Until today, the nature of dark matter (DM) remains elusive despite all our efforts. This missing matter of the Universe has not been observed by the already operating DM direct-detection experiments, but we can infer its gravitational effects. Galaxies and clusters of galaxies are most likely to contain DM trapped to their gravitational field. This leads us to the natural assumption that compact objects might contain DM too. Among the compact objects exist in galaxies, neutron stars are considered as natural laboratories, where theories can be tested, and observational data can be received. Thus, many models of DM have proposed its presence in those stars. In particular, in the present study we focus on two types of dark matter particles, namely, fermions and bosons with a mass range of [0.01–1.5] GeV and self-interaction strength in the range [${10}^{-4}–{10}^{-1}$] ${\mathrm{MeV}}^{-1}$. By employing the two-fluid model, we discovered a stable area in the mass-radius diagram of a celestial formation consisting of neutron star matter and DM that is substantial in size. This formation spans hundreds of kilometers in diameter and possesses a mass equivalent to 100 or more times the solar mass. To elucidate, this entity resembles an enormous celestial body of DM, with a neutron star at its core. This implies that a supramassive stellar compact entity can exist without encountering any issues of stability and without undergoing a collapse into a black hole. In any case, the present theoretical prediction can, if combined with corresponding observations, shed light on the existence of DM and even more on its basic properties.

The understanding of the neutron star equation of state hinges on a comprehensive analysis of multimessenger, multiwavelength data. The recent scrutiny of PSR $\mathrm{J}0030+0451$ data by NICER introduces complexities, unveiling a tension with another x-ray observation of the central compact object in HESS J1731-347, specifically concerning the mass-radius constraint of low-mass neutron stars. This tension persists when integrating NICER’s updated data with LIGO/Virgo’s gravitational-wave data from the GW170817 binary neutron star merger. Despite attempts to reconcile these disparate observations, the current combined data still cannot distinguish different types of neutron stars—whether they are pure neutron stars or hybrid stars. Bayesian inference indicates only modest changes in the posterior ranges of parameters related to the nuclear matter and deconfinement phase transition. This ongoing exploration underscores the intricate challenges in precisely characterizing neutron stars. It also points out that it is possible to probe the equation of state at different density regimes from future more accurate radii of neutron stars with various masses.

This paper presents a machine learning-based method for the detection of the unique gravitational microlensing signatures of extended dark objects, such as boson stars, axion miniclusters and subhalos. We adapt MicroLIA, a machine learning-based package tailored to handle the challenges posed by low-cadence data in microlensing surveys. Using realistic observational time stamps, our models are trained on simulated light curves to distinguish between microlensing by pointlike and extended lenses, as well as from other object classes which give a variable magnitude. We focus on boson stars and Navarro-Frenk-White (NFW) subhalos and show that the former, which are examples of objects with a relatively flat mass distribution, can be confidently identified for $0.8\lesssim r/r_E\lesssim 3$. Intriguingly, we also find that more sharply peaked structures, such as NFW subhalos, can be distinctly recognized from point lenses under regular observation cadence. Our findings significantly advance the potential of microlensing data in uncovering the elusive nature of extended dark objects. The code and dataset used are also provided.

We employ a data-driven approach to investigate the rigidity and spatial dependence of the diffusion of cosmic rays in the turbulent magnetic field of the Milky Way. Our analysis combines datasets from the experiments Voyager, AMS-02, CALET, and DAMPE for a range of cosmic ray nuclei from protons to oxygen. Our findings favor models with a smooth behavior in the diffusion coefficient, indicating a good qualitative agreement with the predictions of self-generated magnetic turbulence models. Instead, the current cosmic-ray data do not exhibit a clear preference for or against inhomogeneous diffusion, which is also a prediction of these models. Future progress might be possible by combining cosmic-ray data with gamma rays or radio observations, enabling a more comprehensive exploration.

