In this work we study the background evolution and the early time behavior of scalar cosmological perturbations with an ultralight vector dark matter. We present a model for vector dark matter in an anisotropic Bianchi type I universe. Vector fields source anisotropies in the early Universe characterized by a shear tensor which rapidly decays once the fields start oscillating, making them viable dark matter candidates. We present the set of equations needed to evolve scalar cosmological perturbations in the linear regime, both in synchronous gauge and Newtonian gauge. We show that the shear tensor has to be taken into account in the calculation of adiabatic initial conditions.

The theory of inflation provides an elegant explanation for the nearly flat Universe observed today, which represents one of the pillars of the standard cosmological model. However, recent studies have reported some deviations from a flat geometry, arguing that a closed universe would be instead favored by observations. Given its central role played in the cosmological context, this paper revisits the issue of spatial curvature in light of the stochastic gravitational wave background signal recently detected by the NANOGrav Collaboration. For this purpose, we investigate the primordial gravitational waves generated during inflation and their propagation in the postinflationary Universe. We propose a new parametrization of the gravitational wave power spectrum, taking into account spatial curvature, the tensor-to-scalar ratio, and the spectral index of tensor perturbations. Therefore, we compare the theoretical predictions with NANOGrav data to possibly constrain the geometry of the Universe. We find that the choice of the priors has a significant effect on the computed posterior distributions. In particular, using flat uniform priors results in ${\mathrm{\Omega }}_{\mathcal{K},0}=0.00\pm 0.67$ at the 68% confidence level. On the other hand, imposing a Planck prior, we obtain ${\mathrm{\Omega }}_{\mathcal{K},0}=-0.05\pm 0.17$ at the 68% confidence level. This result aligns with the analysis of the cosmic microwave background radiation, and no deviations from a flat universe are found.

We present a novel mechanism for gravitational wave generation in the early Universe. Light spectator scalar fields during inflation can acquire a blue-tilted power spectrum due to stochastic effects. We show that this effect can lead to large curvature perturbations at small scales (induced by the spectator field fluctuations) while maintaining the observed, slightly red-tilted curvature perturbations at large cosmological scales (induced by the inflaton fluctuations). Along with other observational signatures, such as enhanced dark matter substructure, large curvature perturbations can induce a stochastic gravitational wave background (SGWB). The predicted strength of SGWB in our scenario, ${\mathrm{\Omega }}_{\mathrm{GW}}{h}^2\simeq {10}^{-20}–{10}^{-15}$, can be observed with future detectors, operating between ${10}^{-5}\mathrm{Hz}$ and 10 Hz. We note that, in order to accommodate the newly reported NANOGrav observation, one could consider the same class of spectator models. At the same time, one would need to go beyond the simple benchmark considered here and consider a regime in which a misalignment contribution is also important.

Recent measurements of the 4-point correlation functions (4PCF) from spectroscopic surveys provide evidence for parity violations in the large-scale structure of the Universe. If physical in origin, this could point to exotic physics during the epoch of inflation. However, searching for parity violations in the 4PCF signal relies on a large suite of simulations to perform a rank test, or an accurate model of the 4PCF covariance to claim a detection, and this approach is incapable of extracting parity information from the higher-order $N$-point functions. In this work we present an unsupervised method which overcomes these issues, before demonstrating the approach is capable of detecting parity violations in a few toy models using convolutional neural networks. This technique is complementary to the 4-point method and could be used to discover parity violations in several upcoming surveys including DESI, Euclid, and Roman.

Astrometric perturbations of critical curves in strong lens systems are thought to be one of the most promising probes of substructures down to small-mass scales. While a smooth mass distribution creates a symmetric geometry of critical curves with radii of curvature about the Einstein radius, substructures introduce small-scale distortions on critical curves, which can break the symmetry of gravitational lensing events near critical curves, such as highly magnified individual stars. We derive a general formula that connects the fluctuation of critical curves with the fluctuation of the surface density caused by substructures, which is useful when constraining models of substructures from observed astrometric perturbations of critical curves. We numerically check that the formula is valid and accurate as long as substructures are not dominated by a small number of massive structures. As a demonstration of the formula, we also explore the possibility that an anomalous position of an extremely magnified star, recently reported as “Mothra,” can be explained by fluctuations in the critical curve due to substructures. We find that cold dark matter subhalos with masses ranging from $5\times {10}^7{M}_{\odot }/h$ to ${10}^9{M}_{\odot }/h$ can well explain the anomalous position of Mothra, while in the fuzzy dark matter model, the very small mass of $\sim {10}^{-24}\mathrm{eV}$ is needed to explain it.

