Based on a sample of $4.\text{5\hspace{0.17em}\hspace{0.17em}}{\mathrm{fb}}^{-1}$ of $e^{+}{e}^{-}$ annihilation data collected in the energy region between 4.6 GeV and 4.7 GeV with the BESIII detector at BEPCII, two singly Cabibbo-suppressed decays ${\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^0{K}^{+}$ and ${\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^{+}{K}_S^0$ are studied. The ratio of the branching fraction $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^0{K}^{+})$ relative to $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^0{\pi }^{+})$ is measured to be $0.0361\pm 0.0073(\mathrm{stat}.)\pm 0.0005(\mathrm{syst}.)$, and the ratio of $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^{+}{K}_S^0)$ relative to $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^{+}{\pi }^{+}{\pi }^{-})$ is measured to be $0.0106\pm 0.0031(\mathrm{stat}.)\pm 0.0004(\mathrm{syst}.)$. After taking the world-average branching fractions of the reference decay channels, the branching fractions $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^0{K}^{+})$ and $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^{+}{K}_S^0)$ are determined to be $(4.7\pm 0.9(\mathrm{stat}.)\pm 0.1(\mathrm{syst}.)\pm 0.3(\mathrm{ref}.))\times {10}^{-4}$ and $(4.8\pm 1.4(\mathrm{stat}.)\pm 0.2(\mathrm{syst}.)\pm 0.3(\mathrm{ref}.))\times {10}^{-4}$, respectively. The branching fraction of the ${\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^{+}{K}_S^0$ decay is measured for the first time.

The center-flavor symmetry of a gauge theory specifies the global form of consistent gauge and flavor bundle background field configurations. For 6D gauge theories which arise from a tensor branch deformation of a superconformal field theory (SCFT), we determine the global structure of such background field configurations, including possible continuous Abelian symmetry and R-symmetry bundles. Proceeding to the conformal fixed point, this provides a prescription for reading off the global form of the continuous factors of the zero-form symmetry, including possible nontrivial mixing between flavor and R-symmetry. As an application, we show that this global structure leads to a large class of 4D $\mathcal{N}=2$ SCFTs obtained by compactifying on a $T^2$ in the presence of a topologically nontrivial flat flavor bundle characterized by an ’t Hooft magnetic flux. The resulting “Stiefel-Whitney twisted” compactifications realize several new infinite families of 4D $\mathcal{N}=2$ SCFTs, and also furnish a 6D origin for a number of recently discovered rank one and two 4D $\mathcal{N}=2$ SCFTs.

The Maxwell field with a general gauge fixing (GF) term is nontrivial: not only the longitudinal and temporal modes are mixed up in the field equations, but also unwanted consequences might arise from the GF term. We derive the complete set of solutions in de Sitter space, and implement the covariant canonical quantization which restricts the residual gauge transformation down to a quantum residual gauge transformation. Then, in the Gupta-Bleuler (GB) physical state, we calculate the stress tensor which is amazingly independent of the gauge fixing constant and is also invariant under the quantum residual gauge transformation. The transverse components are simply the same as those in the Minkowski spacetime, and the transverse vacuum stress tensor has only one UV divergent term ($\propto k^4$), which becomes zero by the zeroth-order adiabatic regularization. The longitudinal-temporal stress tensor in the GB state is zero due to a cancellation between the longitudinal and temporal parts. More interesting is the stress tensor of the GF term. Its particle contribution is zero due to the cancellation in the GB state, and its vacuum contribution is twice that of a minimally coupling massless scalar field, containing $k^4$ and $k^2$ divergences. After the second-order adiabatic regularization, the GF vacuum stress tensor becomes zero too, so that there is no need to introduce a ghost field, and the zero GF vacuum stress tensor cannot be a possible candidate for the cosmological constant. Thus, all the physics predicted by the Maxwell field with the GF term will be the same as that without the GF term. We also carry out analogous calculation in the Minkowski spacetime, and the stress tensor is similar to, but simpler than that in de Sitter space.

