We investigate the excitation of quasinormal modes (QNMs) in gravitational lensing by a Schwarzschild black hole using a scalar field model. By employing a time-domain mode-sum method, we analyze the complex interplay between an incident burst signal and the black hole spacetime. We find that the incident waves can nonresonantly excite a substantial number of high-$l$ modes, with amplitudes for modes as high as $l=20$ remaining significant compared to the fundamental $l=0$ mode. We confirm through QNM template fitting that the late-time behaviors of these excited modes are indeed QNMs. After passing through the black hole, we find that the lensed waves form a highly directional and coherent Gaussian beam whose cross-sectional intensity profile is well-described by a Gaussian profile. Unlike spherical waves, this beam’s amplitude does not decrease with distance from the black hole but remains nearly constant in the near-field region. Moreover, due to the superposition of numerous QNMs, oscillations largely cancel each other out. The lensed temporal waves do not exhibit typical oscillatory patterns.

We propose a new mechanism of primordial black hole formation via an interrupted phase transition during the early matter-dominated stage of reheating after inflation. In reheating, induced by the decay of a pressureless fluid dominating the Universe at the end of inflation, dubbed as reheaton, the temperature of the radiation bath typically increases, reaching a maximum temperature $T_{\max }$, and then decreases. We consider a first-order phase transition induced by the increase of the temperature that is aborted, as $T_{\max }$ is higher than the critical temperature but not sufficiently high for the bubble nucleation rate to overcome the expansion of the Universe. Although bubbles never fully occupy the space, some may be nucleated and expand until the temperature once again decreases to the critical temperature. We argue that these bubbles shrink and disappear as the temperature drops further, leaving behind macroscopic spherical regions with positive density perturbations. These perturbed regions accrete the surrounding matter (reheaton) and eventually collapse into primordial black holes whose mass continues to grow until the onset of radiation domination. We estimate the abundance of these primordial black holes in terms of the bubble nucleation rate at $T_{\max }$, and we demonstrate that the abundance can be significantly large from a phenomenological perspective.

We investigate the gravitational wave background predicted by a two-scalar-field cosmological model that aims to unify primordial inflation with the dark sector, namely, late-time dark energy and dark matter, in a single and self-consistent theoretical framework. The model is constructed from an action inspired by several extensions of general relativity and string-inspired scenarios and features a nonminimal interaction between the two scalar fields, while both remain minimally coupled to gravity. In this context, we derive the gravitational wave energy spectrum over wavelengths ranging from today’s Hubble horizon to those at the end of inflation. We employ the continuous Bogoliubov coefficient formalism, originally introduced to describe particle creation in an expanding Universe, in analogy to the well-established mechanism of gravitational particle production and, in particular, generalized to gravitons. Using this method, which enables an accurate description of graviton creation across all cosmological epochs, we find that inflation provides the dominant gravitational wave contribution, while subdominant features arise at the inflation-radiation, radiation-matter, and matter-dark energy transitions, i.e., epochs naturally encoded inside our scalar field picture. The resulting energy density spectrum is thus compared with the sensitivity curves of the planned next-generation ground- and space-based gravitational wave observatories. The comparison identifies frequency bands where the predicted signal could be probed, providing those windows associated with potentially detectable signals, bounded by our analyses. Consequences of our recipe are thus compared with numerical outcomes and the corresponding physical properties are discussed in detail.

Perturbations in the cosmic neutrino background produce a characteristic phase shift in the acoustic oscillations imprinted in the anisotropies of the cosmic microwave background (CMB), providing a unique observational probe of neutrino physics. In this work, we explore how this phase shift signature is altered in the presence of neutrino interactions with temperature-dependent scattering rates, motivated by physical constructions for neutrino self-interactions and neutrino–dark matter couplings. A key finding is that the phase shift in these realistic models—characterized by gradual rather than instantaneous decoupling—maintains the same functional form as the free-streaming template, with only the asymptotic amplitude decreasing for stronger interactions that delay decoupling. This simple parametrization enables us to directly constrain neutrino interactions through phase shift measurements in the temperature and polarization power spectra from CMB observations. Analyzing the latest data from Planck, the Atacama Cosmology Telescope, and the South Pole Telescope, we derive strong constraints on the neutrino decoupling redshift. Our global analysis indicates that neutrinos have been freely streaming since deep within the radiation-dominated epoch. We also explore flavor-dependent scenarios in which only one neutrino species interacts. Overall, our work establishes a signature-driven framework that exploits the clean phase shift signal in the acoustic oscillations of the CMB as a precise and robust probe of nonstandard neutrino interactions in the early Universe.

