In this paper, we present the first complete treatment of incoherent photon-initiated production in ultraperipheral heavy ion collisions, focusing on the dilepton and diphoton final states. In the former case we compare to the A Toroidal LHC Apparatus ATLAS measurement of dielectron production and find that our predictions match the data very well. In the latter case we show that this contribution is too small to explain the observed broad in diphoton acoplanarity background to the purely coherent light-by-light scattering signal, after the inclusion of appropriate fiducial cuts. We in addition consider a new “quark emission” topology, which while naïvely might be expected to dominate the incoherent diphoton production channel, is in fact found to be kinematically suppressed. Finally, we revisit QCD-initiated diphoton production and issue of theoretical uncertainties in this case. We find that this again cannot explain the observed size of the higher acoplanarity background. The production mechanism leading to this background to light-by-light production, and the reason for its observed enhancement in comparison to the dilepton case, therefore remains unclear.

We analyze the charmless two-body decays of the $B$ meson into a pseudoscalar and a vector meson, referred to as $B\to PV$ decay, within the framework of the modified perturbative QCD (PQCD) approach, which was originally developed to solve the long-standing puzzles, the so-called $\pi \pi$ and $\pi K$ puzzles. In this method, based on the conventional PQCD calculations, soft form factors and contributions arising from color-octet quark-antiquark components in the final state are introduced, which involve essentially nonperturbative dynamics. By employing the flavor SU(3) symmetry and its breaking effect, the parameters describing soft contributions are correlated and subsequently reduced into a more concise set of SU(3) parameters. Through a ${\chi }^2$ analysis procedure applied to the experimental data, these parameters are determined, from which the corresponding theoretical results for the branching ratios and $CP$ asymmetries in $B\to PV$ decays are derived. Within this framework, it is demonstrated that the theoretical calculations align well with experimental measurements, suggesting that the method developed for solving $\pi \pi$ and $\pi K$ puzzles can be extended to more decay modes of the $B$ meson. The numerical analysis shows that these soft contributions have a significant influence on the theoretical results. Furthermore, more precise experimental data are needed for deeper investigations of the $CP$ asymmetries.

Soft factorization theorems can be reinterpreted as Ward identities for (asymptotic) symmetries of scattering amplitudes in asymptotically flat space-time. In this letter we study the symmetries implied by the all-loop soft-photon theorems when all the charged particles are highly energetic and the relation $\omega \ll m\ll E$ holds where $E$ is the typical energy of a charged particle, $m$ is the typical mass and $\omega$ is the soft photon energy. Loop-level soft theorems are qualitatively different from the tree-level soft theorems because loop-level soft factors contain multiparticle sums. If we want to interpret them as Ward identities or define Celestial operator product expansion between soft and hard operators then we need to introduce additional fields which live on the Celestial sphere but do not appear as asymptotic states in any scattering experiment. For example, if we want to interpret the one-loop exact $\mathcal{O}(\ln \omega )$ soft theorem for a positive helicity soft photon (with energy $\omega$) as a Ward identity then we need to introduce a pair of antiholomorphic currents on the Celestial sphere which transform as a doublet under the $SL(2,\mathbb{R}{)}_R$. We call them dipole currents because the corresponding charges measure the monopole and the dipole moment of an electrically charged particle on the Celestial sphere. More generally, the soft photon theorem at $\mathcal{O}({\omega }^{2j-1}(\ln \omega {)}^{2j})$ for every $j\in \frac{1}{2}{\mathbb{Z}}_{+}$ gives rise to ($2j+1$) antiholomorphic currents which transform in the spin-$j$ representation of the $SL(2,\mathbb{R}{)}_R$. These currents exist in the quantum theory because they follow from loop-level soft theorems. We argue that under certain circumstances the (classical) algebra of the higher-spin currents is the wedge subalgebra of the $w_{1+\infty }$.

