Solutions to the angular Teukolsky equation have been used to solve various applied problems in physics and are extremely important to black-hole physics, particularly in computing quasinormal modes and in the extreme-mass-ratio inspiral problem. The eigenfunctions of this equation, known as spin-weighted spheroidal functions, are essentially generalizations of both the spin-weighted spherical harmonics and the scalar spheroidal harmonics. While the latter functions are quite well understood analytically, the spin-weighted spheroidal harmonics are only known analytically in the spherical and oblate asymptotic limits. Attempts to understand them in the prolate asymptotic limit have met limited success. Here, we make use of a high-accuracy numerical solution scheme to extensively explore the space of possible prolate solutions and extract analytic asymptotic expansions for the eigenvalues in the prolate asymptotic limit. Somewhat surprisingly, we find two classes of asymptotic behavior. The behavior of one class, referred to as “normal,” is in agreement with the leading-order behavior derived analytically in prior work. The second class of solutions was not previously predicted, but solutions in this class are responsible for unexplained behavior seen in previous numerical prolate solutions during the transition to asymptotic behavior. The behavior of solutions in this “anomalous” class is more complicated than that of solutions in the normal class, with the anomalous class separating into different types based on the behavior of the eigenvalues at different asymptotic orders. We explore the question of when anomalous solutions appear and find necessary but not sufficient conditions for their existence. It is our hope that this extensive numerical investigation of the prolate solutions will inspire and inform new analytic investigations into these important functions.

We study the effects of explicit spacetime-symmetry breaking on primordial tensor fluctuations using an effective-field theory for Lorentz/CPT violation. We find that the graviton is still massless, but that the propagation speed of tensor modes is modified, and we obtain a constraint on the coefficient determining the symmetry breaking on the order of ${10}^{-15}$ from the recent measurements of the speed of gravity. Due to the symmetry breaking, the de-Sitter phase is modified, and during this inflationary epoch, the power spectrum assumes a slow oscillation around the general-relativity limit; further, we find that the primordial tensor power spectrum retains its scale invariance, but that the amplitude is modified. We also find that the modes which become subhorizon during radiation domination acquire a phase shift proportional to the coefficient for Lorentz violation.

Cosmic microwave background (CMB) spectral distortion from Rayleigh scattering is calculated for the first time in rigorous second-order cosmological perturbation theory. The new spectral distortion is sensitive to acoustic dissipation at ${10}^{-2}<k\mathrm{Mpc}/h<1$, which slightly extends the scale constrained by the CMB anisotropies. The spectral shape is different from either temperature perturbations or other traditional spectral distortions from Compton scattering, such as $y$ and $\mu$. The new spectral distortion is not formed in the late Universe, unlike the thermal Sunyaev-Zel’dovich effect degenerated with the primordial $y$ distortion since photons must be hot for Rayleigh scattering. Therefore, ideal measurements can distinguish the signal from the other effects and extract new information during recombination. Assuming cosmological parameters consistent with the recent CMB anisotropy measurements, we find the new spectral distortion is $6.5\times {10}^{-3}\mathrm{Jy}/\mathrm{sr}$, which is one order of magnitude smaller than the currently proposed target sensitivity range of Voyage 2050.

Light primordial black holes may comprise a dominant fraction of the dark matter in our Universe. This paper critically assesses whether planned and future gravitational wave detectors in the ultrahigh-frequency band could constrain the fraction of dark matter composed of subsolar primordial black holes. Adopting the state-of-the-art description of primordial black hole merger rates, we compare various signals with currently operating and planned detectors. As already noted in the literature, our findings confirm that detecting individual primordial black hole mergers with currently existing and operating proposals remains difficult. Current proposals involving gravitational wave to electromagnetic wave conversion in a static magnetic field and microwave cavities feature a technology gap with respect to the loudest gravitational wave signals from primordial black holes of various orders of magnitude. However, we point out that one recent proposal involving resonant LC circuits represents the best option in terms of individual merger detection prospects in the range $(1-100)\mathrm{MHz}$. In the same frequency range, we note that alternative setups involving resonant cavities, whose concept is currently under development, might represent a promising technology to detect individual merger events. We also show that a detection of the stochastic gravitational wave background produced by unresolved binaries is possible only if the theoretical sensitivity of the proposed Gaussian beam detector is achieved. Such a detector, whose feasibility is subject to various caveats, may be able to rule out some scenarios for asteroidal mass primordial black hole dark matter. We conclude that pursuing dedicated studies and developments of gravitational wave detectors in the ultrahigh-frequency band remains motivated and may lead to novel probes on the existence of light primordial black holes.

