Motivated by different approaches to quantum gravity, one could consider that Lorentz invariance is not an exact symmetry of nature at all energy scales. Following this spirit, modified dispersion relations have been used to encapsulate quantum gravity phenomenology. In the present work, we propose a class of Lorentz invariance violating phenomenological dispersion relations, which could be different for each particle species, to study the generalized vacuum Cherenkov radiation process. We identify the kinematic regions where the process is allowed and then compute the energy loss rate due to the emission of vacuum electromagnetic and gravitational Cherenkov radiation. Furthermore, we estimate constraints for the Lorentz invariance breaking parameters of protons and gravitons taking into account the existence (or absence) of vacuum gravitational Cherenkov radiation using ultrahigh energy cosmic ray detections.

It has recently been proved that a third law of black hole mechanics does not hold for Einstein-Maxwell theory coupled to a massless charged scalar field: there exist solutions that describe gravitational collapse to form an exactly extremal Reissner-Nordström black hole in finite time. In this paper it is proved that such solutions do not exist in theories with matter fields satisfying a local mass-charge inequality. In such a theory, if a 2-surface has the same metric, extrinsic curvature, and Maxwell field as a cross section of an extremal Reissner-Nordström horizon then this surface cannot have a compact interior and so cannot be a horizon cross section of a black hole formed in gravitational collapse. This result is proved using spinorial techniques, which are also used to prove a mass-charge inequality for a modified version of the Dougan-Mason quasilocal mass.

The Brill and Teukolsky gravitational waves are two of the most commonly used initial datasets for vacuum axisymmetric spacetimes. Their numerical evolution reveals distinct behaviors, particularly in the context of critical gravitational collapse. These differences can be traced back to the linear level, where Brill waves exhibit a multipolar structure, while Teukolsky waves are purely quadrupolar. Despite these structural disparities, we demonstrate an unexpected similarity between the two: both gravitational wave initial data follow a nonextensive scaling law for the distribution of the Arnowitt-Deser-Misner mass as a function of the initial wave amplitude, a remarkable feature of systems with long-range interactions.

We provide the most complete analysis so far of quasinormal modes of rotating black holes in a general higher-derivative extension of Einstein’s theory. By finding the corrections to the Teukolsky equation and expressing them in a simple form, we are able to apply a generalized continued fraction method that allows us to find the quasinormal mode frequencies including overtones. We obtain the leading-order corrections to the Kerr quasinormal mode frequencies of all the $(l,m,n)$ modes with $l=2$, 3, 4, $-l\le m\le l$ and $n=0$, 1, 2 and express them as a function of the black hole spin $\chi$ using polynomial fits. We estimate that our results remain accurate up to spins between $\chi \sim 0.7$ and $\chi \sim 0.95$, depending on the mode. We report that overtones are overall more sensitive to corrections, which is expected from recent literature on this topic. We also discuss the limit of validity of the linear corrections to the quasinormal mode frequencies by estimating the size of nonlinear effects in the higher-derivative couplings. All our results are publicly available in an online repository.

Cosmological neutrino mass bounds are becoming increasingly stringent. The latest limit within $\mathrm{\Lambda }\mathrm{CDM}$ from Planck $2018+\mathrm{ACT}$ $\mathrm{lensing}+\mathrm{DESI}$ is $\sum m_{\nu }<0.072\mathrm{eV}$ at 95% CL, very close to the minimum possible sum of neutrino masses ($\sum m_{\nu }>0.06\mathrm{eV}$), hinting at vanishing or even “negative” cosmological neutrino masses. In this context, it is urgent to carefully evaluate the origin of these cosmological constraints. In this paper, we investigate the robustness of these results in three ways: (i) we check the role of potential anomalies in Planck CMB and DESI BAO data; (ii) we compare the results for frequentist and Bayesian techniques, as very close to physical boundaries subtleties in the derivation and interpretation of constraints can arise; (iii) we investigate how deviations from $\mathrm{\Lambda }\mathrm{CDM}$, potentially alleviating these anomalies, can alter the constraints. From a profile likelihood analysis, we derive constraints in agreement at the $\sim 10\%$ level with Bayesian posteriors. We find that the weak preference for negative neutrino masses is mostly present for Planck 18 data, affected by the well-known “lensing anomaly.” It disappears when the new Planck 2020 HiLLiPoP is used, leading to significantly weaker constraints. Additionally, the pull toward negative masses in DESI data stems from the $z=0.7$ bin, which contains a BAO measurement in $\sim 3\sigma$ tension with Planck expectations. Without this bin, and in combination with HiLLiPoP, the bound relaxes to $\sum m_{\nu }<0.11\mathrm{eV}$ at 95% CL. The recent preference for dynamical dark energy alleviates this tension and further weakens the bound. As we are at the dawn of a neutrino mass discovery from cosmology, it will be very exciting to see if this trend is confirmed by future data.

