Collective neutrino oscillations play a crucial role in transporting lepton flavor in astrophysical settings, such as supernovae, where the neutrino density is large. In this regime, neutrino-neutrino interactions are important and simulations in the mean-field approximation show evidence for collective oscillations occurring at timescales much shorter than those associated with vacuum oscillations. In this work, we study the out-of-equilibrium dynamics of a corresponding spin model using matrix product states and show how collective bipolar oscillations can be triggered by many-body correlations if appropriate initial conditions are present. We find entanglement entropies scaling at most logarithmically in the system size suggesting that classical tensor network methods could be efficient in describing collective neutrino dynamics more generally. These observation provide a clear path forward, not only to increase the accuracy of current simulations, but also to elucidate the mechanism behind collective flavor oscillations without resorting to the mean-field approximation.

As a well-motivated dark matter candidate, axions can be detected through the axion-photon resonant conversion in the magnetospheres of magnetic white dwarf stars or neutron stars. In this work, we utilize Omega Centauri, which is the largest globular cluster in the Milky Way and is suggested to be the remnant core of a dwarf galaxy, to probe the axion dark matter through radio signals that originate from all the neutron stars and magnetic white dwarf stars in it. With 100 h of observation, the combination of the radio telescopes Square Kilometer Array phase 1 and Low-Frequency Array can effectively probe the parameter space of the axion-photon coupling $g_{a\gamma }$ up to ${10}^{-14}\sim {10}^{-15}{\mathrm{GeV}}^{-1}$ for the axion mass range of $0.1\sim 30\mu \mathrm{eV}$. Depending on the choice of neutron star evolution model, this limitation is 2 or 3.5 orders of magnitude higher than that of the single neutron star or magnetic white dwarf.

We study decoherence effects in neutrino flavor oscillations in curved spacetime with particular emphasis on the lensing in a Schwarzschild geometry. Assuming Gaussian wave packets for neutrinos, we argue that the decoherence length derived from the exponential suppression of the flavor transition amplitude depends on the proper time of the geodesic connecting the events of the production and detection in general gravitational setting. In the weak gravity limit, the proper time between two events of given proper distance is smaller than that in the flat spacetime. Therefore, in presence of a Schwarzschild object, the neutrino wave packets have to travel relatively more physical distance in space to lapse the same amount of proper time before they decoher. For nonradial propagation applicable to the lensing phenomena, we show that the decoherence, in general, is sensitive to the absolute values of neutrino masses as well as the classical trajectories taken by neutrinos between the source and detector along with the spatial widths of neutrino wave packets. At distances beyond the decoherence length, the probability of neutrino flavor transition due to lensing attains a value which depends only on the leptonic mixing parameters. Hence, the observability of neutrino lensing significantly depends on these parameters and in-turn the lensing can provide useful information about them.

Type-Z models, where charged leptons, up type quarks, and down type quarks each couple to a different scalar, are only possible when there are three or more Higgs doublets. We consider the type-Z three-Higgs-doublet model imposed by a softly broken ${\mathbb{Z}}_3$ symmetry. We take into account all theoretical and experimental constraints, including perturbative unitarity and bounded from below conditions that we develop here. Since there can be cancellations between the two charged Higgs in $B\to X_s\gamma$ (and in $h\to \gamma \gamma$), the lower bounds obtained on the charged Higgs masses are alleviated. We find regions of parameter space where both charged scalars can be relatively light. We also discuss in detail the important physical differences between exact alignment and approximate alignment, and present some useful benchmark points.

We extract the leading Fock state light-front wave functions (LF-LFWFs) of both the light and heavy pseudoscalar mesons, e.g., the pion (at masses of 130, 310, and 690 MeV), ${\eta }_c$ and ${\eta }_b$, from their covariant Bethe-Salpeter wave functions within the rainbow-ladder truncation. It is shown that the LF-LFWFs get narrower in $x$ (the longitudinal momentum fraction of the meson carried by the quark) with the increasing current quark mass, and the leading twist parton distribution amplitudes inherit this feature. In the case of the pion, the LF-LFWFs only contribute about 30% of the total Fock state normalization, indicating the presence of significant higher Fock states within. In contrast, in the cases of the ${\eta }_c$ and ${\eta }_b$, the LF-LFWFs contribute more than 90%, suggesting the $Q\overline{Q}$ valence Fock state truncation as a good approximation for heavy mesons. We thus study the three-dimensional parton distributions of the ${\eta }_c$ and ${\eta }_b$ with the unpolarized generalized parton distribution function (GPD) and the transverse momentum-dependent parton distribution function. Through the gravitational form factors in connection with the GPD, the mass radii of the ${\eta }_c$ and ${\eta }_b$ in the light-cone frame are determined to be $r_{E,\mathrm{LC}}^{{\eta }_c}=0.150$ and $r_{E,\mathrm{LC}}^{{\eta }_b}=0.089\mathrm{fm}$, respectively.