We use a particular machine learning approach, called the genetic algorithms (GAs), in order to place constraints on deviations from general relativity (GR) via a possible evolution of Newton’s constant $\mu \equiv G_{\mathrm{eff}}/G_{\mathrm{N}}$ and of the dark energy anisotropic stress $\eta$, both defined to be equal to one in GR. Specifically, we use a plethora of background and linear-order perturbations data, such as Type Ia supernovae, baryon acoustic oscillations, cosmic chronometers, redshift space distortions, and $E_g$ data. We find that although the GA is affected by the lower quality of the currently available data, especially from the $E_g$ data, the reconstruction of Newton’s constant is consistent with a constant value within the errors. On the other hand, the anisotropic stress deviates strongly from unity due to the sparsity and the systematics of the $E_g$ data. Finally, we also create synthetic data based on a next-generation survey and forecast the limits of any possible detection of deviations from GR. In particular, we use two fiducial models: one based on the cosmological constant $\mathrm{\Lambda }\mathrm{CDM}$ model and another on a model with an evolving Newton’s constant, dubbed $\mu \mathrm{CDM}$. We find that the GA reconstructions of $\mu (z)$ and $\eta (z)$ can be constrained to within a few percent of the fiducial models and in the case of the $\mu \mathrm{CDM}$ mocks, they can also provide a strong detection of several $\sigma \mathrm{s}$, thus demonstrating the utility of the GA reconstruction approach.

The extraction of the nuclear matter properties from neutron star (NS) observations is nowadays an important issue, in particular, the properties that characterize the symmetry energy which are essential to describe correctly asymmetric nuclear matter. We use deep neural networks (DNNs) to map the relation between cold $\beta$-equilibrium NS matter and the nuclear matter properties. Assuming a quadratic dependence on the isospin asymmetry for the energy per particle of homogeneous nuclear matter and using a Taylor expansion up to fourth order in the isoscalar and isovector contributions, we generate a dataset of different realizations of $\beta$-equilibrium NS matter and the corresponding nuclear matter properties. The DNN model was successfully trained, attaining great accuracy in the test set. Finally, a real-case scenario was used to test the DNN model, where a set of 33 nuclear models, obtained within a relativistic mean-field approach or a Skyrme force description, were fed into the DNN model and the corresponding nuclear matter parameters recovered with considerable accuracy; in particular, the standard deviations $\sigma (L_{\mathrm{sym}})=12.85\mathrm{MeV}$ and $\sigma (K_{\mathrm{sat}})=41.02\mathrm{MeV}$ were obtained, respectively, for the slope of the symmetry energy and the nuclear matter incompressibility at saturation.

When traveling in the heliosphere, Galactic cosmic rays (CRs) are subjected to the solar modulation effect, a quasiperiodical change of their intensity caused by the 11-year cycle of solar activity. Here we investigate the association of solar activity and cosmic radiation over five solar cycles, from 1965 to 2020, using a collection of multichannel data from neutron monitors, space missions, and solar observatories. In particular, we focus on the time lag between the monthly sunspot number and the CR flux variations. We show that the modulation lag is subjected to a 22-year periodical variation, ranging from about 2 to 14 months and following the polarity cycle of the Sun’s magnetic field. We also show that the lag is remarkably decreasing with increasing energy of the CR particles. These results reflect the interplay of basic physics phenomena that cause the CR modulation effect: the drift motion of charged particles in the interplanetary magnetic field, the latitudinal dependence of the solar wind, the energy dependence of their residence time in the heliosphere. Based on this interpretation, we end up with a global effective formula for the modulation lag and testable predictions for the flux evolution of cosmic particles and antiparticles over the solar cycle.

In the study of radiation mechanisms of active galactic nuclei (AGN) jets, hadronuclear ($pp$) interactions are commonly neglected, because the number density of cold protons in the jet is considered insufficient. Very recently, our previous work proves that $pp$ interactions in the low TeV luminosity AGN, which have the potential to generate detectable very-high-energy (VHE) emission, could be important. Based on this, the one-zone $pp$ model is employed to study low-state quasisimultaneous spectral energy distributions of a sample of low TeV luminosity AGN in this work. Our modeling results show that the $\gamma$ ray generated in $pp$ interactions can explain the observed TeV spectra and contribution to the higher-energy band that could be detected by the Large High Altitude Air Shower Observatory (LHAASO). In the sample, we suggest that M 87, Mrk 421, and Mrk 501 are the most likely objects to be detected by LHAASO in the near future. Other possible origins of VHE emission are also briefly discussed.

