Thermal dark matter at the MeV mass scale has its abundance set during the highly nontrivial epochs of neutrino decoupling and electron annihilation. The technical obstacles attached to solving Boltzmann equations of multiple interacting sectors being both relativistic and nonrelativistic have to-date prevented the full treatment of this problem. Here, for the first time, we calculate the freeze-out of light dark matter, taking into account the energy transfer between the dark sector, neutrinos, and the electromagnetically interacting plasma from annihilation and elastic scattering processes alike. We develop a numerically feasible treatment that allows to track photon and neutrino temperatures across freeze-out and to arrive at a precision prediction of $N_{\mathrm{eff}}$ for arbitrary branching ratios of the dark matter annihilation channels. In addition, our treatment resolves for the first time the dark matter temperature evolution across freeze-out involving three sectors. It enters in the efficiency of velocity-dependent annihilation channels and for a flavor-blind $p$-wave annihilation into electron- and neutrino-pairs of all generations, we find the present Planck data exclude a complex scalar dark matter particle of mass of $m_{\varphi }\le 7\mathrm{MeV}$.

We present a gauged baryon number model as an example of models where all new fermions required to cancel out the anomalies help to solve phenomenological problems of the standard model (SM). Dark fermion doublets, along with the isosinglet charged fermions, in conjunction with a set of SM-singlet fermions, participate in the generation of small neutrino masses through the Dirac-dark Zee mechanism. The other SM-singlets explain the dark matter in the Universe, while their coupling to an inert singlet scalar is the source of the $CP$ violation. In the presence of a strong first-order electroweak phase transition, this “dark” $CP$ violation allows for a successful electroweak baryogenesis mechanism.

We explore the effective field theory of a vector field $X^{\mu }$ that has a Stückelberg mass. The absence of a gauge symmetry for $X^{\mu }$ implies Lorentz-invariant operators are constructed directly from $X^{\mu }$. Beyond the kinetic and mass terms, allowed interactions at the renormalizable level include $X_{\mu }{X}^{\mu }{H}^{†}H$, $(X_{\mu }{X}^{\mu }{)}^2$, and $X_{\mu }{j}^{\mu }$, where $j^{\mu }$ is a global current of the SM or of a hidden sector. We show that all of these interactions lead to scattering amplitudes that grow with powers of $\sqrt{s}/m_X$, except for the case of $X_{\mu }{j}^{\mu }$ where $j^{\mu }$ is a nonanomalous global current. The latter is well known when $X$ is identified as a dark photon coupled to the electromagnetic current, often written equivalently as kinetic mixing between $X$ and the photon. The power counting for the energy growth of the scattering amplitudes is facilitated by isolating the longitudinal enhancement. We examine in detail the interaction with an anomalous global vector current $X_{\mu }{j}_{\mathrm{anom}}^{\mu }$, carefully isolating the finite contribution to the fermion triangle diagram. We calculate the longitudinally-enhanced observables $Z\to X\gamma$ (when $m_X<m_Z$), $f\overline{f}\to X\gamma$, and $Z\gamma \to Z\gamma$ when $X$ couples to the baryon number current. Introducing a “fake” gauge-invariance by writing $X^{\mu }=A^{\mu }-{\partial }^{\mu }\pi /m_X$, the would-be gauge anomaly associated with $A_{\mu }{j}_{\mathrm{anom}}^{\mu }$ is canceled by $j_{\mathrm{anom}}^{\mu }{\partial }_{\mu }\pi /m_X$; this is the four-dimensional Green-Schwarz anomaly-cancellation mechanism at work. Our analysis demonstrates there is a much larger set of possible interactions that an EFT with a Stückelberg vector field can have, revealing scattering amplitudes that grow with energy. The growth of these amplitudes can be tamed by a dark Higgs sector, but this requires dark Higgs boson interactions (and reintroduces fine-tuning in the dark Higgs sector) that can be separated from $X$ interactions only in the limit $g\ll 1$.

The light axial vector mesons can couple to $K^{*}\overline{K}+\mathrm{c}.\mathrm{c}.$ in an $S$ wave at the tree level. Because of the near-threshold $S$-wave interactions, the couplings can be affected by the final state interactions. It is of peculiar interest that the pion exchange between $K^{*}\overline{K}+\mathrm{c}.\mathrm{c}.$ can go through a triangle diagram which is within the kinematics of the triangle singularity. This mechanism will introduce energy dependence and a $D$-wave amplitude to the vertex couplings. Hence, it should be necessary to investigate the role played by the $K^{*}\overline{K}+\mathrm{c}.\mathrm{c}.$ threshold in order to have a better understanding of the light axial vector spectrum.