The inflationary reheating phase begins when accelerated expansion ends. As all Standard Model particles are coupled to gravity, gravitational interactions will lead to particle production. This includes the thermal bath, dark matter, and gravitational radiation. Here, we compute the spectrum of gravitational waves from the inflaton condensate during the initial phase of reheating. As particular examples of inflation, we consider the Starobinsky model and T models, all of which are in good phenomenological agreement with cosmic microwave background anisotropy measurements. The T models are distinguished by the shape of the potential about its minimum and can be approximated by $V\sim {\varphi }^k$, where $\varphi$ is the inflaton. Interestingly, the shape of the gravitational wave spectrum (when observed) can be used to distinguish among the models considered. As we show, the Starobinsky model and T models with $k=2$, provide very different spectra when compared to models with $k=4$ or $k>4$. Observation of multiple harmonics in the spectrum can be interpreted as a direct measurement of the inflaton mass. Furthermore, the cutoff in frequency can be used to determine the reheating temperature.

We develop an optimization-based maximum likelihood approach to analyze the cross-correlation of the cosmic microwave background (CMB) and large-scale structure induced by the kinetic Sunyaev-Zeldovich (kSZ) effect. Our main goal is to reconstruct the radial velocity field of the Universe. While the existing quadratic estimator (QE) is statistically optimal for current and near-term experiments, the likelihood can extract more signal-to-noise in the future. Our likelihood formulation has further advantages over the QE, such as the possibility of jointly fitting cosmological and astrophysical parameters and the possibility of unifying several different kSZ analyses. We implement an autodifferentiable likelihood pipeline in JAX, which is computationally tractable for a realistic survey size and resolution, and evaluate it on the Agora simulation. We also implement a machine-learning-based estimate of the electron density given an observed galaxy distribution, which can increase the signal-to-noise for both the QE and the likelihood method.

The influence of the dark matter mass ($M_{\chi }$) and the Fermi momentum ($k_F^{\mathrm{DM}}$) on the $f_0$-mode oscillation frequency, damping time parameter, and tidal deformability of hadronic stars are studied by employing a numerical integration of hydrostatic equilibrium, nonradial oscillation, and tidal deformability equations. The matter inside the hadronic stars follows the NL3* equation of state. We obtain that the influence of $M_{\chi }$ and $k_F^{\mathrm{DM}}$ is observed in the $f_0$-mode, damping tome parameter, and tidal deformability. Finally, the correlation between the tidal deformability of the GW170817 event with $M_{\chi }$ and $k_F^{\mathrm{DM}}$ are also investigated.

We explore the possibility that high-energy (HE) neutrinos produced from choked jets can be annihilated with low-energy neutrinos emitted from the accretion disk around a black hole in binary neutron star mergers and rare core-collapse supernovae. For HE neutrinos produced close to the stellar center ($\lesssim {10}^9–{10}^{12}\mathrm{cm}$), we find that the emerging all-flavor spectrum for neutrinos of $E\gtrsim 0.1–1\mathrm{PeV}$ could be modified by a factor $E^{-n}$ with $n\gtrsim 0.4–0.5$ under realistic conditions. Flavor evolution of low-energy neutrinos does not affect this result but can change the emerging flavor composition of HE neutrinos. As a consequence, the above annihilation effect may need to be considered for HE neutrinos produced from choked jets at small radii. We briefly discuss the annihilation effects for different HE neutrino production models and point out that such effects could be tested through precise measurements of the diffuse neutrino spectrum and flavor composition.

Very recent work has identified a new satellite galaxy, Ursa Major III/UNIONS I, which is the faintest such system ever observed. Dynamical considerations indicate that if the system is in equilibrium, it is likely to be highly dark matter dominated. This, in combination with its proximity, predicts that it may be the preeminent dwarf spheroidal galaxy target for dark matter indirect detection searches. We utilize 15 years of Fermi-LAT data to search for $\gamma$-ray emission from Ursa Major III. Finding no excess, we set strong constraints on dark matter annihilation. Intriguingly, if the high J-factor of Ursa Major III is confirmed, standard thermal dark matter annihilation to $b\overline{b}$ final states would be ruled out for dark matter masses up to 4 TeV. The discovery of Ursa Major III, combined with recent tentative measurements of other high J-factor systems, suggests the exciting possibility that near-future data could produce transformative constraints on thermal dark matter.

