We demonstrate, by rigorously constructing the Kerr-Newman metric with the aid of Sibgatullin’s method, that the hyperextreme branch of this metric in the positive mass case does not develop a naked ring singularity, and the regions of causality violation are absent in it when its parameters verify a simple inequality $m^4+a^2(3m^2-q^2)>0$. Our results suggest that a physically meaningful “no horizon” gravitational collapse might be possible, which seems to make the cosmic censorship conjecture empty.

In this Letter we explore, for the first time, the constraints on lepton flavor violating (LFV) dark matter (DM) scenarios via the astrophysical photons and positrons, including both the annihilation and decay modes, $\mathrm{DM}(+\mathrm{DM})\to e^{\pm }{\mu }^{\mp },e^{\pm }{\tau }^{\mp },{\mu }^{\pm }{\tau }^{\mp }$. Given the presence of LFV interactions in various DM models and the challenge of probing such interactions at terrestrial facilities, such as DM direct detection and collider experiments, indirect detection offers a unique approach to investigating them. We utilize the currently available photon datasets from the XMM-Newton, INTEGRAL, and Fermi-LAT telescopes, along with the positron datasets from the AMS-02 satellite, to establish stringent bounds on the relevant annihilation cross sections or decay widths. In particular, we include contributions to the photon spectrum from final state radiation, radiative decays, and inverse Compton scattering. We find that the INTEGRAL (AMS-02) provides the most stringent bound on the annihilation cross sections and decay widths for DM mass below (above) approximately 20 GeV, which are comparable to those of their lepton flavor conserving counterparts.

In this paper, we present the complete transformations of a generic metric from (generalized) harmonic to Newman-Unti coordinates up to the second post-Minkowskian order $(G^2)$. This allows us to determine the asymptotic shear, the Bondi mass aspect, and the angular-momentum aspect at both orders.

Recent work has shown the possibility of detecting dense dark-matter distributions surrounding intermediate or extreme mass-ratio inspirals through gravitational waves using LISA. Modeling these systems requires evolving the coupled dynamics of the binary and the dark matter. This also requires setting reasonable initial conditions for the dark-matter distribution, which itself relies upon understanding the formation history of these systems. In this paper, we investigate how two aspects of these systems’ formation histories shape the dark-matter distribution: accretion onto the primary and prior merger events. We model accretion by introducing a minimum allowed angular momentum of dark-matter particles, which removes such particles that would have been accreted by the primary. When simulating an inspiral within such a distribution, we find a smaller dephasing of the gravitational-wave signal from a vacuum binary as compared to an inspiral without such a cutoff, particularly for more extreme mass-ratios. We also simulate an inspiral, which takes place within a dark-matter distribution that remains after a prior merger. We find that the decrease in dephasing from vacuum binaries when compared to the prior inspiral is most significant for less extreme mass-ratios. Nevertheless, the environmental effects from the dark matter for these different cases of initial data are still expected to be measurable by future space-based detectors.

Extra radiation injection after neutrino decoupling in the early Universe contributes to the effective number of neutrino species that can be constrained by the cosmic microwave background (CMB). However, any effective neutrino number itself cannot uniquely determine the underlying source. We argue that the degeneracy can be relaxed by CMB spectral distortions, which are caused by energy exchange between the extra radiation and photons. We consider neutrinogenic CMB spectral distortions, where extra energy is released in the form of neutrinos but still creates the CMB spectral distortions via electroweak interactions. Focusing on the CMB $\mu$ distortion for illustration purposes, we show that the synergy between the effective neutrino number and the CMB $\mu$ distortion provides a complementary probe of hidden sectors that dominantly couple to neutrinos, opening up parameter space that can be targeted by joint CMB anisotropy and spectral distortion experiments.

