In this paper, we revisit and extend the analysis of the no-boundary wave function for the minisuperspace model in which the universe is described by a biaxial Bianchi IX metric. As matter content, we simply assume a positive cosmological constant. We find that two Stokes phenomena occur, at large squashing parameters of the spatial section of the Universe. These Stokes phenomena eliminate potentially dominant Taub-Bolt-de Sitter saddle point geometries and are crucial for the consistency of the model. They also imply that phase transitions occur at certain levels of squashing, where NUT and Bolt saddle points exchange dominance.

Galaxy clusters identified in optical imaging surveys suffer from projection effects: Physically unassociated galaxies along a cluster’s line of sight can be counted as its members and boost the observed richness (the number of cluster members). To model the impact of projection on cluster cosmology analyses, we apply a halo occupation distribution model to $N$-body simulations to simulate the red galaxies contributing to cluster members, and we use the number of galaxies in a cylinder along the line of sight (counts in cylinders) to model the impact of projection on cluster richness. We compare three projection models: uniform, quadratic, and Gaussian, and we convert between them by matching their effective cylinder volumes. We validate our mock catalogs using SDSS redMaPPer clusters’ data vectors, including counts vs richness, stacked lensing signal, spectroscopic redshift distribution of member galaxies, and richness remeasured on a redshift grid. We find the former two are insensitive to the projection model, while the latter two favor a quadratic projection model with a width of $\approx 180h^{-1}\mathrm{Mpc}$ (equivalent to the volume of a uniform model with a width of $100h^{-1}\mathrm{Mpc}$ and a Gaussian model with a width of $110h^{-1}\mathrm{Mpc}$, or a Gaussian redshift error of 0.04). Our framework provides an efficient and flexible way to model optical cluster data vectors, paving the way for a simulation-based joint analysis for clusters, galaxies, and shear.

We present the big-bang nucleosynthesis (BBN) simulation with a bubble universe scenario around a rotating black hole (BH) in Kerr-${\mathrm{AdS}}_5$ spacetime to explain recently updated observations of light elements such as the primordial helium abundance. In this scenario, the geometry of the 4D-early Universe is described as a vacuum bubble that undergoes quasi–de Sitter expansion in Kerr-${\mathrm{AdS}}_5$ spacetime. We find that the BH mass and spin parameter, which show an anticorrelation against the total radiation, are important to resolve the ${}^4\mathrm{He}$ anomaly. The present results provide clues to finding a connection between the observed results of light-element nucleosynthesis and the scenario of the 4D-bubble universe in ${\mathrm{AdS}}_5$ spacetimes.

Extensive air showers (EASs), produced by cosmic rays in the atmosphere, serve as probes of particle interactions, providing access to energies and kinematical regimes beyond the reach of laboratory experiments. Measurements from multiple cosmic-ray detectors indicate a significant, yet unexplained, discrepancy between the observed muon content in EASs and that predicted by state-of-the-art interaction models, suggesting a need for refinements in our understanding of fundamental physics. Here we show that a tiny, experimentally allowed, violation of the Lorentz invariance violation (LIV) may result in the suppression of the number of electrons in EASs, leaving the muon number intact and explaining both the “muon excess” and its energy dependence. On the other hand, we use the lack of a much stronger discrepancy between EAS data and simulations to obtain strict constraints on the LIV scale. Future experimental tests of this LIV scenario are outlined.

Some neutron stars known as magnetars possess very strong magnetic fields, with surface fields as large as ${10}^{15}\mathrm{G}$ and internal fields that are possibly stronger. Recent observations of the radio pulsar GLEAM-X J1627 suggest it may have a surface field as strong as ${10}^{16}\mathrm{G}$. In the presence of a strong magnetic field, Leinson and Perez showed and Baiko and Yakovlev confirmed that the energy levels of electrons and protons are quantized and the direct Urca process allows neutron stars to cool rapidly, even at low density. For the case of magnetic fields $B\gtrsim {10}^{16}\mathrm{G}$, we find features in the emissivity due to energy quantization that are not captured by the frequently employed quasiclassical approximation where energy levels are treated as nearly continuous. Resonances can result in amplification of the neutrino emissivity at specific densities compared to a calculation that neglects quantization, particularly at low temperature. These effects are not important for the thermal evolution of an entire neutron star, but may be relevant for phenomena that depend on behavior at specific densities. We present a fully relativistic calculation of the direct Urca rate in a strong magnetic field using the standard V-A weak Lagrangian incorporating mean field nuclear effects and discuss approaches to the numerical challenge the modified wave functions present and a new semianalytic approximation. These tools are also applicable to calculating neutrino opacities in strong magnetic fields in the ejecta of binary neutron star mergers. We calculate the opacities for neutrinos capturing on free nucleons at subsaturation densities and temperatures exceeding an MeV. We find an enhancement to capture processes of the lowest energy neutrinos by an order of magnitude or more due to suppression of electron Pauli blocking in the case of capture on neutrons, and from the effect of the nucleon magnetic moments in the case of capture on protons.

