We show that for a topological star the renormalized angular momentum parameter, $\nu$, appearing in the Mano-Suzuki-Takasugi-type or in the quantum-Seiberg-Witten-type approaches of the perturbation equations, (1) has a direct link with the geodesic radial action computed along the null orbits of the background and (2) admits an exact resummation in terms of hypergeometric functions, generalizing previous results valid in the Schwarzschild case; see [M. M. Ivanov, Y. Z. Li, J. Parra-Martinez, and Z. Zhou, Resummation of universal tails in gravitational waveforms, arXiv:2504.07862.].

This article investigates the averaging of a scalar degree of freedom that couples universally to matter. It quantifies the approximation of smoothing the matter distribution before solving the Klein-Gordon equation. In the case of Yukawa theories, which enjoy a linear Klein-Gordon equation, the averaging commutes with the field equation as one might expect. While all small-scale distributions of matter lead to field distributions with the same mean, the latter can have different energy densities and pressures when the Compton wavelength of the field is smaller than the smoothing scale. In the nonlinear case, such as chameleon theories, this study quantifies the error made by averaging the matter distribution before solving the Klein-Gordon equation. While field fluctuations can become arbitrarily large when the matter source is screened, the commutativity property of linear theories is recovered in the unscreened regime. Implications for cosmology—and in particular the equation of state in extended quintessence models—and for laboratory experiments in low density medium are discussed. This analysis, although based on a simplifying description, sheds light on the effects of the small-scale distribution of matter as well as on the care required to define their equation of state and their cosmological signature.

Black hole quasinormal modes (QNMs) can exhibit resonant excitations associated with avoided crossings in their complex frequency spectrum. Such resonance phenomena can serve as novel signatures for probing new physics, where additional degrees of freedom are commonly introduced. Motivated by this possibility, we investigate QNMs in systems where multiple degrees of freedom are coupled with each other and introduce a definition of excitation factors suitable for such systems. To demonstrate our formulation, we apply it to a black hole in the Einstein-Maxwell-axion theory, where we find that avoided crossings can appear even between longest-lived modes originating from the fundamental modes of different degrees of freedom, in contrast to the Kerr case in general relativity. We show that the excitation factors are indeed amplified as a manifestation of resonance at parameter values corresponding to the avoided crossings.

As next-generation telescopes and observational surveys continue to expand the boundaries of our understanding, tensions and discrepancies between observational datasets are becoming increasingly prominent. In this work, we focus on one such discrepancy: the differences between 2D and 3D baryon acoustic oscillation (BAO) measurements. Without extending beyond the standard $\mathrm{\Lambda }\mathrm{CDM}$ framework, we systematically study and highlight this discrepancy in different parameter spaces. This work examines the constraints on fundamental cosmological parameters ($H_0$, $r_d$, ${\mathrm{\Omega }}_m$) derived from BAO and Type Ia supernovae (SNe Ia) data. By analyzing BAO observational datasets from two distinct methodologies (2D and 3D) alongside the Pantheon Plus SNe Ia sample, we identify a significant systematic difference: 2D BAO measurements consistently yield higher values of $h{r}_d$ compared to both 3D BAO and Dark Energy Spectroscopic Instrument analyses. While 2D BAO measurements appear to bridge the Hubble tension by simultaneously accommodating both a higher $H_0$ value (aligning with SH0ES) and a larger sound horizon $r_d$ (matching Planck), this apparent reconciliation comes at the cost of introducing tension with the well-constrained Planck measurement of ${\mathrm{\Omega }}_{m0}{h}^2$. This behavior arises because of systematically higher values of the product $H_0{r}_d$ observed in 2D BAO analysis compared to 3D analyses. Therefore, given these systematic differences, we advocate for careful consideration when using 2D BAO measurements to address the Hubble tension, suggesting that understanding the origin of this 2D-3D discrepancy should be a priority for future investigations.

