We obtain a coordinate independent algorithm to determine the class of conformal Killing vectors of a locally conformally flat $n$-metric $\gamma$ of signature $(r,s)$ modulo conformal transformations of $\gamma$. This is done in terms of endomorphisms in the pseudo-orthogonal Lie algebra $\mathfrak{o}(r+1,s+1)$ up to conjugation of the group $O(r+1,s+1)$. The explicit classification is worked out in full for the Riemannian $\gamma$ case ($r=0$, $s=n$). As an application of this result, we prove that the set of five-dimensional, $(\mathrm{\Lambda }>0)$-vacuum, algebraically special metrics with nondegenerate optical matrix, analyzed in [G. Bernardi de Freitas et al., Commun. Math. Phys. 340, 291 (2015).] is in one-to-one correspondence with the metrics in the Kerr–de Sitter-like class. This class [M. Mars et al., Classical Quantum Gravity 34, 095010 (2017).; M. Mars and C. Peón-Nieto, Phys. Rev. D 105, 044027 (2022).] exists in all dimensions, and its defining properties involve only properties at $\mathcal{I}$. The equivalence between two seemingly unrelated classes of metrics points towards interesting connections between the algebraically special type of the bulk spacetime and the conformal geometry at null infinity.

Chen et al. argued recently that, in Bondi-Sachs spacetimes, the angular momentum at scri (null infinity) should vary continuously with the position of the cut (but not depend sensitively on its derivatives); they showed that this property was enjoyed by some definitions but not others. I show here that the twistor definition has this continuity. The argument is rather different from the one of Chen et al., with the invariant geometry of scri at the forefront. The flux, in the sense of the angular momentum emitted between two infinitesimally separated cuts, is calculated; this flux can be interpreted as the first variation of the angular momentum with respect to the cut. Examining the second variation, one finds that the twistor definition, unlike most others, responds to correlations in radiation between different asymptotic directions. The twistor angular momentum is thus sensitive to a qualitatively different structure in the asymptotic field than are the currently more used ones.

All-sky searches for continuous gravitational waves are generally model dependent and computationally costly to run. By contrast, SOAP is a model-agnostic search that rapidly returns candidate signal tracks in the time-frequency plane. In this work, we extend the SOAP search to return broad Bayesian posteriors on the astrophysical parameters of a specific signal model. These constraints drastically reduce the volume of parameter space that any follow-up search needs to explore, so increasing the speed at which candidates can be identified and confirmed. Our method uses a machine learning technique, specifically a conditional variational auto-encoder, and delivers a rapid estimation of the posterior distribution of the four Doppler parameters of a continuous wave signal. It does so without requiring a clear definition of a likelihood function or being shown any true Bayesian posteriors in training. We demonstrate how the Doppler parameter space volume can be reduced by a factor of $\mathcal{O}({10}^{-7})$ for signals of SNR 100.

Neutron stars are regarded as natural laboratories for the study of dense strong interaction matter. The equation of state (EoS) of dense matter computed in flat spacetime is used to predict the structure of neutron stars by solving the Tolman-Oppenheimer-Volkoff (TOV) equation. Recently, it has been reported that the curved spacetime effect or specifically gravitational time dilation effect on the EoS of dense matter leads to a significant increase of the maximum mass limit of neutron stars [Phys. Rev. D 104, 123005 (2021) and J. Cosmol. Astropart. Phys. 02 (2021) 026]. However, in this work, we show that to study the hydrostatic equilibrium of dense matter within the framework of general relativity and relativistic fluid dynamics, the EoS of dense matter, $p(T,\mu )$, should be the same as that computed in flat spacetime, otherwise it is not consistent with local thermodynamic relations and energy-momentum conservation of the fluid. The gravitation influences the pressure $p$ only through enhancing the temperature $T$ and the chemical potential $\mu$, known as Tolman’s law and Klein’s law. We rewrite the TOV equation as an alternative version so that the EoS computed by using field theoretical methods can be used as a direct input. This may provide a tool to study the EoS of dense matter via deep learning.

One-loop explicit expressions are derived for the gluon Nielsen identity in the formalism of the screened massive expansion for Yang-Mills theory. The gauge-parameter-independence of the poles and residues is discussed in a strict perturbative context and, more generally, in extended resummation schemes. No exact formal proof was reached by the approximate resummation schemes, but some evidence is gathered in favor of an exact invariance of the phase, consistently with previous numerical studies.

