A thorough knowledge of the quark-hadron phase transition in hot and dense matter is essential for constraining the equation of state of neutron stars. In this work, we study the thermodynamics of the quark-hadron mixed phase at finite temperature using the Gibbs construction and examine its impact on hybrid star matter. We systematically explore the role of nuclear saturation properties, including the effective nucleon mass $m^{*}/m$, incompressibility $K_{\mathrm{sat}}$, symmetry energy coefficient $J$, and its slope $L$, together with quark-matter parameters such as the bag constant $B_0^{1/4}$ and the vector coupling strength $G_V$. We find that the width of the mixed phase is mainly controlled by the effective mass and symmetry energy, while the roles of incompressibility and symmetry energy slope are comparatively weak, particularly at higher temperatures. Thermal effects substantially modify the phase structure: Increasing temperature reduces the mixed-phase width and softens the equation of state in the coexistence region due to Gibbs phase equilibrium constraints. These effects are reflected in the behavior of the speed of sound, the trace anomaly, and its derivative. Variations in the symmetry energy, effective mass, and quark parameters significantly affect the hadron-quark transition, stellar radii, and maximum mass, while finite temperature softens the equation of state and enhances radius jumps in the mixed phase. Strong vector repulsion is essential to reconcile massive pulsar observations with NICER constraints, whereas weaker repulsion favors more compact, low-mass configurations.

Bayesian methods for the detection of continuous gravitational waves (CGWs) in pulsar timing array (PTA) data incur substantial computational costs that grow rapidly due to the number of noise and signal parameters characterizing the fitted model being proportional to the size of the PTA. This computational burden limits the scalability of these methods for large-scale PTAs comprising hundreds of pulsars anticipated from next-generation radio astronomy facilities. In this work, we introduce a computationally efficient frequentist method designed to circumvent this challenge. This is achieved by combining an adaptive spline fitting algorithm that nonparametrically suppresses red noise, thereby eliminating the need for complex noise modeling inherent to Bayesian methods, with a novel scheme for optimizing the subsets of pulsars included in the search. We quantify the performance of our method on a simulated dataset based on the NANOGrav 15-yr data release and find that it achieves a performance comparable to that of Bayesian analysis: for a CGW signal with a signal-to-noise ratio of $\approx 10$, our method yields a relative characteristic strain error of 1.0% and a frequency error of 0.072% from the injected values by using the optimal pulsar selections, while the same errors are 1.7% and 0.16%, respectively, for the standard Bayesian analysis. At the same time, our analysis completes in less than 5 h, in contrast to the 1–2 days required by Bayesian methods. This allows us to perform a rigorous study of our method using multiple data realizations and signal parameters, establishing it as an efficient and scalable tool for CGW searches with large-scale PTAs.

We investigate the combined effects of carrier-envelope phase and laser pulse shape on electron-positron pair production in the presence of an external time-dependent asymmetric electric field by solving the quantum Vlasov equation. We analyze how the pulse asymmetry, the envelope type (Gaussian, Lorentzian, and Sauter), and the carrier-envelope phase jointly influence the momentum distribution and the total number of produced pairs per unit volume. Our results show that pair production exhibits extreme sensitivity to both the degree of the temporal asymmetry and the steepness of the envelope on either side of the pulse. These effects are qualitatively explained through a turning-point analysis for the nonanalytic electric field using a regularization scheme. We observe that multiphoton pair production dominates the Schwinger mechanism in the case of a long falling-pulse asymmetry. For a short falling pulse with a flat-topped profile, pair production is further facilitated. We demonstrate that the density of produced pairs can be enhanced by two to three orders of magnitude by choosing certain field parameters.

In this work, we perform a systematic investigation of the hidden-charm tetraquark states with $I^G(J^{PC})=1^{+}(1^{+-})$ within the hadronic molecular picture, placing particular emphasis on systems composed of an $S$-wave $(D,D^{*})$ meson and a $P$-wave $[D_0^{*}(2300),D_1(2430),D_1(2420),D_2^{*}(2460)]$ meson. Adopting the one-boson exchange potential, we solve the Schrödinger equation in momentum space via the complex scaling method. A crucial feature of our approach is the rigorous treatment of the unstable nature of the $P$-wave constituents by incorporating three-body decay effects arising from self-energy corrections and the static limit approximation. Our results demonstrate that these three-body dynamics play a crucial role in determining the pole positions, specifically in reproducing the large decay widths observed experimentally. We identify several broad resonances in the $D^{*}{\overline{D}}_1(2420)$ and $D^{*}{\overline{D}}_2^{*}(2460)$ systems as candidates for the $Z_c(4430)$, while the significantly broader resonances in the $D{\overline{D}}_0^{*}(2300)$ and $D{\overline{D}}_1(2430)$ sectors are suggested as candidates for the $Z_c(4200)$. Focusing on the $D^{*}{\overline{D}}_2^{*}(2460)$ assignment as a specific case study, we further analyze the line shape of the $Z_c(4430)$ candidate using a Flatté-like parametrization with energy-dependent self-energy terms, providing predictions for its open-charm decay modes to guide future experimental searches.