We use the framework of microlensing to show that observations of binary systems, such as those made by Gaia, combined with follow-up weak lensing measurements, can provide a means to probe halos of exotic matter, possibly clumped around compact objects such as black holes. This could potentially cover a broad range of physical scenarios, from dark matter minihalos to black holes with bosonic configurations around them, known as hair. In a dark halo-regular star binary system, assuming that light can freely propagate through the halo of the exotic matter, the companion star will produce characteristic, sizable lensing signatures due to the lens’s potential deviating from a point mass gravitational potential. The signature of the multiple images, the magnification and the light-curve could be the smoking gun of such a dark halo structure. We discuss how the precise observations of the Gaia survey offer an opportunity to search for new, yet undiscovered fundamental fields interacting gravitationally with baryons.

Source inference for deterministic gravitational waves is a computationally demanding task in LISA. In a novel approach, we investigate the capability of Gaussian processes to learn the posterior surface in order to reconstruct individual signal posteriors. We use GPry, which automates this reconstruction through active learning, using a very small number of likelihood evaluations, without the need for pretraining. We benchmark GPry against the cutting-edge nested sampler nessai, by injecting individually three signals on LISA noisy data simulated with Balrog: a white dwarf binary (DWD), a stellar-mass black hole binary (stBHB), and a supermassive black hole binary (SMBHB). We find that GPry needs $\mathcal{O}({10}^{-2})$ fewer likelihood evaluations to achieve an inference accuracy comparable to nessai, with Jensen-Shannon divergence $D_{\mathrm{JS}}\lesssim 0.01$ for the DWD, and $D_{\mathrm{JS}}\lesssim 0.05$ for the SMBHB. Lower accuracy is found for the less Gaussian posterior of the stBHB: $D_{\mathrm{JS}}\lesssim 0.2$. Despite the overhead costs of GPry, we obtain a speedup of $\mathcal{O}({10}^2)$ for the slowest cases of stBHB and SMBHB. In conclusion, active-learning Gaussian process frameworks show great potential for rapid LISA parameter inference, especially for costly likelihoods, enabling suppression of computational costs without the trade-off of approximations in the calculations.

Accreting supermassive black hole binaries are powerful multimessenger sources emitting both gravitational and electromagnetic (EM) radiation. Understanding the accretion dynamics of these systems and predicting their distinctive EM signals is crucial to informing and guiding upcoming efforts aimed at detecting gravitational waves produced by these binaries. To this end, accurate numerical modeling is required to describe both the spacetime and the magnetized gas around the black holes. In this paper, we present two key advances in this field of research. First, we have developed a novel 3D general relativistic magnetohydrodynamics (GRMHD) framework that combines multiple numerical codes to simulate the inspiral and merger of supermassive black hole binaries starting from realistic initial data and running all the way through merger. Throughout the evolution, we adopt a simple but functional prescription to account for gas cooling through photon emission. Next, we have applied our new computational method to follow the time evolution of a circular, equal-mass, nonspinning black hole binary for $\sim 200$ orbits, starting from a separation of $20r_g$ and reaching the postmerger evolutionary stage of the system. We have shown how mass continues to flow toward the binary even after the binary “decouples” from its surrounding disk, but the accretion rate onto the black holes diminishes. We have identified how the minidisks orbiting each black hole are slowly drained and eventually dissolve as the binary compresses. We confirm previous findings that the system’s luminosity decreases by a factor of a few during inspiral; however, we observe an abrupt increase by $\sim 50\%$ in this quantity at the time of merger, likely accompanied by an equally abrupt change in spectrum. Finally, we have demonstrated that during the inspiral, fluid ram pressure regulates the fraction of the magnetic flux transported to the binary that attaches to the black holes’ horizons.

Weakly interacting massive particles (WIMPs) constitute a paradigm in the search for particle dark matter. In contrast to supersymmetry (SUSY), we explore the possibility that WIMP dark matter acts as mediator of neutrino mass generation. We examine in detail the phenomenology of fermionic dark matter in the revamped (or singlet-triplet) scotogenic model and study its collider implications. Unlike SUSY WIMP dark matter, collider searches for the lightest scotogenic particle at LHC/LHC-HL are strongly complementary to charged lepton flavor violation probes and dark matter studies.

