Simultaneous measurement of mass and radius with high precision is essential to unravelling the equation of state of matter at the core of neutron stars. Measurement of massive pulsars indicates that they have to be stiff at low densities. In this work, an ensemble of agnostically constructed equations of state was studied for the mass-radius measurement. The radius of neutron stars obtained from the ensemble was confined within a 10.5–14.5 km bound. Among the NICER measurements, PSR J0437–4715 provides the most stringent constraint on the equation of state. It was found that the detection of stars with smaller radii would prefer a softer equation of state, and the detection of stars with larger radii would prefer a stiffer equation of state. However, irrespective of the detection of stars with a smaller or larger radius, the sound speed peak indicates that stars are likely to have a smooth phase transition at a few times saturation densities, and the matter at the core may not be pure conformal quark matter. A better precision of the radius measurement drastically increases the chances of constraining the equation of state. The equation of state would be more effectively constrained if the measurement of large-radius stars with high precision were to happen. Precise radius measurements of neutron stars with smaller radii provide limited constraints on the equation of state over the density range relevant to neutron stars, largely independent of the stellar mass. Also, measurements for different masses are necessary to constrain the equation of state at all density ranges relevant to neutron stars.

India

Asim Saha

Ritam Mallick

The prospect of confining the equation of state of neutron stars with future mass and radius measurements

In this paper, we investigate the thermodynamical and optical characteristics of a black hole surrounded by massive spin-1 vector fields in the framework of Kaluza–Klein gravity. Motivated by the natural emergence of massive vector fields through the dimensional reduction of higher-dimensional gravity, we explore their role in modifying the near-horizon physics and observable signatures of black holes. These vector fields, akin to dark photons, introduce Yukawa-like corrections to the gravitational potential and mimic dark matter effects without invoking exotic particles. Our thermodynamic analysis, extended via logarithmic-corrected Barrow entropy, reveals that these fields significantly alter black hole temperature, specific heat, and Gibbs free energy. Notably, phase transitions are identified and confirmed using thermodynamic geometry tools, including Quevedo and HPEM metrics, highlighting the presence of stable remnants under quantum gravity corrections. Furthermore, we examine accretion disk structures and black hole shadow images through ray-tracing techniques under both static and infalling spherical accretion models. The direct and secondary images of the disk, as well as photon ring features, exhibit distinct deformations based on $$\gamma $$ and $$\lambda $$ . These modifications affect observable properties such as shadow size, intensity profiles, and lensing behavior, suggesting potential avenues for empirical testing via black hole imaging. Our findings underscore the rich phenomenology induced by massive vector fields in KK gravity, providing a unified perspective on black hole thermodynamics, dynamical stability, and observational signatures.

Saudi Arabia

Ali Koam

Azerbaijan

Pakistan

Shahid Chaudhary

Uzbekistan

Farruh Atamurotov

Ali Ahmad

Ibtisam Masmali

Probing Kaluza–Klein black holes with massive vector fields via thermodynamics, shadows, and accretion disks

The Cabibbo–Kobayashi–Maskawa matrix element $$|V_{\textrm{cb}}|$$ is an important Standard Model parameter, whose value can be determined by using the semi-leptonic decay $$B\rightarrow D^{*}\ell {\bar{\nu }}_\ell $$ . The perturbative QCD (pQCD) corrections to the $$B \rightarrow D^{*}$$ transform form factor $${{\mathcal {F}}}(w)$$ has been known up to the $$\hbox {N}^3$$ LO level, whose magnitude remains sensitive to the choice of renormalization scale $$\mu _r$$ . To improve the precision of $${{\mathcal {F}}}(w)$$ and hence $$|V_{\textrm{cb}}|$$ , we first apply the single-scale approach of Principle of Maximum Conformality (PMC) to eliminate the conventional (Conv.) renormalization scale dependence of the short-distance parameter $$\eta _A$$ and then predict the contribution of its unknown $$\hbox {N}^4$$ LO term via Bayesian analysis. In this paper, we adopt two probabilistic models for Bayesian analysis: the Cacciari–Houdeau model (CH model) and the geometric behavior model (GB model). It is shown that by using the PMC series in combination with Bayesian analysis, one can achieve high degree of reliability in estimating unknown higher-order terms. A more convergent behavior is achieved by applying the PMC, confirmed by the predicted $$\hbox {N}^4$$ LO contributions: for the CH model, $$\eta _A|_{\mathrm{Conv.}}^{\text {N}^{4}\text {LO}}=\{-\,0.0032,+\,0.0052\}$$ and $$\eta _A|_{\textrm{PMC}}^{\text {N}^{4}\text {LO}}=\{-\,0.0004,+\,0.0004\}$$ ; for the GB model, $$\eta _A|_{\mathrm{Conv.}}^{\text {N}^{4}\text {LO}}=\{-\,0.0049,+\,0.0075\}$$ and $$\eta _A|_{\textrm{PMC}}^{\text {N}^{4}\text {LO}}= \{-\,0.0007,+\,0.0007\}$$ . Comparing with the latest experimental measurements, we obtain $$|V_{\textrm{cb}}||_{\textrm{PMC}}=(40.58^{+0.53}_{-0.57})\times 10^{-3}$$ , which is consistent for both CH and GB models and in good agreement with the PDG world average, $$|V_{\textrm{cb}}|_{\textrm{PDG}}=(41.1\pm 1.2)\times 10^{-3}$$ within errors.