Misalignment dynamics, the nonequilibrium evolution of a scalar (or pseudoscalar) condensate in a potential landscape, broadly describes a solution to the strong $CP$ problem, a mechanism for cold dark matter production and (pre)reheating postinflation. Often, when radiative corrections are included phenomenologically by replacing the potential by the effective potential which is a static quantity, its usefulness is restricted to (near) equilibrium situations. We study the misalignment dynamics of a scalar condensate Yukawa coupled to $N_f$ fermions in a manifestly energy conserving, fully renormalized Hamiltonian framework. A large $N_f$ limit allows us to focus on the fermion degrees of freedom, which yield a negative contribution to the effective potential, a radiatively induced instability and ultraviolet divergent field renormalization. We introduce an adiabatic basis and an adiabatic expansion that embodies the derivative expansion in the effective action, the zeroth order is identified with the effective potential, higher orders account for the derivative expansion including field renormalization, and describe profuse particle production. Energy conserving dynamics leads to the conjecture of emergent asymptotic highly excited stationary states with a distribution function $n_k(\infty )\propto 1/k^6$ and an extensive entropy which is identified with an entanglement entropy. Subtle aspects of renormalization associated with the initial value problem are analyzed and resolved. Possible new manifestations of asymptotic spontaneous symmetry breaking (SSB) as a consequence of the dynamics, even in the absence of tree-level SSB, and cosmological inferences are discussed.

At linear order we study perturbations to a Gödel background spacetime which includes expansion in addition to rotation. We investigate the transformation behavior of these perturbations under gauge transformations and construct gauge-invariant quantities. Using the perturbed energy conservation equation we find that there are conserved quantities in expanding Gödel cosmology, in particular a spatial metric trace perturbation, ${\zeta }_{\mathrm{SMTP}}$, which is conserved on large scales for pressureless dust. We finally extend our discussion to a perfect fluid matter content to also obtain conserved quantities in this context.

The low energy effective field theory of interacting neutrinos derived from the Standard Model may be framed as a pointlike interaction and thereby modeled on a lattice of neutrino momenta. We identify a path to take a continuum limit of this lattice problem in the center of momentum frame. In this limit, the weak interaction is found to become trivial between incoming plane waves describing ultrarelativistic particles, unless finite neutrino wave packet sizes are taken into consideration. We follow up with an analytic treatment of interacting neutrino wave packets, demonstrating the importance of the wave packet size for characterizing neutrino-neutrino scattering in dense environments.

We present a comprehensive analysis of high-resolution transition-edge sensors (TESs) as a quantum sensing platform for detecting dark matter (DM). Operating near the thermodynamic noise limit with sub-eV energy resolution, TESs offer a powerful approach for probing light DM in the sub-GeV mass range. Optical TESs, realized on superconducting films with critical temperatures below 150 mK, achieve energy thresholds below 100 meV and enable precise calorimetric detection of individual energy depositions. We model TES response by incorporating fundamental noise sources and applying optimal filtering techniques, and we evaluate their sensitivity across a range of DM interaction channels, accounting for material responses in the target material. We show that even nanogram-month-scale exposures can reach previously unexplored DM-electron scattering cross sections below ${10}^{-27}{\mathrm{cm}}^2$ for sub-MeV masses and can probe the MeV-scale mass range for DM-nucleon couplings. Combining high-energy resolution, photon-number sensitivity, and scalability, optical TESs provide a compelling quantum sensing platform for rare-event searches at the intersection of particle physics and quantum metrology.

The electromagnetic structure of axial-vector mesons is investigated via elastic and two-photon transition form factors (TFFs). To this end, we employ a framework based on the Dyson-Schwinger and Bethe-Salpeter equations within a contact interaction (CI) model. This largely algebraic approach exposes the role of symmetries and their breaking in a transparent manner, and has proven successful in describing anomaly-sensitive processes, including pseudoscalar to two-photon TFFs, $\gamma \to 3\pi$, and vector-to-pseudoscalar radiative decays. Restricting our analysis to the lowest-lying axial-vector meson multiplet, $\mathrm{A}=\{a_1,f_1,f_1^{\prime }\}$, we also explore the corresponding light-by-light contribution to the muon anomalous magnetic moment. This contribution is underestimated in the CI model mainly due to the normalization of the TFFs. After applying a phenomenologically motivated rescaling to the TFFs, a process required given the limitations of the CI model, we obtain $a_{\mu }^{\mathrm{A}}=8.16_{-1.02}^{+1.22}\times {10}^{-11}$, consistent with contemporary assessments.