We investigate charged lepton flavor violating top quark flavor-changing neutral current interactions at the proposed asymmetric muon-electron collision stage of the $\mu \mathrm{TRISTAN}$ collider, operating at a center-of-mass energy of 346 GeV. Specifically, we study the process ${\mu }^{+}{e}^{-}\to tq$ ($t\overline{q}+\overline{t}q$) with $q=u$, $c$, within the framework of three classes of four-fermion contact interactions: scalar, vector, and tensor operators. A cut-based analysis is performed using boost-invariant kinematic observables, followed by a likelihood-based statistical treatment to derive projected sensitivities for each operator. For an integrated luminosity of $100{\mathrm{fb}}^{-1}$, the projected constraints improve upon current LHC bounds on the corresponding effective couplings by approximately an order of magnitude. Projections for $1{\mathrm{ab}}^{-1}$ indicate even stronger sensitivity, indicating improved reach at higher luminosity. Additionally, we explore the impact of initial-state beam polarization on these projections, showing how it can further enhance sensitivity to specific operator structures.

We employ an approximate conserved quantum number [defined as “$b$ parity” in Phys. Rev. Lett. 86, 3722 (2001)] of the Standard Model (SM): $b_P=(-1{)}^n$, where $n$ is the number of produced $b$ jets in the reaction $e+p/A\to n·j_b+X$, to explore new TeV-scale flavor-changing interactions involving the third-generation quarks at the Electron-Ion Collider (EIC); simply by counting the number of $b$ jets in the final state. In particular, the SM single and dijet production at the EIC, which occurs through charge current interactions, $e+p/A\to j+{\cancel{E}}_T$ and $e+p/A\to 2·j+{\cancel{E}}_T$, are $b_P$ even since the $b_P$-violating (i.e., $b_P=-1$) SM signals for these processes are necessarily Cabibbo-Kobayashi-Maskawa suppressed and, therefore, have a vanishingly small production rate. In contrast, new flavor physics can generate $b_P=-1$ signals at the EIC whose only significant SM background is due to $b$-jet misidentification. We thus show that $b_P$ can be used as a simple and sensitive probe of new flavor-violating physics; specifically, we find that counting single $b$-jet events in $e+p/A\to j+{\cancel{E}}_T$ at the EIC with a center-of-mass (c.m.) energy of $\sqrt{s}\sim 140\mathrm{GeV}$ can probe scales of new physics up to $\mathrm{\Lambda }\lesssim \mathcal{O}(5)\mathrm{TeV}$ for a certain type of new chiral flavor-changing physics in third-generation interactions. This is remarkably more than 30 times larger than the assumed EIC c.m. energy and it critically depends on the $b$-tagging efficiency and purity as well as the feasibility of electron beam polarization. The sensitivity of the dijet process, $e+p/A\to 2j+{\cancel{E}}_T$, to these types of new physics is reduced compared to the single-jet channel.

We point out opportunities to probe invisible particles, left- and right-handed neutrinos, axionlike particles and dark photons $(Z^{\prime })$ with rare decays of charm hadrons. We employ and recast existing searches in $D\to (\pi ,\omega )X$, $D^0\to X$ and ${\mathrm{\Lambda }}_c\to pX$, where $X$ denotes one of the above invisible final states including dineutrinos. The branching ratios are clean null tests of the standard model yet are essentially unconstrained for some parameters of light new physics, limited only by weak lifetime constraints at the level of $\mathcal{O}({10}^{-1})$. On the other hand, if models are probed, branching ratios still reach up to ${10}^{-3}$ ($Z^{\prime }$) and ${10}^{-4}$ (axionlike particles). Chirality-preserving operators from heavy new physics in the dimension-six standard model effective theory imply tighter upper limits, up to few $\times {10}^{-5}$. Constraints on chirality-flipping heavy new physics, such as lepton number violation from dimension-seven standard model effective theory, or with light sterile neutrinos, are weaker, with branching ratios up to $\mathrm{few}\times {10}^{-4}$. Sensitivities to different couplings arise with ${\mathrm{\Lambda }}_c\to pX$ and $D\to \pi \pi X$ decays, in particular in relation with the other modes. Processes can be studied at running and future experiments with high charm luminosities, BESIII, Belle II, a super-tau-charm factory and $Z$ factories, such as the Future Circular Collider and the Circular Electron Positron Collider.