The intergalactic medium (IGM) underwent intense heating that resulted in pressure disequilibrium in the wake of ionization fronts during cosmic reionization. The dynamical relaxation to restore pressure balance may have driven small-scale turbulence and, hence, the amplification of intergalactic magnetic fields. We investigate this possibility for the first time using a suite of $\approx 100\mathrm{pc}$ resolution radiation-hydrodynamics simulations of IGM gas dynamics. We show that as the spatial resolution improves beyond that achieved with most prior studies, much of the IGM becomes turbulent unless it was preheated to $\gg 100\mathrm{K}$ before reionization. In our most turbulent simulations, we find that the gas energy spectrum follows the expected $k^{-5/3}$ Kolmogorov scaling to the simulation’s resolution, and the eddy turnover time of the turbulence is $<1\mathrm{Gyr}$ at $k\approx 1{\mathrm{kpc}}^{-1}$. Turbulence will grow magnetic fields, and we show that the fields grown by reionization-driven turbulence could explain lower limits on the strength of volume-filling B fields from observations of TeV blazars. As reionization sweeps over the cosmos, this mechanism could create turbulence throughout the cosmic volume with a character that only depends on the amount of IGM preheating.

With periods much longer than the duration of current pulsar timing surveys, gravitational waves in the picohertz (pHz) regime are not detectable in the typical analysis framework for pulsar timing data. However, signatures of these low-frequency signals persist in the slow variation of pulsar timing parameters. In this work, we present the results of the first Bayesian search for continuous pHz gravitational waves using the drift of two sensitive pulsar timing parameters—the time derivative of pulsar binary orbital period ${\dot{P}}_b$ and the second-order time derivative of pulsar spin period $\ddot{P}$. We apply our new technique to a dataset with more than double the number of pulsars as previous searches in this frequency band, achieving an order-of-magnitude sensitivity improvement. No continuous wave signal is detected in current data; however, we show that future observations by the Square Kilometre Array will provide significantly improved sensitivity and the opportunity to observe continuous pHz signals, including the early stages of supermassive black hole mergers. We explore the detection prospects for this signal by extending existing population models into the pHz regime, finding that future observations will probe phenomenologically interesting parameter space. Our new Bayesian technique and leading sensitivity in this frequency domain pave the way for new discoveries in both black hole astrophysics and the search for new physics in the early Universe.

In this paper, we propose an experiment, LANSCE-mQ, aiming to detect fractionally charged and millicharged particles (mCPs) using an 800 MeV proton beam fixed target at the Los Alamos Neutron Science Center (LANSCE) facility at Los Alamos National Laboratory. This search can shed new light on numerous fundamental questions, including charge quantization, the predictions of string theories and grand unification theories, the gauge symmetry of the Standard Model, dark sector models, and the tests of cosmic reheating. We propose to install two-layer scintillation detectors made of plastic (such as EJ-200) or ${\mathrm{CeBr}}_3$ to search for mCPs. Dedicated geant4 detector simulations and in situ measurements have been conducted to obtain a preliminary determination of the background rate. The dominant backgrounds are beam-induced neutrons and coincident dark current signals from the photomultiplier tubes, while beam-induced high-energy photons ($\gamma$’s) and cosmic muons are subdominant. We determined that LANSCE-mQ, the dedicated mCP experiment, has the leading mCP sensitivity for mass between $\sim 1$ and 300 MeV.

Within the method of parity-projected QCD sum rules, we study the mass spectra of light hybrid baryons with $I(J^P)=1/2(1/2^{\pm }),3/2(1/2^{\pm }),1/2(3/2^{\pm }),3/2(3/2^{\pm })$ by constructing the local $qqqg$ interpolating currents. We calculate the correlation functions up to dimension eight condensates at the leading order of ${\alpha }_s$. The stable QCD Lapalce sum rules can be established for the positive-parity $N_{1/2^{+}},{\mathrm{\Delta }}_{3/2^{+}},{\mathrm{\Delta }}_{1/2^{+}}$ and negative-parity $N_{1/2^{-}},N_{3/2^{-}},{\mathrm{\Delta }}_{1/2^{-}}$ channels to extract their mass spectra. The lowest-lying hybrid baryons are predicted to be the positive-parity $N_{1/2^{+}}$ state around 2.01 GeV. These hybrid baryons mainly decay into conventional baryon plus meson final states. We propose to search for the light hybrid baryons through the $\mathrm{\Upsilon }/\psi (3686)$ decays via the three-gluon emission mechanism in BESIII and BelleII experiments. Hopefully, our studies of the light hybrid baryons will be useful for understanding the excited baryon spectrum and the behavior of gluonic degrees of freedom in QCD.

