Momentum space entanglement of four fermion field theory is calculated from the Wilsonian effective action pertubatively using replica trick, local terms in low energy effective action are proved to be nonrelevant pertubatively, and nonlocal terms are the only source of entanglement between different momentum modes. The final result can be represented by a set of basketball Feynman diagrams with new Feynman rules proposed to interpret them.

Spacetimes exhibiting spontaneous Lorentz symmetry-breaking have recently attracted much attention, with Kalb-Ramond (KR) gravity providing a notable example. In this context, we examine the free-fall motion of a test particle toward an electrically charged black hole arising from the coupling of the KR field with the Maxwell one in general relativity. We investigate how the Lorentz symmetry-breaking parameter affects the free-fall velocity of the particle as it approaches black hole inner regions. Additionally, we analyze the influence of this parameter on the emission and detection of signals by observers in different frames. We furthermore explore modifications to the radial and angular components of tidal forces in this spacetime and compare the results with those obtained for the Reissner-Nordström black hole. Finally, we analytically solve the geodesic deviation equation under two different conditions, identifying a subtle effect of the Lorentz symmetry-breaking parameter in the charged KR metric, and compare it with two other spacetime metrics with spontaneous symmetry breaking. These findings provide useful insights into how models of spontaneous Lorentz symmetry breaking influence gravitational dynamics in the spacetimes of charged black holes.

Gravitational wave (GW) astronomy has been hailed as a gateway to discovering unexpected phenomena in the universe. Over the last decade there have been close to one hundred GW observations of compact-binary mergers. While these signals are largely consistent with mergers of binary black holes, binary neutron stars, or black hole-neutron star systems, some events suggest the intriguing possibility of binaries involving exotic compact objects (ECOs). Identifying and characterizing an ECO merger would require accurate ECO waveform models. Using large numbers of numerical relativity simulations to develop customized models for ECO mergers akin to those used for binary black holes would be not only computationally expensive but also challenging due to the limited understanding of the underlying physics. Alternatively, key physical imprints of the ECO on the inspiral or merger could in principle be incorporated phenomenologically into waveform models, sufficient to quantify generic properties. In this work we present a first application of this idea to assess the detectability and distinguishability of ECO mergers, and we propose a phenomenological approach that can iteratively incorporate features of ECO mergers, laying the groundwork for an effective exotic compact object identifier in compact binary coalescences. Using Bayesian parameter estimation on the data for the GW event GW150914, we find the inferred compactness to be consistent with that expected for black holes, within this framework. The efficacy of the identifier can be refined by adding information from numerical relativity simulations involving fundamental fields. Conversely, such an identifier framework can help focus future numerical relativity and modeling efforts for exotic objects.

Many efforts were made in order to better understand the energy extraction via magnetic reconnection from a rotating black hole, following the work of Comisso and Asenjo in 2021. We also tried to make some progress in our previous works, in which we discussed differences between bulk plasma with different streamlines and also defined the covering factor as an internal property of an accretion system to quantify its capability on extracting energy via magnetic reconnection from its central black hole. In this study, we aim to explore this topic within the framework of a Kerr–Sen-like spacetime induced from Bumblebee gravity, which, among various alternative theories of gravity beyond pure Einstein gravity, stands out as a promising candidate for explaining certain high-energy astrophysical phenomena. More specifically, we would like to analyze the influence of the rate of Lorentz symmetry breaking and the Bumblebee charge, the two additional parameters in Bumblebee gravity except for the black hole mass and spin, on the energy extraction via magnetic reconnection. By analyzing the allowed regions for energy extraction and the variations of the covering factor, we find that energy extraction becomes more likely to succeed and tends to occur closer to the central region when the spacetime carries a bigger rate of Lorentz symmetry breaking and Bumblebee charge. Furthermore, our results indicate that the most favorable spacetime configuration for energy extraction via magnetic reconnection, when the extractable energy of the central black hole is determined, corresponds to the scenario in which the cosmic censorship hypothesis is marginally not violated.