We study the processes ${\nu }_{\tau }n\to {\mathrm{\Lambda }}_c{\tau }^{-}({\pi }^{-}{\nu }_{\tau })$ and ${\overline{\nu }}_{\tau }p\to \mathrm{\Lambda }{\tau }^{+}({\pi }^{+}{\overline{\nu }}_{\tau })$, with particular emphasis on the pion energy and angular distributions, as a possible signal for lepton flavor universality violation, and in general of physics beyond the Standard Model (SM), as well as a sensitive probe of the $\tau$ polarization vector. We work within an effective low-energy extension of the SM with all dimension-six four-fermion operators. In this framework, complex Wilson coefficients which encode new physics can generate $CP$-violating contributions. We propose an observable that provides a genuine $CP$-odd signal due to its sensitivity to particular transverse components of the $\tau$ polarization vector. Namely, we show that the asymmetry in the azimuthal-angle distribution of the pion in the decay ${\tau }^{\pm }\to {\pi }^{\pm }{\nu }_{\tau }$ constitutes a smoking-gun prediction of such a beyond the SM scenario. We estimate the strength of this effect extrapolating nucleon-hyperon form factors recently obtained from lattice QCD calculations.

We study single-top production in association with a $W$ boson at the Large Hadron Collider (LHC) as a probe of dimension-6 Standard Model effective field theory (SMEFT) at leading order, next-to-leading order, and approximate next-to-next-to-leading order accuracy in quantum chromodynamics (QCD). The process is sensitive to operators that modify the top-quark weak and chromomagnetic dipole interactions, and we perform three-parameter linear and quadratic SMEFT fits using doubly differential top-quark distributions in transverse momentum and rapidity for the Run II and Run III configurations at the LHC. We provide a detailed account of the uncertainties and quantify the impact of the different uncertainty components across bins and perturbative orders. We find that effective scales up to 2 TeV can be probed in nonmarginalized fits, while in marginalized fits the corresponding scales are around 0.5 and 1.5 TeV for linear and quadratic fits, respectively.

Testing new-physics (NP) scenarios that couple predominantly to the third generation is notoriously difficult experimentally, as exemplified by comparing limits for the $\tau$ lepton dipole moments to those of electrons and muons. In this case, extracting limits from processes such as $e^{+}{e}^{-}\to {\tau }^{+}{\tau }^{-}$ often relies on effective-field-theory (EFT) arguments, which allow for model-independent statements, but only apply if the NP scale is sufficiently large compared to the center-of-mass energy. In this work we offer a comprehensive analysis of light NP contributions to the $\tau$ dipole moments, providing a detailed account of the interpretation of asymmetry measurements in $e^{+}{e}^{-}\to {\tau }^{+}{\tau }^{-}$ that are tailored toward the extraction of dipole moments, for the test cases of new light spin-0 and spin-1 bosons. Moreover, we study the decoupling to the EFT limit in these scenarios and discuss the complementarity to constraints from other related processes, such as production in $e^{+}{e}^{-}$ reactions. While covering a wide range of light NP scenarios, as specific case study we present a detailed discussion of a tauphilic gauge vector boson at Belle II.

We investigate the electromagnetic polarizabilities of singly heavy mesons and doubly heavy baryons within the framework of heavy hadron chiral perturbation theory up to $\mathcal{O}(p^3)$. We estimate the low-energy constants using the nonrelativistic constituent quark model. A striking prediction of our study is the giant electric polarizabilities of the $D^{*}$ mesons: ${\alpha }_E({\overline{D}}^{*0})\approx 294\times {10}^{-4}{\mathrm{fm}}^3$ and ${\alpha }_E(D^{*-})\approx 1.42–64.5\mathrm{i}\times {10}^{-4}{\mathrm{fm}}^3$. These anomalously large values arise from the near-degenerate mass between $D^{*}$ and $D\pi$, which are orders of magnitude larger than those of their bottom counterparts. This kinematic coincidence induces a pronounced cusp structure in the chiral loops, reflecting the long-range dynamics of a pion cloud. For doubly heavy baryons, polarizabilities depend strongly on heavy-flavor composition: the $bcq$ system differs markedly from $ccq$ and $bbq$ due to mixing with scalar heavy-diquark states. Using heavy diquark–antiquark symmetry (HDAS), we unify the chiral dynamics of singly heavy mesons and doubly heavy baryons in the heavy-quark limit. The pion-loop contributions dominate the electromagnetic structure of heavy hadrons and provide essential benchmarks for future lattice QCD simulations.