The dissipative properties of relativistic strongly interacting nuclear matter significantly influence the damping of stellar oscillations and density fluctuations during compact star mergers. In this work, we derive the evolution equation for the bulk viscous pressure in unpaired quark matter under small deviations from equilibrium. Our analysis reveals that it behaves like a two-component Burgers fluid. We identify four key transport coefficients—two relaxation times and two bulk viscosity coefficients—expressed in terms of equilibrium parameters and electroweak nonleptonic and semileptonic decay rates. The transport coefficients are evaluated for two distinct equations of state: one based on perturbative quantum chromodynamics and the other on a modified MIT bag model, valid in different density regimes. We also determine the temperature and density region where nonleptonic electroweak processes dominate the dissipation. Our formulation establishes a new way of describing bulk viscous effects in quark matter, applicable for numerical simulations of compact star mergers.

It is well known that in the study of mixing between nonlocal gluon and quark bilinear operators there exists an ambiguity when relating coordinate space and momentum space results. In this work, we show that this ambiguity is due to the lack of a proper regularization prescription of the singularity that arises when the separation between the gluon/quark fields approaches zero. We then demonstrate that dimensional regularization resolves this issue and yields consistent results in both coordinate and momentum space. This prescription is also compatible with lattice extractions of parton distributions from nonlocal operators.

Most existing and proposed high-energy neutrino experiments have excellent muon charge identification capabilities, enabling the distinction of ${\nu }_{\mu }$ and ${\overline{\nu }}_{\mu }$ charged current interactions. In contrast, distinguishing electrons and positrons from ${\nu }_e$ and ${\overline{\nu }}_e$ interactions is typically impossible, as they quickly interact within the characteristically dense detector material and fail to reach the spectrometer. In this letter, we propose a compact and cost-effective plastic target, placed right before the spectrometer, to maximize the rate of electrons and positrons that reach the spectrometer before interacting. We demonstrate that, when installed at the FASER experiment, the Forward Physics Facility, or SHiP, this setup could enable the first separate measurement of ${\nu }_e$ and ${\overline{\nu }}_e$ cross sections at high energy. Additionally, this setup opens new opportunities to study forward particle production at collider neutrino experiments, such as constraining forward $\mathrm{\Lambda }$ hyperon production, and, by reducing flux uncertainties, significantly improve limits on nonstandard neutrino interactions in neutral currents.

We consider the Anti-de Sitter (AdS) Veneziano amplitude describing the scattering of four gluons in type IIB string theory on ${\mathrm{AdS}}_5\times S^3$. We propose a set of powerful monodromy relations between different color-ordered amplitudes. These relations arise as a consequence of the emergent worldsheet description of open string scattering on AdS. In flat space, they reduce to the usual monodromy relations for the Veneziano amplitude, and they hold order by order in the small curvature expansion. The relations hold for the results available in the literature, including the scattering of arbitrary Kaluza-Klein modes.

We classify and construct supersymmetric solutions of $D=3$, $N=2$ gauged supergravity extended with a Fayet-Iliopoulos term, and null and timelike warped anti–de Sitter (AdS) spacetimes are among them. From the first one, it is possible to obtain a well-defined black hole by periodic identification. We also find charged string solutions that interpolate between two supersymmetric AdS or Minkowski extrema of the scalar potential, one of which corresponds to a horizon with a singularity behind it, and the other which determines the asymptotic geometry.

We propose, in ($3+1$)-dimensional spacetimes, a novel astrophysical source of squeezed graviton states, due to superradiant axionic clouds surrounding rotating (Kerr-type) black holes (BHs). The microscopic origin of these axions is diverse, ranging from the Kalb-Ramond (model-independent) axions and compactification axions in string theory, to contorted geometries exemplified by a totally antisymmetric component of torsion in Einstein-Cartan theory. The axion fields couple to chiral gauge and gravitational Chern-Simons (CS) anomaly terms in the effective gravitational actions. In the presence of a Kerr BH background, such axions lead, upon acquiring a mass, to superradiance and the production of pairs of entangled gravitons in a squeezed state. The specific microscopic origin of the axions is not important, provided they are massive. We explain, by means of simplified but representative examples, how this multimode squeezed-graviton state can be studied via an Autonne-Takagi decomposition, used in quantum optics. In the effective action it is shown that squeezing effects associated with conventional general relativity (GR) dominate, by many orders of magnitude, the corresponding effects due to the CS gravitational anomaly terms. For a sufficiently long lifetime of the axionic cloud of the BH, we find that significant squeezing (quantified through the average number of gravitons with respect to the appropriate vacuum) can be produced from the GR effects. Our approach also allows for an imposition of phenomenological upper bounds on axion-cloud lifetimes, due to the nonobservation of squeezed graviton states in current interferometers. In addition, it is demonstrated explicitly that the structure of the entangled states (when the latter are expressed in a left-right polarization basis) depends highly on whether GR or the anomalous CS effects produce the entanglement.