The DARWIN collaboration recently argued that DARWIN (dark matter wimp search with liquid xenon) can collect, via neutrino-electron scattering, a large, useful sample of solar $pp$-neutrinos, and measure their survival probability with subpercent precision. We explore the physics potential of such a sample in more detail. We estimate that, with 300 ton-years of data, DARWIN can also measure, with the help of current solar neutrino data, the value of ${\sin }^2{\theta }_{13}$, with the potential to exclude ${\sin }^2{\theta }_{13}=0$ close to the three-sigma level. We explore in some detail how well DARWIN can constrain the existence of a new neutrino mass-eigenstate ${\nu }_4$ that is quasimass-degenerate with ${\nu }_1$ and find that DARWIN’s sensitivity supersedes that of all current and near-future searches for new, very light neutrinos. In particular, DARWIN can test the hypothesis that ${\nu }_1$ is a pseudo-Dirac fermion as long as the induced mass-squared difference is larger than ${10}^{-13}{\mathrm{eV}}^2$, one order of magnitude more sensitive than existing constraints. Throughout, we allowed for the hypotheses that DARWIN is filled with natural xenon or ${}^{136}\mathrm{Xe}$-depleted xenon.

We show the discrepancy between the isospin-rotated $e^{+}{e}^{-}\to \eta {\pi }^{-}{\pi }^{+}$ cross section—measured by various collaborations—and the Belle ${\tau }^{-}\to \eta {\pi }^{-}{\pi }^0{\nu }_{\tau }$ spectrum, which cannot be explained by heavy new physics nonstandard interactions. We give for the first time the framework needed to study these beyond the standard model contributions in three-meson tau decays.

We postulate a supplemental power counting within the heavy quark effective theory (HQET) that results in a small, highly constrained set of second-order power corrections, compared to the standard approach. We determine all $\overline{B}\to D^{(*)}$ form factors, both within and beyond the standard model to $\mathcal{O}({\alpha }_s/m_{c,b},1/m_{c,b}^2)$, under truncation by this power counting. We show that the second-order power corrections to the zero-recoil normalization of the $\overline{B}\to D^{(*)}l\nu$ matrix elements ($l=e$, $\mu$, $\tau$) are fully determined by hadron mass parameters and are in good agreement with lattice QCD (LQCD) predictions. We develop a parametrization of these form factors under the postulated truncation, that achieves excellent fits to the available LQCD predictions and experimental data, and we provide precise updated predictions for the $\overline{B}\to D^{(*)}\tau \overline{\nu }$ decay rates, lepton flavor universality violation ratios $R(D^{(*)})$, and the Cabibbo-Kobayashi-Maskawa matrix element $|V_{cb}|$. We point out some apparent errors in prior literature concerning the $\mathcal{O}(1/m_c{m}_b)$ corrections and note a tension between commonly used simplified dispersive bounds and current data.

We consider multicomponent dark matter in a model where one dark matter component is feebly interacting (FIMP) while the second is weakly interacting (WIMP). The model contains an inert scalar doublet and a complex scalar singlet and features a discrete $Z_4$ symmetry. Using new features of micromegas that allow us to compute the relic density for multicomponent dark matter including WIMPs and FIMPs, we determine the parameter space that satisfies theoretical constraints, collider constraints, relic density as well as direct and indirect detection limits. We discuss the possibility to probe the model through collider and astrophysical searches. We find that it is possible that the FIMP forms the dominant dark matter (DM) component, in this case the astrophysical signatures of the WIMP are much suppressed. We also explore the case where the doublet can decay into pairs of singlets leaving only one DM component, the FIMP. These scenarios are constrained by cosmology, notably big bang nucleosynthesis, and can be explored at colliders while astrophysical signatures are suppressed.

We study one-dimensional QCD at finite quark density by using the sign optimization framework. The fermion sign problem is mitigated by deforming the path integral domain $SU(3)$ to a complexified one $\mathcal{M}\subset SL(3)$, explicitly constructed to reduce the phase fluctuations. The complexification is constructed using the angular representation of $SU(3)$. We provide a physical explanation of the optimization procedure in terms of complex saddle points. This picture connects the sign optimization framework to the generalized Lefschetz thimbles.