The photon radiation induced by rescattering in a magnetized medium is investigated in relativistic heavy-ion collisions. Within the high-energy limit, the photon emission rate and the associated electromagnetic energy loss are derived using the Gyulassy-Levai-Vitev formalism at first order in opacity, for a quark jet propagating a quark-gluon plasma under a background magnetic field. Quantitative analysis shows a slight suppression of the overall photon radiation over a broad range of jet energies in this process. This reduction in photon yield consequently leads to a moderate decrease in the electromagnetic energy loss of the jet. Our results contribute to a better understanding of the electromagnetic properties of strongly interacting matter in high-energy nucleus-nucleus collisions and motivate experimental comparison of photon yields from quark-gluon plasma with similar properties but distinct magnetic field strengths.

The flat space limit of bulk scalar fields in anti–de Sitter (AdS) is discussed within a Lorentzian canonical quantization setup. We construct their Lorentzian wave functions and use time dependent perturbation theory to compute amplitudes. These can be computed once the wave functions of the incoming and outgoing states, relevant to set up an scattering problem, have been determined. To get the flat limit we need states tailored so that the flat S-matrix arises naturally. This limit is provided by the algebraic action of the Ìnönü-Wigner contraction on the wave functions we construct. We develop the embedding formalism to describe the bulk AdS scalar primary wave functions as holomorphic functions. Flat space massive particle states are built out of the AdS primary together with AdS boosted wave functions. We compute their inner products and show that these become orthogonal in the flat limit, resulting in the correct continuous spectrum for a standard unitary representation of the Lorentz group. In this same limit the original AdS descendants become null states. We also argue how the flat space S-matrix emerges from standard perturbation theory in the interaction picture. To obtain flat space massless particles requires to consider a double scaled limit in which the boost rapidity is scaled to infinity keeping the average particle energy in the flat space limit fixed. We comment on how this limit generates interesting massless state wave functions with nontrivial shape profiles that remember the dimension of the AdS operator. We discuss some of the puzzles attached to these.

We investigate the backaction from a spatially pointlike particle detector on a quantum scalar field, as characterized by the expectation value of the field’s stress-energy tensor, without conditioning on a measurement of the detector. First, assuming the field to be initially in a zero-mean Gaussian Hadamard state in a globally hyperbolic spacetime, we evaluate the field’s two-point function in second-order perturbation theory by techniques of covariant curved spacetime quantum field theory, which allow a full control of the time and space localization of the interaction, and do not rely on field mode decompositions or nonlocal particle countings. The detector’s two-point function splits into a deterministic and a fluctuating part, and we show that this split is maintained in the backaction. We then specialize to a two-level Unruh-DeWitt detector, prepared in an energy eigenstate, for which the backaction is fully fluctuating. We compute the renormalized stress-energy tensor for a massless scalar field in ($3+1$)-dimensional Minkowski spacetime for a general detector trajectory, using the manifestly causal two-point function. We present explicit analytic and numerical results for an inertial detector and a uniformly linearly accelerated detector, switched on in the asymptotic past. The energy flux into and out of the accelerated detector accounts exactly for the energy gained and lost by the detector in its transitions due to the Unruh effect. The same holds for the outward flux associated with deexcitations of the inertial detector, which has a vanishing excitation rate and no inward flux. A novelty with the accelerated detector is two regions of negative energy density when the detector is initially prepared in its ground state, one near the Rindler horizon that bounds the causal future of the trajectory, the other in the far future of the trajectory.

In this work we study the relativistic kinetic theory of a boost-invariant conformal gas on a static, maximally symmetric background $d{S}_3\times \mathbb{R}$, considering all constant-curvature slicings of $d{S}_3$—flat, spherical, or hyperbolic—and their associated symmetry groups. Using a symmetry-driven cotangent bundle approach, we show that the isometry group of each slicing acts on phase space in such a way that only its Casimir invariants and the timelike coordinate are unconstrained, so the distribution function depends solely on these quantities. This yields a unified boost-invariant exact solution of the Boltzmann equation valid for each constant–curvature foliation of $d{S}_3\times \mathbb{R}$. Specializing this general solution to the flat and spherical foliations reproduces the Bjorken and Gubser flows, respectively, while its restriction to the hyperbolic foliation produces a genuinely new analytic solution (“Grozdanov flow”). Hydrodynamics and free streaming emerge naturally as limiting regimes of this novel exact solution. We further comment on several relevant aspects of the new boost-invariant solution on the hyperbolic slicing and on their interpretation once mapped back to Minkowski space.