Axions are a well-motivated dark matter candidate. They may be detectable from radio line emission due to resonant conversion in neutron star magnetospheres. While radio data collection for this signal has begun, further efforts are required to solidify the theoretical predictions for the resulting radio lines. Usually, the flat spacetime Goldreich-Julian model of the neutron star magnetosphere is used, while a Schwarzschild geometry is assumed for the ray tracing. We assess the impact of incorporating the spacetime curvature into the magnetosphere model. We examine a range of neutron star and axion masses and find an average difference of 37% and 22% in radiated power compared to the standard Goldreich-Julian magnetosphere model for a $1\mathrm{\mu }\mathrm{eV}$ and $10\mathrm{\mu }\mathrm{eV}$ mass axion, respectively, in the case of a $2.2M_{\odot }$ mass neutron star. A much lesser difference is found for lower-mass neutron stars, as in that case axion-photon conversion occurs further from the Schwarzschild radius.

We investigate the influence of a phase transition from hadronic matter to a deconfined quark phase inside a neutron star on its cooling behavior including the appearance of twin star solutions in the mass-radius diagram. We find that while the inferred neutrino luminosity of cold transiently accreting star in MXB 1659-29 is reproduced in all of the constructed twin star models, the luminosity of a colder source, the neutron star in SAX J1808.4-3658, cannot be described by equations of state with quark-hadron transition densities below 1.7 saturation density, suggesting that twin stars with such low density transitions to the quark phase are not realized in nature. We also discuss how constraints to the quark-hadron phase transition density are strongly dependent on the cooling effectiveness of neutrino reactions in the quark phase.

The final stage of black hole evaporation is a potent probe of physics beyond the Standard Model: Hawking-Bekenstein radiation may be affected by quantum gravity “memory burden effects,” or by the presence of “dark,” beyond-the-Standard-Model degrees of freedom in ways that are testable with high-energy gamma-ray observations. We argue that information on either scenario can best be inferred from measurements of the evaporation’s light curve and by correlating observations at complementary energies. We offer several new analytical insights in how such observations map on the fundamental properties of the evaporating black holes and of the possible exotic particles they can evaporate into.

One of the primary sources of gravitational waves (GWs) anticipated to be detected by the Laser Interferometer Space Antenna (LISA) are Galactic double white dwarf binaries (DWDs). However, most of these binaries will be unresolved, and their GWs will overlap incoherently, creating a stochastic noise known as the Galactic foreground. Similarly, the population of unresolved systems in the Milky Way’s (MW) satellites is expected to contribute to a stochastic gravitational wave background (SGWB). Due to their anisotropy and the annual motion of the LISA constellation, both the Galactic foreground and the satellite SGWB fall into the category of cyclostationary processes. Leveraging this property, we develop a purely frequency-based method to study LISA’s capability to detect the MW foreground and SGWBs from the most promising MW satellites. We analyze both mock data generated by an astrophysically motivated SGWB spectrum, and realistic ones from a DWD population generated via binary population synthesis. We are able to recover or put constrains on the candidate foregrounds, reconstructing—in the presence of noise uncertainties—their sky distribution and spectrum. Our findings highlight the significance of the interplay between the astrophysical spectrum and LISA’s sensitivity to detect the satellites’ SGWB. Considering an astrophysically motivated prior on the satellite positions improves their detectability, which becomes otherwise challenging in the presence of the Galactic foreground. Furthermore, we explore the potential to observe a hypothetical satellite located behind the Galactic disk. Our results suggest that a Large Magellanic Cloud-like satellite could indeed be observable by LISA.

