We investigate Cherenkov radiation in isotropic chiral matter using Carroll-Field-Jackiw electrodynamics, with an axion angle linear in time, to describe a charge moving at constant velocity. By solving the modified Maxwell’s equations in cylindrical coordinates and in the space-frequency domain, we derive closed expressions for the circularly polarized electromagnetic fields contributing independently to the radiation. The dispersion relations are obtained by imposing causality at a cylindrical surface at infinity, ensuring outgoing waves. Contrary to initial suppositions, each spectral energy distribution is gauge invariant and positive, describing radiation at a characteristic angle. We characterize the angles and identify frequency ranges that allow for zero, one, or two Cherenkov cones. Notably, one sector of the model enables threshold-free Cherenkov radiation from slowly moving charges. Our results agree with partial findings in the nonrelativistic limit of earlier iterative analysis and clarify the regimes in which Cherenkov radiation arises in isotropic chiral matter.

Geometric phases can manifest when a relativistic quantum particle moves cyclically along a loop in parameter space. The phase can be affected by the presence of a background field and can be accompanied by nontrivial topological features. The appearance of adiabatic geometric phases in momentum space is demonstrated for a Lorentz-violating Weyl fermion, where the role of the background is played by the coefficients for Lorentz violation. As explicit examples, the Berry curvature and the first Chern number are derived for two cases with large Lorentz violation, one incorporating $CPT$ violation and one preserving $CPT$ symmetry. Some alternative topological invariants are also obtained. In certain scenarios with large Lorentz violation, the physical vacuum is associated with a topological phase.

We study the $CP$-even neutral Higgs boson decays $h^0\to c\overline{c},b\overline{b},b\overline{s},\gamma \gamma ,gg$ in the minimal supersymmetric standard model (MSSM) with a general quark flavor violation (QFV) due to squark generation mixings, identifying the $h^0$ as the Higgs boson with a mass of 125 GeV. We compute the widths of the $h^0$ decays to $c\overline{c},b\overline{b},b\overline{s}$ at the full one-loop level. For the $h^0$ decays to $\gamma \gamma$ and $gg$, we compute the widths at NLO QCD level. For the first time, we perform a systematic MSSM parameter scan for these widths, respecting all the relevant theoretical and experimental constraints, such as those from B-meson data, and the 125 GeV Higgs boson data from recent LHC experiments, as well as the limits on supersymmetric (SUSY) particle (sparticle) masses from the LHC experiments. We also take into account the expected sparticle mass limits from the future HL-LHC experiment in our analysis. In strong contrast to the usual studies in the MSSM with minimal flavor violation (MFV), we find that the deviations of these MSSM decay widths from the Standard Model (SM) values can be quite sizable and that there are significant correlations among these deviations. All of these sizable deviations in the $h^0$ decays are mainly due to large scharm-stop mixing and large sstrange-sbottom mixing. Such sizable deviations from the SM can be observed at high signal significance in future lepton colliders such as ILC, CLIC, CEPC, FCC-ee, and muon collider even after the failure of SUSY particle discovery at the HL-LHC. In case the deviation pattern shown here is really observed at the lepton colliders, then it would strongly suggest the discovery of QFV SUSY (the MSSM with general QFV).

We propose searching for physics beyond the Standard Model in the low-transverse-momentum tracks accompanying hard-scatter events at the LHC. TeV-scale resonances connected to a dark QCD sector could be enhanced by selecting events with anomalies in the track distributions. As a benchmark, a quirk model with microscopic string lengths is developed, including a setup for event simulation. For this model, strategies are presented to enhance the sensitivity compared to inclusive resonance searches: a simple cut-based selection, a supervised search, and a model-agnostic weakly supervised anomaly search with the CATHODE method. Expected discovery potentials and exclusion limits are shown for $140{\mathrm{fb}}^{-1}$ of 13 TeV proton-proton collisions at the LHC.