We present a calculation of the $\cos (2{\varphi }_h)$ asymmetry in $J/\psi$ production in electron-proton collisions at the future electron-ion collider (EIC), a useful channel to probe the transverse momentum dependent gluon distribution functions also known as gluon transverse momentum dependent parton distributions (TMDs). The dominant subprocess for the $J/\psi$ production is the virtual-photon-gluon fusion process ${\gamma }^{*}+g\to J/\psi +g$. The production of $J/\psi$ is calculated in the nonrelativistic quantum chromodynamics framework with the inclusion of both color singlet and color octet contributions. Numerical estimates of the $\cos (2{\varphi }_h)$ asymmetry are given in the kinematical region to be accessed by the future EIC. The asymmetry depends on the parametrization of the gluon TMDs, as well as on the long distance matrix elements. We use both Gaussian-type parametrization and the McLerran-Venugopalan model for the TMDs in the kinematical region of small $x$, where the gluons play a dominant role. The asymmetry may be useful to probe the ratio of the linearly-polarized and the unpolarized gluon distribution in the proton.

We investigate the axial-vector nucleon-to-delta transition form factors in the framework of relativistic baryon chiral perturbation theory at the one-loop order using the complex-mass renormalization scheme. We determine the available six free parameters by fitting to an empirical parametrization of the form factors obtained from the BNL neutrino bubble chamber experiments. A unique feature of our calculation is the prediction of a nonvanishing form factor $C_3^A(Q^2)$. Moreover, our results show a surprising sensitivity to the coupling constant ${\mathtt{g}}_1$ of the leading-order Lagrangian ${\mathcal{L}}_{\pi \mathrm{\Delta }}^{(1)}$.

A quantum field of $s=1/2$ in the vicinity of a dust shell contracting at a distance $r(t_0)$ to near its gravitational radius $r_s$ as seen by a FIDO observer is considered. Such an observer perceives a batch of particles around the event horizon. The origin of the particles around the spherical surface of radius $r=r_s+\epsilon$ lies in the thermal excitations in the Boulware vacuum state, ${|0⟩}_B$ for an external observer. The foregoing is done based on thermo field dynamics, as it allows one to explain the origin of $S_{\mathrm{BH}}$ as a state of entanglement between the modes of the fermionic field spreading through the Kruskal variety $S_{\mathrm{Ent}}\propto S_{\mathrm{BH}}$ with respect to a FIDO observer. A location of the degrees of freedom responsible for $S_{\mathrm{BH}}$ entropy is given. The occupation number for particles of a half-integer spin $s=1/2$ is estimated, and it is compared with the occupation number of particles of spin $s=0$, finding that the occupation number of the Dirac field is slightly lower than the occupation number of scalar particles in the vicinity of the gravitational radius; this allows confirming the exclusion principle near event horizons. The other thermodynamic properties of the field are estimated.

We study a set of four-dimensional $\mathcal{N}=2$ superconformal field theories (SCFTs) $\widehat{\mathrm{\Gamma }}(G)$ labeled by a pair of simply laced Lie groups $\mathrm{\Gamma }$ and $G$. They are constructed out of gauging a number of ${\mathcal{D}}_p(G)$ and $(G,G)$ conformal matter SCFTs; therefore, they do not have Lagrangian descriptions in general. For $\mathrm{\Gamma }=D_4,E_6,E_7,E_8$, and some special choices of $G$, the resulting theories have identical central charges ($a=c$) without taking any large $N$ limit. Moreover, we find that the Schur indices for such theories can be written in terms of that of $\mathcal{N}=4$ super-Yang-Mills theory upon rescaling fugacities. Especially, we find that the Schur index of ${\widehat{D}}_4(SU(N))$ theory for $N$ odd is written in terms of MacMahon’s generalized sum-of-divisor function, which is quasimodular. For generic choices of $\mathrm{\Gamma }$ and $G$, it can be regarded as a generalization of the affine quiver gauge theory obtained from $\text{D}3$-branes probing singularity of type $\mathrm{\Gamma }$. We also comment on a tantalizing connection regarding the theories labeled by $\mathrm{\Gamma }$ in the Deligne-Cvitanović exceptional series.