We compute photon emission rate enhancement near the QCD critical point using an effective theory of dynamic critical phenomena and derive a universal photon spectrum. The emission rate scales similar to conductivity, increasing with the correlation length ($\xi$), diverging at the critical point. The spectrum exhibits $\omega d{N}_{\gamma }/d^{3}k\propto {\omega }^{-1/2}$ in the scaling regime, with the transition occurring at a frequency comparable to shear damping rate $\omega \sim {\gamma }_{\eta }/{\xi }^2$, reflecting the nonequilibrium properties of the near-critical liquid.

In high-energy proton-proton ($pp$) collisions at the LHC, nonprompt charm hadrons, originating from beauty hadron decays, provide a valuable probe for beauty quark dynamics, particularly at low transverse momentum where direct beauty measurements are challenging. We employ a multiphase transport (AMPT) model of string melting version coupled with pythia8 initial conditions to study the beauty hadron and nonprompt charm hadron productions in $pp$ collisions at $\sqrt{s}=13\mathrm{TeV}$. In this work, the beauty quark mass during the generation stage has been increased to reproduce the measured $b\overline{b}$ cross section, and a beauty flavor-specific coalescence parameter $r_{BM}^b$ is introduced to match LHCb measurements of beauty baryon-to-meson ratios. With these refinements, the AMPT model achieves a reasonable agreement with experimental data on beauty hadron yields and nonprompt charm hadron production from ALICE and LHCb. We present the transverse momentum and multiplicity dependence of nonprompt-to-prompt charm hadron ratios, providing new insights into the interplay between beauty quark production and the hadronization process. We emphasize that the multiplicity dependence of the nonprompt to prompt charm hadron productions can be useful to constrain the flavor dependences of the coalescence dynamics. This work establishes a unified framework for future studies of heavy quark transport and collective flow behavior in small collision systems.

We introduce spin-$1/2$ baryons in the $\mathrm{string}+{{}^{3}P}_0$ model of hadronization, previously restricted to the production of pseudoscalar and vector mesons. Baryons are modeled as quark–diquark bound states, and baryon production is described by the tunneling of diquark–antidiquark pairs at string breaking points. Diquarks can be scalar or pseudovector, the latter being produced in the relative ${{}^{5}D}_0$ state. Introducing the quark–baryon–diquark coupling, the relevant splitting amplitudes for the emission of baryons are constructed and used to explore analytically the model predictions. We find a Collins effect for baryon production in the fragmentations of transversely polarized quarks or diquarks as well as a baryon spontaneous ${\mathbf{p}}_{\mathrm{T}}$-dependent transverse polarization. The model is presented in a form suitable for implementation in a Monte Carlo event generator. The hadronic decays of polarized hyperons are also included.

We build up a complete description of QCD phase structure by applying the parametrization of the chiral and deconfinement order parameters upon the calculations from functional QCD approaches. In particular in the first order phase transition region at high chemical potential, both the phase transition line using Maxwell construction and the coexistence boundary lines from the spinodal decomposition are determined. We compute the thermodynamic quantities including the number density, the energy density, the pressure, and also the free energy for both stable and unstable phases of QCD. Additionally, after applying a phenomenological description of the inhomogeneity of the QCD free energy, we obtain the surface tension of the first order phase transition of QCD.

The decay $\psi (3686)\to \gamma {\pi }^{+}{\pi }^{-}{\pi }^0$ is studied using a sample of $(2712.4\pm 14.3)\times {10}^6\psi (3686)$ events collected with the BESIII detector. The decay $\eta (1405)\to {\pi }^{+}{\pi }^{-}{\pi }^0$ is observed for the first time in $\psi (3686)$ decays via the intermediate state $f_0(980)$ and the product branching fraction $\mathcal{B}(\psi (3686)\to \gamma \eta (1405))\times \mathcal{B}(\eta (1405)\to f_0(980){\pi }^0)\times \mathcal{B}(f_0(980)\to {\pi }^{+}{\pi }^{-})$ is determined to be $(3.77\pm 0.43\pm 0.30)\times {10}^{-7}$, where the first uncertainty is statistical and the second is systematic. The branching fraction of isospin-violating decay $\psi (3686)\to \gamma f_1(1285)\to \gamma f_0(980){\pi }^0\to \gamma {\pi }^{+}{\pi }^{-}{\pi }^0$ is determined to be $(7.36\pm 2.25\pm 2.36)\times {10}^{-8}$ with statistical significance of $2.9\sigma$. Since no ${\eta }_c$ signal is evident in either the ${\pi }^{+}{\pi }^{-}{\pi }^0$ or $f_0(980){\pi }^0$ mass spectrum, upper limits are set to be $\mathcal{B}(\psi (3686)\to \gamma {\eta }_c)\times \mathcal{B}({\eta }_c\to {\pi }^{+}{\pi }^{-}{\pi }^0)<3.09\times {10}^{-7}$ and $\mathcal{B}(\psi (3686)\to \gamma {\eta }_c)\times \mathcal{B}({\eta }_c\to f_0(980){\pi }^0)\times \mathcal{B}(f_0(980)\to {\pi }^{+}{\pi }^{-})<7.97\times {10}^{-8}$ at 90% confidence level, respectively.