This work is devoted to the production of axion particles in the vicinity of supermassive Kerr black holes, and this article is the second part of our work presenting the physical processes necessary for the production of axions. The framework is the physics of the magnetosphere in general relativity that contains the Blandford-Znajek mechanism of jet launching supplemented by a version of the Goldreich-Julian charge generation adapted to the magnetosphere of a Kerr black hole, which leads to the formation of “gaps” like in a pulsar magnetosphere. These gaps produced close to the horizon result from the generation of an intense poloidal component of the electric field such that $\overrightarrow{E}·\overrightarrow{B}\ne 0$, which is necessary for the production of axion particles. These gaps are steady or oscillating and the creation of new axions stems from oscillating gaps, which are described in order to reveal their appropriate characteristics for this purpose. High-energy radiation plays an essential role in determining the parameters of the oscillating gaps and the power of axion emission. With reasonable parameters, it is found that the axion emission in active galactic nuclei and quasars can significantly feed their halos with axion dark matter.

The hypothetical axion particles have received great attention in recent years in both particle physics, where they contribute to solving some difficulties with the Standard Model, and in astrophysics, where they could be a serious candidate for dark matter and solve problems with the $\mathrm{\Lambda }\mathrm{CDM}$ model. We expect that the most powerful radiation sources in the Universe—quasars and, more generally, active galactic nuclei (AGNs)—could produce a significant amount of axions. The central engine of these high-energy objects is a Kerr black hole surrounded by a magnetosphere, where structures called “gaps” form close to the black hole horizon and generate intense electric fields such that $\overrightarrow{E}·\overrightarrow{B}\ne 0$; such a configuration is favorable for the production of axions, especially in the unsteady regime. First investigations of this sort have been performed for pulsars because of their very intense magnetic fields; however, extragalactic sources are far more powerful and more suitable to produce a large flux of axions particles. Moreover, the axions of interest would have a Compton wavelength comparable with the gravitational radius of their black hole. The primary energy supply stems from the rotation of a black hole threaded by a magnetic field, which powers a Poynting flux through the Blandford-Znajek mechanism that drives relativistic jets, which is supplemented by the Goldreich-Julian generation of an electric charge density whose unsteady screening generates a strong oscillating electric field component aligned with the main magnetic field that threads the black hole. Both processes provide a permanent source of energy for the emission of axion particles through two channels: the internal generation of axion power in vibrating gaps which generates forward and backward axion waves, and the slight extraction of the Blandford-Znajek luminosity by the axions themselves inside the gaps. The work is presented in two parts. In this first part, the astrophysical conditions under which the interaction takes place are presented and the efficiency of axion production is estimated, offering some hope for a cosmological solution in the form of a hot axion dark matter component in halos surrounding quasars and AGNs. In the second part (a separate paper), a detailed investigation of the physics of a Kerr black hole magnetosphere with the production of oscillating gaps reveals their capacity to be a powerful source of axions, in particular how axions participate in the Blandford-Znajek process.

We present the first constraints on tidal heating for the binary black holes detected in the LIGO-Virgo-KAGRA (LVK) gravitational wave data. Tidal heating, also known as tidal dissipation, characterizes the viscous nature of an astrophysical body and provides a channel for exchanging energy and angular momentum with the tidal environment. Using the worldline effective field theory formalism, we introduce a physically motivated and easily interpretable parametrization of tidal heating valid for an arbitrary compact astrophysical object. We then derive the imprints of the spin-independent and linear-in-spin tidal heating effects of generic binary components on the waveform phases and amplitudes of quasicircular orbits. Notably, the mass-weighted spin-independent tidal heating coefficient derived in this work, ${\mathcal{H}}_0$, is the dissipative analog of the tidal Love number. We constrain the tidal heating coefficients using the public LVK O1-O3 data. Our parameter estimation study includes two separate analyses: the first treats the catalog of binary events as binary black holes (BBH), while the second makes no assumption about the nature of the binary constituents and can therefore be interpreted as constraints for exotic compact objects. In the former case, we combine the posterior distributions of the individual BBH events and obtain a joint constraint of $-13<{\mathcal{H}}_0<20$ at the 90% credible interval for the BBH population. This translates into a bound on the fraction of the emitted gravitational wave energy lost due to tidal heating (or gained due to radiation enhancement effects) at $|\mathrm{\Delta }{E}_H/\mathrm{\Delta }{E}_{\infty }|\lesssim 3\times {10}^{-3}$. Our work provides the first robust framework for deriving and measuring tidal heating effects in merging binary systems, demonstrating its potential as a powerful probe of the nature of binary constituents and tests of new physics.

