We introduce a modification of the Dyson series based on perturbative unitarity as a starting point. The presented approach systematically avoids singularities and double-counting related to the presence of unstable particles as intermediate states and, at the same time, does not rely on a specific choice of the renormalization scheme.

We propose a simple model of dark matter and $CP$ violation and consider the associated triple and quadruple productions of 125 GeV Higgs bosons at the Large Hadron Collider (LHC). In the model, the dark matter is a vectorlike dark fermion $(\overline{\chi },\chi )$ interacting with the Standard Model only through a complex messenger scalar $S$ which is an electroweak singlet. New sources of $CP$ violation reside in the most general scalar potential involving the doublet $H$ and the singlet $S$, as well as in the dark Yukawa coupling between $S$ and $(\overline{\chi },\chi )$. We study current experimental constraints from Higgs measurements, searches for new scalars at the LHC, precision electroweak measurements, EDM measurements, dark matter relic density, as well as direct and indirect detections of dark matter. A smoking-gun signature of $CP$ violation could come from the Higgs-to-Higgs decays, $h_3\to h_2{h}_1$, where $h_3/h_2/h_1$ are the heaviest scalar, second heaviest scalar and the SM-like 125-GeV Higgs, respectively. Taking into account other Higgs-to-Higgs decays, such as $h_3\to 2h_2$ and $h_3/h_2\to 2h_1$, then gives rise to novel $3h_1$ and $4h_1$ final states, which have yet to be searched for experimentally. We present four benchmarks and show the event rates for $3h_1$ and $4h_1$ final states could be as large as $\mathcal{O}(10)\mathrm{fb}$ and $\mathcal{O}(1)\mathrm{fb}$, respectively, at the 14-TeV LHC. This work opens up a new frontier of searching for triple and quadruple Higgs bosons at a high energy collider.

We propose a new application of lattice QCD to calculate the quark-diquark potential, diquark mass, and quark mass required for the diquark model. As a concrete example, we consider the ${\mathrm{\Lambda }}_c$ baryon and treat it as a charm-diquark ($c$-[$ud$]) two-body bound state. We extend the HAL QCD method to calculate the charm-diquark potential, which reproduces the equal-time Nambu-Bethe-Salpeter wave function of the S-wave state [${\mathrm{\Lambda }}_c({\frac{1}{2}}^{+})$]. The diquark mass is determined so as to reproduce the difference between the S-wave and the spin-orbit averaged P-wave energies, i.e., the difference between the ${\mathrm{\Lambda }}_c({\frac{1}{2}}^{+})$ level and the average of the ${\mathrm{\Lambda }}_c({\frac{1}{2}}^{-})$ and the ${\mathrm{\Lambda }}_c({\frac{3}{2}}^{-})$ levels. Numerical calculations are performed on a ${32}^3\times 64$ lattice with lattice spacing of $a\simeq 0.0907\mathrm{fm}$ and the pion mass of $m_{\pi }\simeq 700\mathrm{MeV}$. Our charm-diquark potential is given by the $\mathrm{Coulomb}+\mathrm{linear}$ (Cornell) potential, where the long range behavior is consistent with the charm-anticharm potential, while the Coulomb attraction is considerably smaller. This weakening of the attraction may be attributed to the diquark size effect. The obtained diquark mass is $m_D=1.273(44)\mathrm{GeV}$. Our diquark mass lies slightly above the conventional estimates, namely the $\rho$ meson mass and twice the constituent quark mass $2m_N/3$.

We present a relativistic and model-independent method to derive structure-dependent electromagnetic finite-size effects. This is a systematic procedure, particularly well-suited for automation, which works at arbitrarily high orders in the large-volume expansion. Structure-dependent coefficients appear as zero-momentum derivatives of physical form factors which can be obtained through experimental measurements or auxiliary lattice calculations. As an application we derive the electromagnetic finite-size effects on the pseudoscalar meson mass and leptonic decay amplitude, through orders $\mathcal{O}(1/L^3)$ and $\mathcal{O}(1/L^2)$, respectively. The structure dependence appears at this order through the meson charge radius and the real radiative leptonic amplitude, which are known experimentally.

We present calculations of the $S$-wave isospin-zero and isospin-two pion-pion scattering lengths within a nucleon-meson model with parity doubling. Both scattering lengths are computed in various approximations, ranging from a mean-field (MF) calculation toward the inclusion of loop corrections by means of the functional renormalization group (FRG). The bosonic part of the investigated nucleon-meson model is formulated in terms of stereographic projections as a “natural” set of coordinates on the respective vacuum manifold. We thereby elucidate subtleties concerning the truncation of the effective action with respect to higher-derivative pion interactions and the “successful” computation of the scattering lengths. As the main result, we find simultaneous agreement for the isospin-zero and isospin-two scattering lengths with experimental data within the ${\mathrm{LPA}}^{\prime }$ truncation of the FRG, together with chiral-symmetry breaking (roughly) occurring at the characteristic scale of $4\pi f_{\pi }$. The isoscalar $\sigma$ mass is dynamically generated by the FRG integration of momentum modes and is a prediction of the model. It ends being of the order of 500 MeV, i.e., much lower than the value ($>1\mathrm{GeV}$) found in MF or one-loop treatment of this or related models. Finally, the convergence of the corresponding low-energy expansion of the quantum effective action in terms of pion momenta is discussed.