We study the collider phenomenology of the $B-L$ extension of the Standard Model (BLSM), focusing on the production and decay of a heavy neutral gauge boson ($Z^{\prime }$) at the Large Hadron Collider (LHC). In this framework, the $Z^{\prime }$ can decay into pairs of heavy right-handed neutrinos (${\nu }_R$), which subsequently decay into charged leptons and $W$ bosons. These processes give rise to three distinctive final states: (i) two leptons plus four jets ($2\ell +4j$), (ii) four leptons plus missing transverse energy ($4\ell +\mathrm{MET}$), and (iii) three leptons plus two jets and MET ($3\ell +2j+\mathrm{MET}$). To enhance signal sensitivity and suppress Standard Model backgrounds, we employ multivariate analysis techniques based on boosted decision trees (BDTs), as well as selection optimizations using the xgboost framework. The classifiers are trained on kinematic observables sensitive to the masses of the $Z^{\prime }$ and ${\nu }_R$. We demonstrate that all three final states offer significant discovery potential for both the $Z^{\prime }$ and heavy ${\nu }_R$ at the High-Luminosity LHC. Our results highlight the testability of the BLSM at current and future collider experiments, and provide a promising avenue for probing the origin of neutrino masses and the baryon asymmetry of the Universe.

We consider the double parton scattering (DPS) initiated by direct photons in $\gamma p$ and $\gamma A$ collisions. We extend the previously known results for photoproduction to the case of electroproduction with nonzero photon virtuality $Q^2$, and then consider the DPS for both photo and electroproduction for HERA and EIC (electron ion collider) kinematics. The number of DPS events at the EIC is shown to be of the same order as in HERA and is even larger, with increase in luminosity compensating the decrease of the center-of-mass energy.

We present a light-cone QCD sum rule (LCSR) analysis of the semileptonic decays of ${\mathrm{\Xi }}_c$ baryons, focusing on the channels ${\mathrm{\Xi }}_c^0\to {\mathrm{\Xi }}^{-}{\ell }^{+}{\nu }_{\ell }$, and ${\mathrm{\Xi }}_c^{+}\to {\mathrm{\Xi }}^0{\ell }^{+}{\nu }_{\ell }$. The transition form factors are calculated within the light-cone quantum chromodynamics (QCD) sum rules framework, using the distribution amplitudes of the heavy ${\mathrm{\Xi }}_c$ baryons. The obtained form factors are then used to compute the differential and total decay widths, as well as the branching fractions. Our numerical results for the branching fractions are $\mathcal{B}({\mathrm{\Xi }}_c^0\to {\mathrm{\Xi }}^{-}{\ell }^{+}{\nu }_{\ell })=(3.73\pm 1.04)\%$, $\mathcal{B}({\mathrm{\Xi }}_c^0\to {\mathrm{\Xi }}^{-}{\mu }^{+}{\nu }_{\mu })=(3.59\pm 1.01)\%$, $\mathcal{B}({\mathrm{\Xi }}_c^{+}\to {\mathrm{\Xi }}^0{\ell }^{+}{\nu }_{\ell })=(11.2\pm 3.25)\%$, and $\mathcal{B}({\mathrm{\Xi }}_c^{+}\to {\mathrm{\Xi }}^0{\mu }^{+}{\nu }_{\mu })=(10.8\pm 3.13)\%$. These results are in good agreement with recent lattice QCD calculations, while being larger than the current experimental measurements and differing from the predictions of other theoretical approaches.

It is customary to identify ${\psi }_{+}={\nu }_R+C{\overline{{\nu }_R}}^T$ with a Majorana fermion on the basis of chirality changing charge conjugation $\tilde{C}:{\nu }_R\to C{\overline{{\nu }_R}}^T$ and parity $\tilde{P}:{\nu }_R\to i{\gamma }_4{\nu }_R$. The theorem on the absence of a Majorana-Weyl fermion in $d=4$ states $\tilde{C}{\gamma }_5{\tilde{C}}^{-1}=-{\gamma }_5$ with $\tilde{C}=C{\gamma }_4^T$, and, thus, the charge conjugation of the equivalent Majorana ${\psi }_{+}=(\frac{1+{\gamma }_5}{2}){\nu }_R+(\frac{1-{\gamma }_5}{2})C{\overline{{\nu }_R}}^T$ vanishes without subsidiary ${\gamma }_5\to -{\gamma }_5$, namely, not defined in field theory. To be consistent with the theorem, it is common to use a doublet representation of chirality preserving charge conjugation $\widehat{C}:{\nu }_{R,L}\to C{\overline{{\nu }_{L,R}}}^T$ and parity $\widehat{P}:{\nu }_{R,L}\to i{\gamma }_4{\nu }_{L,R}$ in theory containing both ${\nu }_{R,L}$. In the type I seesaw model, the latter formulation is applicable but ${\psi }_{+}={\nu }_R+C{\overline{{\nu }_R}}^T$ is not a Majorana fermion. An analog of the Bogoliubov transformation converts ${\psi }_{\pm }={\nu }_{R,L}\pm C{\overline{{\nu }_{R,L}}}^T$, which are obtained by a precise diagonalization of the seesaw model, to Majorana fermions ${\psi }_{M_{1,2}}=(\psi \pm C{\overline{\psi }}^T)/\sqrt{2}$ with a Dirac-type fermion $\psi$, as originally defined by Majorana. A chiral projection $[(1+{\gamma }_5)/2]{\psi }_{M_1}$ of a Majorana fermion is not a chiral fermion, which ensures the presence of the neutrinoless double beta decay.