The wave equation obeyed by the extraordinary component of the electric field in a hyperbolic metamaterial was shown to be a massless Klein-Gordon field living in a flat spacetime with two timelike and two spacelike dimensions. Such a wave equation, unexpectedly, allows dispersionless propagation albeit having two spatial dimensions. Here we show that the same equation can be naturally interpreted as a particular massive Klein-Gordon equation with the usual one timelike and two spacelike dimensions in a de Sitter (dS) background spacetime. The mass parameter of the scalar field is given in terms of the cosmological constant, Planck constant, and the speed of light as $m=\sqrt{\mathrm{\Lambda }}\frac{\hslash }{c}$ which corresponds to the point for which the left and right conformal weights of the boundary conformal field theory (CFT) (via the de Sitter/CFT correspondence) are equal. This particular mass corresponds to the gapless mode in the dS spacetime for which the dispersion relation is linear in the wave number.

We study nonlinear sigma models on target manifolds with constant (positive or negative) curvature using the functional renormalization group and the background field method. We pay particular attention to the splitting Ward identities associated to the invariance under reparametrization of the background field. Implementing these Ward identities imposes to use the curvature as a formal expansion parameter, which allows us to close the flow equation of the (scale-dependent) effective action consistently to first order in the curvature. We shed new light on previous work using the background field method.

Extreme mass-ratio inspirals (EMRIs) detectable by the Laser Interferometer Space Antenna are unique probes of the nature of supermassive compact objects. We compute the gravitational-wave signal emitted by a stellar-mass compact object in a circular equatorial orbit around a Kerr-like horizonless supermassive object defined by an effective radius and a reflectivity coefficient. The Teukolsky equations are solved consistently with suitable (frequency-dependent) boundary conditions, and the modified energy and angular-momentum fluxes are used to evolve the orbital parameters adiabatically. The gravitational fluxes have resonances corresponding to the low-frequency quasinormal modes of the central object, which can contribute significantly to the gravitational-wave phase. Overall, the absence of a classical event horizon in the central object can affect the gravitational-wave signal dramatically, with deviations even larger than those previously estimated by a model-independent analysis of the tidal heating. We estimate that EMRIs could potentially place the most stringent constraint on the reflectivity of supermassive compact objects at the remarkable level of $\mathcal{O}({10}^{-6})\%$ and would allow one to constrain various models which are not ruled out by the ergoregion instability. In particular, an EMRI detection could allow one to rule out (or provide evidence for) signatures of quantum black-hole horizons with Boltzmann reflectivity. Our results provide motivation for performing rigorous parameter estimation to assess the detectability of these effects.

We discuss the uniqueness of asymptotically flat and static spacetimes in the $n$-dimensional Einstein-conformal scalar system. This theory potentially has a singular point in the field equations where the effective Newton constant diverges. We will show that the static spacetime with the conformal scalar field outside a certain surface $S_p$ associated with the singular point is unique.

We consider strongly gravitating configurations consisting of coupled real Higgs scalar field and vector (Proca) field of mass ${\mu }_P$. For such a system, we find static regular axially symmetric solutions describing asymptotically flat configurations which may be referred to as Proca-Higgs miniboson stars, since their total mass and spatial dimension are of order $M_{\mathrm{Pl}}^2/{\mu }_P$ and ${\mu }_P^{-1}$, respectively. The system possesses an axially symmetric dipole field and may be regarded as a Proca dipole.

We use equations of motion containing gravitational radiation-reaction terms through 4.5 post-Newtonian order to calculate the late-time eccentricities of inspiralling binary systems of nonspinning compact bodies as they cross the detection threshold of ground-based gravitational-wave interferometers. The initial eccentricities can be as large as 0.999. We find that the final eccentricities are systematically smaller than those predicted by the leading quadrupole approximation, by as much as 30 percent for a 300 solar mass binary crossing the LIGO/Virgo detection threshold at 10 Hz, or eight percent smaller for a 60 solar mass binary. We find an analytic formula for the late-time eccentricity that accurately accounts for the higher-order post-Newtonian effects, generalizing a formula derived by Peters and Mathews in the 1960s. We also find that the final eccentricities are independent of the ratio of the masses of the two compact bodies to better than two percent.