We develop tools of Bayesian inference on the moduli space of Calabi–Yau (CY) manifolds. We sample from the invariant Weil–Petersson (WP) measure using Markov Chain Monte Carlo and normalizing flows on Kähler moduli space with dimension up to $h^{1,1}=30$, and present results on the spectrum of the CY volume and properties of divisors when the measure is restricted in physically meaningful ways. We furthermore present a theory-informed prior on axion masses and decay constants $(m_a,f_a)$ marginalized over the WP measure for all inequivalent CYs constructable from the Kreuzer–Skarke database with $h^{1,1}\le 5$. We then impose likelihoods based on axion physics. We demonstrate how detection of a relatively heavy QCD axion at small $h^{1,1}$, e.g., by the Axion Dark Matter Experiment, provides detailed information about CY geometry and topology. Finally, we compute a full forward model incorporating likelihoods from the cosmic microwave background and Lyman-alpha forest and find the maximum posterior probability region on the moduli space of a given CY favored by a resolution of the tension in these data by an ultralight axion composing $\mathcal{O}(1\%)$ of the dark matter. This demonstration serves as a blueprint for future statistical analyses within string phenomenology.

We study successive Rindler-like transformations in Minkowski spacetime and the corresponding sequence of vacuum states perceived by observers restricted to respective wedges. Interestingly, once more than one transformation is applied, the resulting multi-Rindler observers become nonuniformly accelerating. The characteristic trajectories, confined to nested wedges, exhibit characteristic accelerations and horizon shifts depending on transformation parameters $g_1,g_2,\dots ,g_n$. For the second-level transformation (Rindler Rindler case), the late time acceleration asymptotically approaches $2g_2$ for one branch and diverges for the other. We study Minkowski, Rindler, and Rindler Rindler vacuum states from the perspective of Unruh-DeWitt (UDW) detectors along inertial, Rindler, and Rindler Rindler trajectories. The response of the UDW detector coupled to a real massless scalar field confirms the thermality: the transition rate of Rindler Rindler observer in Minkowski vacuum matches that of a standard Rindler detector with acceleration $2g_2$, yielding a Planckian spectrum at late times. The conclusions are discussed.

We present a full 3D numerical evolution code to study neutron stars in massive scalar-tensor theories. The code is embedded in the einstein toolkit framework and its implementation constitutes a modified version of the Baumgarte-Shapiro-Shibata-Nakamura formalism with an additional nonminimally coupled scalar field. The approach we follow preserves the standard hydrodynamic evolution for matter fields, allowing eventually for a straightforward inclusion of more microphysical effects and better flexibility. Using this code, we examine the gravitational collapse of rapidly rotating, scalarized neutron stars to a black hole by exploring the influence of the scalar field on the dynamical features of the process and on the gravitational-wave emission. We find that for the configurations studied in this work, there is an observational degeneracy in the tensorial gravitational-wave emission between collapsing scalarized stars and their counterparts in general relativity. However, this degeneracy can be broken through the emission of scalar radiation, which carries an energy of $\sim {10}^{-3}{M}_{\odot }{c}^2$. This is orders of magnitude higher than the quadrupolar emission ($\sim {10}^{-7}{M}_{\odot }{c}^2$) and might be used as an observational probe of modified gravity. We also find that rapid rotation can enhance this signal, since fast rotating stars can sustain larger scalar field amplitudes.

We study the conformal Killing equation for generic Vaidya-like spacetimes, including those with rotation. We show that these spacetimes admit a unique class of conformal Killing vectors that are homothetic for mass, charge, or rotation parameters being linear functions of the advanced null-time. For the Kerr-Vaidya metric, the solution to the conformal Killing equation exists if and only if both mass and rotation parameters become dynamic. The presence of a homothetic Killing vector (HKV) for such a spacetime enables one to conformally map the original dynamical spacetime to a stationary spacetime, enabling access to the standard methods pertaining to a Killing horizon. The surface where an HKV becomes null is termed the homothetic Killing horizon. We discuss the thermodynamic properties of such homothetic Killing horizons and formulate a version of the first law (or flux balance law) for spherically symmetric Vaidya spacetimes. We further study the maximal analytic extension of a charged Vaidya metric and indicate its implications for studying particle creation in such backgrounds.