We propose a novel strategy to derive explicit and uniform upper bounds on the particle spectrum of six-dimensional gravitational theories with minimal supersymmetry, focusing initially on the tensor sector. The strategy is motivated by considerations of F-theory compactifications on elliptic Calabi-Yau threefolds. However, it admits a clear bottom-up interpretation and is, thus, applicable to general supergravity theories modulo certain physical conjectures. At the heart of the strategy are two key structures, most natural in birational geometry: One concerns the singularity of the natural pairs on the base manifolds, and the other the fibration generically exhibited by the bases. Put physically, the former structure keeps the effective theories from decompactifying, and the latter ensures the (generic) presence of a heterotic string. We sketch our bounding strategy and present, for an illustration, the explicit bounds thereby derived on the tensor spectrum, with the technical details relegated to a companion paper [C. Birkar and S. J. Lee, arXiv:2507.06317].

We analyze the renormalization group flow of quantum gravity at sixth order in the derivative expansion within the background field approximation. Nonlinear field redefinitions are used to ensure that only essential couplings flow. Working within the universality class of general relativity, with a vanishing cosmological constant, redundant couplings are fixed to their values at the Gaussian fixed point. This reduces the theory space to two dynamical essential couplings given by Newton’s and the Goroff-Sagnotti coupling. Furthermore, it implements the condition that no extra degrees of freedom are present beyond those of general relativity, in contrast to higher derivative theories and derivative expansions in a conventional renormalization scheme. We find a unique ultraviolet fixed point with a single relevant direction and analyze the phase diagram of the theory. Our results suggest resilience of the gravitational Reuter fixed point under the inclusion of higher order curvature invariants and show several signs of near perturbativity. The regulator dependence of our results is investigated in detail and shows that qualitative and quantitative features are robust to a large extent.

We adapt the diffusion method employed in fundamentally nonlocal field theories to determine the number of initial conditions for the classicized dynamics of unitary field theories with fakeons, characterized by inverse powers of the d’Alembertian operator $\square$. We show that this number is two and we recover all the results obtained with a direct calculation elsewhere, including explicit solutions of linear toy models. Possible applications to nonlocal gravity are discussed.

GW200105_162426 is the first neutron star–black hole merger to be confidently confirmed through either gravitational-wave or electromagnetic observations. Although initially analyzed after detection, the event has recently gained renewed attention following a study [Morras et al. arXiv:2503.15393] that employed a post-Newtonian inspiral-only waveform model and reported strong evidence for orbital eccentricity. In this work, we perform a detailed analysis of GW200105 using state-of-the-art effective-one-body waveform models. Importantly, we present the first study of this event utilizing a physically complete model that incorporates both orbital eccentricity and spin precession across the full inspiral, merger, and ringdown stages, along with higher-order gravitational wave modes. Our results support the presence of eccentricity in the signal, with zero eccentricity excluded from the 99% credible interval, but yielding a mass ratio closer to the original LIGO-Virgo-KAGRA analysis, differing from the findings of [Morras et al. arXiv:2503.15393]. Additionally, similar to a previous eccentric-only analysis [de Lluc Planas et al. Astrophys. J. 995, 47 (2025).], we observe a multimodal structure in the eccentricity posterior distribution. We conduct targeted investigations to understand the origin of this multimodality and complement our analysis with numerical relativity simulations to examine how the inclusion of eccentricity impacts the merger dynamics.