Correlation functions of light scalar fields in de Sitter spacetime, computed via standard perturbation theory, often exhibit secular growth characterized by time-dependent divergent terms in the form of powers of $\ln a(t)$, where $a(t)$ is the scale factor describing cosmic expansion. It is widely believed that loop corrections further enhance this secular growth. We argue that this is not necessarily the case: Loop corrections can be systematically handled using standard perturbative techniques, such as dimensional regularization, without introducing new $\ln a(t)$ terms. We focus on a canonical massless scalar field $\phi$ with self-interactions described by a potential $\mathcal{V}(\phi )$, and analyze correlation functions represented by diagrams with a single vertex and an arbitrary number of loops. In this framework, infrared divergences can be systematically eliminated with counterterms at each order in perturbation theory, leading to loop-corrected correlation functions that are indistinguishable from their tree-level forms, with no secular growth from loops. Furthermore, adopting a Wilsonian perspective, we explore the role of cutoffs in computing loop corrections within effective field theory and identify the effective potential ${\mathcal{V}}_{\mathrm{eff}}(\phi )$, which guarantees cutoff-independent observables. We conclude that when infrared comoving cutoffs are used to regularize loop integrals, time-dependent Wilsonian coefficients are necessary to maintain cutoff-free correlation functions. Neglecting this time dependence results in secular growth from loops.

Knowing the kind of remnant produced after the merger of a binary neutron star system, e.g., if a black hole forms or not, would not only shed light on the equation of state describing the extremely dense matter inside neutron stars, but also help understand the physical processes involved in the postmerger phase. Moreover, in the event of a gravitational-wave detection, predicting the presence of a neutron star remnant is crucial in order to advise potential electromagnetic follow-up campaigns. In this work, we use gradient boosted decision trees and publicly available data from numerical relativity simulations to construct a classifier that predicts the outcome of binary neutron star mergers, based on the binary’s parameters inferred from gravitational-wave inspiral signals: total mass, mass-weighted tidal deformability, mass ratio, and effective inspiral spin. Employing parameters that can be estimated from the inspiral part of the signal only allows us to predict the remnant independently on the detection of a postmerger gravitational-wave signal. We build three different classifiers to distinguish between various potential scenarios, and we estimate their accuracy and the confidence of their predictions. Finally, we apply the developed classifiers to real events data, finding that GW170817 most likely led to the formation of a hypermassive neutron star, while GW190425 to a prompt collapse to a black hole.

The new tools of gravitational wave and multimessenger astronomy allow for the study of astrophysical phenomenon in new ways and enables light to be shed on some of the longest-enduring mysteries of high-energy astrophysics. Among the latter stands the Galactic Center gamma-ray excess, associated with a source whose nature could be annihilating dark matter or a yet-unresolved population of millisecond pulsars (MSPs). MSPs are most likely asymmetric about their axis of rotation and are thus thought to also source quasimonochromatic gravitational waves, that dark matter processes would not emit. Using statistical methods, we simulate realistic MSP population samples with differing morphology and moment of inertia, that could give rise to the gamma-ray excess, and we compute the corresponding gravitational wave signal amplitude and frequency. We find that the gravitational wave signal frequency likely ranges between $\sim 200$ and 1400 Hz, and that the collective dimensionless strain from the center of the Galaxy has an amplitude between ${10}^{-26}$ and ${10}^{-24}$, thus most likely beyond current and near-term detectors, unless the unresolved MSPs are extraordinarily gamma-ray dim.