Recent observations have granted to us two unique insights into the early Universe: the presence of a low-frequency stochastic gravitational wave background detected by the NANOGrav and Pulsar Timing Array (PTA) experiments and the emergence of unusually massive galaxy candidates at high redshifts reported by the James Webb Space Telescope (JWST). In this paper, we consider the possibility that both observations have a common origin, namely primordial black holes (PBHs) in the mass range between ${10}^6{M}_{\odot }$ and ${10}^{13}{M}_{\odot }$. While superheavy PBHs act as seeds for accelerated galaxy formation capable of explaining the JWST extreme galaxies, they can also form binary mergers that source gravitational waves which can be potentially identified as the PTA signal. The analysis is performed taking into account the constraints on the relevant region of the PBH parameter space including the novel bound imposed by the ultraviolet luminosity function of galaxies observed by the Hubble Space Telescope. We conclude that PTA’s and JWST’s interpretations in terms of PBH binary mergers and Poissonian gas of PBHs, respectively, are strongly excluded.

A novel table-top experiment is introduced to detect photon-axion conversion: WISP searches on a fiber interferometer (WISPFI). The setup consists of a Mach-Zehnder-type interferometer with a fiber placed inside an external magnetic field, where mixing occurs which is detected by measuring changes in amplitude. Hollow-core photonic crystal fibers (HC-PCF) will be used to achieve resonant mixing that is tuneable by regulating the gas pressure in the fiber. An unexplored axion mass-range (28 meV–100 meV) can be probed reaching the two-photon coupling expected for the QCD axion.

We demonstrate analytically and numerically that “optimized partial dressing” (OPD) thermal mass resummation, which uses gap equation solutions inserted into the tadpole, efficiently tames finite-temperature perturbation theory calculations of the effective thermal potential, without necessitating use of the high-temperature approximation. An analytical estimate of the scale dependence for OPD resummation, standard Parwani resummation (Daisy resummation), and dimensional reduction shows that OPD has similar scale dependence to dimensional reduction, greatly improving Parwani resummation. We also elucidate how to construct and solve the gap equation for realistic numerical calculations, and demonstrate OPD’s improved accuracy for a toy scalar model. OPD’s improved accuracy is most physically significant when the high-temperature approximation breaks down, rendering dimensional reduction unusable and Parwani resummation highly inaccurate, with the latter underestimating the maximal gravitational wave amplitude for the model by 2 orders of magnitude compared to OPD. Our work highlights the need to bring theoretical uncertainties under control even when analyzing broad features of a model. Given the simplicity of the OPD compared to two-loop dimensional reduction, as well as the ease with which this scheme handles departures from the high-temperature expansion, we argue this scheme has great potential in analyzing the parameter space of realistic beyond the Standard Model models.

A new “SK24” nonsinglet QCD analysis of the structure functions at the NNLO approximation is performed, utilizing the global fit of the data from various charged lepton scattering experiments. We extract the valence parton distribution functions (PDFs) and provide a parametrization of them, along with the correlated errors for a wide range of $x$ and $Q^2$. We compare valence PDFs and their uncertainties with those from different PDF sets provided by various groups. We also obtain valence PDFs and the strong coupling constant ${\alpha }_s(M_Z^2)$, taking into account the nuclear correction concerning large $x$ as well as the target mass correction (TMC) and higher twist (HT) effects at the NNLO. In the large $x$ region, we extract the higher twist contributions of $x{F}_3(x,Q^2)$, $F_2^p(x,Q^2)$, and $F_2^d(x,Q^2)$. We determine ${\alpha }_s(M_Z^2)$ without and with considering the TMC and HT corrections and perform a comparison with the world average of ${\alpha }_s(M_Z^2)$ and other reported results. The extracted results concerning valence PDFs with their uncertainties and ${\alpha }_s(M_Z^2)$ value agree with available theoretical models.