In this article, we study grand-canonical symmetric orbifolds of conformal field theories. We propose to define them as the direct sum of symmetric orbifolds of all degrees. The natural basis of operators is one that mixes all sectors. We describe this basis in terms of partial permutations and explain how to define and calculate the operator product expansion in that framework. Our construction provides a conformal field theory interpretation of the central charge operator $\mathcal{I}$ in ${\mathrm{AdS}}_3$ string theory.

Topological quantum field theory (TQFT) is a powerful tool to describe homologies, which normally involve complexes and a variety of maps/morphisms, what makes a functional integration approach with a sum over a single kind of map seemingly problematic. In TQFT this problem is overcome by exploiting the rich set of zero modes of BRST operators, which appear sufficient to describe complexes. We explain what this approach looks like for the important class of Khovanov-Rozansky (KR) cohomologies, which categorify the observables (Wilson lines or knot polynomials) in 3D Chern-Simons theory. We develop a construction of odd differential operators, associated with all link diagrams, including tangles with open ends. These operators become nilpotent only for a diagram with no external legs, but even for open tangles one can develop a factorization formalism, which preserves Reidemeister/topological invariance—the symmetry of the problem. This technique seems much more “physical” than the conventional language of homological algebra and should have many applications to various problems beyond Chern-Simons theory. We also hope that this language will provide efficient algorithms, and finally allow one to computerize the calculation of KR cohomologies—for closed diagrams and for open tangles.

We study quantum mechanical wave functions near highly curved spaces, i.e., black holes. By utilizing the formalism developed by DeWitt, we derive the Schrödinger equations in the vicinity of the Schwarzschild and the Reissner-Nordström black hole geometries. The quantum electron cloud for the “black hydrogen atom”—an electron trapped by black holes—is particularly studied. We solve the equations and find that black holes generally attract the wave functions, localizing them near the horizon where the electrons are most likely to be trapped. These results imply that not only classical objects but also the quantum material and even the chemical properties of the atoms are affected by strong gravity. We also discuss black hydrogen molecules composed of multicentered Majumdar-Papapetrou black holes.

We discuss the emission of pairs of photons by charges with generic worldlines in the Minkowski vacuum from the viewpoint of inertial observers and interpret them from the perspective of Rindler observers. We show that the emission of pairs of Minkowski photons—commonly referred to as Unruh radiation—corresponds, in general, to three distinct processes according to Rindler observers: scattering, and emission and absorption of pairs of Rindler photons. In the special case of uniformly accelerated charges, the radiation observed in the inertial frame can be fully described by the scattering channel in the Rindler frame. Therefore, the emission of pairs of Minkowski photons can be seen as further evidence supporting the Unruh effect.

We study classical localized configurations—solitons—in a theory of self-interacting complex Proca field with the global $U(1)$ symmetry. We focus on spherically symmetric solitons near the nonrelativistic limit, which are supported by the quartic interactions of the neutral Proca field. Such solitons can source the radial electric (magnetic) field if one introduces a parity-even (parity-odd) coupling of the Proca field to the electromagnetic field tensor. We discuss the conditions of existence of such nontopological “electromagnetic hedgehogs” and their properties.

Current ground-based interferometers are optimized for sensitivity from a few tens of Hz to about 1 kHz. While they are not currently utilized for gravitational wave (GW) detection, interferometric detectors also feature narrow bands of strong sensitivity at higher frequencies where the sideband fields created by a GW are resonantly amplified in the optical system. Small changes to system parameters allow the narrow band of high sensitivity to be scanned over a much larger range of frequencies. In this paper, we investigate whether simply modifying the detuning angle of the signal-recycling mirror of the GEO600 interferometer can make this experiment sensitive to GWs in the kilohertz frequency range. We compute the strain sensitivity for GEO600 across a frequency range from several kHz to tens of kHz for various detuning angles. We also show that LIGO cannot attain the same effect assuming that the optical components are not changed due to the narrow band response of the Fabry-Perot cavities. We then calculate the sensitivity of GEO600 to various proposed high-frequency GW sources and compare it to the sensitivity of other ground-based detectors.