The present study investigates the negative energy orbits and energy extraction efficiency using the magnetic Penrose process in various regular black hole geometries surrounded by electromagnetic fields. Utilizing numerical simulations, we analyze the efficiency of this process in Kerr and Simpson-Visser geometries, focusing on extremal black holes. Interestingly, our study demonstrates that the energy extraction efficiency remains indistinguishable between Kerr and Simpson-Visser geometries, regardless of the regularization parameter ($l$); this trend is consistent with previous studies of the Penrose process and superradiance. Additionally, we present results for the rotating Hayward black hole, showing that efficiency is influenced by spin and deviation parameters ($g$), as well as the induced magnetic field and charge of the compact object. Notably, we observe that energy extraction efficiency is highest in the rotating Hayward black hole compared to Kerr and Simpson-Visser geometries, particularly in scenarios where the magnetic field and charge are minimal. Our study highlights the significant role of spin, charge, and magnetic field characteristics in maximizing energy extraction efficiency, particularly in the rotating Hayward black hole context.

Ultralight dark matter, such as kinetically mixed dark-photon dark matter (DPDM) or axion-like-particle dark matter (axion DM), can source an oscillating magnetic-field signal at Earth’s surface. Previous work searched for this signal in a publicly available dataset of global magnetometer measurements maintained by the SuperMAG collaboration. This “low-fidelity” dataset reported measurements with a 1-min time resolution, allowing the search to set leading direct constraints on DPDM and axion DM with Compton frequencies $f_{\mathrm{DM}}\le 1/(1\min )$ (corresponding to masses $m_{\mathrm{DM}}\le 7\times {10}^{-17}\mathrm{eV}$). More recently, a dedicated experiment undertaken by the SNIPE Hunt collaboration has also searched for this same signal at higher frequencies $f_{\mathrm{DM}}\ge 0.5\mathrm{Hz}$ (or $m_{\mathrm{DM}}\ge 2\times {10}^{-15}\mathrm{eV}$). In this work, we search for this signal of ultralight DM in the SuperMAG “high-fidelity” dataset, which features a 1-sec time resolution, allowing us to probe the gap in parameter space between the low-fidelity dataset and the SNIPE Hunt experiment. The high-fidelity dataset exhibits lower geomagnetic noise than the low-fidelity dataset and features more data than the SNIPE Hunt experiment, making it a powerful probe of ultralight DM. Our search finds no robust DPDM or axion DM candidates. We set constraints on DPDM and axion DM parameter space for ${10}^{-3}\mathrm{Hz}\le f_{\mathrm{DM}}\le 0.98\mathrm{Hz}$ (or $4\times {10}^{-18}\mathrm{eV}\le m_{\mathrm{DM}}\le 4\times {10}^{-15}\mathrm{eV}$). Our results are the leading direct constraints on both DPDM and axion DM in this mass range, and our DPDM constraint surpasses the leading astrophysical constraint in a narrow range around $m_{A^{\prime }}\approx 2\times {10}^{-15}\mathrm{eV}$.

Inspired by recent advances in the study of the $K^{(*)}{\overline{K}}^{(*)}$ molecular tetraquarks and the $H$-dibaryon, we focus on the spectroscopic properties of the ${\overline{K}}^{(*)}{\overline{K}}^{(*)}$ systems, which exhibit an exotic flavor quantum number of $ss\overline{q}\overline{q}$. A dynamical analysis is performed using the one-boson-exchange model to describe the effective interactions for these systems, accounting for both $S\text{−}D$ wave mixing and coupled-channel effects. By solving the coupled-channel Schrödinger equation, we identify the $I(J^P)=0(1^{+})$ $\overline{K}{\overline{K}}^{*}$ and $I(J^P)=0(1^{+}){\overline{K}}^{*}{\overline{K}}^{*}$ states as the most likely candidates for double-strangeness molecular tetraquarks. Furthermore, we estimate their strong decay behaviors based on the effective Lagrangian approach, with several channels exhibiting considerable decay widths. Meanwhile, we investigate their magnetic moments and M1 radiative decay widths, shedding light on their inner structures, within the constituent quark model. Finally, we encourage experimentalists to focus on these predicted double-strangeness molecular tetraquark candidates, particularly in $B$ meson decays. Such efforts could pave the way for establishing the molecular tetraquark states in the light-quark sector.