The polarization characteristics of the linear Breit-Wheeler (LBW) pair-production process in polarized $\gamma \gamma$ colliders have been investigated via our developed spin-resolved binary collision simulation method. We find that the polarization of $\gamma$-photons modifies the kinematics of scattering particles and induces the correlated energy-angle shift of LBW pairs, and the latter’s polarization characteristic depends on the helicity configures of scattering particles. We confirm that the polarized $\gamma \gamma$ collider with an asymmetric setup can be performed with currently achievable laser-driven high-density x rays and high-brilliance $\gamma$-photon beams to produce abundant polarized LBW pairs, fulfilling the detection power of polarimetries. Our method and results on the polarized LBW process have plenty of significant applications in strong-field physics, high-energy physics and astrophysics, such as calibrating and monitoring the polarized $\gamma \gamma$ collider and challenging the current understanding of astrophysical objects through enhancing the opacity of $\gamma$-photons to exacerbate the inconsistency between some observations and standard models.

The parton distribution of the pion is obtained for the first time from the solution of a dynamical equation in Minkowski space. The adopted equation is the homogeneous Bethe-Salpeter one with a ladder kernel, described in terms of (i) constituent quarks and gluons degrees of freedom, and (ii) an extended quark-gluon vertex. The masses of quark and gluon as well as the interaction-vertex scale have been chosen in a range suggested by lattice QCD calculations, and calibrated to reproduce both pion mass and decay constant. In addition to the full parton distribution, we have also calculated the contribution from the light-front valence wave function, corresponding to the lowest Fock component in the expansion of the pion state. After applying an evolution with an effective charge and a LO splitting function, a detailed and inspiring comparison with both the extracted experimental data (with and without resummation effects) and other recent calculations obtained in different frameworks is presented. Interestingly, in a wide region of longitudinal-momentum fraction, the parton distribution function receives sizable contributions from the higher Fock-components of the pion state at the initial scale, while approaching the tail the light-front valence component dominates, as expected. Moreover, an exponent $\sim 3$ is found suitable for describing the tail at the scale 5.2 GeV.

The effective electroweak Hamiltonian in the gradient-flow formalism is constructed for the current-current operators through next-to-next-to-leading-order QCD. The results are presented for two common choices of the operator basis. This allows for a consistent matching of perturbatively evaluated Wilson coefficients and nonperturbative matrix elements evaluated by lattice simulations on the basis of the gradient-flow formalism.

We construct Seiberg-like dualities of 3D $\mathcal{N}=2$ general quiver gauge theories with unitary, symplectic, and orthogonal gauge groups coupled to fundamental and bifundamental matter fields. We illustrate this with several examples of linear, circular, and star-shaped quiver gauge theories. We examine the local operators in the theories by computing supersymmetric indices and also find precise matching for the proposed dualities as strong evidence. We also generalize the dualities in the presence of a boundary on which the theories obey $\mathcal{N}=(0,2)$ chiral half-BPS boundary conditions and check the matching of half-indices.

We study supergravity instantons sourced by axion (and saxion) fields in the Euclidean ${\mathrm{AdS}}_3\times S^3\times {\mathrm{CY}}_2$ vacua of IIB supergravity. Such instantons are described by geodesic curves on the moduli space; the timelike geodesics can describe Euclidean wormholes, the lightlike geodesics describe (generalizations of) D instantons, and spacelike geodesics are subextremal versions thereof. We perform a concrete classification of such geodesics and find that, despite earlier claims, the wormholes fail to be regular. A subclass of the lightlike geodesics is supersymmetric and, up to dualities, lifts to Euclidean strings wrapping 2-cycles in the ${\mathrm{CY}}_2$. The dual of these instantons is expected to be worldsheet instantons of the D1–D5 conformal field theory.