We present a fully analytical method for calculating the key parameters of a Kerr-like gravitational shadow, including its horizontal and vertical diameters, $D_X$ and $D_Y$, the coordinates of its center $X_C$, the average radius $\overline{R}$, the deviation from sphericity $\delta C$, and the mean deviation from the Kerr shadow $\delta K$. Developed within the framework of perturbation theory, this approach yields all characteristic parameters as simple polynomial expressions with an accuracy of $\sim a^5$, where $a$ is the Kerr spin parameter. This eliminates the need for repeated numerical integration of cumbersome parametric equations. Furthermore, our derived formulas account for the effects of a plasma medium—a feature of particular relevance given the prospect of multifrequency astrophysical observations.

We investigate the Newtonian limit of a class of nonlocal gravity models with exponential form factors $f_s(\square )=\exp [(-\square /{\mu }_s^2{)}^{N_s}]$. Our main goal is to identify similarities and differences between models in this family in regard to weak-field solutions. To this end, we use the effective source formalism to compare the related effective delta sources, mass functions, and Newtonian potentials. We obtain a variety of representations for these quantities in terms of series, integrals, and special functions, as well as simple approximations that capture the relevant dependence on the parameters $N_s$ and ${\mu }_s$—which can be used to explore the weak-field phenomenology of nonlocal gravity. We explain why only for $N_s>1$ the Newtonian potential oscillates and prove that, despite the oscillations, the effective masses are positive. Moreover, we verify that these linearized solutions are regular (without curvature singularities). Finally, we also calculate the form of the leading logarithmic quantum correction to the Newtonian potential in these models. In all our considerations, we assume that $N_s$ is a positive real parameter. The cases of noninteger $N_s$ might be applied beyond nonlocal gravity, in effective approaches to implement quantum corrections in the weak field regime.

The accurate computation of quasinormal modes from rotating black holes beyond general relativity is crucial for testing fundamental physics with gravitational waves. In this study, we assess the accuracy of the eikonal and post-Kerr approximations in predicting the quasinormal mode spectrum of a scalar field on a deformed Kerr spacetime. To obtain benchmark results and to analyze the ringdown dynamics from generic perturbations, we further employ a $2+1$-dimensional numerical time-evolution framework. This approach enables a systematic quantification of theoretical uncertainties across multiple angular harmonics, a broad range of spin parameters, and progressively stronger deviations from the Kerr geometry. We then confront these modeling errors with simple projections of statistical uncertainties in quasinormal mode frequencies as a function of the signal-to-noise ratio, thereby exploring the domain of validity of approximate methods for prospective high-precision black-hole spectroscopy. We also report that near-horizon deformations can affect prograde and retrograde modes differently and provide a geometrical explanation.

We extend our previous Schwarzschild metric-based studies of gravitational-electromagnetic (GEM) coupling to rotating black holes by working directly in a curvature-based Newman-Penrose/Teukolsky framework on Kerr spacetime. Within a minimally coupled Einstein-Maxwell system, we derive explicit quadratic electromagnetic source terms for the spin-$-2$ Teukolsky equation, providing a foundation for future numerical studies of GEM interactions in the framework of black-hole spectroscopy. Moreover, we give order-of-magnitude arguments showing that GEM quadratic quasinormal modes (QQNMs) can become relevant in a range of charged and magnetized astrophysical scenarios. Finally, we show through a brief dilaton-theory example that the GEM QQNM spectrum is sensitive to how gravity couples to electromagnetism, thereby providing a model-based way to test minimal coupling and to constrain hidden $U(1)$ sectors with gravitational-wave observations.

Recent developments in the modified harmonic and modified puncture gauges have opened new possibilities for performing stable numerical evolutions beyond General Relativity. In this work, we utilize techniques developed in the aforementioned formalisms to derive a BSSN-type formalism compatible with certain classes of modified gravity theories. As an intermediate step, we also derived modified versions of the Z4 and Z3 formalisms, thereby completing the connection between these formalisms beyond General Relativity. We then test the robustness of the new modified BSSN formalism by simulating the dynamics of black hole systems and benchmarking the results against the modified CCZ4 formulation. These developments enable the exploration of theories beyond General Relativity in many well-known numerical relativity codes that use different versions of the puncture gauge approach.