The well-known Cornell quark-antiquark potential in momentum space contains singularities both in its one-gluon-exchange (OGE) and linear confining parts, which prevents a direct use of the convenient Nyström method to solve the corresponding bound-state integral equation for the meson masses. While it has been known for a long time how the Coulomb-type singularity in the OGE potential can be treated with a subtraction technique, only very complicated methods have been developed to deal with the stronger singularity in the linear potential. In this work, we present a simple subtraction method to remove this singularity from the kernel, such that the Nyström method becomes applicable. Derivatives of the wave function, that appear as a result of the subtraction, are represented by means of interpolating functions, for which we found Lagrange polynomials to be very efficient. Test calculations show excellent agreement with exactly known energy eigenvalues. By increasing the number of integration points and the order of the Lagrange interpolation polynomials, extremely high accuracy can be achieved. This method can also be extended to relativistic Bethe-Salpeter type equations with singular kernels.

In this paper, the neutral 2SC phase of color superconductivity is investigated in the presence of a magnetic field and for diquark coupling constants and baryonic densities that are expected to characterize neutron stars. Specifically, the behavior of the charged gluons Meissner masses is investigated in the parameter region of interest, taking into account, in addition, the contribution of a rotated magnetic field. It is found that up to moderately high diquark coupling constants the mentioned Meissner masses become tachyonic independently of the applied magnetic-field amplitude, hence signalizing the chromomagnetic instability of this phase. To remove the instability, the restructuring of the system ground state is proposed, which now will be formed by vortices of the rotated charged gluons. These vortices boost the applied magnetic field, having the most significant increase for relatively low applied magnetic fields. Finally, considering that with the stellar rotational frequency observed for magnetars a field of the order of ${10}^8\mathrm{G}$ can be generated by dynamo effect, we show that by the boosting effect just described the field can be amplified to ${10}^{17}\mathrm{G}$ that is in the range of inner core fields expected for magnetars. Thus, we conclude that the described mechanism could be the one responsible for the large fields characterizing magnetars if the cores of these compact objects are formed by neutral 2SC matter.

We consider the possibility that the cosmic neutrino background might have a nonthermal spectrum, and investigate its effect on cosmological parameters relative to standard $\mathrm{\Lambda }$-cold dark matter ($\mathrm{\Lambda }\mathrm{CDM}$) cosmology. As a specific model, we consider a thermal $y$-distortion, which alters the distribution function of the neutrino background by depleting the population of low-energy neutrinos and enhancing the high-energy tail. We constrain the thermal $y$-parameter of the cosmic neutrino background using cosmic microwave background (CMB) and baryon acoustic oscillation (BAO) measurements, and place a 95%-confidence upper bound of $y\le 0.043$. The $y$-parameter increases the number of effective relativistic degrees of freedom, reducing the sound horizon radius and increasing the best-fit value for the Hubble constant $H_0$. We obtain an upper bound on the Hubble constant of $H_0=71.12\mathrm{km}/\mathrm{s}/\mathrm{Mpc}$ at 95% confidence, substantially reducing the tension between CMB/BAO constraints and direct measurement of the expansion rate from type-Ia supernovae. Including a spectral distortion also allows for a higher value of the spectral index of scalar fluctuations, with a best-fit of $n_{\mathrm{S}}=0.9720\pm 0.0063$, and a 95%-confidence upper bound of $n_{\mathrm{S}}\le 0.9842$.

Current and upcoming imaging galaxy surveys are pushing galaxy samples to higher and higher redshifts. This push will be more pronounced for lens galaxies, for which we only need to measure galaxy positions, not shapes. As a result, we will increasingly often have lens galaxy samples at redshifts higher than those of source galaxies, changing the traditional configuration of galaxy-galaxy lensing (GGL). In this paper, we explore this situation, where lens galaxies are behind source galaxies, which we call inverse galaxy-galaxy lensing (IGGL). We take projected lens and source sample specifications from the Vera Rubin Observatory Large Synoptic Survey Telescope Dark Energy Science Collaboration to compare astrophysical and cosmological constraints between traditional GGL and IGGL. We find IGGL to behave in a different way than GGL, being especially sensitive to lensing magnification, intrinsic alignments and cosmology, but largely independent of galaxy bias (as opposed to traditional GGL). In this way, we find IGGL can provide independent and robust cosmological constraints without combination with galaxy clustering and can also probe IA at high redshift and baryonic effects at small scales without being entwined with the effects of nonlinear galaxy bias. When combined with cosmic shear, we find IGGL to improve $S_8$ constraints by 25% compared to cosmic shear alone, while also providing tighter and more robust constraints on IA and baryons.