One of the hottest questions in the cosmology of self-interacting dark matter (SIDM) is whether scatterings can induce detectable core-collapse in halos by the present day. Because gravitational tides can accelerate core-collapse, the most promising targets to observe core-collapse are satellite galaxies and subhalo systems. However, simulating small subhalos is computationally intensive, especially when subhalos start to core-collapse. In this work, we present a hierarchical framework for simulating a population of SIDM subhalos, which reduces the computation time to linear order in the total number of subhalos. With this method, we simulate substructure lensing systems with multiple velocity-dependent SIDM models and show how subhalo evolution depends on the SIDM model, subhalo mass and orbits. We find that an SIDM cross section of $\gtrsim 200{\mathrm{cm}}^2/\mathrm{g}$ at velocity scales relevant for subhalos’ internal heat transfer is needed for a significant fraction of subhalos to core-collapse in a typical lens system at redshift $z=0.5$ and that core-collapse has unique observable features in lensing. We show quantitatively that core-collapse in subhalos is typically accelerated compared to field halos, except when the SIDM cross section is non-negligible ($\gtrsim \mathcal{O}(1){\mathrm{cm}}^2/\mathrm{g}$) at subhalos’ orbital velocities, in which case evaporation by the host can delay core-collapse. This suggests that substructure lensing can be used to probe velocity-dependent SIDM models, especially if line-of-sight structures (field halos) can be distinguished from lens-plane subhalos. Intriguingly, we find that core-collapse in subhalos can explain the recently reported ultrasteep density profiles of substructures found by lensing with the Hubble Space Telescope.

On May 24, 2023, the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO), joined by the Advanced Virgo and KAGRA detectors, began the fourth observing run for a two-year-long dedicated search for gravitational waves. The LIGO Hanford and Livingston detectors have achieved an unprecedented sensitivity to gravitational waves, with an angle-averaged median range to binary neutron star mergers of 152 and 160 Mpc, and duty cycles of 65.0% and 71.2%, respectively, with a coincident duty cycle of 52.6%. The maximum range achieved by the LIGO Hanford detector is 165 Mpc and the LIGO Livingston detector 177 Mpc, both achieved during the second part of the fourth observing run. For the fourth run, the quantum-limited sensitivity of the detectors was increased significantly due to the higher intracavity power from laser system upgrades and replacement of core optics, and from the addition of a 300 m filter cavity to provide the squeezed light with a frequency-dependent squeezing angle, part of the $\mathrm{A}+$ upgrade program. Altogether, the $\mathrm{A}+$ upgrades led to reduced detector-wide losses for the squeezed vacuum states of light which, alongside the filter cavity, enabled broadband quantum noise reduction of up to 5.2 dB at the Hanford observatory and 6.1 dB at the Livingston observatory. Improvements to sensors and actuators as well as significant controls commissioning increased low frequency sensitivity. This paper details these instrumental upgrades, analyzes the noise sources that limit detector sensitivity, and describes the commissioning challenges of the fourth observing run.

We present an improved method for vetoing candidates of continuous gravitational-wave sources during all-sky searches utilizing the frequency Hough pipeline. This approach leverages linear correlations between source parameters induced by the Earth Doppler effect, which can be effectively identified through the Hough transform. Candidates that do not align with these patterns are considered spurious and can thus be vetoed, enhancing the depth and statistical significance of follow-up analyses. Additionally, we provide a comprehensive explanation of the method calibration, which intrinsically linked to the total duration of the observing run. On average, the procedure successfully vetoes 56% of candidates. To assess the method performance, we conducted a MC simulation injecting fake continuous-wave signals into data from the third observing run of the LIGO detectors. This analysis allowed us to infer strain amplitude upper limits at a 90% confidence level. We found that the optimal sensitivity is $h_0^{90\%}=3.62_{-0.22}^{+0.23}\times {10}^{-26}$ in the [128, 200] Hz band, which is within the most sensible frequency band of the LIGO detectors.

