Puzzles are still preventing people from further understanding and manipulating the Casimir interaction in spherical systems. Here we investigate the behaviors of Casimir stresses in the system consisting of a ball immersed in the background, emphasizing the roles of spherical geometry and inhomogeneity. Spherical modes are employed to evaluate Green’s dyadic and thus the Casimir stresses. The inhomogeneity of the media essentially modifies the wave form of the spherical mode, leading to significant impacts on the Casimir stresses, especially when far away from the surface of the ball. As the surface approached, the divergence (surface divergence) in Casimir stresses is seen. For both homogeneous and inhomogeneous cases, the leading behaviors (zero for the radial component, and inverse quantic order of distance for the transverse components) of Casimir stresses are exactly the same as those for the corresponding planar homogeneous wall, involving only properties of media at the surface and reflecting no information about the spherical geometry and the inhomogeneity, which implies the local nature. The other surface divergences are influenced by the spherical geometry and for the transverse component always weaker than the planar contribution. The general impacts from the inhomogeneity of media to the surface divergences are also shown. The inhomogeneity will further soften the surface divergence. For two touching media with permittivities and permeabilities equal up to a high enough order of their expansion over the distance to the surface, surface divergences may disappear together with the interaction Casimir stresses. Other factors, such as the refractivity and anisotropy, are also included, which may raise considerable complexities, but typically not related to divergences. Perspectives on the renormalization of the surface divergence are briefly outlined.

In this paper, we calculate the semileptonic decays $D\to K_0^{*}(1430)\ell {\nu }_{\ell }$ with $\ell =(e,\mu )$ induced by $c\to s\ell {\nu }_{\ell }$ transition. For the key component, $D\to K_0^{*}(1430)$ transition form factors (TFFs) $f_{\pm }(q^2)$ are calculated within the framework of QCD light cone sum rule. Then, we consider two scenarios for $K_0^{*}(1430)$-meson twist-2 distribution amplitude. For the scenario 1 (S1), we take the truncated form based on Gegenbauer polynomial series. Meanwhile, we also consider the scenario 2 (S2) constructed by light cone harmonic oscillator model, where the model parameters are fixed by the $K_0^{*}(1430)$-meson twist-2 distribution amplitude tenth-order $\xi$ moments calculated by using the background field theory. For the TFFs at a large recoil point, we have $f_{+}^{(\mathrm{S}1)}(0)={0.597}_{-0.121}^{+0.122}$ and $f_{-}^{(\mathrm{S}1)}(0)={-0.136}_{-0.035}^{+0.023}$, $f_{+}^{(\mathrm{S}2)}(0)={0.663}_{-0.134}^{+0.135}$, and $f_{-}^{(\mathrm{S}2)}(0)={-0.202}_{-0.046}^{+0.026}$. After extrapolating TFFs to the whole physical $q^2$ region, we calculate the branching fractions of $D^0\to K_0^{*+}(1430){\ell }^{-}{\overline{\nu }}_{\ell }$ and $D^{+}\to K_0^{*0}(1430){\ell }^{+}{\nu }_{\ell }$, which at ${10}^{-4}$-order level for the S1 and S2 cases. Meanwhile, we predict the CKM matrix $|V_{cs}{|}^{(\mathrm{S}1)}=0.973_{-0.183}^{+0.259}$, $|V_{cs}{|}^{(\mathrm{S}2)}={0.880}_{-0.165}^{+0.234}$, and lepton flavor universality ${\mathcal{R}}_{K_0^{*}}^{(\mathrm{S}1)}={0.768}_{-0.368}^{+0.560}$, ${\mathcal{R}}_{K_0^{*}}^{(\mathrm{S}2)}={0.764}_{-0.365}^{+0.555}$. Finally, we discuss the angular observables of forward-backward asymmetries, lepton polarization asymmetries, and $q^2$-differential flat terms for this decay.

The nonadiabatic quantum Vlasov equation in spinor QED is derived, and its relation to the well-known adiabatic one is established by three different methods. One is by deriving an explicit analytical expression. The second is by utilizing the Dirac equation in the length gauge, and the last is by introducing a weak and slowly varying counterfield. The relations obtained using the first two methods are instantaneous. Moreover, a comparative analysis of the nonadiabatic quantum Vlasov equations in both spinor and scalar QED is performed by investigating the time evolution of the distribution functions for a given momentum and the asymptotic momentum distributions of particles created by an electric field with and without an additional counterfield. It is found that after the external field is turned off, the oscillation periods of the distribution functions in both spinor and scalar QED equal pi divided by the positive eigenvalue of the Hamiltonian. The asymptotic momentum distributions in spinor and scalar QED show a novel out-of-phase behavior that cannot be explained by the conventional Stokes phenomenon. These results will further deepen our understanding of quantum Vlasov equations and their applications in vacuum pair production.