In recent years, experimental and theoretical research on the nature of supermassive bodies that inhabit the central regions of galaxies has grown significantly. In this contribution, we study the motion of unitary mass test particles in a perturbed Kerr-like metric. The metric represents the approximate exterior spacetime of a massive rotating body with mass quadrupole moment $q$. Through extensive study of the geodesics, it is found that the chaotic behavior proliferates as the $q$ parameter increases. Several structures are found in the phase space, such as Birkhoff chains of islands and hyperbolic points if $q\ne 0$. Additionally, chaotic regions crossing the null radial momentum axis ($p_r=0$) are studied by analyzing the rotation number, and several islands of stability are found that are preserved as the deformation of the rotating body increases, while others are destroyed. Furthermore, chaotic behavior is found to be dictated by stickiness, chaotic orbits that remain attached to stable ones for a long time before they become divergent and are attracted to the event horizon.

We present a new solution in Einstein’s general relativity representing a Schwarzschild black hole immersed in a rotating universe. Such a solution is constructed analytically by means of the last unexplored Lie point symmetry of the Ernst equations for stationary and axisymmetric spacetimes. This kind of Ehlers transformation is able to embed any given solution into a rotating background, which is not of Newman-Unti-Tamburino type. We analyze the physical properties, ergoregions and geodesics of the new metric, which is regular outside the event horizon and has a well-defined thermodynamics. We finally consider the Kerr generalization.

We investigate the phase space symmetries and conserved charges of homogeneous gravitational minisuperspaces. These ($0+1$)-dimensional reductions of general relativity are defined by spacetime metrics in which the dynamical variables depend only on a time coordinate and are formulated as mechanical systems with a nontrivial field space metric (or supermetric) and effective potential. We show how to extract conserved charges for those minisuperspaces from the homothetic Killing vectors of the field space metric. In the case of two-dimensional field spaces, we exhibit a universal eight-dimensional symmetry algebra $\mathcal{A}=(\mathfrak{sl}(2,\mathbb{R})\oplus \mathbb{R})⨭{\mathfrak{h}}_2$, based on the two-dimensional Heisenberg algebra ${\mathfrak{h}}_2\simeq {\mathbb{R}}^4$. We apply this to the systematic study of the Bianchi models for homogeneous cosmology. This extends the previous results on the $\mathfrak{sl}(2,\mathbb{R})$ algebra for Friedmann-Lemaître-Robertson-Walker cosmology and the Poincaré symmetry for Kantowski-Sachs metrics describing the black hole interior. The presence of this rich symmetry structure already in minisuperspace models opens new doors toward quantization and the study of solution generating mechanisms.

We study the strong gravitational lensing effect around rotating black holes in different gravity theories. By calculating the deflection angle of strong gravitational lensing, we evaluate the lensing observables including the image position, separation, magnification, and the time delays between the relativistic images of different rotating black holes. We argue that the differences in image positions, separations between the rotating black hole in modified gravity (MOG) theory and the Kerr black hole in general relativity (GR) are more significant in SgrA* than those in M87*; however the differences in time delays between rotating black holes in MOG and GR are shorter in SgrA* than that in M87*. Our evaluations on lensing observables in the strong gravity regime can help to distinguish the MOG from GR. Furthermore, we investigate the shadow observables of different rotating black holes. Employing the Event Horizon Telescope observations on the angular shadow radius for supermassive M87* and SgrA* black holes, respectively, we estimate the ranges of MOG parameter and obtain its upper limit constraint $0.350\lesssim {\alpha }_{\mathrm{up}}\lesssim 0.485$ and $0.162\lesssim {\alpha }_{\mathrm{up}}\lesssim 0.285$ correspondingly, relating to black hole spins. This is the first constraint on the MOG parameter for rotating supermassive black holes from Event Horizon Telescope observations on the angular shadow radius. Our constraint on the MOG parameter is much tighter compared with the result obtained from the orbital precession of the S2 star.

Scalar-induced gravitational waves (SIGWs) are attracting growing attention for probing extremely short-scale scalar perturbations via gravitational wave measurements. In this paper, we investigate the SIGWs from statistically anisotropic scalar perturbations, which are motivated in inflationary scenarios in the presence of, e.g., a vector field. While the ensemble average of the SIGW energy spectrum is isotropic for the standard statistically isotropic scalar perturbations, the statistical anisotropy in the source introduces the multipole moments of the differential SIGW energy spectrum. We consider quadrupole anisotropy in the scalar power spectrum and show that the SIGW spectrum has anisotropies up to $\ell =4$. We present generic formulas of the multipole moments and then apply them to the delta-function-like and log-normal source spectra. We find analytic expressions for the former case and show that the infrared scalings of the multipole moments are the same as the isotropic SIGWs. Interestingly, the monopole has an additional local minimum in the high-$k$ tail, a key feature to distinguish from the isotropic SIGWs. The latter log-normal case is analytic for the narrow-peak source, and we perform the numerical calculation for the broad peak. As one expects, the multipole moments become broader with increasing source width. Our results are helpful to test the isotropy of primordial density perturbations at extremely small scales through SIGWs.