The silhouette of a black hole having a critical curve (an unstable bound photon orbit) when illuminated by an optically thin accretion disk whose emission is confined to the equatorial plane shows a distinctive central brightness depression (the shadow) whose outer edge consists of a series of strongly lensed, self-similar rings superimposed with the disk’s direct emission. While the size and shape of the critical curve depend only on the background geometry, the pattern of bright and dark regions (including the size and depth of the shadow itself) in the image is strongly influenced by the (astro)physics of the accretion disk. This aspect makes it difficult to extract clean and clear observational discriminators between the Kerr black hole and other compact objects. In the presence of a second critical curve, however, observational differences become apparent. In this work we shall consider some spherically symmetric black hole and wormhole geometries characterized by the presence of a second critical curve, via a uniparametric family of extensions of the Schwarzschild metric. By assuming three toy models of geometrically thin accretion disks, we show the presence of additional light rings in the intermediate region between the two critical curves. The observation of such rings could represent a compelling evidence for the existence of black hole mimickers having multiple critical curves.

It has recently been demonstrated that magnetized black holes in composed Einstein-Maxwell-scalar-Gauss-Bonnet field theories with a nonminimal negative coupling of the scalar field to the Gauss-Bonnet curvature invariant may support spatially regular scalar hairy configurations. In particular, it has been revealed that, for Schwarzschild-Melvin black-hole spacetimes, the onset of the near-horizon spontaneous scalarization phenomenon is marked by the numerically computed dimensionless critical relation $(BM{)}_{\mathrm{crit}}\simeq 0.971$, where $\{M,B\}$ are respectively the mass and the magnetic field of the spacetime. In the present paper we prove, using analytical techniques, that the boundary between bald Schwarzschild-Melvin black-hole spacetimes and hairy (scalarized) black-hole solutions of the composed Einstein-Maxwell-scalar-Gauss-Bonnet theory is characterized by the exact dimensionless relation $(BM{)}_{\mathrm{crit}}=\sqrt{\frac{\sqrt{6}-2}{2\sqrt{6}}+\sqrt{\frac{\sqrt{6}-1}{2}}}$ for the critical magnetic strength. Intriguingly, we prove that the critical dimensionless magnetic parameter $(BM{)}_{\mathrm{crit}}$ corresponds to magnetized black holes that support a pair of linearized nonminimally coupled thin scalar rings that are characterized by the nonequatorial polar angular relation $({\sin }^2\theta {)}_{\mathrm{scalar}-\mathrm{ring}}=\frac{690-72\sqrt{6}+4\sqrt{3258\sqrt{6}-7158}}{789}<1$. It is also proved that the classically allowed angular region for the negative-coupling near-horizon spontaneous scalarization phenomenon of magnetized Schwarzschild-Melvin spacetimes is restricted to the black-hole poles, ${\sin }^2{\theta }_{\text{scalar}}\to 0$, in the asymptotic large-strength magnetic regime $BM\gg 1$.

The characteristic initial (boundary) value problem has numerous applications in general relativity (GR) involving numerical studies and is often formulated using Bondi-like coordinates. Recently it was shown that several prototype formulations of this type are only weakly hyperbolic. Presently we examine the root cause of this result. In a linear analysis we identify the gauge, constraint, and physical blocks in the principal part of the Einstein field equations in such a gauge, and we show that the subsystem related to the gauge variables is only weakly hyperbolic. Weak hyperbolicity of the full system follows as a consequence in many cases. We demonstrate this explicitly in specific examples, and thus argue that Bondi-like gauges result in weakly hyperbolic free evolution systems under quite general conditions. Consequently the characteristic initial (boundary) value problem of GR in these gauges is rendered ill-posed in the simplest norms one would like to employ. The possibility of finding good alternative norms, in which well-posedness is achieved, is discussed. So motivated, we present numerical convergence tests with an implementation of full GR which demonstrate the effect of weak hyperbolicity in practice.

We present a follow-up method based on supervised machine learning (ML) to improve the performance in the search of gravitational wave (GW) bursts from core-collapse supernovae (CCSNe) using the coherent WaveBurst (cWB) pipeline. The ML model discriminates noise from signal events by using a set of reconstruction parameters provided by cWB as features. Detected noise events are discarded yielding a reduction in the false alarm rate (FAR) and the false alarm probability thus enhancing the statistical significance. We tested the proposed method using strain data from the first half of the third observing run of advanced LIGO, and CCSNe GW signals extracted from 3D simulations. The ML model is tuned using a dataset of noise and signal events, and then used to identify and discard noise events in the cWB analyses. Noise and signal reduction levels were examined in single (L1 and H1) and two detector network (L1H1). The FAR was reduced by a factor of $\sim 10$ to $\sim 100$ resulting in an enhancement in the statistical significance of $\sim 1\sigma$ to $\sim 2\sigma$, while not impacting the detection efficiencies.

Recent work on scattering of massive bodies in general relativity has revealed that the mechanical center of mass of the system (or, more precisely, its relativistic mass moment) undergoes a shift during the scattering process. We show that the same phenomenon occurs in classical scattering of charged particles in flat spacetime and study the effect in detail. Working to leading order in the interaction, we derive formulas for the initial and final values of the mechanical and electromagnetic energy, momentum, angular momentum, and mass moment. We demonstrate that the change in the mechanical mass moment is balanced by an opposite change in the mass moment stored in the electromagnetic field. This is a nonradiative exchange between particles and field, analogous to the exchange of kinetic and potential energy. A simple mechanical analogy is a person scooting forward on the floor, who exchanges mass moment with the floor. We therefore say that electromagnetic scattering results in an electromagnetic scoot.