GW231123 is a short-duration, low-frequency gravitational-wave signal consistent with a binary black hole coalescence and dominated by the merger-ringdown regime due to the high mass of the source. We demonstrate that fits of this ringdown signal using two quasinormal modes are statistically preferred over single-mode fits, for a broad range of fit start times. We also find that two-mode fits give remnant mass and spin measurements consistent with those of the inspiral-merger-ringdown model nrsur7dq4, whereas one-mode fits struggle to do so. Agreement of our fits with those of nrsur7dq4 is achieved by labeling the two quasinormal modes as the $(\ell ,m)=(2,2)$ and (2, 0) Kerr prograde fundamental modes. However, we find some indications that fits with the (2, 1) quasinormal mode instead of the (2, 0) mode may describe the data better, hinting at possible nrsur7dq4 error or other systematics. When fitting at early times near the estimated peak strain, we find that the inclusion of a third mode, an $(\ell ,m,n)=(2,2,1)$ prograde overtone, improves consistency with fits at later times. Finally, we perform a test of general relativity by searching for deviations from the Kerr frequency spectrum. Setting issues of systematics aside, we validate the Kerr frequency and damping rate spectrum to within $\pm 10\%$ at the 90% credible level using a fundamental mode fit, and we also report $\pm 8\%$ constraints using a model with fundamental modes and an overtone fit at times near the peak strain. Understanding the systematic errors that may be affecting the most accurate analyses of GW231123 is crucial in the context of population and binary formation studies—our (2, 1) mode fits return a significantly higher remnant mass and spin than all available inspiral-merger-ringdown models including nrsur7dq4, and this difference in parameter estimates may have astrophysical implications.

We propose a novel approach which implements the relativistic calculations of the photon travel time into a robust timing model for pulsars orbiting supermassive black holes. We demonstrate that timing models relying on the lowest-order post-Newtonian approximation can produce significant discrepancies in strong-field configurations, affecting the predicted relativistic times of arrival at an Earth-based observatory. We also show how a misestimation of the pulsar parameters can lead to the appearance of phase-dependent residual, which hints at a tremendous constraining power of the binary and intrinsic parameters for timing observations of potential pulsars at the Galactic Center.

One of the most promising targets for pulsar timing arrays (PTAs) is identifying an individual supermassive black hole binary (SMBHB) out of the population of binaries theorized to produce a gravitational wave background (GWB). In this work, we emulate an evolving PTA dataset, complete with an increasing number of pulsars and timing baselines, into which we inject a single binary on top of a Gaussian GWB signal. We vary the binary’s source parameters, including sky position and frequency, and create ten noise realizations for each source/PTA combination to synthesize an ensemble of simulated datasets with which we assess current Bayesian binary search techniques. We develop a novel, cross-correlation based model tuned for individual SMBHBs and compare its binary detection and characterization capabilities to two waveform-based template models. This spike pixel (SP) technique is designed to identify the frequency-specific anisotropy induced by an individual SMBHB. We find that a template-based search, including the full gravitational wave signal structure (i.e., both the Earth and pulsar effects of an incident GW) returns the highest Bayes factors (BF) and has the most robust parameter estimations. SP attains a realization-median $\mathrm{BF}>10$ at source strengths $7<(\mathrm{S}/\mathrm{N})<15$. Interestingly, despite being a deterministic model, the Earth-term template struggles to identify and characterize low-frequency binaries (i.e., at 5 nHz). These binaries require higher source strengths ($16<(\mathrm{S}/\mathrm{N})<19$) to reach the same BF threshold. This is likely due to neglected confusion effects between the pulsar and Earth terms. By contrast, the SP shows promise for parameter estimation despite treating a binary’s GW signal as excess directional GW power without phase modeling. Sky location and frequency parameter constraints returned by the SP are only surpassed by the Earth-term template model at $(\mathrm{S}/\mathrm{N})\sim 12–13$. Milestones for a first detection using the full-signal GW model are included in a following paper, Petrov et al. [Expectations for the first supermassive black-hole binary resolved by PTAs. II. Milestones for binary characterization, Phys Rev. D 114, 023033 (2026).].