The ongoing Run 3 at the Large Hadron Collider (LHC) is substantially increasing the luminosity delivered to the experiments during Run 1 and Run 2. The advent of the high-luminosity upgrade of the LHC (Run 4 to 6), as well as the improvements to all detectors, will allow for the collection of an unprecedented amount of data in the next decade. This opens the possibility of performing measurements which have been limited by the smallness of the available data samples. This is the case of multidifferential studies of $\mathrm{J}/\psi$, as well as of $\mathrm{\Upsilon }$ excited states, in exclusive diffractive photon-induced interactions. Here, we present predictions for the cross sections of these processes utilizing the dipole amplitude from the Balitsky-Kovchegov (BK) equation solved in the target rapidity and including the full impact-parameter dependence. Cross sections are computed as a function of the photon-proton center-of-mass energy as well as a function of Mandelstam-$t$. Ratios of cross sections for different states and for the same state at different Mandelstam-$t$ values are also presented. The contribution to these observables of the nonlinear terms in the BK equation is discussed.

Important aspects of quantum chromodynamics (QCD) factorization theorems are the properties of the objects involved that can be identified as universal. One example is that the definitions of parton densities and fragmentation functions for different types of hadrons differ only in the identity of the nonperturbative states that form the matrix elements, but are otherwise the same. This leads to independence of perturbative calculations on nonperturbative details of external states. It also lends support to interpretations of correlation functions as encapsulations of intrinsic nonperturbative properties. These characteristics have usually been presumed to still hold true in fragmentation functions even when the observed nonperturbative state is a small-mass cluster of $n$ hadrons rather than simply a single isolated hadron. However, the multidifferential aspect of cross sections that rely on these latter types of fragmentation functions complicates the treatment of kinematical approximations in factorization derivations. That has led to recent claims that the operator definitions for fragmentation functions need to be modified from the single hadron case with nonuniversal prefactors. With such concerns as our motivation, we retrace the steps for factorizing the unpolarized semi-inclusive $e^{+}{e}^{-}$ annihilation cross section and confirm that they do apply without modification to the case of a small-mass multihadron observed in the final state. In particular, we verify that the standard operator definition from single hadron fragmentation, with its usual prefactor, remains equally valid for the small-mass $n$-hadron case with the same hard parts and evolution kernels, whereas the more recently proposed definitions with nonuniversal prefactors do not. Our results reaffirm the reliability of most past phenomenological applications of dihadron fragmentation functions.

Quantum simulations of non-Abelian gauge theories require efficient mappings onto quantum computers and practical state preparation and measurement procedures. A truncation of the Hilbert space of non-Abelian lattice gauge theories with matter in the heavy quark limit is developed. This truncation is applied to $SU(2)$ lattice gauge theory in $1+1D$ to map the theory efficiently onto a quantum computer. Scalable variational circuits are found to prepare the vacuum and single meson states. It is also shown how these state preparation circuits can be used to perform measurements of the number of mesons produced during the system’s time evolution. A state with a single $q\overline{q}$ pair is prepared on quantum hardware and the inelastic production of $q\overline{q}$ pairs is observed using 104 qubits on IBM’s Heron quantum computer ibm_torino.

The role of asymmetric nuclear medium on the properties of kaon is investigated at zero and finite temperature employing a hybrid approach integrating the light cone quark model and the chiral SU(3) quark mean field model. The in-medium quark masses are calculated within the chiral SU(3) quark mean field model and are used as inputs to study the medium modifications in the kaon properties. In particular, we have analyzed the impact of baryonic density, isospin asymmetry, and temperature on the weak decay constant, distribution amplitudes, and parton distribution functions (PDFs) of valence quarks of kaon. The effects of isospin asymmetry on the kaon doublet $K=(\genfrac{}{}{0ex}{}{K^{+}}{K^0})$ and antikaon doublet $\overline{K}=(K^{-},{\overline{K}}^0)$ are also studied. In order to compare with future experiments, we have also evolved the in-medium PDFs of kaons to $Q^2=16{\mathrm{GeV}}^2$. As compared to the temperature and isospin asymmetry, change in baryonic density of the nuclear medium makes more significant changes to the distribution amplitudes and PDFs of kaons.