Black holes typically inhabit highly dynamical galactic environments and are frequently permeated by accretion media. The inevitable scattering of scalar, electromagnetic, and gravitational waves off rotating and charged black holes provides a remarkable demonstration of the energy extraction and subsequent amplification of scattered waves under the expense of the compact object’s rotational and electromagnetic energy, a phenomenon known as superradiance. Certain circumstances tremendously favor the energy extraction process in such extent that linear superradiant instabilities are triggered. We examine the superradiant amplification of monochromatic charged scalar fields impinging Reissner-Nordström-de Sitter black holes which are known to exhibit superradiantly unstable quasinormal modes. We find that even though the frequency range of superradiance is reduced when a positive cosmological constant is incorporated, the amplification factors are significantly elevated with respect to those occurring in Reissner-Nordström spacetime. Intriguingly, we confirm that the long-lived quasinormal resonances that reside in the superradiant regime induce resonant peaks when the wave’s frequency matches the real part of the quasinormal mode, regardless of the spacetime’s modal stability.

Chern-Simons gravity rotating Kerr-type black hole solutions are revisited from the point of view of their scalarization, namely examining the backreaction of pseudoscalar axion fields on the rotating geometry. To lowest order in an angular momentum expansion, and a long range approximation for both the axion field configuration and its backreaction onto the metric, such solutions had been discussed for the first time in the context of string theory. In this work, we extend the analysis to give analytic expressions for slowly rotating black holes outside the horizon, which formally include an all order expansion in inverse powers of the radial distance from the center of the black hole, which allows one to approach arbitrarily close to the horizon. We also discuss in some detail the way Chern-Simons gravity violates the energy conditions, which leads to secondary axionic hair of the rotating black hole solutions. This discussion is extended to studies of wormhole solutions, which we construct in this article via the thin-shell procedure. We demonstrate that the presence of the axion field enforces the two black hole solutions to be counterrotating. We also show that, for slow rotation, there is no backreaction of the Cotton tensor on the thin-shell of the wormhole.

An Oppenheimer-Snyder (OS)-type collapse is considered for a Dvali-Gabadadze-Porrati (DGP) brane, whereas a Gauss-Bonnet (GB) term is provided for the bulk. We study the combined effect of the DGP induced gravity plus the GB curvature, regarding any modification of the general relativistic OS dynamics. Our paper has a twofold objective. On the one hand, we investigate the nature of singularities that may arise at the collapse end state. It is shown that all dynamical scenarios for the contracting brane would end in one of the following cases, depending on conditions imposed: either a central shell-focusing singularity or what we designate as a “sudden collapse singularity.” On the other hand, we also study the deviations of the exterior spacetime from the standard Schwarzschild geometry, which emerges in our modified OS scenario. Our purpose is to investigate whether a black hole always forms regarding this brane world model. We find situations where a naked singularity emerges instead.

The characterization of nanohertz-frequency gravitational waves (GWs) with pulsar-timing arrays requires a continual expansion of datasets and monitored pulsars. Whereas detection of the stochastic GW background is predicated on measuring a distinctive pattern of interpulsar correlations, characterizing the background’s spectrum is driven by information encoded in the power spectra of the individual pulsars’ time series. We propose a new technique for rapid Bayesian characterization of the stochastic GW background that is fully parallelized over pulsar datasets. This factorized likelihood technique empowers a modular approach to parameter estimation of the GW background, multistage model selection of a spectrally-common stochastic process and quadrupolar interpulsar correlations, and statistical cross-validation of measured signals between independent pulsar subarrays. We demonstrate the equivalence of this technique’s efficacy with the full pulsar-timing array likelihood, yet at a fraction of the required time. Our technique is fast, easily implemented, and trivially allows for new data and pulsars to be combined with legacy datasets without reanalysis of the latter.

In this paper we study the traversability of a wormhole in the context of asymptotically safe gravity (ASG) for two different cases, namely, the spherical case and the pseudospherical case. We carry out an analysis in the throat of the wormhole with a specific choice of the cutoff function $f=\xi R$. Recently, this study has been performed by Moti and Shojai [Phys. Rev. D 104, 066016 (2021)], however the authors consider only a classical source with constant state parameter $\omega$. Here we generalize their study in two ways: (a) with a classical state parameter which is dependent of the position $\omega (r)$, and (b) with an ASG improvement of the source. We have showed that it is possible to have traversability with exotic and nonexotic matter, but the kind of matter is highly dependent on the wormhole’s parameters.