Following the recent evidence for a gravitational wave (GW) background found by pulsar timing array (PTA) experiments, the next major science milestone is resolving individual supermassive black hole binaries (SMBHBs). The detection of these systems could arise via searches using a power-based GW anisotropy model, i.e., a cross-correlation search for single sources, or a deterministic template model. In Schult et al. [Expectations for the first supermassive black-hole binary resolved by PTAs. I. Model efficacy, Phys. Rev. D 114, 023034 (2026).], we compared the efficacy of these models in constraining the GW signal from a single SMBHB using realistic, near-future PTA datasets, and found that the full-signal deterministic continuous wave (CW) search may achieve detection and characterization first. Here, we continue our analyses using only the CW model given its better performance, focusing now on characterization milestones. We examine the order in which CW parameters are constrained as PTA data are accumulated and the signal-to-noise ratio ($\mathrm{S}/\mathrm{N}$) grows. We also study how these parameter constraints vary across sources of different sky locations and GW frequencies. We find that the GW frequency and strain are generally constrained at the same time (or $\mathrm{S}/\mathrm{N}$), closely followed by the sky location, and later the chirp mass (if the source is highly evolving) and inclination angle. At fixed $\mathrm{S}/\mathrm{N}$, sources at higher frequencies generally achieve better precision on the GW frequency, chirp mass, and sky location. The time (and $\mathrm{S}/\mathrm{N}$) at which the signal becomes constrained is dependent on the sky location and frequency of the source, with the effects of pulsar terms and PTA geometry playing crucial roles in source detection and localization.

We derive quantum gravity contributions to the beta functions of the gauge and Yukawa couplings of a matter theory using the Schwinger proper-time flow equation. Working in the Einstein-Hilbert truncation, we investigate the gauge fixing and regulator dependence of the corresponding renormalization group equations. We quantify the sensitivity of our results to unphysical parameters by evaluating the gravitational correction to the running matter couplings at the interactive fixed point of gravity and we compare our findings with existing determinations in alternative schemes. We finally confront the derived contributions with the typical size they should assume to generate observable low-scale predictions in the Standard Model and in several scenarios of new physics.

We derived in [Phys. Rev. D 106, 056009 (2022), Phys. Rev. D 107, 096021 (2023)] a compact expression for the $N$th rank QED polarization tensor ${\mathrm{\Pi }}_{{\mu }_1\cdots {\mu }_N}(k_1,\dots ,k_N)$ in a ($0+1$)-dimensional worldline framework. This fully off-shell object, a function of $N$ external photon 4-momenta, is a key ingredient in high-order computations of cusp anomalous dimensions and lepton anomalous magnetic moments. We demonstrate here that ${\mathrm{\Pi }}_{{\mu }_1\cdots {\mu }_N}$ can further be expressed simply in terms of a small number of independent “head” form factors [each representing $(N-1)!/2$ Feynman diagrams] which have a universal structure in terms of sums over fermion Green’s functions and (proper time derivative of) their boson worldline superpartners. This worldline representation bypasses explicit Wick contractions and avoids tensor reductions to scalar loop integrals à la Passarino and Veltman, order by order in perturbation theory. We give explicit expressions for the fourth and sixth rank head form factors and provide a computer script generalizing these results to arbitrary $N$ external photons. The multiplicity of heads, and their growth with $N$, can be understood in terms of orbits of the permutation group. We employ the Burnside-Cauchy-Frobenius lemma to show that it scales as $e^{N-1}/\sqrt{N}$ terms as opposed to the $e^{N-1}N!/\sqrt{N}$ terms in conventional perturbation theory. We reexpress worldline parameter integrals that define the fourth rank heads as Feynman parameter integrals to reproduce the seminal results by Karplus and Neuman for the on-shell light-by-light amplitude and extend these to the fully off-shell case in massless QED employing a tailored integration-by-parts procedure. In a follow-up paper, we will discuss the direct computation of worldline integrals, potentially providing a further $N!$ advantage relative to Feynman diagram computations at high orders in perturbation theory.

Highly boosted axionlike particles decaying into photon pairs are notoriously hard to detect at the LHC. The collimated decay photons cannot be individually reconstructed using only electromagnetic calorimeter information, making the signal less distinguishable from background. In this paper, we propose a search strategy to address this issue, exploiting the fact that a fraction of the decay photons convert into electron-positron pairs inside the tracking detector. The resulting tracks can be resolved with high resolution, making it possible to separate the two collimated photons and resolve a displaced decay vertex. To demonstrate the effectiveness of this approach, we apply it to ALPs in the challenging MeV–GeV range produced via vector boson fusion. We find that such a search could give sensitivity to untested parameter space.

