show that coupling between particles and SF can essentially complicate the topology of the SCO distributions. In particular, it can lead to new nonoverlapping SCO regions, which are separated by unstable orbits and/or by regions where the circular orbits do not exist.

We generalize to reduced Horndeski theories of gravity, where gravitational waves (GWs) travel at the speed of light, the expression of a statistically homogeneous and unpolarized stochastic gravitational wave background (SGWB) signal measured as the correlation between the individual signals detected by two interferometers in arbitrary configurations. We also discuss some results found in the literature regarding cosmological distances in modified theories, namely, the simultaneous validity of a duality distance relation for GW signals and of the coincidence between the gravitational wave luminosity distance, based on the energy flux, and the distance inferred from the wave amplitude. This discussion allows us to conclude that the spectral energy density per unit solid angle of an astrophysical SGWB signal has the same functional dependency with the luminosity of each emitting source as in general relativity (GR). Using the generalized expression of the GW energy-momentum tensor and the modified propagation law for the tensor modes, we conclude that the energy density of a SGWB maintains the same functional relation with the scale factor as in GR, provided that the modified theory coincides with GR in a given hypersurface of constant time. However, the relation between the detected signal and the spectral energy density is changed by the global factor $G_4(\phi (t_0))$, thus potentially serving as a probe for modified gravity theories.

We present a comprehensive dynamical systems analysis of homogeneous and isotropic Friedmann-Lemaître-Robertson-Walker cosmologies in the Hu-Sawicki $f(R)$ dark energy model for the parameter choice $\{n,C_1\}=\{1,1\}$. For a generic $f(R)$ theory, we outline the procedures of compactification of the phase space, which in general is four dimensional. We also outline how, given an $f(R)$ model, one can determine the coordinate of the phase space point that corresponds to the present-day Universe and the equation of a surface in the phase space that represents the $\mathrm{\Lambda }\mathrm{CDM}$ evolution history. Next, we apply these procedures to the Hu-Sawicki model under consideration. We identify some novel features of the phase space of the model such as the existence of invariant submanifolds and two-dimensional sheets of fixed points. We determine the physically viable region of the phase space and the fixed point corresponding to possible matter-dominated epochs, and discuss the possibility of a nonsingular bounce, recollapse, and cyclic evolution. We also provide a numerical analysis comparing the $\mathrm{\Lambda }\mathrm{CDM}$ evolution and Hu-Sawicki evolution.

Ultralight bosonic dark matter called fuzzy dark matter (FDM) has attracted much attention as an alternative to the cold dark matter. An intriguing feature of the FDM model is the presence of a soliton core, a stable dense core formed at the center of halos. In this paper, we analytically study the dependence of the soliton core properties on the halo characteristics by solving approximately the Schrödinger-Poisson equation. Focusing on the ground-state eigenfunction, we derive a key expression for the soliton core radius, from which we obtain the core-halo mass relations similar to those found in the early numerical work, but involving the factor dependent crucially on the halo concentration and cosmological parameters. Based on the new relations, we find that for a given cosmology, (i) there exist a theoretical bound on the radius and mass of soliton core for each halo mass (ii) incorporating the concentration-halo mass (C-M) relation into the predictions, the core-halo relations generally exhibit a nonpower-law behavior, and with the C-M relation suppressed at the low-mass scales, relevant to the FDM model, predictions tend to match the simulations well (iii) the scatter in the C-M relation produces a sizable dispersion in the core-halo relations, and can explain the results obtained from cosmological simulations. Finally, the validity of our analytical treatment are critically examined. A perturbative estimation suggests that the prediction of the core-halo relations is valid over a wide range of parameter space, and the impact of the approximation invoked in the analytical calculations is small, although it is not entirely negligible.