We use a combination of Planck cosmic microwave background (CMB) anisotropy data and non-CMB data that include $\mathrm{Pantheon}+\text{type}$ Ia supernovae (SNIa), Hubble parameter [$H(z)$], growth factor ($f{\sigma }_8$) measurements, and a collection of baryon acoustic oscillation (BAO) data, but not recent DESI 2024 BAO measurements, to confirm the DESI 2024 ($\mathrm{DESI}+\mathrm{CMB}+\mathrm{PantheonPlus}$) data compilation support for dynamical dark energy with an evolving equation of state parameter $w(z)=w_0+w_{a}z/(1+z)$. From our joint compilation of CMB and non-CMB data, in a spatially-flat cosmological model, we obtain $w_0=-0.850\pm 0.059$ and $w_a=-0.59_{-0.22}^{+0.26}$ and find that this dynamical dark energy is favored over a cosmological constant by $\sim 2\sigma$. Our data constraints on the flat $w_0{w}_a\mathrm{CDM}$ parametrization are slightly more restrictive than the DESI 2024 constraints, with the DESI 2024 and our values of $w_0$ and $w_a$ differing by $-0.27\sigma$ and $0.44\sigma$, respectively. Our data compilation slightly more strongly favors the flat $w_0{w}_a\mathrm{CDM}$ model over the flat $\mathrm{\Lambda }\mathrm{CDM}$ model than does the DESI 2024 data compilation. We note that our CMB and non-CMB data $w_0{w}_a\mathrm{CDM}$ parametrization cosmological constraints are discrepant at $2.7\sigma$, a little larger than the $1.9\sigma$ discrepancy between DESI DR1 BAO and CMB data flat $\mathrm{\Lambda }\mathrm{CDM}$ model cosmological constraints. We also show that if we remove the $\mathrm{Pantheon}+\mathrm{SNIa}$ contribution from the non-CMB data, for the $w_0{w}_a\mathrm{CDM}$ parametrization we still find tension between P18 and non-CMB data ($2.5\sigma$) and $\mathrm{P}18+\mathrm{lensing}$ and non-CMB data ($2.4\sigma$). Even after the exclusion of $\mathrm{Pantheon}+\mathrm{SNIa}$ data the $\mathrm{\Lambda }\mathrm{CDM}$ model is still disfavored at $\sim 2\sigma$ c.l.

The precession of astrophysical jets produced by active-galactic nuclei is likely related to the dynamics of the accretion disks surrounding the central supermassive black holes (BHs) from which jets are launched. Two main mechanisms that can drive jet precession arise from Lense-Thirring precession and tidal torquing. These can explain direct and indirect observations of precessing jets; however, such explanations often utilize crude approximations of the disk evolution and observing jet precession can be challenging with electromagnetic facilities. Simultaneously, the Laser Interferometer Space Antenna (LISA) is expected to measure gravitational waves from the mergers of massive binary BHs with high accuracy and probe their progenitor evolution. In this paper, we connect the LISA detectability of binary BH mergers to the possible jet precession during their progenitor evolution. We make use of a semianalytic model that self-consistently treats disk-driven BH alignment and binary inspiral and includes the possibility of disk breaking. We find that tidal torquing of the accretion disk provides a wide range of jet precession timescales depending on the binary separation and the spin direction of the BH from which the jet is launched. Efficient disk-driven BH alignment results in shorter timescales of $\sim 1\mathrm{yr}$ which are correlated with higher LISA signal-to-noise ratios. Disk breaking results in the longest possible times of $\sim {10}^7\mathrm{yrs}$, suggesting a deep interplay between the disk critical obliquity (i.e., where the disk breaks) and jet precession. Studies such as ours will help to reveal the cosmic population of precessing jets that are detectable with gravitational waves.