We present new constraints on light dark matter boosted by cosmic rays (CRDM) using the 205.4 kg day data of the CDEX-10 experiment conducted at the China Jinping Underground Laboratory. The Monte Carlo simulation package cjpl_ess was employed to evaluate the Earth shielding effect. Several key factors have been introduced and discussed in our CRDM analysis, including the contributions from heavier CR nuclei than proton and helium, the inhomogeneity of CR distribution, and the impact of the form factor in the Earth attenuation calculation. Our result excludes the dark matter–nucleon elastic scattering cross section region from $1.7\times {10}^{-30}$ to ${10}^{-26}{\mathrm{cm}}^2$ for dark matter of $10\mathrm{keV}/c^2$ to $1\mathrm{GeV}/c^2$.

A haloscope of the QUAX–$a\gamma$ experiment, composed of an high-$Q$ resonant cavity immersed in a 8 T magnet and cooled to $\sim 4.5\mathrm{K}$ is operated to search for galactic axions with mass $m_a\simeq 42.8\mu \mathrm{eV}$, not accessible to other running experiments. The design of the cavity with hollow dielectric cylinders concentrically inserted in a OFHC Cu cavity, allowed us to maintain a loaded quality-factor $\mathrm{Q}\sim 300000$ during the measurements in presence of magnetic field. Through the cavity tuning mechanism it was possible to modulate the resonance frequency of the haloscope in the region $10.35337-10.35345\mathrm{GHz}$ and thus acquire different datasets at different resonance frequencies. Acquiring each datasets for about 50 minutes, combining them and correcting for the axion’s signal estimation-efficiency, we set a limit on the axion-photon coupling $g_{a\gamma \gamma }<0.731\times {10}^{-13}{\mathrm{GeV}}^{-1}$ with the confidence level set at 90%.

The fixed area states are previously discussed in the quantum error-correction codes interpretation of $\mathrm{AdS}/\mathrm{CFT}$. The dual bulk geometry is constructed by gravitational path integrals. In this paper we show the fixed area states correspondence in conformal field theories (CFTs), which are associated with the spectrum decomposition of reduced density matrix ${\rho }_A$ for a subsystem $A$. For two-dimensional CFTs we directly build the bulk metric, which is consistent with the expected geometry of the fixed area states. For arbitrary pure state $|\psi ⟩$ with a geometric dual in the bulk we also find the consistency by using the gravity dual of Rényi entropy. We also obtain the parameters relation between the bulk geometry and boundary state. The pure state $|\psi ⟩$ can be expanded as a superposition of the fixed area states. Motivated by this, we propose an area operator ${\widehat{A}}^{\psi }$. The fixed area state is the eigenstate of ${\widehat{A}}^{\psi }$, the associated eigenvalue is related to the Rényi entropy of subsystem $A$ in this state. The Ryu-Takayanagi formula can be expressed as the expectation value $⟨\psi |{\widehat{A}}^{\psi }|\psi ⟩$ divided by $4G$, where $G$ is the Newton constant. We further show the fluctuation of the area operator in the geometric state $|\psi ⟩$ is suppressed in the semiclassical limit $G\to 0$.

The Unruh effect states an accelerated particle detector registers a thermal response when moving through the Minkowski vacuum, and its thermal feature is believed to be inseparable from Lorentz symmetry: Without the latter, the former disappears. Here we propose to observe the analog circular Unruh effect using an impurity atom in a quasi-two-dimensional Bose-Einstein condensate (BEC) with dominant dipole-dipole interactions between atoms or molecules in the ultracold gas. Quantum fluctuations in the condensate possess a Bogoliubov spectrum ${\omega }_{\mathbf{k}}=c_0|\mathbf{k}|f(\hslash c_0|\mathbf{k}|/M_{*})$, working as an analog Lorentz-violating quantum field with the Lorentz-breaking scale $M_{*}$, and the impurity acts as an effective Unruh-DeWitt detector thereof. When the detector travels close to the sound speed, observation of the Unruh effect in our quantum fluid platform becomes experimentally feasible. In particular, the deviation of the Bogoliubov spectrum from the Lorentz-invariant case is highly engineerable through the relative strength of the dipolar and contact interactions, and thus a viable laboratory tool is furnished to experimentally investigate whether the thermal characteristic of the Unruh effect is robust to the breaking of Lorentz symmetry.