We investigate the cosmological consequences of axion interactions with standard model fermions accurately and precisely. Our analysis is entirely based on a phase space framework that allows us to keep track of the axion distribution in momentum space across the entire expansion history. First, we consider flavor-diagonal couplings to charged leptons and quantify the expected amount of dark radiation as a function of the coupling strength. Leptophilic axions are immune from complications due to strong interactions and our predictions do not suffer from theoretical uncertainties. We then focus on flavor-diagonal interactions with the three heavier quarks whose masses are all above the scale where strong interactions become nonperturbative. The top quark case is rather safe because its mass is orders of magnitude above the confinement scale, and the consequent predictions are solid. The bottom and charm masses are in more dangerous territory because they are very close to the QCD crossover. We present a comprehensive discussion of theoretical uncertainties due to both the choice of the scale where we stop the Boltzmann evolution and the running of QCD parameters. Finally, we compute the predicted amount of dark radiation expressed as an effective number of additional neutrino species. We compare our predictions with the ones obtained via standard approximate procedures, and we find that adopting a rigorous phase space framework alters the prediction by an amount larger than the sensitivity of future cosmic microwave background observatories.

The way a relativistic system approaches fluid dynamical behavior can be understood physically through the signals that will contribute to its linear response to perturbations. What these signals are is captured in the analytic structure of the retarded correlation function. The nonanalyticities can be grouped into three types based on their dimension in the complex frequency plane. In this paper, we will use kinetic theory in the (momentum-dependent) relaxation time approximation to find how we can calculate their corresponding signals. In the most general case of a system with particles that have a continuum of thermalization rates, we find that a nonanalytic region appears. To calculate its signal, we introduce the “nonanalytic area density” that describes the properties of this region, and we construct a method to calculate it. Further, to take into account the ambiguity present in signal analysis, following from manipulations of the nonanalyticities, we will identify two specific choices called “pictures” with interesting analytic properties and compare in what scenarios each picture is most useful.

The dynamical Sauter-Schwinger mechanism of electron-positron pair creation by a time-dependent electric field pulses is considered using the $S$-matrix approach and reduction formulas. They lead to the development of framework that treats the external field to all orders and is based on the solutions of the Dirac equation with the Feynman- or anti-Feynman boundary conditions. The asymptotic properties of those solutions are linked to the electron and positron spin-resolved probability amplitudes of created pairs. The same concerns the helicity-resolved amplitudes. Most importantly, the corresponding spin- or helicity-resolved distributions, when summed over spin or helicity configurations, reproduce the momentum distributions of created particles calculated with other methods that are typically used in this context, i.e., the Dirac-Heisenberg-Wigner function approach or the spinorial one. In contrast to those approaches, however, the $S$-matrix method allows us to investigate the vortex structures in momentum distributions of produced particles, as it provides access to the phase of the probability amplitude. As we also illustrate numerically, the method is applicable to arbitrary time-dependent electric fields with, in general, elliptical polarization. This proves its great flexibility.

We study the symmetry breaking and restoration behavior of a self-interacting charged scalar field theory under the influence of a constant electric field and finite temperature. Our study is performed in the context of the optimized perturbation theory. The dependence of the effective potential with constant electric fields is established by means of the bosonic propagators in the Schwinger proper-time method. Explicit analytical expressions for the electric and thermal contributions are found. Our results show a very weak decreasing behavior of the vacuum expectation value as a function of the electric field, which is strengthened by the temperature effect. A first-order phase transition that occurs at zero/weak electric fields changes to a second-order phase transition under strong electric fields. The critical temperature for the phase transition exhibited a very weak dependence on the electric field. Additionally, we computed the vacuum persistence probability rate for the interacting theory, finding a peak at the critical point. The maximum value of this rate at the critical point is found to be independent of the coupling constant but depended solely on the magnitude of the electric field.