We describe and study an instantaneous definition of eccentricity to be applied at the initial moment of full numerical simulations of binary black holes. The method consists of evaluating the eccentricity at the moment of maximum separation of the binary. We estimate it using up to third post-Newtonian (3PN) order and compare these estimates with the results of evolving (conservative) 3PN equations of motion for a full orbit and compute the eccentricity $e_r$ from the radial turning points, finding excellent agreement. We then include terms with spins up to 3.5PN and next compare this initial data eccentricity estimate method with the turning points estimates of the eccentricity $e_r^{NR}$ during full numerical evolutions of spinning binary black holes, characterized invariantly by a fractional factor $0\le f\le 1$ of the initial tangential momenta to a quasicircular one. We find that our initial instantaneous definition is a particularly useful and accurate tool to predict and characterize even highly eccentric full numerical simulations.

One of the most common assumptions has been made that the pressure inside the star is isotropic in nature. However, the pressure is locally anisotropic in nature which is a more realistic case. In this study, we investigate certain properties of anisotropic neutron stars with the scalar pressure anisotropy model. Different perfect fluid conditions are tested within the star with the relativistic mean-field model equation of states (EOSs). The anisotropic neutron star properties such as mass ($M$), radius ($R$), compactness ($C$), Love number ($k_2$), dimensionless tidal deformability ($\mathrm{\Lambda }$), and the moment of inertia ($I$) are calculated. The magnitude of the quantities as mentioned above increases (decreases) with the positive (negative) value of anisotropy except $k_2$ and $\mathrm{\Lambda }$. The universal relation $I-\mathrm{Love}-C$ is calculated with almost 58 EOS spans from relativistic to nonrelativistic cases. We observed that the relations between them get weaker when we include anisotropicity. With the help of the GW170817 tidal deformability limit and radii constraints from different approaches, we find that the anisotropic parameter is less than 1.0 if one uses the Bowers-Liang (BL) model. Using the universal relation and the tidal deformability bound given by the GW170817, we put a theoretical limit for the canonical radius, $R_{1.4}=10.74_{-1.36}^{+1.84}\mathrm{km}$, and the moment of inertia, $I_{1.4}=1.77_{-0.09}^{+0.17}\times {10}^{45}\mathrm{g}{\mathrm{cm}}^2$ with 90% confidence limit for isotropic stars. Similarly, for anisotropic stars with ${\lambda }_{\mathrm{BL}}=1.0$, the values are $R_{1.4}=11.74_{-1.54}^{+2.11}\mathrm{km}$, $I_{1.4}=2.40_{-0.08}^{+0.17}\times {10}^{45}\mathrm{g}{\mathrm{cm}}^2$ respectively.

In this paper we explore the existing tensions in the local cosmological expansion rate, $H_0$, and amplitude of the clustering of the large-scale structure at $8h^{-1}\mathrm{Mpc}$, ${\sigma }_8$, as well as models that claim to alleviate these tensions. We consider seven models: evolving dark energy ($w\mathrm{CDM}$), extra radiation ($N_{\mathrm{eff}}$), massive neutrinos, curvature, primordial magnetic fields (PMF), self-interacting neutrino models, and early dark energy (EDE). We test these models against three datasets that span the full range of measurable cosmological epochs, have significant precision, and are well-tested against systematic effects: the Planck 2018 cosmic microwave background data, the Sloan Digital Sky Survey baryon acoustic oscillation scale measurements, and the Pantheon catalog of type Ia supernovae. We use the recent SH0ES $H_0$ measurement and several measures of ${\sigma }_8$ (and its related parameter $S_8={\sigma }_8\sqrt{{\mathrm{\Omega }}_{\mathrm{m}}/0.3}$). We find that four models are above the “strong” threshold in Bayesian model selection, $w\mathrm{CDM}$, $N_{\mathrm{eff}}$, PMF, and EDE. However, only EDE also relieves the $H_0$ tension in the full datasets to below $2\sigma$. We discuss how the $S_8/{\sigma }_8$ tension is reduced in recent observations. However, even when adopting a strong tension dataset, no model alleviates the $S_8/{\sigma }_8$ tension, nor does better than $\mathrm{\Lambda }\mathrm{CDM}$ in the combined case of both $H_0$ and $S_8/{\sigma }_8$ tensions.

A quantitative description of the properties of hot nuclear matter will be needed for the interpretation of the available and forthcoming astrophysical data, providing information on the postmerger phase of a neutron star coalescence. We have employed a recently developed theoretical model, based on a phenomenological nuclear Hamiltonian including two- and three-nucleon potentials, to study the temperature dependence of average and single-particle properties of nuclear matter relevant to astrophysical applications. The possibility to represent the results of microscopic calculations using simple and yet physically motivated parametrizations of thermal effects, suitable for use in numerical simulations of astrophysical processes, is also discussed.