We study a Jordanian deformation of the ${\mathrm{AdS}}_5\times S^5$ superstring that preserves 12 superisometries. It is an example of homogeneous Yang-Baxter deformations, a class that generalizes TsT deformations to the non-Abelian case. Many of the attractive features of TsT carry over to this more general class, from the possibility of generating new supergravity solutions to the preservation of world sheet integrability. In this paper, we exploit the fact that the deformed $\sigma$-model with periodic boundary conditions can be reformulated as an undeformed one with twisted boundary conditions and discuss the construction of the classical spectral curve and its semiclassical quantization. First, we find global coordinates for the deformed background and identify the global time corresponding to the energy that should be computed in the spectral problem. Using the curve of the twisted model, we obtain the one-loop correction to the energy of a particular solution, and we find that the charge encoding the twisted boundary conditions does not receive an anomalous correction. Finally, we give evidence suggesting that the unimodular version of the deformation (giving rise to a supergravity background) and the nonunimodular one (whose background does not solve the supergravity equations) have the same spectrum at least to one-loop.

Recently it has been shown by Almheiri and Lin [1] that the reconstruction of a black-hole interior is sensitive to knowing the exact coupling of the boundary theory even if the coupling is irrelevant. This motivates us to enlarge the set of the one-time and two-time toy models inspired from the Sachdev-Ye-Kitaev by deforming the same with “irrelevant” coupling. We find that half-wormholes, as well as the wormholes, persist in the presence of the deformation, leading to a similar mechanism for curing the factorization problem. While for the one-time case, the deformed partition function and its moments change by an overall factor, which can completely be absorbed into a renormalization of coupling; for the two-time (or coupled one-time) Sachdev-Ye-Kitaev we find nontrivial dynamics of the saddles as the couplings are varied. Curiously, the irrelevant deformations that we consider can also be thought of as an ensemble average over an overall scaling of the original undeformed Hamiltonian with an appropriate probability distribution; this allows for the possibility that half-wormholes may also be present in suitably defined ensemble of theories.

Observation of gravitationally induced entanglement between two massive particles can be viewed as implying the existence of the nonclassical nature of gravity. However, weak interaction in the gravitational field is extremely small so that gravitationally induced entanglement is exceptionally challenging to test in practice. For addressing this key challenge, here we propose a criterion based on the logical contradictions of weak entanglement, which may boost the sensitivity of the signal due to the gravitationally induced entanglement. Specifically, we make use of the weak-value scenario and Einstein-Podolsky-Rosen steering. We prove that it is impossible for a classical mediator to act on two local quantum objects to simulate amplified-weak-value phenomenon in two-setting Einstein-Podolsky-Rosen steering. Our approach can amplify the signal of gravitationally induced entanglement that were previously impossible to observe by any desired factor that depends on the magnitude of the weak value. Our results not only open up the possibility of exploring nonclassical nature of gravity in the near future, but they also pave the way for weak entanglement criterion of a more general nature.

We explore the dynamics of boson stars in the presence of axionic couplings through nonlinear evolutions of Einstein’s field equations. We show that, for large axionic couplings, isolated boson stars become unstable, and decay via a large burst of electromagnetic radiation, becoming less massive and more dilute. Our full nonlinear results are in good agreement with flat-space estimates for the critical couplings. We then consider head-on collisions of subcritical boson stars and study the electromagnetic and gravitational signal. Boson stars cluster around the critical point via interactions, and we argue that mergers will generically be also sources of electromagnetic radiation, in addition to gravitational waves, which can be used to place constraints on the axionic coupling if such multimessenger signals are detected.

Higher-order photon rings can be expected to be detected in a more detailed image of the black hole found in future observations. These rings are lensed images of the luminous matter surrounding the black hole and are formed by photons that loop around it. In this paper we have succeeded to derive an analytical expression for the shape of the higher-order rings in the form that is most convenient for application: the explicit equation of the curve in polar coordinates. The formula describes the apparent shape of the higher-order image of the circular ring with the given radius around Schwarzschild black hole as viewed by distant observer with an arbitrary inclination. For the derivation, the strong deflection limit of the gravitational deflection is used. Our formula is a simple and efficient alternative to the numerical calculation of ray trajectories, with the main application to studying the shape of $n=2$ and $n=3$ photon rings.

With the advent of gravitational-wave astronomy it has now been possible to constrain modified theories of gravity that were invoked to explain the dark energy. In a class of dilaton models, distances to cosmic sources inferred from electromagnetic and gravitational wave observations would differ due to the presence of a friction term. In such theories, the ratio of the Newton’s constant to the fine structure constant varies with time. In this paper we explore the degree to which it will be possible to test such models. If collocated sources (e.g., supernovae and binary neutron star mergers), but not necessarily multimessengers, can be identified by electromagnetic telescopes and gravitational-wave detectors one can probe if light and gravitational radiation are subject to the same laws of propagation over cosmological distances. This helps in constraining the variation of Newton’s constant relative to fine-structure constant. The next generation of gravitational wave detectors, such as the Cosmic Explorer and Einstein Telescope, in tandem with the Vera Rubin Observatory and gamma ray observatories such as the Fermi Space Observatory will be able to detect or constrain such variations at the level of a few parts in 100. We apply this method to GW170817 with distances inferred by the LIGO and Virgo detectors and the observed Kilonova.