In general relativity, the static tidal Love numbers of black holes vanish identically. Whether this remains true for time-dependent tidal fields—i.e., in the case of dynamical tidal Love numbers—is an open question, complicated by subtle issues in the definition and computation of the tidal response at finite frequency. In this work, we analyze the dynamical tidal perturbations of a Schwarzschild black hole to quadratic order in the tidal frequency. By employing the Teukolsky formalism in advanced null coordinates, which are regular at the horizon, we obtain a particularly clean perturbative scheme. Furthermore, we introduce a response function based on the full solution of the perturbation equation, which does not depend on any arbitrary constant. Our analysis recovers known results for the dissipative response at linear order and the logarithmic running at quadratic order, associated with scale dependence in the effective theory. In addition, we find a finite, nonvanishing conservative correction at second order in frequency, thereby possibly demonstrating a genuine dynamical deformation of the black hole geometry. Although removing any ambiguity in the dynamical tidal response would require a matching with some gauge-invariant coefficient, we assess the impact of these effects on the gravitational-wave phase. These contributions enter at eighth post-Newtonian order, and can be expressed in terms of generic $\mathcal{O}(1)$ coefficients, which have to be matched to the perturbative result. Regardless of the matching ambiguities, we argue that such corrections are too small to be observable even with future-generation gravitational wave detectors. Moreover, the corresponding phase shifts are degenerate with unknown point-particle contributions entering at the same post-Newtonian order.

Spinning black holes could produce ultralight particles via the superradiance instability. These particles form a dense cloud around the host black hole, introducing new opportunities for the detection of ultralight new physics. When the black hole is part of a binary system, the binary can trigger transitions among different states of the cloud configuration. Such transitions backreact on the orbital dynamics, modifying the frequency evolution of the emitted gravitational waves. Based on this observation, black hole binaries were proposed as a way to test the existence of ultralight particles. We investigate the effects of the self-gravity of the cloud on the orbital evolution and on the gravitational wave emission. We find that cloud self-gravity could lead to a density-dependent modification of the energy levels of ultralight particles and that it could alter the order of hyperfine energy levels. The crossing of hyperfine levels prevents binaries from triggering resonant hyperfine transitions, and allows them to approach radii that could trigger resonant transitions of fine levels. We study the implications of these findings, especially in the context of future space-borne gravitational wave observatory, the Laser Interferometer Space Antenna (LISA). For quasicircular, prograde, and equatorial orbits, we find that LISA could probe ultralight particles in the mass range ${10}^{-15}\mathrm{eV}–{10}^{-13}\mathrm{eV}$ through gravitational wave observations.

We study theories of the “general relativity and Yang-Mills” type in four-dimensional spacetime with cosmological constant, focusing on formulations where the basic variables are connections and curvatures (but no metric). We present a new Lagrangian for general relativity (GR) coupled to Yang-Mills theory, which uses the same kinds of variables for both sectors and is suggestive of the double-copy structure. This Lagrangian comes in both nonchiral (real) and chiral (complex) versions. The chiral version makes it easy to isolate the self-dual sector. The latter lends itself to a higher-spin (HS) generalization, which combines the HS self-dual GR and HS self-dual Yang-Mills theory of Krasnov et al. We then descend from the covariant formulation to the light cone gauge and construct a cubic-exact light cone action. For HS self-dual Yang-Mills theory, we solve the light cone field equations to all orders in perturbation theory. Finally, we discuss the relation between light cone foliations that share a light ray—a setup relevant for the scattering problem in the de Sitter space static patch. We derive this relation at the linearized level and argue from causality and symmetry that it cannot receive nonlinear corrections. We explore the associated gauge transformations in the nonlinear covariant theory.