Binary black holes formed via different pathways are predicted to have distinct spin properties. Measuring these properties with gravitational waves provides an opportunity to unveil the origins of binary black holes. Recent work draws conflicting conclusions regarding the spin distribution observed by LIGO-Virgo-KAGRA (LVK). Some analyses suggest that a fraction of the observed black-hole spin vectors are significantly misaligned (by $>90°$) relative to the orbital angular momentum. This has been interpreted to mean that some binaries in the LVK dataset are assembled dynamically in dense stellar environments. Other analyses find support for a subpopulation of binaries with negligible spin and no evidence for significantly misaligned spin—a result consistent with the field formation scenario. In this work, we study the spin properties of binary black holes in the third LVK gravitational-wave transient catalog. We find that there is insufficient data to resolve the existence of a subpopulation of binaries with negligible black-hole spin (the presence of this subpopulation is supported by a modest Bayes factor of 1.7). We find modest support for the existence of mergers with extreme spin tilt angles $>90°$ (the presence of extreme-tilt binaries is favored by a Bayes factor of 10.1). Only one thing is clear based on gravitational-wave measurements of black hole spin: at least some of the LVK binaries formed in the field. At most 89% of binaries are assembled dynamically (99% credibility), though, the true branching fraction could be much lower, even negligible.

Extracting gravitational wave (GW) signals from individual Galactic binaries (GBs) against their self-generated confusion noise is a key data analysis challenge for space-borne detectors operating in the $\approx 0.1$ to $\approx 10\mathrm{mHz}$ range. Given the likely prospect that there will be multiple such detectors, namely Laser Interferometer Space Antenna (LISA), Taiji, and Tianqin, with overlapping operational periods in the next decade, it is important to examine the extent to which the joint analysis of their data can benefit GB resolution and parameter estimation. To investigate this, we use realistic simulated LISA and Taiji data containing the set of $30\times {10}^6$ GBs used in the first LISA data challenge (Radler) and an iterative source extraction method called GBSIEVER introduced in an earlier work. We find that a coherent network analysis of LISA-Taiji data boosts the number of confirmed sources by $\approx 75\%$ over that from a single detector. The residual after subtracting out the reported sources from the data of any one of the detectors is much closer to the confusion noise expected from an ideal, but infeasible, multisource resolution method that perfectly removes all sources above a given signal-to-noise ratio threshold. While parameter estimation for sources common to both the single detector and network improves broadly in line with the enhanced signal-to-noise ratio of GW sources in the latter, deviation from the scaling of error variance predicted by Fisher information analysis is observed for a subset of the parameters.

We present results for the scalar and tensor isovector-couplings ($g_S$ and $g_T$) of the nucleon measured at the physical point ($M_{\pi }=135\mathrm{MeV}$) with a single lattice spacing of 0.085 fm in $2+1$ flavor QCD. Our calculations are carried out with two ensembles of gauge configurations generated by the PACS Collaboration with nonperturbatively $\mathcal{O}(a)$ improved Wilson quark action and Iwasaki gauge action on $(10.9\mathrm{fm}{)}^4$ and $(5.5\mathrm{fm}{)}^4$ lattices, where the finite-size effect on the nucleon mass was not shown at the level of statistical precision less than 0.5%. We compute the nucleon three-point correlation functions in the vector, axial, scalar, and tensor channels. We confirm that our previous result of the nucleon axial coupling on the large spatial volume of $(10.9\mathrm{fm}{)}^4$ has no finite-size effect at the level of the statistical precision of 1.9%. For the renormalization, we first renormalize $g_S$ and $g_T$ nonperturbatively using the $\mathrm{RI}/{\mathrm{SMOM}}_{({\gamma }_{\mu })}$ scheme, a variant of Rome-Southampton RI/MOM scheme with reduced systematic errors, as the intermediate scheme. We evaluate our final results at the renormalization scale of 2 GeV in the $\overline{\mathrm{MS}}$ scheme through the matching procedure between the $\mathrm{RI}/{\mathrm{SMOM}}_{({\gamma }_{\mu })}$ and $\overline{\mathrm{MS}}$ schemes with the help of perturbation theory, and then obtain $g_S=0.927(83{)}_{\mathrm{stat}}(22{)}_{\mathrm{syst}}$ and $g_T=1.036(6{)}_{\mathrm{stat}}(20{)}_{\mathrm{syst}}$.