The $s$-channel resonant production of the Higgs boson at a 125 GeV muon collider enables a unique way to determine the Higgs properties. However, a clear picture of the achievable Higgs precision has not yet been established. We perform a phenomenological study of the Higgs measurements at such a resonant muon collider Higgs factory and present a systematic, detailed, and consistent extraction of Higgs precision measurements. Many new aspects about the line shape scan, including the scaling with luminosity, optimal scan range, minimal scan steps, correlations with exclusive measurement, effective cross section modeling, etc., are quantitatively studied in this work. All major exclusive Higgs channels are simulated and analyzed with Standard Model background, detection efficiencies, acceptance, angular distributions, and cross-channel correlations. Global analyses of the Higgs couplings are performed in the $\kappa$ framework and the effective-field-theory one. The results suggest that the 125 GeV muon-collider Higgs factory provides significant improvement to the Higgs coupling reach of the High-Luminosity LHC and provides independent and distinct Higgs precision information concerning future $e^{+}{e}^{-}$ colliders. We report results for both 5 and $20{\mathrm{fb}}^{-1}$ integrated luminosity. These results provide comprehensive and quantitative physics understandings helpful in planning for the muon collider road map and global high-energy physics programs.

We previously proposed that entanglement across a planar surface can be obtained from the partition function on a Euclidean hourglass geometry. Here we extend the prescription to spherical entangling surfaces in conformal field theory. We use the prescription to evaluate log terms in the entropy of a conformal field theory in two dimensions, a conformally coupled scalar in four dimensions, and a Maxwell field in four dimensions. For Maxwell we reproduce the extractable entropy obtained by Soni and Trivedi. We take this as evidence that the hourglass prescription provides a Euclidean technique for evaluating extractable entropy in quantum field theory.

Black-hole superradiance has been used to place very strong bounds on a variety of models of ultralight bosons such as axions, new light scalars, and dark photons. It is common lore to believe that superradiance bounds are broadly model independent and therefore pretty robust. In this work we show however that superradiance bounds on dark photons can be challenged by simple, compelling extensions of the minimal model. In particular, if the dark photon populates a larger dark sector and couples to dark fermions playing the role of dark matter, then superradiance bounds can easily be circumvented, depending on the mass and (dark) charge of the dark matter.

We consider vortices in scalar electrodynamics and compute the leading quantum correction to their energies for the BPS case of identical classical masses of the Higgs and gauge fields. In particular, we focus on the winding number $n$ dependence of these corrections, from which we can extract the binding energies of configurations with larger $n$. For both dimensionalities, $D=2+1$ and $D=3+1$, we find that quantum corrections are negative and scale approximately linearly with $n$, so that combined vortices are favored over isolated ones.

The dynamical evolution of spin of a massive probe fermion in a hot QED plasma at local equilibrium is investigated through the quantum kinetic theory. We consider the massive probe fermion undergoing 2-by-2 Coulomb scattering with the massless fermions in the medium. The axial kinetic equation is derived including the collision terms to the first order of gradients and leading logarithmic order of the coupling. The collision terms are vanishing at global equilibrium, around which the relaxation time can be extracted as an operator. We further decompose the axial kinetic equation into kinetic equations of axial-charge density as well as the transverse magnetic dipole moment. The polarization rate and diffusion rate are estimated in massless limit and nonrelativistic limit, between both limit, polarization and diffusion effects are illustrated through preliminary numerical analysis.

We investigate the tachyonic instability of Kerr-Newman (KN) black holes in the Einstein-Maxwell-scalar (EMS) theory with a positive coupling parameter $\alpha$. This corresponds to exploring the onset of spontaneous scalarization for KN black holes. For this purpose, we use the hyperboloidal foliation method to solve the linearized scalar equation numerically. We obtain a 3D graph [${\log }_{10}\alpha (a,Q)$] which indicates the onset surface for spontaneous scalarization of KN black holes in the EMS theory. We find that there is no lower bound on the rotational parameter $a$, but its upper bound is given by $M^2-Q^2\ge a^2$. Also, we confirm that the high rotation enhances spontaneous scalarization of KN black holes in the EMS theory.