Monte Carlo (MC) algorithms are commonly employed to explore high-dimensional parameter spaces constrained by data. All the statistical information obtained in the output of these analyses is contained in the Markov chains, which one needs to process and interpret. The marginalization technique allows us to digest these chains and compute the posterior distributions for the parameter subsets of interest. In particular, it lets us draw confidence regions in two-dimensional planes, and get the constraints for the individual parameters. It is very well known, though, that the marginalized results can suffer from volume effects, which can introduce a non-negligible bias into our conclusions. The impact of these effects are barely studied in the literature. In this paper we first illustrate the problem through a very clear and simple example in two dimensions, and suggest the use of the profile distributions (PDs) as a complementary tool to detect marginalization biases directly from the MC chains. We apply our method to four cosmological models: the standard $\mathrm{\Lambda }\mathrm{CDM}$, early dark energy, coupled dark energy and the Brans-Dicke model with a cosmological constant. We discuss the impact of the volume effects on each model and the cosmological tensions, using the full Planck 2018 likelihood, the Pantheon compilation of supernovae of type Ia and data on baryon acoustic oscillations. Our test is very efficient and can be easily applied to any MC study. It allows us to estimate the PDs at a derisory computational cost not only for the main cosmological parameters, but also for the nuisance and derived ones, and to assess the need to perform a more in-depth analysis with the exact computation of the PDs.

A claimed detection of cosmological tensor perturbations from inflation via $B$-mode polarization of the cosmic microwave background requires distinguishing other possible $B$-mode sources. One such potential source of confusion is primordial magnetic fields. For sufficiently low-amplitude $B$-mode signals, the microwave background temperature and polarization power spectra from power-law tensor perturbations and from a power-law primordial magnetic field are indistinguishable. However, we show that such a magnetic field will induce a small-scale Faraday rotation which is detectable using four-point statistics analogous to gravitational lensing of the microwave background. The Faraday rotation signal will distinguish a magnetic-field-induced $B$-mode polarization signal from tensor perturbations for effective tensor-to-scalar ratios larger than 0.001, detectable in upcoming polarization experiments.

The observed pattern of linear polarization of the cosmic microwave background photons is a sensitive probe of physics violating parity symmetry under inversion of spatial coordinates. A new parity-violating interaction might have rotated the plane of linear polarization by an angle $\beta$ as the cosmic microwave background photons have been traveling for more than 13 billion years. This effect is known as “cosmic birefringence.” In this paper, we present new measurements of cosmic birefringence from a joint analysis of polarization data from two space missions, $Planck$ and WMAP. This dataset covers a wide range of frequencies from 23 to 353 GHz. We measure $\beta =0.342{°}_{-0.091°}^{+0.094°}$ [68% confidence level (CL)] for nearly full-sky data, which excludes $\beta =0$ at 99.987% CL. This corresponds to the statistical significance of $3.6\sigma$. There is no evidence for frequency dependence of $\beta$. We find a similar result, albeit with a larger uncertainty, when removing the Galactic plane from the analysis.

The system of $B_s^0\to D_s^{\mp }{K}^{\pm }$ decays offers a theoretically clean determination of the angle $\gamma$ of the unitarity triangle. A corresponding LHCb analysis resulted in a surprisingly large result, which is in tension with other determinations and global analyses of the unitarity triangle. Paying special attention to discrete ambiguities, we confirm this picture and resolve a final ambiguity. Moreover, we extract the branching ratios of the underlying ${\overline{B}}_s^0\to D_s^{+}{K}^{-}$ and ${\overline{B}}_s^0\to D_s^{-}{K}^{+}$ modes. Combining them with information from semileptonic $B_{(s)}$ decays, we arrive at another puzzling situation, which we obtain also for other decays with similar dynamics. These patterns could be footprints of New Physics in the $b\to c\overline{u}s$ and $b\to u\overline{c}s$ processes which govern the dynamics of the ${\overline{B}}_s^0\to D_s^{\mp }{K}^{\pm }$ channels. Employing a model-independent parametrization, we present a strategy to reveal such effects. Applying it to the present data, we obtain strongly correlated New-Physics contributions with potentially large $CP$-violating phases. We find that new contributions sizeably smaller than the Standard Model amplitudes could actually accommodate the current data. This strategy offers an exciting probe for new sources of $CP$ violation at the future high-precision frontier of $B$ physics.