We analyze the low- and high-momentum rest frame modes in the second-order spin hydrodynamics and check the asymptotic causality of the theory. A truncation scheme of the Israel-Stewart formalism derived in our earlier work is proposed that extends the minimal causal formulation. It consists of altogether 40 interconnected relaxation-type dynamical equations—16 (24) of them correspond to the independent components of the energy-momentum (spin) tensor. Similarly to previous studies, we find that the stability of the perturbations and asymptotic causality require using the spin equation of state that satisfies the generalized Frenkel condition demanding that the “electric” and “magnetic” components of the spin density tensor have opposite signs. For low-momentum modes this behavior is similar to that found earlier for the first-order (Navier-Stokes) spin hydrodynamics.

Extreme mass-ratio inspirals, a target source for the space-based gravitational wave detector LISA, are a sensitive probe of fundamental scalar fields coupled to gravity. We assess the capability of LISA to detect whether the secondary compact object is endowed with a scalar field, in the case of inclined orbits. We show that the imprint of the scalar field depends on the orbital inclination, and is significantly larger for prograde orbits.

Standard stellar evolution models predict that black holes in the range of approximately $50-140M_{\odot }$ should not exist directly from stellar evolution. This gap appears because stars with masses between 100 and $240M_{\odot }$ are expected to undergo a pair instability supernova and leave behind no remnant, or a pulsational pair instability supernova and leave behind a remnant much smaller than their initial stellar mass. However, black holes have been discovered by the LIGO/Virgo collaboration within this mass range. In previous work [J. Ziegler and K. Freese, Filling the black hole mass gap: Avoiding pair instability in massive stars through addition of nonnuclear energy, Phys. Rev. D 104, 043015 (2021).], we used the stellar evolution code MESA to show that the addition of non-nuclear energy (such as from annihilation of dark matter) could alter the evolution of a $180M_{\odot }$ star so that the observed black holes could be produced from isolated stars. In this paper, we extend this analysis to stars of other masses, and find that sufficient amounts of non-nuclear energy can allow any star to avoid pair instability, and could produce a black hole of mass comparable to the initial stellar mass. In addition, we produce examples of the type of black hole initial mass function that can be produced from this mechanism. These illustrative examples suggest that adding non-nuclear energy to stars offers a way to fully close the mass gap.

Using a formalism that was recently developed in a companion Letter, we rigorously prove the equivalence, in the linear regime, of a number of apparently different relativistic hydrodynamic theories proposed in the literature. In particular, we show that $\mathrm{Hydro}+$ is indistinguishable from the Israel-Stewart theory for bulk viscosity, which in turn is indistinguishable from a reacting mixture. The two-fluid model for superfluidity coincides with the Israel-Stewart theory for heat conduction in the limit of infinite conductivity, and this explains why the latter has a second sound. Also, ${\mathrm{MIS}}^{*}$ is equivalent to the Burgers model for viscoelasticity, and this implies that the former must exhibit an elastic behavior at high frequencies. Additionally, we show that if the degrees of freedom and the conservation laws of a hydrodynamic theory have the same geometric character as those of the Israel-Stewart theory, then such theory must be indistinguishable from the Israel-Stewart theory in the linear regime. This explains why all second-order theories turn out to be identical near equilibrium. Finally, we construct the first linearized model, to our knowledge, for a relativistic supersolid that is proven to be causal, stable, and strongly hyperbolic.

We study a domain wall induced by spontaneously broken ${\mathbb{Z}}_2$ symmetry and its gravitational wave signature in the standard model with a complex scalar in connection with dark matter physics. In a minimal setup, a linear term of the singlet field is added to the scalar potential as an explicit ${\mathbb{Z}}_2$ breaking term to make the domain wall unstable. We obtain its minimal size from cosmological constraints and show that the parameter space that can be probed by current and future pulsar time array experiments requires the vacuum expectation value of the singlet field to be greater than $\mathcal{O}(10–100)\mathrm{TeV}$, along with a singletlike Higgs mass of $\mathcal{O}(1–100)\mathrm{TeV}$. However, such a region is severely restricted by the dark matter relic density, which places an upper bound on the singlet vacuum expectation value at approximately 200 TeV, and limits the dark matter mass to about half of the singletlike Higgs boson mass.