We derive the approximate analytical solutions of the bound timelike geodesic orbits in the effective-one-body frame with an extreme-mass ratio limit. The analytical solutions are expressed in terms of the elliptic integrals using Mino time $\lambda$ as the independent variable. Since Mino time decouples the $r$ and $\theta$ motion, we also give explicit expressions for three orbital frequencies ${\mathrm{\Omega }}_r,{\mathrm{\Omega }}_{\theta },{\mathrm{\Omega }}_{\varphi }$ using the Fourier series expansion. With these analytical expressions at hand, we can perform Fourier expansions in Mino time $\lambda$ for any function expressed in terms of the coordinates $(r,\theta ,\varphi )$. In particular, the observer’s time $t$ is decomposed into Mino time $\lambda$, and the frequency-domain description is constructed from the $\lambda$-Fourier expansion and the expansion of $t$. These analytical expressions are quite simple to implement, and can be applicable for calculating gravitational waves from extreme mass-ratio inspirals with the frequency-domain Teukolsky equation.

We present a numerical relativity study of eccentric mergers of equal-mass rotating $\overline{m}=1$ Proca stars, focusing on their gravitational-wave (GW) emission. By systematically varying key binary parameters, such as the initial orbital boost, which determines the orbital angular momentum, and the relative phase between the stars, we examine how the internal phase structure of the Proca field influences the merger dynamics and the properties of the emitted GWs. Our simulations demonstrate that the relative phase has paramount impact on the postmerger evolution, resulting in prompt black hole formation accompanied by a transient Proca remnant, the formation of a hypermassive $\overline{m}=1$ Proca star or even the emergence of a dynamically unstable spinning $\overline{m}=2$ Proca star. Under certain conditions, the GW signal exhibits significant odd modes (e.g., the $\ell =m=3$ mode) that are absent in conventional black hole mergers, potentially serving as unique signatures of these exotic objects. Our findings offer new insights into the phenomenology of bosonic star mergers and the potential astrophysical role of ultralight bosonic fields.

We study the dynamics of gravitons in a squeezed vacuum state under a thermal radiation background. Unlike traditional treatments that rely on the Boltzmann equation, we employ the Heisenberg equation and average it over general quantum states. In contrast to the usual Boltzmann-based descriptions, our approach captures the subtleties arising from quantum coherence in different number eigenstates, which is essential for soft graviton modes in the squeezed vacuum state. Our new method successfully reproduces the previous one-loop results within the in-in formalism when the expansion parameter is small and deviates significantly as the parameter increases, indicating that our results extend beyond the one-loop in-in formalism. We examine the implications of graviton emission effects stimulated by quantum coherence in both flat and expanding backgrounds. In the flat background, it is found that backreaction of radiation on the spacetime dynamics is crucial for significant stimulated emission. In the expanding background, to avoid the subtleties associated with superhorizon modes, we investigate the effect of emission within the horizon immediately after reheating and find a significant effect. We also examined the IR graviton evolution from a symmetry perspective and propose a regularization prescription to eliminate the secular growth problem.

The gas density profile around galaxies, shaped by feedback and affecting the galaxy lensing signal, is imprinted on the cosmic microwave background (CMB) by the kinematic Sunyaev-Zel’dovich effect (kSZ). We precisely measure this effect ($S/N\approx 10$) via velocity stacking with 825,283 spectroscopically confirmed luminous red galaxies (LRG) from the Dark Energy Spectroscopic Instrument Year 1 (DESI Y1) survey, which overlap with the Atacama Cosmology Telescope (ACT) Data Release 6 temperature maps over $\ge 4,000{\mathrm{deg}}^2$. We explore the kSZ dependence with various galaxy parameters and find no significant trend with redshift but clear trends with stellar mass and absolute magnitude in $g$, $r$, and $z$ bands. Our analysis suggests that the gas extends beyond the dark matter halo (99.5% confidence level, i.e., probability to exceed $(\mathrm{PTE})=0.005$). We find a tentative preference for hydrodynamical simulation models with stronger feedback that drives gas further out (Illustris $z=0.5$, $\mathrm{PTE}=0.37$) over weaker-feedback cases (IllustrisTNG $z=0.8$, $\mathrm{PTE}=0.045$), though with limited statistical significance. In all cases, a free multiplicative amplitude was fit to the simulated profiles, and further modeling work is required to firm up these conclusions. We find consistency between kSZ profiles around spectroscopic and photometric LRG, with comparable statistical power, thus increasing our confidence in the photometric analysis. Additionally, we present the first kSZ measurement around the DESI Y1 bright galaxy sample (BGS) and the emission-line galaxies (ELG) whose features match qualitative expectations. Finally, we forecast $S/N\sim 50$ for future stacked kSZ measurements using data from the ACT, the DESI Y3, and the Rubin Observatory. These measurements will serve as an input for galaxy formation models and baryonic uncertainties in galaxy lensing.