Unified dark matter cosmologies economically combine missing matter and energy in a single fluid. Of these models, the standard Chaplygin gas is theoretically motivated, but faces problems in explaining large scale structure if linear perturbations are directly imposed on the homogeneous fluid. However, early formation of a clustered component of small halos is sufficient (and necessary) for hierarchical clustering to proceed in a cold dark matter (CDM) component as in the standard scenario, with the remaining homogeneous component acting as dark energy. We examine this possibility. A linear analysis shows that a critical Press-Schechter threshold for collapse can generally only be reached for generalized Chaplygin gas models that mimic $\mathrm{\Lambda }\mathrm{CDM}$, or ones where superluminal sound speeds occur. However, the standard Chaplygin gas case turns out to be marginal, with overdensities reaching order one in the linear regime. This motivates a nonlinear analysis. A simple infall model suggests that collapse is indeed possible for perturbations of order 1 kpc and above; for, as opposed to standard gases, pressure forces decrease with increasing densities, allowing for the collapse of linearly stable systems. This suggests that a cosmological scenario based on the standard Chaplygin gas may not be ruled out from the viewpoint of structure formation, as often assumed. On the other hand, a “nonlinear Jeans scale,” constricting growth to scales $R\gtrsim \mathrm{kpc}$, which may be relevant to the small scale problems of CDM, is predicted. Finally, the background dynamics of clustered Chaplygin gas cosmologies is examined and confronted with observational datasets. It is found to be viable (at 1-sigma), with a mildly larger $H_0$ than $\mathrm{\Lambda }\mathrm{CDM}$, if the clustered fraction is larger than 90%.

The leading contribution to the uncertainties of atmospheric neutrino flux calculations arise from the cosmic-ray nucleon flux and the production cross sections of secondary particles in hadron-air interactions. The data-driven model developed in this work parametrizes particle yields from fixed-target accelerator data. The propagation of errors from the accelerator data to the inclusive muon and neutrino flux predictions results in smaller uncertainties than in previous estimates, and the description of atmospheric flux data is good. The model is implemented as part of the MCEq package, and hence can be flexibly employed for theoretical flux error estimation at neutrino telescopes.

TianQin is a proposed geocentric space-based gravitational wave observatory mission, which requires time-delay interferometry (TDI) to cancel laser frequency noise. With high demands for precision, the solar-wind plasma environment at $\sim {10}^5\mathrm{km}$ above the Earth may constitute a non-negligible noise source to laser interferometric measurements between satellites, as charged particles perturb the refractivity along light paths. In this paper, we first assess the plasma noises along single links from space-weather models and numerical orbits, and analyze the time and frequency domain characteristics. Particularly, to capture the plasma noise in the entire measurement band of ${10}^{-4}–1\mathrm{Hz}$, we performe additional space-weather magnetohydrodynamic simulations in finer spatial and temporal resolutions and utilize Kolmogorov spectra in high-frequency data generation. Then, we evaluate the residual plasma noises of the first- and second-generation TDI combinations. Both analytical and numerical estimations have shown that under normal solar conditions, the plasma noise after TDI is less than the secondary noise requirement. Moreover, TDI is shown to exhibit moderate suppression on the plasma noise below $\sim {10}^{-2}\mathrm{Hz}$ due to noise correlation between different arms, when compared with the secondary noise before and after TDI.

Although there are some experimental hints for the higher excited $\rho$ mesons, our knowledge of their properties is theoretically very poor. Based on our recent work about excited $\rho$ mesons [Z. Y. Li et al., Phys. Rev. D 104, 034013 (2021)], we present the mass spectra and decay properties of the higher excited $\rho$ mesons with the modified Godfrey-Isgur quark model and the ${}^3{P}_0$ strong decay model, and compare our predictions with the experimental hints, which should be helpful to search for these higher excited $\rho$ mesons.