Background: The transverse densities ${\rho }_{1,2}(b)$ describe the distributions of electric charge and magnetic moment at fixed light-front time and connect the nucleon’s elastic form factors with its partonic structure. The dispersive representation of the form factors $F_{1,2}(t)$ expresses the densities in terms of exchanges of hadronic states in the $t$-channel and permits their analysis using hadronic physics methods. Purpose: Compute the densities at peripheral distances $b=\mathcal{O}(M_{\pi }^{-1})$, where they are generated predominantly by the two-pion states in the dispersive representation. Quantify the uncertainties. Methods: Dispersively improved chiral effective field theory ($\mathrm{DI}\chi \mathrm{EFT}$) is used to calculate the isovector spectral functions $\mathrm{Im}{F}_{1,2}(t)$ on the two-pion cut. The method includes $\pi \pi$ interactions ($\rho$ resonance) through elastic unitarity and provides realistic spectral functions up to $t\approx 1{\mathrm{GeV}}^2$. Higher-mass states are parametrized by effective poles and constrained by sum rules (charges, radii, superconvergence relations). The densities ${\rho }_{1,2}(b)$ are obtained from their dispersive representation. Uncertainties are quantified by varying the spectral functions. The method respects analyticity and ensures the correct $b\to \infty$ asymptotic behavior of the densities. Results: Accurate densities are obtained at all distances $b\gtrsim 0.5\mathrm{fm}$, with correct behavior down to $b\to 0$. The region of distances is quantified where transverse nucleon structure is governed by the two-pion state. The light-front current distributions in the polarized nucleon are computed and discussed. Conclusions: Peripheral nucleon structure can be computed from first principles using $\mathrm{DI}\chi \mathrm{EFT}$. The method can be extended to generalized parton distributions and other nucleon form factors.

Nonextensive statistics has attracted attention as a description of particle spectra in nuclear collisions at QCD energies. First, we construct the equation of state by incorporating Tsallis statistics based on the hadron resonance gas and parton gas models. Thermodynamic conditions are found to impose constraints on the $q$-parameter of Tsallis distribution. Next, we apply the equation of state to the relativistic hydrodynamic modeling of nuclear collisions. The Cooper-Frye prescription is consistently modified. Numerical demonstrations indicate that the model may describe charged particle spectra at Large Hadron Collider in the transverse momentum range up to 6–8 GeV. Elliptic flow, on the other hand, suggests a narrower range of applicability.

We provide a detailed reconsideration of the theoretical basis for the treatment of Coulomb-nuclear interference (CNI) and a corresponding thorough analysis of the procedure of extraction of the basic parameters ${\rho }^{pp},{\sigma }_{\mathrm{tot}}^{pp}$, and $B^{pp}$ from the TOTEM data at $\sqrt{s}=13\mathrm{TeV}$. A more substantiated account of CNI, as well as an in-depth statistical analysis of the TOTEM data at low transferred momenta, gives results that differ from those published by the TOTEM collaboration.