In this study, we investigate the constraints on secret self-interactions of neutrinos by examining the impact of radiative scattering of ultrahigh-energy neutrinos. These neutrinos are produced from the decay of superheavy dark matter and interact with the cosmic neutrino background. We explore how these interactions influence the 21-cm hydrogen signal during the cosmic dark ages and cosmic dawn, periods relatively free from astrophysical uncertainties, providing a clearer signal for studying nonstandard neutrino interactions. By analyzing the global brightness temperature measurements, we constrain the scattering cross section of ultrahigh-energy self-interacting neutrinos, determining the coupling constant $g$ to be within $\sim {10}^{-4}$ to $\sim {10}^{-3}$ for neutrino energies in the PeV to EeV range. Interestingly, these constraints are more competitive than those from existing astrophysical and collider experiments. As future 21-cm experiments focus on measuring brightness temperature across a wide range of redshifts from the cosmic dark ages to reionization, using the epoch of 21-cm to probe neutrino properties could provide crucial insights into dark matter and neutrino physics.

Supermassive black holes in active galactic nuclei (AGNs) launch relativistic jets that shine through the entire electromagnetic spectrum. Blazars are a subclass of AGN where nonthermal radiation from the jet is strongly beamed, as the jet is directed nearly toward the observer. Multifrequency polarimetry is emerging as a powerful probe of blazar jets, especially with the advent of the Imaging X-ray Polarimetry Explorer (IXPE) space observatory. IXPE mostly targeted high synchrotron peaked (HSP) blazars, where both optical and x-ray emissions can be attributed to synchrotron radiation from a population of nonthermal electrons. Observations of HSP blazars show that the polarization degree is strongly chromatic (${\mathrm{\Pi }}_{\mathrm{X}}/{\mathrm{\Pi }}_{\mathrm{O}}\sim 2–7$), whereas the electric vector position angle (EVPA) is nearly independent of the observed frequency (${\mathrm{\Psi }}_{\mathrm{X}}\simeq {\mathrm{\Psi }}_{\mathrm{O}}$). The strong chromaticity of the polarization degree was interpreted as evidence that nonthermal electrons are accelerated by shocks. We present an alternative scenario that naturally explains IXPE observations. We study the polarization of synchrotron radiation from stationary axisymmetric jets viewed nearly on axis. We show that the polarization degree increases significantly at high photon frequencies, as the distribution of the emitting electrons becomes softer, whereas the EVPA is nearly constant. The chromaticity of the polarization degree is much stronger in axisymmetric jets than in the case of a uniform magnetic field. Our results show that the topology of the electromagnetic fields is key to interpreting multifrequency polarimetric observations of blazar jets. On the other hand, these observations may be less sensitive than previously thought to the specific particle acceleration process (e.g., shocks or magnetic reconnection).

We consider the quantum dynamics of Bose-Einstein condensates at absolute zero, and demonstrate that an analog gravity model going beyond the standard linearized analog gravity paradigm à la Unruh must take into account the backreaction of quasiparticle excitations onto the condensate background. This requires that one expands to second order in perturbation amplitude and thus takes the intrinsic nonlinearity of the theory into account. It is shown that, as a result, significant modifications of the standard paradigm occur. In particular, to obtain a fully Lorentz-covariant equation in curved spacetime for second-order perturbations, we demonstrate that it is necessary to introduce, to leading order in powers of the formal mean-field expansion parameter $N^{-1/2}$ (where $N$ is total particle number), a quantum-fluctuation-renormalized spacetime metric which substantially differs from the Unruh acoustic spacetime metric and, to subleading order $1/N$, two emergent vector fields and a mass term. Both the renormalized metric as well as the vector fields and the mass then keep track of the backreaction of the quasiparticles onto the condensate up to the order in powers of $N^{-1/2}$ considered. Finally, we apply our formalism to an analog-cosmological Friedmann-Lemaître-Robertson-Walker metric and establish its renormalized form due to the quantum many-body backreaction exerted by the excitation cloud.