We investigate the effects of the asymmetric pulse shapes on electron-positron pair production in a field with three different cases of chirping via the real-time Dirac-Heisenberg-Wigner formalism. Our findings reveal the disappearance of interference effects with shorter falling pulse length, and the peak is concentrated on the left side of the momentum spectrum. As the falling pulse length extends, an incomplete multiring structure appears in the momentum spectrum. The number density of particles are very sensitive to the asymmetry of the pulse. With a long falling pulse, the number density can be significantly enhanced by over four orders of magnitude when certain frequency chirps are utilized. These results highlight the impact of the effective dynamically assisted mechanism and the frequency chirp on pair creation.

In this work, we discuss the electromagnetic properties of the $S$-wave and $D$-wave $T_{cc}^{+}$ molecular states, which include the magnetic moments, transition magnetic moments, and radiative decay widths. According to our results, the magnetic moment of $T_{cc}^{+}$ state observed experimentally is $-0.09{\mu }_N$. Meanwhile, we also discuss the relations between the transition magnetic moments of the $S$-wave $T_{cc}^{+}$ molecular states and the radiative decay widths, and we analyze the proportionality between the magnetic moments of the $T_{cc}^{+}$ molecular states. These results provide further information on the inner structure of $T_{cc}^{+}$ molecular states and deepen the understanding of electromagnetic properties of doubly charmed tetraquarks.

We investigate anomalies in the class of nonlocal field theories that have been proposed as an ultraviolet completion of four-dimensional quantum field theory with generalizing the kinetic energy operators to an infinite series of higher derivatives inspired by the string field theory and ghost-free nonlocal approaches to quantum gravity. We explicitly calculate the vector and chiral anomalies in a string-inspired nonlocal extension of QED. We show that the vector anomaly vanishes as required by gauge invariance and the Ward identity. On the other hand, although the chiral anomaly vanishes to the leading order with massless fermions, it nonetheless does not vanish with the massive fermions and we calculate it to the leading order in the scale of nonlocality. We also calculate the nonlocal vector and axial currents explicitly and present an illustrative example by applying our results to the decay of ${\pi }^0\to \gamma \gamma$.

The simplest cosmologies motivate the consideration of dark matter subcomponents that interact significantly with normal matter. Moreover, such strongly coupled relics may have evaded detection to date if upon encountering the Earth they rapidly thermalize down to terrestrial temperatures, $T_{\oplus }\sim 300\mathrm{K}\sim 25\mathrm{meV}$, well below the thresholds of most existing dark matter detectors. This shedding of kinetic energy implies a drastic enhancement to the local density, motivating the consideration of alternative detection techniques sensitive to a large density of slowly moving dark matter particles. In this work, we provide a rigorous semianalytic derivation of the terrestrial overdensities of strongly coupled relics, with a particular focus on millicharged particles (MCPs). We go beyond previous studies by incorporating improved estimates of the MCP-atomic scattering cross section, new contributions to the terrestrial density of sub-GeV relics that are independent of the Earth’s gravitational field, and local modifications that can arise due to the cryogenic environments of precision sensors. We also generalize our analysis in order to estimate the terrestrial density of thermalized MCPs that are produced from the collisions of high-energy cosmic rays and become bound by the Earth’s electric field.

Motivated by the observation that tiny neutrino mass cannot be explained within the framework of the Standard Model, we consider extra gauge extended scenarios in which tiny neutrino masses are generated through the seesaw mechanism. These scenarios are equipped with a beyond the Standard Model neutral gauge boson called $Z^{\prime }$ in the general $U(1{)}_X$ symmetry, which is a linear combination of $U(1{)}_Y$ and $U(1{)}_{B-L}$. In this case, left- and right-handed fermions interact differently with the $Z^{\prime }$. The $Z^{\prime }$ gives rise to different processes involving neutrino-nucleon, neutrino-electron, electron-nucleus, and electron-muon scattering processes. By comparing with proton and electron beam-dump experiment data, recast data from searches for the long-lived and dark photon at BABAR, LHCb, and CMS experiments, the electron and muon $g-2$ data, and the data of the dilepton and dijet searches at the LEP experiment, we derive bounds on the gauge coupling and the corresponding gauge boson mass for different $U(1{)}_X$ charges and evaluate the prospective limits from the future beam-dump scenarios at DUNE, FASER (2), and ILC. We conclude that large parameter regions could be probed by scattering, beam-dump, and collider experiments in the future.