The discrepancies between data on rare $b$-hadron decays, controlled by the underlying neutral-current transitions $b\to s{\ell }^{+}{\ell }^{-}(\ell =e,\mu )$, and the corresponding Standard Model predictions constitute one of the most intriguing hints for new physics. Leptoquarks are prime candidates to solve these anomalies and, in particular, the scalar leptoquark, $S_3$, triplet under $SU(2{)}_L$ with hypercharge $Y=-1/3$, provides a very good fit to data. Here, we entertain the possibility that the same scalar leptoquark $S_3$, responsible for the lepton flavor universality anomalies, is the portal to a fermionic dark sector consisting of two additional vectorlike fermions, one of which is a candidate for the cosmological dark matter. We study two scenarios, where the dark matter candidate belongs to an $SU(2{)}_L$ singlet and triplet respectively, and discuss the theory parameter space in the context of the dark matter candidate’s relic density and prospects for direct and indirect dark matter searches. Direct detection rates are highly suppressed and generically below the neutrino floor. Current observations with, and future prospects for, high-energy gamma-ray telescopes such as HESS and the Cherenkov Telescope Array are much more promising, as they already provide powerful constraints on the models under consideration, and will potentially probe the full parameter space in the future.

The possibility of a vectorlike top partner decaying to a new colorless weak-singlet scalar or pseudoscalar has attracted some attention in the literature. We investigate the production of a weak-singlet charge-$2/3$ $T$ quark that can decay to a spinless boson ($\mathrm{\Phi }$) and a top quark at the LHC. Earlier [A. Bhardwaj et al., Roadmap to explore vectorlike quarks decaying to a new scalar or pseudoscalar, arXiv:2203.13753.], we showed that in a large part of the parameter space, the $T\to t\mathrm{\Phi }$ and the loop-induced $\mathrm{\Phi }\to gg$ decays become the dominant decay modes for these particles. Here, we investigate the discovery prospects of the $T$ quark in this region through the above decays. In particular, we focus on the $pp\to TT\to (t\mathrm{\Phi })(t\mathrm{\Phi })\to (t(gg))(t(gg))$ channel. Separating this signal from the huge Standard Model background is a challenging task, forcing us to employ a multivariate machine-learning technique. We find that the above channel can be a discovery channel of the top partner in the large part of the parameter space where the above decay chain dominates. Our analysis is largely model independent, and hence our results would be useful in a broad class of new physics models.

We discuss a model that can accommodate the $B$-physics anomalies, based on combining two scalar leptoquarks, $R_2$ and $S_3$, of mass $\mathcal{O}(1\mathrm{TeV})$, and that we proposed in our previous paper. We update the analysis of its parameter space and show that a model remains viable and consistent with a number of low energy and high energy flavor physics constraints. Since the model predicts a nonzero new physics phase, we discuss the possibility to test its contribution to the neutron electric dipole moment and to the angular distributions of the exclusive $b\to c\tau \overline{\nu }$ decays. We find that the model can provide a significant enhancement to $\mathcal{B}(B\to K^{(*)}\nu \nu )$ and provides both the upper and lower bounds to $\mathcal{B}(B\to K^{(*)}\mu \tau )$.

An accurate determination of the leading-order hadronic vacuum polarization (HVP) contribution to the anomalous magnetic moment of the muon is critical to understanding the size and significance of any discrepancy between the Standard Model prediction and experimental results being obtained by the Muon g-2 experiment at Fermilab. The Standard Model prediction is currently based on a data-driven approach to the HVP using experimental results for $\sigma (e^{+}{e}^{-}\to \text{hadrons})$. Lattice QCD aims to provide a result with similar uncertainty from calculated vector-vector correlation functions, but the growth of statistical and systematic errors in the $u/d$ quark correlation functions at large Euclidean time has made this difficult to achieve. We show that restricting the lattice contributions to a one-sided window $0<t<t_1$ can greatly improve lattice results while still capturing a large fraction of the total HVP. We illustrate this by comparing windowed lattice results based on the 2019 Fermilab Lattice/HPQCD/MILC HVP analysis with corresponding results obtained from the KNT19 analysis of $R_{e^{+}{e}^{-}}$ data. For $t_1=1.5\mathrm{fm}$, 70% of the total HVP is contained within the window and our lattice result has an error of 0.7%, only about twice as big as the error from the $e^{+}{e}^{-}$ analysis. We see a tension of $2.7\sigma$ between the two results. With increased statistics in the lattice data the one-sided windows will allow stringent tests of lattice and $R_{e^{+}{e}^{-}}$ results that include a large fraction of the total HVP contribution.