The gravitational waves emitted by massive black hole binaries can be affected by a variety of environmental effects, which, if detected, could inform astrophysics and cosmology. We here study how gravitational waves emitted by black holes in quasicircular orbits are affected by the presence of an ultralight, vector field, dark-matter environment that is minimally coupled to the binary. This dark-matter environment induces oscillatory gravitational potentials that perturb the orbit of the binary, leaving an imprint in the binary’s binding energy, and thus on the gravitational waves emitted. We here compute the effect of this environment on the gravitational wave phase using the stationary-phase approximation within the post-Newtonian formalism. We then perform a Fisher analysis to estimate the detectability of this environmental effect with a four-year Laser Interferometric Space Antenna (LISA) observation, focusing on vector fields with ultralight masses in the $({10}^{-19},{10}^{-16})\mathrm{eV}$ range. We conclude that the observation of such gravitational waves with spaceborne interferometers, like LISA, could yield a measurement or constraint on local, vector dark-matter environments, provided the dark-matter density is larger than roughly ${10}^{14}{M}_{\odot }/{\mathrm{pc}}^3$.

The possibility of discovering twin stars, two neutron stars (NSs) with the same mass but different radii, is usually studied in forward modelings by using a restricted number of NS matter equations of state (EOSs) encapsulating a first-order phase transition from hadronic to quark matter (QM). Informing our likelihood function with the NS radius data from GW170817 and using a metamodel with nine parameters capable of mimicking most NS EOSs available in the literature, we conduct a Bayesian quantification of the observability and underlying EOSs of twin stars. Of the accepted EOSs, between 12 and 18% yield twin stars, depending on the restrictions we place on the second branch. The possibility of twin stars remains robust even under recent observational constraints. We show that many of these twin star scenarios are observable with currently available levels of accuracy in measuring NS radii. We also present the marginalized posterior probability density functions (PDFs) of every EOS parameter for each of four mass-radius correlation topologies. We find that the inferred EOS depends sensitively on not only whether twin stars are present, but also the category of twin stars, indicating that the observation of twin stars would provide a strong constraint on the underlying EOS. In particular, for two coexisting hybrid stars having QM cores at different densities, the PDF for QM speed of sound squared $c_{\mathrm{qm}}^2$ has two peaks, one below and another above the conformal limit $c_{\mathrm{qm}}^2=1/3$ predicted by perturbative QCD.

The streaming of neutrinos in an inhomogeneous medium is known to affect the physics of flavor conversion. We employ an ensemble of single-crossed angular distributions and explore the physics of flavor conversion, while neutrinos propagate across a one-dimensional inhomogeneous medium. The advective term in the neutrino equations of motion is responsible for the cascade of flavor waves toward ever smaller spatial and angular scales. However, as the system evolves, perturbations with large wave numbers are damped, with a resulting smearing of the flavor configuration. We provide a simple recipe that allows to forecast the steady-state flavor configuration achieved by neutrinos without solving their kinetic equations. In particular, we find that flavor equipartition on one side of the angular spectrum and the cancellation of the spectral crossing in the lepton number distributions, proposed in the literature as generic flavor outcome, is a special solution depending on the degree of neutrino-antineutrino asymmetry. This work constitutes a step forward toward the development of semianalytic schemes to account for flavor conversion physics in hydrodynamic simulations of core-collapse supernovae and neutron-star merger remnants.

We consider a class of models in the framework of metric-affine gravity and establish their correspondence to the bosonic sector of a class of no-scale supergravity models. The excellent inflationary behavior of the gravitational models considered is carried over to the corresponding supergravity ones, thus, enriching the landscape of inflation-compatible models.