We consider integral kernels for functions $f(\widehat{F})$ of a minimal second-order differential operator $\widehat{F}(\nabla )$ on a curved spacetime. We show that they can be expanded in a functional series, analogous to the DeWitt expansion for the heat kernel, by integrating the latter term-by-term. This procedure leads to a separation of two types of data: all information about the bundle geometry and the operator $\widehat{F}(\nabla )$ is still contained in the standard heat kernel coefficients ${\widehat{a}}_k[F|x,x^{\prime }]$ (we call this property “off-diagonal functoriality”), while information about the function $f$ is encoded in some new scalar functions ${\mathbb{B}}_{\alpha }[f|\sigma ]$ and ${\mathbb{W}}_{\alpha }[f|\sigma ,m^2]$, which we call basis and complete massive kernels, respectively. These objects are calculated for operator functions of the form $\exp (-\tau {\widehat{F}}^{\nu })/({\widehat{F}}^{\mu }+\lambda )$ as multiple Mellin-Barnes integrals. The article also discusses subtle issues such as the validity of the term-by-term integration, the regularization of IR divergent integrals, and the physical interpretation of the resulting expansions.

We investigate Krylov state complexity as a probe of the quantum Mpemba effect in quantum spin chains. For models without global $U(1)$ symmetry, Krylov complexity exhibits clear Mpemba-like crossings, consistent with conventional diagnostics such as the trace distance, while offering a complementary interpretation in terms of Hilbert-space exploration and dynamical delocalization. In $U(1)$-symmetric systems, we confirm that the recently proposed symmetric component of Krylov complexity serves as a robust and reliable indicator of the quantum Mpemba effect, capturing anomalous relaxation even in cases where the total complexity fails to do so.

The major source of ground-based gravitational wave detectors, the inspiral and merger of comparable mass binary black holes (BBH), consists of a slow quasicircular inspiral, a merger to form a single remnant hole, and the quasinormal ringing of that remnant. The first and last of these epochs are amenable to well-developed and familiar approximations: Newtonian or post-Newtonian for the first and BH perturbation methods for the last. The middle epoch, the merger, generates most of the gravitational wave emission, yet has been accessible so far only to numerical relativity. Here, we add the close-limit approximation for the phenomenology of the merger. With the completed set of methods (Newtonian/post-Newtonian; close limit; BH perturbation theory), we show that not only can we understand the results of BBH coalescence, but—with reasonable accuracy—we can predict aspects of resulting radiation and remnant.

In the present work, the scattering between a light scalar particle $\varphi$ and a heavy scalar $\sigma$ in the eikonal limit is considered, for gravity scenarios containing higher order derivatives. It is suggested that if one of the new gravity scales introduced in the higher order action is smaller than the Planck mass, for instance of the order of $M_{\mathrm{GUT}}\sim {10}^{15}\mathrm{GeV}$, the functional form of the GR eikonal formulas appears changed by a factor. However, in this situation, the conditions for the eikonal approximation to hold has to be revised; this issue is analyzed in the text. The statements of the present work should be taken with a grain of salt, as the Schwarzschild radius for these polynomials theories is not yet established. The results presented here, in our opinion, are in agreement with the suppression of corrections to GR pointed out in other literature regarding Stelle gravity. The next-to-leading-order approximation and part of the seagull diagrams are estimated. Different to the GR case, this order generically is nonvanishing. An explicit regularization scheme is presented, based on Riesz and Hadamard procedures. The need of a regularization is partially expected, as the inclusion of small energy fluctuations may spoil the eikonal approximation.