We construct a kind of thermal potential and then put the black hole thermodynamic system in it. In this regard, some thermodynamic properties of the black hole are related to the geometric characteristics of the thermal potential. Driven by the intrinsic thermodynamic fluctuations, the behavior of the black hole in the thermal potential is stochastic. With the help of solving the Fokker-Planck equation analytically, we obtain the discrete energy spectrum of Schwarzschild and Banados-Teitelboim-Zanelli (BTZ) black holes in the thermal potential. For Schwarzschild black holes, the energy spectrum is proportional to the temperature of the ensemble, which is an external parameter, and the ground state is nonzero. For BTZ black hole, the energy spectrum only depends on the anti–de Sitter radius, which is the intrinsic parameter. Moreover, the ground state of the BTZ black hole in thermal potential is zero. This also reflects the difference between three-dimensional and four-dimensional gravity.

We place observational constraints on two models within a class of scenarios featuring an elastic interaction between dark energy and dark matter that only produces momentum exchange up to first order in cosmological perturbations. The first one corresponds to a perfect-fluid model of the dark components with an explicit interacting Lagrangian, where dark energy acts as a dark radiation at early times and behaves as a cosmological constant at late times. The second one is a dynamical dark energy model with a dark radiation component, where the momentum exchange covariantly modifies the conservation equations in the dark sector. Using cosmic microwave background (CMB), baryon acoustic oscillations (BAO), and supernovae type Ia (SnIa) data, we show that the Hubble tension can be alleviated due to the additional radiation, while the ${\sigma }_8$ tension present in the $\mathrm{\Lambda }$-cold-dark-matter model can be eased by the weaker galaxy clustering that occurs in these interacting models. Furthermore, we show that, while $\mathrm{CMB}+\mathrm{BAO}+\mathrm{SnIa}$ data put only upper bounds on the coupling strength, adding low-redshift data in the form of a constraint on the parameter $S_8$ strongly favors nonvanishing values of the interaction parameters. Our findings are in line with other results in the literature that could signal a universal trend of the momentum exchange among the dark sector.

Light bosonic scalars (e.g., axions) may form clouds around black holes via superradiant instabilities or via accretion if they form some component of the dark matter. It has been suggested that their presence may lead to a distinctive dephasing of the gravitational wave signal when a small compact object spirals into a larger black hole. Motivated by this, we study numerically the dynamical friction force on a black hole moving at relativistic velocities in a background scalar field with an asymptotically homogeneous energy density. We show that the relativistic scaling is analogous to that found for supersonic collisional fluids, assuming an approximate expression for the pressure correction which depends on the velocity and scalar mass. While we focus on a complex scalar field, our results confirm the expectation that real scalars would exert a force which oscillates between positive and negative values in time with a frequency set by the scalar mass. The complex field describes the time averaged value of this force, but in a real scalar, the rapid force oscillations could, in principle, leave an imprint on the trajectory. The approximation we obtain can be used to inform estimates of dephasing in the final stages of an extreme mass ratio inspiral.

In this work we aim at reproducing, simultaneously, the spectral feature at $\sim 10\mathrm{TeV}$ in the cosmic-ray proton spectrum, recently reported by the DAMPE Collaboration, together with the spectral break at $\sim 1\mathrm{TeV}$ measured by H.E.S.S. in the lepton spectrum. Those features are interpreted as signatures of one nearby hidden cosmic-ray accelerator. We show that this interpretation is consistent with the dipole-anisotropy data as long as the rigidity scaling of the diffusion coefficient features a hardening at $\sim 200\mathrm{GV}$, as suggested by the light-nuclei data measured with high accuracy by the AMS-02 Collaboration. Such rigidity-dependent diffusion coefficient is applied consistently to the large-scale diffuse cosmic-ray sea as well as to the particles injected by the nearby source.

We perform general relativistic one-dimensional supernova (SN) simulations to identify observable signatures of enhanced axion emission from the pion-induced reaction ${\pi }^{-}+p\to n+a$ inside a newly born protoneutron star (PNS). We focus on the early evolution after the onset of the supernova explosion to predict the temporal and spectral features of the neutrino and axion emission during the first 10 s. Pions are included as explicit new degrees of freedom in hot and dense matter. Their thermal population and their role in axion production are both determined consistently to include effects due to their interactions with nucleons. For a wide range of ambient conditions encountered inside a PNS, we find that the pion-induced axion production dominates over nucleon-nucleon bremsstrahlung processes. By consistently including the role of pions on the dense matter equation of state and on the energy loss, our simulations predict robust discernible features of neutrino and axion emission from a galactic supernova that can be observed in terrestrial detectors. For axion couplings that are compatible with current bounds, we find a significant suppression with time of the neutrino luminosity during the first 10 s. This suggests that current bounds derived from the neutrino signal from SN 1987A can be improved and that future galactic supernovae may provide significantly more stringent constraints.