In this paper, we investigate the overlapping of photon rings—higher-order images of a black hole’s luminous environment, concentrated near the shadow boundary and expected to be resolved in future observations. We consider a broad class of static spherically symmetric spacetimes and a geometrically thin equatorial accretion disk with a prescribed inner radius and infinite outer extent, viewed by a polar observer. Depending on the inner radius of the disk, the thickness of each photon ring varies, and the rings may or may not overlap. By overlapping, we mean that portions of images appear at the same angular position on the observer’s sky. To characterize the overlapping, we introduce the radius of merging—the value of the disk’s inner radius at which two photon rings of given orders begin to overlap. Since each radius of merging is labeled by two indices corresponding to the image orders, it becomes possible to arrange these radii in the form of an infinite-dimensional matrix where only the upper right-hand corner is filled. This matrix, which we call the “matrix of merging,” is a signature of spacetime only, and, once known, it provides a qualitative understanding of the overlapping pattern for any chosen value of the inner radius of the disk. Remarkably, the matrix of merging exhibits several universal properties that hold for all spherically symmetric metrics and can be established even without explicit calculation of light trajectories. Based on these properties, we demonstrate that certain overlapping patterns are universally forbidden across all such spacetimes and for any inner radius of the disk. Examples for the Schwarzschild and Reissner-Nordström black holes are provided. The main application of our study is constraining the spacetime metric and the accretion model using observed photon ring overlaps.

When testing general relativity (GR) with gravitational wave observations, parametrized tests of deviations from the expected strong-field source dynamics are one of the most widely used techniques. We present an updated version of the parametrized framework with the state-of-art IMRPhenomX waveform family. Our new framework incorporates deviations in the dominant mode as well as in the higher-order modes of the waveform. We demonstrate that the missing physics of either higher-order modes or precession in the parametrized model can lead to a biased conclusion of false deviation from GR. Our new implementation mitigates this issue and enables us to perform the tests for highly asymmetric and precessing binaries without being subject to systematic biases due to missing physics. Finally, we apply the improved test to analyze events observed during the second half of the third observing run of LIGO and Virgo (O3b). We provide constraints on GR deviations by combining O3b results with those from previous observation runs. Our findings show no evidence for violations of GR.

Initial conditions in cosmological $N$-body simulations are typically generated by displacing particles from a regular cubic lattice using a correlated field derived from the linear power spectrum, often via the Zel’dovich approximation. While this procedure reproduces the target two-point statistics (e.g., the power spectrum or correlation function), it introduces subtle anisotropies due to the underlying lattice structure. These anisotropies, invisible to angle-averaged diagnostics, become evident through directional measures such as the Angular Distribution of Pairwise Distances. Analyzing two Cold Dark Matter simulations with varying resolutions and box sizes, we show that these anisotropies are not erased but rather are amplified by gravitational evolution. They seed filamentary structures that persist into the linear regime, remaining visible even at redshift $z=0$. Our findings demonstrate that such features are numerical artifacts emerging from the anisotropic coupling between the displacement field and the lattice—not genuine predictions of an isotropic cosmological model. These results underscore the importance of critically reassessing how initial conditions are constructed, particularly when probing the large-scale, quasi-linear regime of structure formation.

We investigate the complementary information to be gained from inflationary gravitational wave (IGW) signals and searches for quantum chromodynamics (QCD) axion dark matter. We focus on postinflationary Peccei-Quinn (PQ) breaking axion models that are cosmologically safe. Recent work has shown that a greater number of such models exist. This is because the heavy quarks required for the color anomaly can provoke a period of heavy quark domination (HQD), which, through decay, dilutes the axion abundance. In this work we show for the first time that the axion dark matter mass can be as low as $m_a\sim {10}^{-8}\mathrm{eV}$ for models where the heavy quarks decay via dimension 6 terms. This is achieved by allowing the mass of the heavy quarks to differ from the axion decay constant, $m_Q\ne f_a$. Consequently, the observables that would distinguish between pre- and postinflationary PQ breaking, $m_a$ and the additional relativistic degrees of freedom $\mathrm{\Delta }{N}_{\mathrm{eff}}$, now become indiscernible. To solve this, we propose using blue-tilted IGWs to probe HQD. In scenarios where such a blue tilt is present, the enhanced GW signal allows future interferometers to place nontrivial constraints on the parameters $m_Q$ and $f_a$, thereby complementing haloscope searches. While some degeneracies with other parameters such as $m_Q$ remain, detectors such as Big Bang Observer and Einstein Telescope will be able to optimistically probe $f_a\gtrsim {10}^{14}\mathrm{GeV}$.