In this paper, we have studied the consequences of the $\mu \text{−}\tau$ reflection symmetry for leptogenesis in the type-I seesaw model with diagonal Dirac neutrino mass matrix. We have first obtained the phenomenologically allowed values of the model parameters, which show that there may exist zero or equal entries in the Majorana mass matrix for the right-handed neutrinos, and then studied their predictions for three right-handed neutrino masses, which show that there may exist two nearly degenerate right-handed neutrinos. Then, we have studied the consequences of the model for leptogenesis. Due to the $\mu \text{−}\tau$ reflection symmetry, leptogenesis can only work in the two-flavor regime. Furthermore, leptogenesis cannot work for the particular case of $r=1$. Accordingly, for some benchmark values of $r\ne 1$, we have given the constraints of leptogenesis for relevant parameters. Furthermore, we have investigated the possibilities of leptogenesis being induced by the renormalization group evolution effects for two particular scenarios. For the particular case of $r=1$, the renormalization group evolution effects will break the orthogonality relations among different columns of $M_{\mathrm{D}}$ and consequently induce leptogenesis to work. For the low-scale resonant leptogenesis scenario which is realized for nearly degenerate right-handed neutrinos, the renormalization group evolution effects can break the $\mu \text{−}\tau$ reflection symmetry and consequently induce leptogenesis to work.

Numerical studies of lattice quantum field theories are conducted in finite spatial volumes, typically with cubic symmetry in the spatial coordinates. Motivated by these studies, this work presents a general algorithm to construct multiparticle interpolating operators for quantum field theories with cubic symmetry. The algorithm automates the block diagonalization required to combine multiple operators of definite linear momentum into irreducible representations of the appropriate little group. Examples are given for distinguishable and indistinguishable particles including cases with both zero and nonzero spin.

Hidden-heavy hadrons can decay into pairs of heavy hadrons through transitions from confining Born-Oppenheimer potentials to hadron-pair potentials with the same Born-Oppenheimer quantum numbers. The transitions are also constrained by conservation of angular momentum and parity. From these constraints, we derive model-independent selection rules for decays of hidden-heavy hadrons into pairs of heavy hadrons. The coupling potentials are expressed as sums of products of Born-Oppenheimer transition amplitudes and angular-momentum coefficients. If there is a single dominant Born-Oppenheimer transition amplitude, it factors out of the coupling potentials between hidden-heavy hadrons in the same Born-Oppenheimer multiplet and pairs of heavy hadrons in specific heavy-quark-spin-symmetry doublets. If furthermore the kinetic energies of the heavy hadrons are much larger than their spin splittings, we obtain analytic expressions for the relative partial decay rates in terms of Wigner $6j$ and $9j$ symbols. We consider in detail the decays of quarkonia and quarkonium hybrids into the lightest heavy-meson pairs. For quarkonia, our model-independent selection rules and relative partial decay rates agree with previous results from quark-pair-creation models in simple cases and give stronger results in other cases. For quarkonium hybrids, we find disagreement even in simple cases.

We present a simple holographic QCD model that provides a unified description of vector mesons and nucleons in a confining background based on Einstein-dilaton gravity. For the confining background, we consider analytical solutions of the Einstein-dilaton equations where the dilaton is a quadratic function of the radial coordinate far from the boundary. We build actions for the 5D gauge field and the 5D Dirac field dual to the 4D flavor current and the 4D nucleon interpolator, respectively. In order to obtain asymptotically linear Regge trajectories, we impose for each sector the condition that the effective Schrödinger equation has a potential that grows quadratically in the radial coordinate far from the boundary. For the vector mesons, we show that this condition is automatically satisfied by a 5D Yang-Mills action minimally coupled to the metric and the dilaton. For the nucleons, we find that the mass term of the 5D Dirac action needs to be generalized to include couplings to the metric and the dilaton. Using Sturm-Liouville theory, we obtain a spectral decomposition for the hadronic correlators consistent with large $N_c$ QCD. Our setup contains only three parameters: the mass scale associated with confinement, the 5D gauge coupling, and the 5D Dirac coupling. The last two are completely fixed by matching the correlators at high energies to perturbative QCD. We calculate masses and decay constants and compare our results against available experimental data. Our model can be thought of as a consistent embedding of soft wall models in Einstein-dilaton gravity.