We propose a scale invariant radiative neutrino mass model with custodial symmetry by introducing two real singlet scalars to the scotogenic model. Masses of an inert doublet scalar and right-handed neutrinos are induced by a vacuum expectation value (VEV) of a singlet scalar caused through the Coleman-Weinberg mechanism. It violates spontaneously both the custodial symmetry and the scale invariance. The weak scale can take a suppressed value compared with the singlet scalar VEV because of the custodial symmetry. In this framework we study phenomenological consequences for neutrino mass, dark matter, and baryon number asymmetry by assuming a texture for neutrino Yukawa couplings. Since the required dark matter abundance cannot be explained by a neutral component of the inert doublet scalar in that case, the lightest right-handed neutrino should be dark matter. Mass of the dark matter is predicted to be less than $O(1)\mathrm{MeV}$ and baryon number asymmetry could be explained through resonant leptogenesis.

We investigate the electromagnetic properties of the fully charm tetraquark states, particularly incorporating contributions from internal gluon radiation. The paper first presents analytical expressions for the next-to-leading-order QCD corrections to the decay amplitudes of fully charm tetraquarks into two photons. It is found that the QCD corrections are significant for the $J^{PC}=0^{++}$ and $J^{PC}=2^{++}$ fully charm tetraquark decay process. Subsequently, by considering photon-photon fusion in ultraperipheral high-energy collisions of protons and nuclei and in electron-positron collision, we provide theoretical predictions for the production cross sections of fully charm tetraquark states. The results presented in this work regarding the electromagnetic production and decay of fully charm tetraquarks shall be tested in current and future experiments.

We study the hadron-quark mixed phase within a two-phase model for symmetric and asymmetric matter. For the quark sector we employ the ($2+1$) Polyakov-extended Nambu–Jona-Lasinio model (PNJL) with vector interactions. We investigate how the hadronic equation of state affects the phase diagram and the thermodynamic properties inside the mixed phase. The behavior of isentropic trajectories in the mixed phase depends on the fixed entropy per baryon ($s/{\rho }_B$), with trajectories near the critical end point (CEP) exhibiting a pronounced cooling pattern, while isentropic trajectories with low entropy per baryon undergo pronounced heating as the baryonic density increases. The adiabatic squared speed of sound displays characteristic peak and dip structures that depend on $s/{\rho }_B$. The polytropic index along isentropic and isothermal trajectories, including in the vicinity of the CEP are also investigated. The effects of vector interactions and isospin asymmetry on thermodynamic observables likewise depend on the chosen $s/{\rho }_B$ value. Finally, we discuss the population of hyperons along isentropic trajectories and their influence on the phase diagram. The main effect of hyperons is to shift the onset of deconfinement to larger densities and decrease the density extension of the mixed phase.

We write a long-distance effective field theory (EFT) for QCD at finite temperature just below the crossover temperature $T_{co}$. The low energy constants of this EFT are obtained from lattice measurements of the screening mass of pions at two temperatures for $N_f=2+1$ using lattice results obtained at physical values of pion and Kaon masses, and $N_f=2$ where the lattice simulations were performed with a heavier pion mass. The EFT gives good predictions for other static pion properties for $N_f=2$, where lattice results are available. We show the corresponding predictions for $N_f=2+1$, where they are not yet measured. We demonstrate that EFT gives excellent predictions for the phase diagram in $N_f=2+1$. The predictions for the pressure are investigated, and predictions are also given for a Wick-rotated real-time quantity called the kinetic mass.

We study the semileptonic decays $B_s\to D_s^{(*)}\tau \overline{\nu }$ as a promising probe for new physics (NP) beyond the standard model (SM). The extension of the SM is done through the introduction of four-fermion operators beyond the $V-A$ structure with the corresponding Wilson coefficients characterizing their contribution. The constraints on these coefficients are obtained from recent experimental data. Form factors describing hadron transitions are calculated in our covariant quark model with infrared confinement. Theoretical predictions for the full set of observables in these channels are provided. We analyze possible NP effects to be tested in future experiments.