Intersecting D6-brane models without discrete torsion typically suffer from unstabilized open-string moduli arising from D-brane positions and Wilson lines. These moduli generate additional massless adjoint fields, obstructing the realization of negative $\beta$ functions necessary for asymptotic freedom unless they are decoupled around the string scale. A viable solution involves utilizing rigid cycles, which eliminate these unwanted adjoint fields. In this work, we for the first time present a class of consistent three-family supersymmetric Pati-Salam models from rigid intersecting D6-branes on the factorizable ${\mathbb{T}}^6/({\mathbb{Z}}_2\times {\mathbb{Z}}_2^{\prime })$ orientifold with discrete torsion. These models satisfy all the known consistency conditions, including $\mathcal{N}=1$ supersymmetry, K-theory constraints, tadpole cancellation, and recent swampland bounds on the maximal gauge group rank. We provide detailed particle spectra, analyze their phenomenological implications, and discuss the decoupling of exotic states through strong dynamics in the hidden sector.

We show that the recently proposed tetraquark hypothesis for the nature of the ${\chi }_{c1}(3872)$ results in a formalism for inclusive production rates that has no unknown parameters. We employ this formalism to compute hadroproduction rates of ${\chi }_{c1}(3872)$ at the Large Hadron Collider, which agree with measured prompt and nonprompt cross sections. Thus, we find that the tetraquark hypothesis for ${\chi }_{c1}(3872)$ is well supported by hadroproduction data.

We provide a detailed analysis of event-shape observables, namely the energy correlation function and jet angularity, for heavy-flavor jets produced in electron-positron collisions, focusing on quantum chromodynamics (QCD) interactions. Using modern jet substructure techniques, we investigate the dead-cone effect, where QCD radiation is suppressed around a heavy quark within an angle proportional to its mass. Our analysis achieves next-to-leading logarithmic accuracy, combined with partial fixed-order contributions, to improve the description of the transition near the dead-cone threshold. To ensure a comprehensive perspective, we compare our analytical results with predictions from the pythia, herwig, and sherpa Monte Carlo simulations at past and future lepton colliders.

We investigate a fifth force mediated by a light vector boson that couples to lepton spins, characterized by axial-vector couplings to leptons and vector couplings to nucleons. This interaction generates a potential proportional to the inner product of the lepton spin vector and the nucleon-lepton relative velocity vector, a feature extensively explored with precision spin sensors. Employing weak symmetry, we show that left-handed charged lepton couplings naturally extend to left-handed neutrinos, enabling this fifth force to influence neutrino oscillations. For electron-nucleon couplings, we find that solar and reactor neutrino experiments provide comparable constraints to those from spin sensors and surpass them in the short-range fifth force region. For muon-nucleon couplings, neutrino oscillation experiments exclude the fifth force as a viable explanation for the muon $g-2$ anomaly in the context of a vector mediator, tightening the bounds by 2 orders of magnitude in coupling strength by solar and atmospheric neutrino data. Our results highlight the critical role of neutrino oscillations in probing fifth forces acting across all three generations of lepton spins.

We propose a quantum mechanical theory of quantum spaces described by large $N$ noncommutative geometry as a model for quantum gravity. The model admits a fuzzy sphere as a static solution. Over the fuzzy geometry, the quantum mechanics of the fermions is given by a sum of oscillators with equal frequency. The energy state where exactly half of the Fermi sea is filled contains the maximal amount of degeneracy. This state of the fuzzy sphere obeys the mass-radius relation of a Schwarzschild black hole if the fuzzy sphere is identified with the black hole horizon. Moreover, the set of states in the Fermi sea gives precisely the Bekenstein-Hawking entropy. We thus propose that quantum black holes are described by fuzzy spheres with a half-filled Fermi sea in our model. We also consider a system of two fuzzy spheres by embedding them as blocks in the matrix quantum mechanics. When the distance $r$ between the two fuzzy spheres is small, the total energy of the system can be computed using perturbation theory. We show that, in the leading order of large $N$ limit, the interaction energy depends on $-G{M}_1{M}_2$ exactly in the manner as in Newton gravity. To reproduce the correct $r$ dependence in the long range, we expect the inclusion of large $N$ corrections and quantum effects will be needed.