We present a new analysis on sterile neutrino cosmologies using the Dark Energy Spectroscopic Instrument (DESI) second data release baryon acoustic oscillation (BAO) measurements in combination with cosmic microwave background (CMB), CMB lensing, and supernova data. We show that BAO observables are intrinsically less sensitive to the combined effects of relativistic energy density, $N_{\mathrm{eff}}$, and the sum of neutrino masses, $\mathrm{\Sigma }{m}_{\nu }$, which are both augmented in sterile neutrino cosmologies. With SH0ES local expansion rate, $H_0$, data, we find $N_{\mathrm{eff}}=3.43\pm 0.13$, reducing the Hubble tension to $2.4\sigma$. For a 0.1 eV sterile neutrino, we find $N_{\mathrm{eff}}=3.50$ as the best fit. For this representative $N_{\mathrm{eff}}$, we find an upper limit of $m_s<0.17\mathrm{eV}$ (95% CL), greater than a factor of four weaker than standard constraints on $\mathrm{\Sigma }{m}_{\nu }$. When SH0ES is included, light sterile neutrinos with masses $m_s\simeq 0.1–0.2\mathrm{eV}$ are favored at $\gtrsim 3\sigma$, whereas eV-scale sterile masses remain strongly excluded by the data in the cosmologies we study. Our findings confirm our previous results that partially thermalized sub-eV sterile neutrinos are preferred by the SH0ES $H_0$ data. The preferred $m_s$ mass scale overlaps with, but is not identical to, that favored in neutrino oscillation solutions to short-baseline anomalies.

Tidal deformabilities are one of the observable quantities characterizing neutron stars, which are strongly associated with the stellar compactness, the ratio of the stellar mass to the radius. In addition to the tidal deformability, the quasinormal modes excited in a neutron star are also an important property for extracting information about the neutron star interior, adopting gravitational wave asteroseismology. In this study, we especially focus on the magnetic tidal deformability, which acts on the gravitational waveform from a neutron star binary merger as a higher-order effect than the electric tidal deformability, and derive the universal relations expressing the quasinormal modes, such as the fundamental ($f$-), first pressure ($p_1$-), and first spacetime ($w_1$-) modes, as a function of the magnetic tidal deformability. The universal relations derived in this study exhibit accuracy more or less comparable to those of the electric tidal deformability.

Cold dark matter (DM) may form dense structures around supermassive black holes (SMBHs), significantly influencing their local environments. These dense regions are ideal sites for the formation of extreme mass-ratio inspirals (EMRIs), in which stellar-mass compact objects gradually spiral into SMBH, emitting gravitational waves (GWs). Space-based gravitational-wave (GW) observatories such as LISA and Taiji will be sensitive to these signals, including early-stage EMRIs (E-EMRIs) that persist in the low-frequency band for extended periods. Here we investigate the impact of DM-induced dynamical friction on E-EMRIs in the Milky Way Center, model its effect on the trajectory, and calculate the resulting GW spectrum. Our analysis suggests that this influence might be sizable and lead to detectable deviations in the spectrum when DM density is very high. We find that cold DM does not alter the event rate of EMRIs at formation but decreases the number of E-EMRIs during later evolution and circularizes their orbits for high initial eccentricity. Consequently, this would cause suppression of the GW spectrum at low frequencies and enhancement at high frequencies, therefore potential observable by future GW detectors in space.

We obtain the electromagnetic pion form factor (emFF) $F_{\pi }$ for spacelike midrange of momentum transfer in quantum chromodynamics (QCD). We use renormalization group (RG) summation within the light cone sum rules (LCSRs) to obtain the QCD radiative corrections to the $F_{\pi }$ and involve contributions of the leading twist 2 and, twists 4, 6. The additional conditions to apply here this RG summation are discussed in details. The strong coupling constants in this approach are free of Landau singularities, which allows one to go down to the lower transferred momentum $Q^2$. The prediction of the calculations performed reproduces the experimental data below/around $Q^2=1{\mathrm{GeV}}^2$ significantly better than analogous predictions based on a fixed-order power-series expansion in the standard QCD.