Collective coordinates are frequently employed in path integrals to manage divergences caused by fluctuations around saddle points that align with classical symmetries. These coordinates parametrize a manifold of zero modes and more broadly provide judicious coordinates on the space of fields. However, changing from local coordinates around a saddle point to more global collective coordinates is remarkably subtle. The main complication is that the mapping from local coordinates to collective coordinates is generically multivalued. Consequently one is forced to either restrict the domain of path integral in a delicate way, or otherwise correct for the multivaluedness by dividing the path integral by certain intersection numbers. We provide a careful treatment of how to fix collective coordinates while accounting for these intersection numbers, and then demonstrate the importance of the fix for free theories. We also provide a detailed study of the fix for interacting theories and show that the contributions of higher intersections to the path integral can be nonperturbatively suppressed. Using a variety of examples ranging from single-particle quantum mechanics to quantum field theory, we explain and resolve various pitfalls in the implementation of collective coordinates.

Dark photons, hypothetical feebly interacting massive vector bosons, appear in many extensions of the Standard Model. This study investigates their production and subsequent decay during supernova explosions. We demonstrate that the decay of dark photons, with masses ranging from 200 to 400 MeV, can lead to the emission of neutrinos with energies surpassing those emitted by supernovae. These neutrinos therefore serve as a distinct signal of new physics, allowing for the exploration of previously uncharted regions of the dark photon parameter space and complementing both accelerator-based searches and other astrophysical constraints. The signal is largely unaffected by the specifics of the supernova’s temperature and density radial profiles outside the SN core. Our results indicate that searching for high-energy neutrinos accompanying supernova explosions provides a novel approach to probe physics beyond the Standard Model, including dark photons, heavy neutral leptons, and other feebly interacting particles with masses in the hundreds of MeV range.

Tachyons have fascinated generations of physicists due to their peculiar behavior, but they did not solve any real physical problem. This may have changed with the recent works of Dragan et al. [J. Paczos et al., Covariant quantum field theory of tachyons, Phys. Rev. D 110, 015006 (2024); A. Dragan and A. Ekert, Quantum principle of relativity, New J. Phys. 22, 033038 (2020); A. Dragan and A. EkertNew J. Phys.25, 088002(A) (2023); A. Dragan, K. Dębski, S. Charzyński, K. Turzyński, and A. Ekert, Relativity of superluminal observers in $1+3$ spacetime, Classical Quantum Gravity 40, 025013 (2023); J. Paczos, S. Cedrowski, K. Turzyński, and A. Dragan, Higgs field as a source of tachyons, arXiv:2407.06640], who have shown that superluminal observers may be related to the foundations of quantum mechanics (QM) because they require introducing nondeterminism and wavelike behavior at the fundamental level. Unfortunately, we show that the tachyon quantum field theory proposed as a part of this program is not quantum since the tachyon field commutes at all points and the canonical commutations relations of a quantum scalar field are not satisfied. We also discuss other authors’ theories, e.g., we show that the Dhar-Sudarshan’s formula for the Feynman propagator violates unitarity, and we apply the Lehmann–Symanzik–Zimmermann (LSZ) formalism to tachyons for the first time, where we find that one cannot prove the LSZ asymptotic condition just by replacing plane waves with wave packets.

The $SU(2{)}_L\times U(1{)}_Y$ invariance of the Standard Model effective field theory (SMEFT) imposes relations among different low-energy effective field theory Wilson coefficients (WCs), any deviations from which would signal the presence of physics beyond SMEFT. In this work, we investigate two such relations (${\mathcal{C}}_S=-{\mathcal{C}}_P$, ${\mathcal{C}}_S^{\prime }={\mathcal{C}}_P^{\prime }$) among the scalar and the pseudoscalar new physics WCs that can contribute to $b\to s\tau \tau$ processes. We show that, even when new physics violating these relations would not be measurable in the branching ratios of $B_s\to {\tau }^{+}{\tau }^{-}$ and $B\to K^{(*)}{\tau }^{+}{\tau }^{-}$ at HL-LHC and FCC-ee, it can still manifest itself in the angular distribution of $B\to K^{*0}{\tau }^{+}{\tau }^{-}$. We identify the combinations of angular observables in this decay channel that are sensitive to scenarios beyond SMEFT. We find that the two observables $S_6^c$ and $A_7$, and their combination, have the potential to identify physics beyond SMEFT.

The deviations of the recent measurements of the muon magnetic moment and the $W$-boson mass from their SM predictions hint to new physics beyond the SM. In this article, we address the observed discrepancies in the $W$-boson mass and muon anomalous magnetic moment in the Inert Two Higgs Doublet Model extended by a complex scalar field singlet under the SM gauge group. The model is constrained from the existing Large Electron Positron Collider (LEP) data and the measurements of partial decay widths to gauge bosons at LHC. It is shown that a large subset of the constrained parameter space of the model can accommodate both the experimentally measured as well as SM global fit value of $W$-boson mass while simultaneously explaining the observed muon $g-2$ anomaly.