We consider the thermodynamics of a color-confined phase of quantum chromodynamics (QCD) and pure gauge theory within a string-inspired corresponding to a physical spatial dimension, $d=3$. We show that the physical mass spectrum of massive mesons—in both the strange and nonstrange sectors separately—is reasonably well described and extended by the exponential mass spectrum of open strings, $\rho (m)$, characterized by a unique Hagedorn temperature $T_H=\sqrt{3\sigma /2\pi }$, expressed by the string tension $\sigma$. This $T_H$ is the value appropriate for $d=3$ spatial dimensions and is of the order of $T_H\sim 300\mathrm{MeV}$ for typical values of the string tension. It is much larger than the values of $T_H$ which have been phenomenologically extracted so far to describe the meson spectrum. Glueball states in pure gauge theory, modeled by closed strings, exhibit a similarly large Hagedorn temperature, highlighting a universal feature of the exponential spectrum. We further analyze the thermodynamic properties of the equation of state at finite temperature and demonstrate that, in the confined phase, the string models agree with lattice QCD results. This lends further support to the recent interpretation of the QCD phase diagram that incorporates strings as relevant degrees of freedom.

Monte Carlo simulations are an essential tool in particle physics data analysis. Events are typically generated alongside weights that redistribute the cross section of the simulated process across the phase space. These weights can be negative, and several post hoc methods have been developed to eliminate or mitigate the negative values. All of these methods share the common strategy of approximating the average weight as a function of phase space. We introduce an alternative approach, which, instead of reweighting to the average, refines the initial weights with a scaling transformation, utilizing a phase space-dependent factor. Since this new refinement method does not need to model the full weight distribution, it can be more accurate. High-dimensional and unbinned phase space is processed using neural networks for the refinement method. In addition to the refinement method, we introduce a new resampling protocol, which can be used in conjunction with any weight transformation to not only preserve the average weight but also the statistical uncertainties of the initial distribution. Using both realistic and synthetic examples, we show that the new neural refinement method is able to match or exceed the accuracy of similar weight transformations and that the new resampling protocol is simpler in implementation than previous methods while exhibiting equivalent statistical properties.

We solve the Lippmann-Schwinger equation (LSE) with a kernel that includes a regular finite-range potential and additional contact terms with derivatives. We employ distorted wave theory and dimensional regularization, as proposed in Nieves [Phys. Lett. B 568, 109 (2003)]. We analyze the spin singlet nucleon-nucleon $S$-wave as case of study, with the regular one-pion exchange (OPE) potential in this partial wave and up to $\mathcal{O}(Q^6)$ (six derivatives) contact interactions. We discuss in detail the renormalization of the LSE and show that the scattering amplitude solution of the LSE fulfills exact elastic unitarity and inherits the left-hand cut of the long-distance OPE amplitude. Furthermore, we proof that the LSE amplitude coincides with that obtained from the exact $N/D$ calculation, with the appropriate number and typology of subtractions to reproduce the effective range parameters taken as input to renormalize the LSE amplitude. The generalization to a higher number of derivatives is straightforward.

Building on our automated framework that uses ring diagrams for classifying $CP$ basis invariants Neda Darvishi et al., [Phys. Rev. D 108, 115030 (2023)], this paper broadens the application of the methodology with more extensive examples and a wider scope of theoretical frameworks. Here, we showcase its versatility through detailed analyses of specific operators in the Standard Model effective field theory (SMEFT), such as a four-fermion operator at dimension-6 and a Yukawa operator extended up to dimension-$2n$ terms while maintaining a dimension-6 core, as well as in SMEFT with sterile neutrinos ($\nu \mathrm{SMEFT}$) up to dimension-7. By integrating the ring-diagram technique with the Cayley-Hamilton theorem, we have developed a system that not only simplifies the process of identifying basic and joint invariants but also enables the automatic differentiation between $CP$-even and $CP$-odd invariants from the lowest orders. Additionally, this work presents a comparison of our results with those derived using the traditional Hilbert-Poincaré series and its Plethystic logarithm. While these conventional approaches primarily yield the numerical count of invariants, our framework provides a complete structure of invariants, thereby surpassing the limitations of these traditional methods.