China

Wang Li

Xing-Gang Wu

Hua Zhou

Xu-Chang Zheng

Determination of $$|V_{\textrm{cb}}|$$ using Bayesian analysis of the $$B \rightarrow D^{*}\ell {\bar{\nu }}_\ell $$ semileptonic decay width with four-loop QCD corrections

Progress in the theoretical understanding of parton branching dynamics within an expanding Quark Gluon Plasma relies on detailed and fair comparisons with experimental data for reconstructed jets. Such comparisons are only meaningful when the computed jet, be it analytically or via event generation, accounts for the complexity of jets reconstructed in the challenging environment of heavy-ion collisions. Jet reconstruction in heavy-ion collisions involves a necessarily imperfect subtraction of the large and fluctuating underlying event: reconstructed jets always include underlying event contamination. To identify true jet quenching effects, modifications due to the interaction of the branching partonic system with the Quark Gluon Plasma, we establish a baseline that accounts for possible background contamination on unmodified jets. In practical terms, jet quenching effects are only those not present in jets produced in proton-proton collisions that have been embedded in a realistic heavy-ion background and where subtraction has been carried out analogously to that in the heavy ion case. With this setup, we assess the sensitivity to underlying event of commonly discussed jet quenching observables and its impact on the robustness of Machine Learning studies, aimed at classifying jets according to their degree of modification by the Quark Gluon Plasma, that rely on those observables. We find the discrimination power of a simple Boosted Decision Tree to be robust in the realistic scenario where both medium response and underlying event are present, giving support to portability to the experimental context.

Portugal

J. Gonçalves

J. Milhano

Apples to apples in jet quenching: robustness of Machine Learning classification of quenched jets to underlying event contamination

We develop a framework based on the full one-loop finite-temperature effective potential model, within which the bubble wall velocity is calculated using the local thermal equilibrium (LTE) approximation, and the kinetic energy fraction $\textit{K}$ is computed directly. In cosmological phase transitions, these quantities play a critical role in determining the resulting gravitational wave signals. Using the xSM as a benchmark model, we compute the peak gravitational wave spectra under different methods for determining the wall velocity and the kinetic energy fraction $\textit{K}$, and compare these results to those obtained using the commonly employed bag model. Within the scanned parameter space, we find: (1) Deflagration is the most prevalent mode of fluid motion.(2) Gravitational wave spectra based on the full effective potential with LTE-derived wall velocity and integrated $\textit{K}$ can differ significantly from those using the bag model with fitted $\textit{K}$. In the deflagration regime, discrepancies reach up to 48% in peak frequency and 90% in amplitude. (3) The bag model provides a good approximation to the full equation of state in many cases. Notably, in deflagration scenarios with input wall velocity, the gravitational wave spectra obtained from the bag model more closely resemble the LTE-based results than those derived using the full potential with this input wall velocity ( ).

Zongguo Si

Hongxin Wang

Lei Wang

Yang Xiao

Yang Zhang

The bubble wall velocity in local thermal equilibrium and energy budget with full effective potential

We investigate the harvesting of quantum steering and its asymmetry between two static detectors locally interacting with a vacuum massless scalar field near an infinite, perfectly reflecting boundary. The detectors are arranged either parallel or orthogonal to the boundary, with detector $\textit{B}$ assumed to have an energy gap greater than or equal to that of detector $\textit{A}$. It is interesting to observe that, with increasing distance between the detectors and the boundary, the boundary tends to suppress quantum steering in one direction while enhancing it in the opposite direction. In the case of identical detectors, steering is symmetric when they are aligned parallel to the boundary. However, orthogonal alignment breaks this symmetry due to their unequal spatial proximity to the boundary. For non-identical detectors in the parallel configuration, the steering from $\textit{A}$ to $\textit{B}$ ($\textit{A}$ → $\textit{B}$) generally surpasses that from $\textit{B}$ to $\textit{A}$ ($\textit{B}$ → $\textit{A}$). In contrast, when the detectors are oriented orthogonally to the boundary, the relative strength of $\textit{A}$ → $\textit{B}$ and $\textit{B}$ → $\textit{A}$ steerability depends on the interplay between the boundary effects and the detectors’ energy gap difference. Across most of the parameter space, the orthogonal alignment tends to enhance $\textit{B}$ → $\textit{A}$ steering while suppressing $\textit{A}$ → $\textit{B}$ steering compared to the parallel setup. These findings suggest that boundary configurations should be flexibly adjusted according to the directional dependence of steering harvesting in order to optimize quantum information extraction.