We investigate the ${\varphi }^{2n}$ deformations of the $\mathrm{O}(N)$-symmetric (generalized) free theories with a flat boundary, where $n\ge 2$ is an integer. The generalized free theories refer to the ${\square }^k$ free scalar theories with a higher derivative kinetic term, which is related to the multicritical generalizations of the Lifshitz type. We assume that the (generalized) free theories and the deformed theories have boundary conformal symmetry and $\mathrm{O}(N)$ global symmetry. The leading anomalous dimensions of some boundary operators are derived from the bulk multiplet recombination and analyticity constraints. We find that the ${\epsilon }^{1/2}$ expansion in the ${\varphi }^6$-tricritical version of the special transition extends to other multicritical cases with larger odd integer $n$, and most of the higher derivative cases involve a noninteger power expansion in $\epsilon$. Using the analytic bootstrap, we further verify that the multiplet-recombination results are consistent with boundary crossing symmetry.

Scalar-tensor theories with a scalar field coupled to the Gauss-Bonnet invariant can evade no-hair theorems and allow for nontrivial scalar profiles around black holes. This coupling is characterized by a length scale $\lambda$, which, in an effective field theory perspective, sets the threshold below which deviations from general relativity become significant. LIGO/VIRGO constraints indicate $\lambda$ is small, implying supermassive black holes should not scalarize. However, recent work suggests that scalarization can occur within a narrow window of masses, allowing supermassive black holes to scalarize, while leaving LIGO/VIRGO sources unaffected. We explore the impact of this scenario on the stochastic gravitational wave background recently observed by pulsar timing arrays. We find that scalarization can alter the characteristic strain produced by circularly inspiralling supermassive black hole binaries and that current data show a marginal preference for a nonzero $\lambda$. However, similar signatures could arise from astrophysical effects such as orbital eccentricity or environmental interactions, emphasizing the need for improved modeling and longer observations to discriminate among the different scenarios.

There exist two branches of static and spherically symmetric black hole solutions in Einstein-Weyl theory: one is the Schwarzschild black hole, and the other is a numerically constructed black hole that bifurcates from the Schwarzschild solution. Similarly, there are two branches of charged black holes in Einstein-Weyl-Maxwell theory. We have uncovered the relationships between the charged black holes and the neutral ones. The two charged black holes branch out from the bifurcation point of the neutral ones once the charge is added. We found that one of the charged black holes is entirely different from the Reissner-Nordström (RN) black hole, while the other is similar to the RN black hole. In particular, the RN-like black hole approaches the RN black hole as the charge increases. We calculated the charge-to-mass ratio of the RN-like charged black hole in the near-extremal limit, and the value is less than that of the extremal RN black hole. Since we consider the higher-derivative Weyl square term as part of the classical gravity theory, rather than as a quantum effect, our result sets a lower bound on the charge-to-mass ratio in the context of the weak gravity conjecture.