We investigate three intriguing anomalies within the framework of the general next-to-minimal supersymmetric standard model. These anomalies include a significant deviation of the experimental results for the muon anomalous magnetic moment from its standard model prediction, with a confidence level of $5.1\sigma$; a joint observation by the CMS and ATLAS Collaborations of a diphoton excess with a local significance of $3.1\sigma$ in the invariant mass distribution around 95.4 GeV; and a reported excess in the $b\overline{b}$ production at the Large Electron-Positron Collider with a local significance of $2.3\sigma$. Through analytical and numerical analyses, we provide unified interpretations across an extensive parameter space that remain consistent with current experimental restrictions from data on the Higgs boson at 125 GeV, $B$-physics measurements, and dark matter observables, as well as existing searches for supersymmetry and extra Higgs bosons. We attribute the muon anomaly to loops involving muon-smuon-neutralino and muon-sneutrino-chargino interactions, while attributing the diphoton and $b\overline{b}$ excesses to the resonant production of a singlet-dominated scalar. These proposed solutions are poised for experimental tests at the high-luminosity LHC and future linear colliders.

According to recent measurements, the dark matter magnetic dipole moment is strongly constrained. In the composite Higgs models the magnetic dipole moment of the Dirac dark matter fermion and its mass can be suppressed by the approximate $U(1)$ symmetry. We consider the $E_6$ inspired composite Higgs model (${\mathrm{E}}_6\mathrm{CHM}$) with $U(1)$ symmetry violating operators, which give rise to dark matter’s mass and coupling constant to Higgs boson. The dependence of the spin-independent dark matter-nucleon scattering cross section on the ${\mathrm{E}}_6\mathrm{CHM}$ parameters is explored. We argue that there are regions of the parameter space which are still safe from all current constraints and may lead to spectacular LHC signatures.

If millicharged particles (MCPs) exist they can be created in the atmosphere when high energy cosmic rays collide with nuclei and could subsequently be detected at neutrino experiments. We extend previous work, which considered MCPs from decays of light mesons and proton bremsstrahlung, by including production from $\mathrm{\Upsilon }$ meson decays and the Drell-Yan process. MCPs with masses below a GeV primarily arise from proton bremsstrahlung, while heavier MCPs predominantly originate from heavy meson decays and Drell-Yan. We analyze the resulting single scatter and multiple scatter signals at SuperK and JUNO. Searches for low energy coincident signals at JUNO will be sensitive to MCPs with millicharges up to an order of magnitude beyond current constraints for MCP masses between 2 and 10 GeV.

The QCD crossover line in the temperature ($T$)-baryochemical potential (${\mu }_B$) plane has been computed by several lattice groups by calculating the chiral order parameter and its susceptibility at finite values of ${\mu }_B$. In this work we focus on the deconfinement aspect of the transition between hadronic and quark gluon plasma phases. We define the deconfinement temperature as the peak position of the static quark entropy [$S_Q(T,{\mu }_B)$] in $T$, which is based on the renormalized Polyakov loop. We extrapolate $S_Q(T,{\mu }_B)$ based on high statistics finite temperature ensembles on a ${16}^3\times 8$ lattice to finite density by means of a Taylor expansion to eighth order in ${\mu }_B$ (NNNLO) along the strangeness neutral line. For the simulations the 4HEX staggered action was used with $2+1$ flavors at physical quark masses. In this setup the phase diagram can be drawn up to unprecedentedly high chemical potentials. Our results for the deconfinement temperature are in rough agreement with phenomenological estimates of the freeze-out curve in relativistic heavy ion collisions. In addition, we study the width of the deconfinement crossover. We show that up to ${\mu }_B\approx 400\mathrm{MeV}$, the deconfinement transition gets broader at higher densities, disfavoring the existence of a deconfinement critical endpoint in this range. Finally, we examine the transition line without the strangeness neutrality condition and observe a hint for the narrowing of the crossover towards large ${\mu }_B$.