A scalar charged particle moving in a curved background spacetime will emit a field affecting its own motion; the resolving of this resulting motion is often referred to as the self-force problem. This also serves as a toy model for the astrophysically interesting compact-body binaries, extreme mass ratio inspirals, targets for the future space-based gravitational wave detector, LISA. In the modeling of such systems, a point-particle assumption leads to problematic singularities which need to be safely removed to solve for the motion of the particle regardless of the scenario; scalar, electromagnetic, or gravitational. Here, we concentrate on a scalar charged particle and calculate the next order of the Detweiler-Whiting singular field and its resulting regularization parameter when employing the mode-sum method of regularization. This enables sufficiently faster self-force calculations giving the same level of accuracy with significantly less $\ell$ modes. Due to the similarity of the governing equations, this also lays the groundwork for similar calculations for an electromagnetic or mass charged particle in Kerr spacetime and has applications in other regularization schemes like the effective source and matched expansion.

We present an analog model for the Bañados, Teitelboim, Zanelli (BTZ) black hole based on a hydrodynamical flow. We numerically solve the fully nonlinear hydrodynamic equations of motion and observe the excitation and decay of the analog BTZ quasinormal modes in the process. We consider both a small perturbation in the steady state configuration of the fluid and a large perturbation; the latter could be regarded as an example of formation of the analog (acoustic) BTZ black hole.

Spatially homogeneous cosmological spacetimes evolving in the presence of a positive cosmological constant and matter satisfying some reasonable energy conditions, typically approach the de Sitter geometry asymptotically (at least locally). In this work, we propose an alternative way to characterize this phenomena. We focus on a subset of such models admitting a generalized Kerr-Schild representation. We argue that the functions which define such a representation can be chosen, such that, their asymptotic behavior makes the evolution toward the de Sitter spacetime manifest through the representation. We verify our claim for the Kantowski-Sachs family of cosmological spacetimes.

We use observations of ultrafaint dwarf (UFD) galaxies to constrain the particle mass of ultralight dark matter. Potential fluctuations created by wave interference in virialized “fuzzy” dark matter (FDM) halos dynamically heat stellar orbits in UFDs, some of which exhibit velocity dispersions of $\lesssim 3\mathrm{km}/\mathrm{s}$ and sizes $\lesssim 40\mathrm{pc}$. Using simulations of FDM halos, and existing measurements of sizes and stellar radial velocities in Segue 1 and Segue 2 UFDs, we derive a lower limit on the dark matter particle mass of $m_{\mathrm{FDM}}>3\times {10}^{-19}\mathrm{eV}$ at 99% confidence, marginalized over host halo circular velocity. This constraint is conservative as it is derived under the assumption that soliton heating is negligible, and that no other sources of non-FDM dynamical heating of stars operate to increase velocity dispersion. It can potentially be strengthened by future spectroscopic observations of additional stars in ultrafaint galaxies and by tightening theoretical constraints on the soliton size-halo mass relation. However, even the current conservative lower limit on the ultralight dark matter mass makes it indistinguishable from cold dark matter at the scales probed by existing astronomical observations.

We consider a general choice of integration constants in the resolution of the dynamical equations derived from a recently proposed effective model that describes black hole spacetimes in the context of loop quantum cosmology. The interest of our analysis is twofold. On the one hand, it allows for a study of the entire space of solutions of the model, which is absent in the literature and is fundamental for understanding the relation with any underlying quantum theory. On the other hand, choices of integration constants that generalize the type of solutions considered so far may lead to exotic behaviors in the effective black hole geometry, as well as modified thermodynamical properties. With these motivations in mind, we discuss the interior and exterior geometries, and present the conditions that a satisfactory matching at the horizons imposes. Then, we turn our attention to the Hawking temperature associated with the black horizon of the model, which we find to be affected by the freedom of choice of integration constants. Finally, we briefly comment on the asymptotic structure of the general solution and compare different notions of mass.

Recent progress in phonon-mediated detectors with eV-scale nuclear recoil energy sensitivity requires an understanding of the effect of the crystalline defects on the energy spectrum expected from dark matter or neutrino coherent scattering. We perform molecular dynamics simulations to determine the amount of energy stored in the lattice defects as a function of the recoil direction and energy. This energy cannot be observed in the phonon measurement, thus affecting the observed energy spectrum compared to the underlying true recoil energy spectrum. We describe this effect for multiple commonly used detector materials and demonstrate how the predicted energy spectrum from dark matter scattering is modified.