The cosmological information extracted from photometric surveys is most robust when multiple probes of the large scale structure of the Universe are used. Two of the most sensitive probes are the clustering of galaxies and the tangential shear of background galaxy shapes produced by those foreground galaxies, so-called galaxy-galaxy lensing. Combining the measurements of these two two-point functions leads to cosmological constraints that are independent of the way galaxies trace matter (the galaxy bias factor). The optimal choice of foreground, or lens, galaxies is governed by the joint, but conflicting requirements to obtain accurate redshift information and large statistics. We present cosmological results from the full $5000{\mathrm{deg}}^2$ of the Dark Energy Survey’s first three years of observations (Y3) combining those two-point functions, using for the first time a magnitude-limited lens sample (MagLim) of 11 million galaxies, especially selected to optimize such combination, and 100 million background shapes. We consider two flat cosmological models, the Standard Model with dark energy and cold dark matter ($\mathrm{\Lambda }\mathrm{CDM}$) a variation with a free parameter for the dark energy equation of state ($w\mathrm{CDM}$). Both models are marginalized over 25 astrophysical and systematic nuisance parameters. In $\mathrm{\Lambda }\mathrm{CDM}$ we obtain for the matter density ${\mathrm{\Omega }}_m={0.320}_{-0.034}^{+0.041}$ and for the clustering amplitude $S_8\equiv {\sigma }_8({\mathrm{\Omega }}_m/0.3{)}^{0.5}={0.778}_{-0.031}^{+0.037}$, at 68% C.L. The latter is only $1\sigma$ smaller than the prediction in this model informed by measurements of the cosmic microwave background by the Planck satellite. In $w\mathrm{CDM}$ we find ${\mathrm{\Omega }}_m={0.32}_{-0.046}^{+0.044}$, $S_8={0.777}_{-0.051}^{+0.049}$ and dark energy equation of state $w=-{1.031}_{-0.379}^{+0.218}$. We find that including smaller scales, while marginalizing over nonlinear galaxy bias, improves the constraining power in the ${\mathrm{\Omega }}_m-S_8$ plane by 31% and in the ${\mathrm{\Omega }}_m-w$ plane by 41% while yielding consistent cosmological parameters from those in the linear bias case. These results are combined with those from cosmic shear in a companion paper to present full DES-Y3 constraints from the three two-point functions ($3\times 2\mathrm{pt}$).

Recently, the cross-correlation between $E$- and $B$-mode polarization of the cosmic microwave background, which is well explained by cosmic birefringence with rotation angle $\beta \approx 0.3\mathrm{deg}$, has been found in cosmic microwave background polarization data. We carefully investigate the possibility of explaining the observed $EB$ correlation by the primordial chiral gravitational waves, which can be generated in the parity-violating theories in the primordial Universe. We found that the chiral gravitational wave scenario does not work due to the overproduction of the $BB$ autocorrelation, which far exceeds the observed one by SPTPol and POLARBEAR.

Recent local measurements of the Hubble constant made using supernovae have delivered a value that differs by $\sim 5\sigma$ (statistical error) from predictions using the cosmic microwave background (CMB), or using baryon acoustic oscillations (BAO) and big-bang nucleosynthesis (BBN) constraints, which are themselves consistent. The effective volume covered by the supernovae is small compared to the other probes, and it is therefore interesting to consider whether sample variance (often also called cosmic variance) is a significant contributor to the offset. We consider four ways of calculating the sample variance: (i) perturbation theory applied to the luminosity distance, which is the most common method considered in the literature; (ii) perturbation of cosmological parameters, as is commonly used to alleviate supersample covariance in sets of N-body simulations; (iii) a new method based on the variance between perturbed spherical top-hat regions; (iv) using numerical N-body simulations. All give consistent results showing that, for the Pantheon supernova sample, sample variance can only lead to fluctuations in $H_0$ of order $\pm 1\mathrm{km}{\mathrm{s}}^{-1}{\mathrm{Mpc}}^{-1}$ or less. While this is not in itself a new result, the agreement between the methods used adds to its robustness. Furthermore, it is instructive to see how the different methods fit together. We also investigate the internal variance of the $H_0$ measurement using SH0ES and Pantheon data. By searching for an offset between measurements in opposite hemispheres, we find that the direction coincident with the CMB dipole has a higher $H_0$ measurement than the opposite hemisphere by roughly $4\mathrm{km}{\mathrm{s}}^{-1}{\mathrm{Mpc}}^{-1}$. We compare this with a large number of simulations and find that the size of this asymmetry is statistically likely, but the preference of direction may indicate that further calibration is needed.

Many compelling dark matter (DM) scenarios feature Coulomb-like interactions between DM particles and baryons, in which the cross section for elastic scattering scales with relative particle velocity as $v^{-4}$. Previous studies have invoked such interactions to produce heat exchange between cold DM and baryons and alter the temperature evolution of hydrogen. Here, we present a comprehensive study of the effects of Coulomb-like scattering on structure formation, in addition to the known effects on the thermal history of hydrogen. We find that interactions which significantly alter the temperature of hydrogen at Cosmic Dawn also dramatically suppress the formation of galaxies that source the Lyman-$\alpha$ background, further affecting the global 21-cm signal. In particular, an interaction cross section at the current observational upper limit leads to a decrease in the abundance of star-forming halos by a factor of $\sim 2$ at $z\sim 20$, relative to cold, collisionless DM. We also find that DM that is 100% millicharged cannot reproduce the depth and the timing of the reported EDGES anomaly in any part of the parameter space. These results critically inform modeling of the global 21-cm signal and structure formation in cosmologies with DM–baryon scattering, with repercussions for future and upcoming cosmological data analysis.