Stimulated by the observation of a new structure, named ${\mathrm{\Lambda }}_c(2910)$, in the ${\mathrm{\Sigma }}_c(2455{)}^{0,++}{\pi }^{+,-}$ decay channel from B meson decay process by the Belle Collaboration, and the similarity of the ${\mathrm{\Lambda }}_c(2910)/{\mathrm{\Lambda }}_c(2940)$ and $P_c$ states, we investigate the decay behavior of the ${\mathrm{\Lambda }}_c(2910)$ and ${\mathrm{\Lambda }}_c(2940)$ in the $N{D}^{*}$ molecular frame with the possible $J^P$ quantum numbers to be $1/2^{-}$ and $3/2^{-}$. We employ an effective Lagrangian approach to evaluate the partial widths of $ND$, ${\mathrm{\Sigma }}_c\pi$, and ${\mathrm{\Sigma }}_c^{*}\pi$ channels. The estimations in the present work indicate that the $J^P$ quantum numbers of ${\mathrm{\Lambda }}_c(2910)$ and ${\mathrm{\Lambda }}_c(2940)$ are preferred to be $1/2^{-}$ and $3/2^{-}$, respectively. From the present estimations, we also find the branching ratio of ${\mathrm{\Lambda }}_c(3/2)\to {\mathrm{\Sigma }}_c^{*}\pi$ is much larger than that of ${\mathrm{\Lambda }}_c(1/2)\to {\mathrm{\Sigma }}_c^{*}\pi$, thus ${\mathrm{\Sigma }}_c^{*}\pi$ could be a good channel to distinguish the $J^P$ quantum numbers of ${\mathrm{\Lambda }}_c(2910)$ and ${\mathrm{\Lambda }}_c(2940)$. Therefore, we suggest searching for the structure in ${\mathrm{\Sigma }}_c^{*}\pi$ invariant mass distribution in Belle II.

Recently, the BESIII collaboration performed a precise measurement of the $e^{+}{e}^{-}\to \eta J/\psi$ cross section. It is puzzling that the resonance parameters of the reported $Y(4230)$ show a substantial divergence from the previously measured results in both the open-charmed and hidden-charmed decay channels, and the line shape asymmetry of the data approaching 4.2 GeV also suggests that it might be difficult to characterize the details of the structure around 4.2 GeV by a single resonance. This has motivated our great curiosity about how the charmonium states are distributed in the measured energy range and how they shape the puzzling data of the $e^{+}{e}^{-}\to \eta J/\psi$ cross section. In this work, we use five theoretically constructed charmonia in the range of 4.0–4.5 GeV, i.e., $\psi (4040)$, $\psi (4160)$, $\psi (4220)$, $\psi (4380)$, and $\psi (4415)$, to apply a combined fit to the data, in which their calculated decay ratios into $\eta J/\psi$ via hadronic loop mechanism are taken as input. The fit results can reproduce the measured cross section data well, especially for the subtle line shape around 4.2 GeV, showing that the structure around 4.2 GeV is possible from the contribution of both $\psi (4160)$ and $\psi (4220)$.

Using a data sample of $e^{+}{e}^{-}$ collision data corresponding to an integrated luminosity of $19{\mathrm{fb}}^{-1}$ collected with the BESIII detector at the BEPCII collider, we search for the production of deuterons and antideuterons via $e^{+}{e}^{-}\to pp{\pi }^{-}\overline{d}+\mathrm{c}.\mathrm{c}.$ for the first time at center-of-mass energies between 4.13 and 4.70 GeV. No significant signal is observed and the upper limit of the $e^{+}{e}^{-}\to pp{\pi }^{-}\overline{d}+\mathrm{c}.\mathrm{c}.$ cross section is determined to be from 9.0 to 145 fb depending on the center-of-mass energy at the 90% confidence level.