Kinematics restricts the ability of rare charm decays to explore the charged lepton-flavor-violation processes mediated by the quark-level $c\to u\ell \tau$ transition. To fill the gap, we propose exploring new physics (NP) through the quasielastic scattering process $e^{-}p\to {\tau }^{-}{\mathrm{\Lambda }}_c$ and the polarization of the $\tau$ lepton. As analyzing modes for the $\tau$ polarization, we consider the decays ${\tau }^{-}\to {\pi }^{-}{\nu }_{\tau }$, ${\tau }^{-}\to {\rho }^{-}{\nu }_{\tau }$, and ${\tau }^{-}\to {\ell }^{-}{\overline{\nu }}_{\ell }{\nu }_{\tau }$, and show that the $\tau$ polarization components can be extracted from analyzing the kinematics of the $\tau$ visible decay products. In the framework of a general low-energy effective Lagrangian, we then perform a detailed analysis of the polarization components in various aspects and scrutinize possible NP signals. With one upcoming experimental setup, we finally demonstrate promising event rate can be expected for the cascade process and, even in the worst-case scenario—no signals are observed at all—it can still provide a competitive potential for constraining the NP, compared with those from the high-$p_T$ dilepton invariant mass tails at high-energy colliders.

With the motivation of explaining the dark matter and achieving the electroweak baryogenesis via the spontaneous $CP$ violation at high temperature, we propose a complex singlet scalar ($S=\frac{\chi +i{\eta }_s}{\sqrt{2}}$) extension of the two-Higgs-doublet model respecting a discrete dark $CP$ symmetry: $S\to -S^{*}$. The dark $CP$ symmetry guarantees $\chi$ to be a dark matter candidate on one hand and on the other hand allows ${\eta }_s$ to have mixings with the pseudoscalars of the Higgs doublet fields, which play key roles in generating the $CP$ violation sources needed by the electroweak baryogenesis at high temperature. The Universe undergoes multistep phase transitions, including a strongly first-order electroweak phase transition during which the baryon number is produced. At the present temperature, the observed vacuum is produced and the $CP$ symmetry is restored so that the stringent electric dipole moment experimental bounds are satisfied. Considering relevant constraints, we study the simple scenario of $m_{\chi }$ around the Higgs resonance region, and find that the dark matter relic abundance and the baryon asymmetry can be simultaneously explained. Finally, we briefly discuss the gravitational wave signatures at future space-based detectors and the LHC signatures.

We study $S$-wave interactions in the $I(J^p)=1/2(1/2^{-}){\mathrm{\Lambda }}_c{K}^{+}-p{D}_s$ system on the basis of the coupled-channel Hadrons to Atomic nuclei from Lattice Quantum ChromoDynamics method. The potentials which are faithful to QCD S-matrix below the $p{D}^{*}$ threshold are extracted from Nambu-Bethe-Salpeter wave functions on the lattice in flavor SU(3) limit. For the simulation, we employ 3-flavor full QCD gauge configurations on a ${(1.93\mathrm{fm})}^3$ volume at $m_{\pi }\simeq 872\mathrm{MeV}$. We present our results of the S-wave coupled-channel potentials for the ${\mathrm{\Lambda }}_c{K}^{+}-p{D}_s$ system in the $1/2(1/2^{-})$ state as well as scattering observables obtained from the extracted potential matrix. We observe that the coupling between ${\mathrm{\Lambda }}_c{K}^{+}$ and $p{D}_s$ channels is weak. The phase shifts and scattering length obtained from the extracted potential matrix show that the ${\mathrm{\Lambda }}_c{K}^{+}$ interaction is attractive at low energy and stronger than the $p{D}_s$ interaction though no bound state at $m_{\pi }\ge 872\mathrm{MeV}$.

We study the effect of external proper time-dependent longitudinal forces on the evolution of the distribution function using the Boltzmann equation with a relaxation time collision kernel under Bjorken flow. We derive an exact solution and study the early time attractor behavior of different components of energy-momentum tensor under Bjorken symmetry. We show that the arbitrary initial data approaches the attractor solution but is influenced by the external force with slightly broken Bjorken symmetry.

We use the linear sigma model with quarks to study the magnetic-field-induced modifications on the longitudinal screening mass for the neutral pion at one-loop level. The effects of the magnetic field are introduced into the self-energy, which contains the contributions from all the model particles. We find that, to obtain a reasonable description for the behavior with the field strength, we need to account for the magnetic field dependence of the particle masses. We also find that the couplings need to decrease fast enough with the field strength to then reach constant and smaller values as compared to their vacuum ones. The results illustrate the need to treat the magnetic corrections to the particle masses and couplings in a self-consistent manner, accounting for the backreaction of the field effects for the magnetic field dependence of the rest of the particle species and couplings in the model.