The matter power spectrum, $P(k)$, is one of the fundamental quantities in the study of large-scale structure in cosmology. Here, we study its small-scale asymptotic limit, and show that for cold dark matter in $d$ spatial dimensions, $P(k)$ has a universal $k^{-d}$ asymptotic scaling with the wave number $k$, for $k\gg k_{\mathrm{nl}}$, where $k_{\mathrm{nl}}^{-1}$ denotes the length scale at which nonlinearities in gravitational interactions become important. We propose a theoretical explanation for this scaling, based on a nonperturbative analysis of the system’s phase-space structure. Gravitational collapse is shown to drive a turbulent phase-space flow of the quadratic Casimir invariant, where the linear and nonlinear time scales are balanced, and this balance dictates the $k$ dependence of the power spectrum. A parallel is drawn to Batchelor turbulence in hydrodynamics, where large scales mix smaller ones via tidal interactions. The $k^{-d}$ scaling is also derived by expressing $P(k)$ as a phase-space integral in the framework of kinetic field theory, which is analyzed by the saddle-point method; the dominant critical points of this integral are precisely those where the time scales are balanced. The coldness of the dark-matter distribution function—its nonvanishing only on a $d$-dimensional submanifold of phase space—underpins both approaches. The theory is accompanied by 1D Vlasov-Poisson simulations, which confirm it.

Dark matter halos with self-interacting dark matter (SIDM) experience a unique evolutionary phenomenon, in that their central regions eventually collapse to high density through the runaway gravothermal process after initially forming a large and low-density core. When coupled with orbital evolution, this is expected to naturally produce a large diversity in dark-matter halos’ inner mass distribution, potentially explaining the diversity problem of dwarf galaxies. However, it remains unknown how the diversity in SIDM dark matter halos propagates to the more easily observed luminous matter at the center of the halo, especially the stellar component. In this work, we use idealized N-body simulations with two species of particles (dark matter and stars) to study the response of the stellar properties of field and satellite dwarf galaxies to SIDM evolution and orbital effects on their halos. Galaxies’ stellar components, including galaxy size, mass-to-light ratio, and stellar velocity dispersion, display a much larger scatter in SIDM than the standard cold dark matter model. Importantly, we find signs of universality in the evolution pathways, or “tidal tracks”, of SIDM dwarf satellites, which are physically interpretable and potentially parametrizable. This type of tidal-track model can be layered onto larger-scale, cosmological simulations to reconstruct the evolution of populations of SIDM dwarfs in cases where high-resolution simulations of galaxies are otherwise prohibitively expensive.

Our studies are novel in that the stochastic gravitational wave (GW) signals of torsion during the reheating stage are investigated for the first time. We construct the phenomenological interaction vertex describing the coupling between a single inflaton and four fermions based on the effective theory of torsion within the first-order formalism for gravity and fermions. Subsequently, we compute the resulting GW spectrum arising from torsion-induced five-body decay, assuming a perturbative decay process in which the inflaton decays into two pairs of fermions along with the emission of a single graviton. Our results uncover that the dimensionless amplitude of the GW background from torsion-induced five-body decay is of the same order of magnitude as that generated by the standard three-body perturbative inflaton decay via Yukawa interactions. These findings suggest that future high-frequency GW detectors, such as resonant cavities, may have the potential to detect such signals in the GHz range, offering valuable insights into the twisted geometric structure of the early Universe’s spacetime.

A crucial ingredient affecting fast neutrino flavor conversion in core-collapse supernovae (SNe) is the shape of the angular distribution of the electron-neutrino lepton number (ELN). The presence of an ELN crossing signals favorable conditions for flavor conversion. However, the dependence of ELN crossings on the SN properties is only partially understood. We investigate a suite of 12 spherically symmetric neutrino-hydrodynamics simulations of the core collapse of a SN with a mass of $18.6M_{\odot }$; each model employs different microphysics (i.e., three different nuclear equations of state, with and without muon creation) and includes or not a mixing-length treatment for proto-neutron star convection. We solve the Boltzmann equations to compute the neutrino angular distributions relying on static fluid properties extracted from each of the SN simulations in our suite for six selected postbounce times. We explore the dependence of the ELN distributions on the SN microphysics and proto-neutron star convection. We find that the latter shifts the proto-neutron star radius outward, favoring the appearance of ELN crossings at larger radii. On the other hand, muon creation causes proto-neutron star contraction, facilitating the occurrence of ELN crossings at smaller radii. These effects mildly depend on the nuclear equation of state. Our findings highlight the subtle impact of the SN microphysics, proto-neutron star convection, and neutrino transport on the ELN angular distributions.