We study the in-medium properties of kaons and antikaons in isospin asymmetric hot and dense resonance matter within the chiral SU(3) hadronic mean field model. Along with nucleons and hyperons, the interactions of $K$ and $\overline{K}$ mesons with all decuplet baryons (${\mathrm{\Delta }}^{++,+,0,-},{\mathrm{\Sigma }}^{*\pm ,0},{\mathrm{\Xi }}^{*0,-},{\mathrm{\Omega }}^{-}$) are explicitly considered in the dispersion relations. The properties of mesons in the chiral SU(3) model are modified at finite density and temperature of asymmetric resonance matter through the exchange of scalar fields $\sigma$, $\zeta$, and $\delta$ and the vector fields $\omega$, $\rho$, and $\varphi$. The presence of resonance baryons in the medium at finite temperature is observed to modify significantly the effective masses of $K$ and $\overline{K}$ mesons. We also calculated the optical potentials of kaons and antikaons as a function of momentum in resonance matter. The present study of in-medium masses and optical potentials of kaons and antikaons will be important for understanding the experimental observables from the heavy-ion collision experiments where hot and dense matter may be produced. Our results indicate that when resonance baryons are present within the medium at finite baryonic density, the mass reduction of kaons and antikaons becomes more pronounced as the temperature of the medium increases from zero to 100 and 150 MeV. The study of the optical potentials of kaons and antikaons reveals a stronger correlation with strangeness fraction compared to isospin asymmetry.

The double pion photoproduction off nucleons near threshold is analyzed in a covariant baryon chiral perturbation theory up to next to leading order, where the $\mathrm{\Delta }(1232)$, $N^{*}(1400)$, and $\rho (770)$ resonances are included as explicit degrees of freedom. For the process $\gamma p\to {\pi }^{+}{\pi }^{0}n$, the chiral results of total cross sections, invariant-mass distributions, and beam-helicity asymmetry are in good agreement with the experimental data within uncertainties. For the process $\gamma p\to {\pi }^0{\pi }^{0}p$, the prediction of total cross section deviates from the existing experimental data. Once the final-state interaction of $\pi \pi$ in the isoscalar S-wave channel is taken into account, a good description of the cross section is achieved. The effect of the Roper resonance always turns out be negligible, and hence can be thrown away in future study of this process.

We discuss the relation between the Koonin-Pratt femtoscopic correlation function (CF) and invariant mass distributions from production experiments. We show that the equivalence is total for a zero source-size and that a Gaussian finite-size source provides a form-factor for the virtual production of the particles. Motivated by this remarkable relationship, we study an alternative method to the Koonin-Pratt formula, which connects the evaluation of the CF directly with the production mechanisms. The differences arise mostly from the $T$–matrix quadratic terms and increase with the source size. We study the case of the $D^0{D}^{*+}$ and $D^{+}{D}^{*0}$ correlation functions of interest to unravel the dynamics of the exotic $T_{cc}(3875{)}^{+}$, and find that these differences become quite sizable already for 1 fm sources. We nevertheless conclude that the lack of coherence in high-multiplicity-event reactions and in the creation of the fire-ball source that emits the hadrons certainly make much more realistic the formalism based on the Koonin-Pratt equation. We finally derive an improved Lednicky-Lyuboshits (LL) approach, which implements a Lorentz ultraviolet regulator that corrects the pathological behavior of the LL CF in the punctual source-size limit.

Relativistic heavy-ion collisions produce quark-gluon plasma (QGP), which is locally thermalized. Due to electrically charged particles (quarks), QGP exhibits interesting thermoelectric phenomena during its evolution, resulting in an electromagnetic (EM) field in the medium. In this study, for the first time, we estimate the induced electric field in QGP due to the thermoelectric effect. This phenomenon can induce an EM field even in QGP produced by the head-on heavy-ion collision. In peripheral heavy-ion collisions, the presence of a spectator current generates a transient magnetic field at the early stage, which disrupts the isotropy of the induced electric field. For the numerical estimation, we use a quasiparticle-based model that incorporates the lattice quantum chromodynamics equation of state for QGP. The induced electric field is estimated with cooling rates derived from Gubser hydrodynamic flow. Thermoelectric coefficients such as Seebeck, magneto-Seebeck, and Nernst coefficients play a crucial role in determining the induced field. Additionally, we account for the temperature evolution of QGP using different hydrodynamic cooling rates to calculate the transport coefficients. We also estimate the transport coefficients and the induced electric field in the presence of an external time-varying magnetic field, including the quantum effect of Landau quantization, and explore the effects of the intensity and decay parameter of the magnetic field on the induced electric field. Our findings reveal that the space-time profile of the induced electric field is zero at the center and increases as we go away from the center. During the early stages of evolution, the electric field can reach a maximum value of $eE\approx 1m_{\pi }^2$, decreasing in strength over time.