Xiao-Li Huang

Xiao-Ying Jiang

Yu-Xuan Wang

Si-Yu Liu

Zejun Wang

Shu-Min Wu

Can boundary configuration be tuned to optimize directional quantum steering harvesting?

We propose a new method to determine quark masses using ratios of the vacuum-expectation values ( ) of flowed quark bilinear operators. They can be expressed as functions of the flow time $\textit{t}$ and the $$ \overline{\textrm{MS}} $$ quark mass $$ \overline{m} $$ , which can then be determined by matching with the corresponding lattice results. Motivated by this, we evaluate these perturbatively through next-to-leading order in the strong coupling. We provide the results as expansions in the limits of small and large $$ {\overline{m}}^2t $$ . To this end, we develop a new expansion technique based on the Laplace transform. Additionally, we present numerical results with the exact mass dependence over a wide range of $$ {\overline{m}}^2t $$ . We discuss the expected perturbative precision for the mass determination based on our next-to-leading order perturbative calculations, and possible non-perturbative corrections.

Japan

Hiromasa Takaura

Germany

Robert Harlander

Switzerland

Fabian Lange

A new approach to quark mass determination using the gradient flow

Modular flavor symmetries have been proposed as a new way to address the flavor problem. It is known that they can emerge from string compactifications. We discuss this connection in detail, and show how the congruence subgroups of SL(2$\textit{,}$ ℤ), which underlie many modular flavor symmetries, emerge from stringy duality symmetries by orbifolding. This requires an analysis of massive states, which reveals a picture that is more intricate than the well-known situation on the torus. It involves towers of states of different quantum numbers, related by modular transformations. Members of different towers become massless at different points in moduli space. We also show that, at least in the ℤ orbifold, the string selection rules can be understood as discrete remnants of continuous gauge symmetries. Non-Abelian discrete flavor symmetries arise as relics of various, relatively misaligned, continuous Abelian gauge symmetries. The generators of these U(1) symmetries give rise to $$ \mathcal{CP} $$ -violating Clebsch-Gordan coefficients. If the modulus settles close to a critical point, the corresponding gauge bosons may be light enough to be searched for at future colliders.

United States

Xueqi Li

Xiang-Gan Liu

Hans Nilles

Michael Ratz

Alexander Stewart

Flavor symmetries and winding modes

We explore the relation between two distinct prescriptions for $\textit{γ}$ in dimensional regularization — the Breitenlohner Maison t’Hooft Veltman (BMHV) scheme and Naive Dimensional Regularisation (NDR). The BMHV scheme is the only algebraically consistent scheme, but necessitates chiral symmetry restoring counterterms and it is computationally more expensive, limiting its practical use. We show how the quantum effective action can be translated between both schemes and present these translation rules for the Wilson Coefficients of the Standard Model Effective Field Theory (SMEFT), that can easily be implemented into automated tools for SMEFT computations. Finally, we examine how this scheme dependence manifests itself in matching calculations, identifying the cases in which the dependence cancels in the final result. To examplify this, we consider a concrete UV scenario matched onto the SMEFT at one-loop order in both schemes. Our work aims to facilitate more accurate SMEFT computations and can be considered as a first step towards a comprehensive map between the two continuation schemes.

S. Noi

Italy

R. Gröber

P. Olgoso

Mapping between $\textit{γ}$

We study the recently introduced curve integral formalism that defines a new family of formulas for the scattering amplitudes of the colored scalar tr$\textit{ϕ}$ theory. We find that the curve integral manifests a very surprising fact about these amplitudes: the dependence on the number of particles, $\textit{n}$, and the loop order, $\textit{L}$, is effectively decoupled in these formulas. We derive the curve integrals at tree-level for all $\textit{n}$. We then show that, for higher loop-order, it suffices to study the curve integrals for $\textit{L}$-loop tadpole-like amplitudes, which have just one particle per color trace-factor. By combining these tadpole-like formulas with the tree-level results, we find formulas for the all $\textit{n}$ amplitudes at $\textit{L}$ loops. We illustrate this result by giving explicit curve integrals for all the amplitudes in the theory, including the non-planar amplitudes, through to two loops, for all $\textit{n}$.