It has been known since the earliest days of quantum field theory (QFT) that infrared divergences arise in scattering theory with massless fields. These infrared divergences are manifestations of the memory effect: At order $1/r$ a massless field generically will not return to the same value at late retarded times ($u\to +\infty$) as it had at early retarded times ($u\to -\infty$). There is nothing singular about states with memory, but they do not lie in the standard Fock space. Infrared divergences are merely artifacts of trying to represent states with memory in the standard Fock space. If one is interested only in quantities directly relevant to collider physics, infrared divergences can be successfully dealt with by imposing an infrared cutoff, calculating inclusive quantities, and then removing the cutoff. However, this approach does not allow one to treat memory as a quantum observable and is highly unsatisfactory if one wishes to view the $S$-matrix as a fundamental quantity in QFT and quantum gravity, since the $S$-matrix itself is undefined. In order to have a well-defined $S$-matrix, it is necessary to define “in” and “out” Hilbert spaces that incorporate memory in a satisfactory way. Such a construction was given by Faddeev and Kulish for quantum electrodynamics (QED) with a massive charged field. Their construction can be understood as pairing momentum eigenstates of the charged particles with corresponding memory representations of the electromagnetic field to produce states of vanishing large gauge charges at spatial infinity. (This procedure is usually referred to as “dressing” the charged particles.) We investigate this procedure for QED with massless charged particles and show that, as a consequence of collinear divergences, the required dressing in this case has an infinite total energy flux, so that the states obtained in the Faddeev-Kulish construction are unphysical. An additional difficulty arises in Yang-Mills theory, due to the fact that the “soft Yang-Mills particles” used for the dressing contribute to the Yang-Mills charge-current flux, thereby invalidating the procedure used to construct eigenstates of large gauge charges at spatial infinity. We show that there are insufficiently many charge eigenstates to accommodate scattering theory. In quantum gravity, the analog of the Faddeev-Kulish construction would attempt to produce a Hilbert space of eigenstates of supertranslation charges at spatial infinity. Again, the Faddeev-Kulish dressing procedure does not produce the desired eigenstates because the dressing contributes to the null memory flux. We prove that there are no eigenstates of supertranslation charges at spatial infinity apart from the vacuum. Thus, analogs of the Faddeev-Kulish construction fail catastrophically in quantum gravity. We investigate some alternatives to Faddeev-Kulish constructions but find that these also do not work. We believe that if one wishes to treat scattering at a fundamental level in quantum gravity—as well as in massless QED and Yang-Mills theory—it is necessary to approach it from an algebraic viewpoint on the “in” and “out” states, wherein one does not attempt to “shoehorn” these states into some prechosen “in” and “out” Hilbert spaces. We outline the framework of such a scattering theory, which would be manifestly infrared finite.

We present a complete nonlinear action for the dynamical system of nearly coincident multiple D0-branes (mD0) which possesses, besides manifest spacetime (target superspace) supersymmetry, also the worldline supersymmetry, a counterpart of the local fermionic $\kappa$ symmetry of single D0-brane (Dirichlet superparticle). The action contains an arbitrary nonvanishing function $\mathcal{M}(\mathcal{H})$ of the relative motion Hamiltonian $\mathcal{H}$. The ten-dimensional ($D=10$) mD0 model with particular form of $\mathcal{M}(\mathcal{H})$ can be obtained by dimensional reduction from the action of the $D=11$ multiple M-wave (mM0) system.

We extend to a non-Hermitian fermionic quantum field theory with $\mathcal{PT}$ symmetry our previous discussion of second quantization, discrete symmetry transformations, and inner products in a scalar field theory [Phys. Rev. D 102, 125030 (2020)]. For illustration, we consider a prototype model containing a single Dirac fermion with a parity-odd, anti-Hermitian mass term. In the phase of unbroken $\mathcal{PT}$ symmetry, this Dirac fermion model is equivalent to a Hermitian theory under a similarity transformation, with the non-Hermitian nature of the model residing only in the spinor structure, whereas the algebra of the creation and annihilation operators is just that of a Hermitian theory.

A great deal of evidence has been mounting over the years, showing a deep connection between acceleration, radiation, and the Unruh effect. Indeed, the fact that the Unruh effect can be codified in the Larmor radiation emitted by the charge was used to propose an experiment to experimentally confirm the existence of the Unruh thermal bath. However, such connection has two puzzling issues: (1) how the quantum Unruh effect can be codified in the classical Larmor radiation and (2) the fundamental role played by zero-Rindler-energy modes of the Unruh thermal bath in such a context. Here we generalize a recent analysis made for the scalar case to the more realistic case of Maxwell electrodynamics and settle these two puzzling issues.

Two-phase transition branches of the Euler-Heisenberg (EH) anti–de Sitter (AdS) black hole (BH) were derived from its phase transition critical behavior by Magos et al.. [Phys. Rev. D 102, 084011 (2020)]. We found that the phase transition is unstable. Considering the high-order quantum electrodynamics (QED) correction, we rederive the EHAdS BH solution and investigate its critical thermodynamic quantities. It is found that the corrected EHAdS BH has only one stable phase transition branch, and its critical exponents are equivalent to that of the van der Waals system. From the microscopic point of view, we also derive its normalized scalar curvature based on the Ruppeiner geometry. Different from two concave surfaces of the scalar curvature without considering the high-order QED correction, we show that the corrected Ruppeiner geometry has only one concave surface. Our results indicate that the phase transition instability derived by Magos et al. is due to without considering the high-order QED correction.