Worldline instantons have previously been used to study the probability of Schwinger pair production (both the exponential and preexponential parts) and photon-stimulated pair production (the exponential part). Previous studies obtained the pair-production probability on the probability level by using unitarity, i.e., the imaginary part of the effective action for Schwinger pair production or the imaginary part of the polarization tensor for photon-stimulated pair production. The corresponding instantons are closed loops in the complex plane. Here, we show how to use instantons on the amplitude level, which means open instanton lines with start and end points representing fermions at asymptotic times. The amplitude is amputated with the Lehmann-Symanzik-Zimmermann reduction formula using, in general, field-dependent asymptotic states. We show how to use this formalism for photon-stimulated/Breit-Wheeler pair production and nonlinear Compton scattering.

Two-boson momentum correlations at fixed particle number constraint are studied in a simple analytically solvable model of a thermal expanding system. We show that the increase of expansion rate, as well as increase of particle multiplicity, enhances the ground-state contribution to particle momentum spectra and leads to suppression of the Bose-Einstein momentum correlations. The relations of these findings to the multiplicity-dependent measurements of the Bose-Einstein momentum correlations in high-multiplicity $p+p$ collision events at the LHC are discussed.

A model detector undergoing constant, infinite-duration acceleration converges to an equilibrium state described by the Hawking-Unruh temperature $T_a=(a/2\pi )(\hslash /c)$. To relate this prediction to experimental observables, a pointlike charged particle, such as an electron, is considered in place of the model detector. Instead of the detector’s internal degree of freedom, the electron’s low-momentum fluctuations in the plane transverse to the acceleration provide a degree of freedom and observables which are compatible with the symmetry and thermalize by interaction with the radiation field. General arguments in the accelerated frame suggest thermalization and a fluctuation-dissipation relation but leave underdetermined the magnitude of either the fluctuation or the dissipation. Lab frame analysis reproduces the radiation losses, described by the classical Lorentz-Abraham-Dirac equation, and reveals a classical stochastic force. We derive the fluctuation-dissipation relation between the radiation losses and stochastic force as well as equipartition $⟨p_{\perp }^2⟩=2m{T}_a$ from classical electrodynamics alone. The derivation uses only straightforward statistical definitions to obtain the dissipation and fluctuation dynamics. Since high accelerations are necessary for these dynamics to become important, we compare classical results for the relaxation and diffusion times to strong-field quantum electrodynamics results. We find that experimental realization will require development of more precise observables. Even wakefield accelerators, which offer the largest linear accelerations available in the lab, will require improvement over current technology as well as high statistics to distinguish an effect.

In this work, the cross section of the reaction $\gamma p\to V(J/\psi ,\psi (2S))p$ from the production threshold to medium energy is studied and systematically analyzed within two gluon exchange model. The obtained numerical results are in agreement with experimental data and other theoretical predictions. Under the assumption of the scalar form factor of dipole form, the value of proton mass radius is calculated as $0.55\pm 0.09\mathrm{fm}$ and $0.77\pm 0.12\mathrm{fm}$ from the fit to the predicted $J/\psi$ and $\psi (2S)$ differential cross section, respectively. Finally, the average value of proton mass radius is estimated to be $\sqrt{⟨R_m^2⟩}=0.67\pm 0.11\mathrm{fm}$. Moreover, one finds that extracting mass radius from the near-threshold differential cross section of heavy quarkoniums is always affected by large $|t{|}_{\min }$. These obtained results may provide important theoretical reference for the understanding of nucleon structure and future relevant experiments.

We study the relativistic 2D charge distributions in the case of a spin-1 target. These charge distributions are based on a phase-space approach allowing one to study their frame dependence, and hence to relate the familiar rest-frame picture with the light-front picture developed in the last two decades. Like in the spin-$1/2$ case, we show that relativistic kinematical effects associated with spin are responsible for the distortions of the charge distributions seen in a moving frame. Applying our results to the deuteron, we observe a mild frame dependence compared to the nucleon case.

In the type-I two-Higgs-doublet model, existing theoretical and experimental constraints still permit a light charged Higgs boson with a mass below the top quark mass. We present a complete road map for the light charged Higgs boson at the LHC through a comprehensive phenomenology study, focusing on the normal scenario where the lighter $CP$-even Higgs boson is the observed Higgs boson. In type I, it is challenging to simultaneously accommodate the light mass of the charged Higgs boson and the constraints from theoretical stabilities, electroweak precision data, Higgs data, $b\to s\gamma$, and direct search bounds. Consequently, the parameter space is extremely curtailed, which predicts somewhat definite phenomenological signatures. We find that the mass of the pseudoscalar Higgs boson, $M_A$, is the most crucial factor in the phenomenology of the charged Higgs boson. If $M_A$ is light, the charged Higgs boson decays mainly into $A{W}^{\pm }$. When $M_A$ is above the $A{W}^{\pm }$ threshold, the dominant decay mode is into ${\tau }^{\pm }\nu$. Over the entire viable parameter space, we study all the possible production and decay modes of charged Higgs bosons at the LHC and suggest three efficient channels: (i) $pp\to H^{+}{H}^{-}\to [\tau \nu ][\tau \nu ]$, (ii) $pp\to HA/HH/AA\to H^{\pm }{W}^{\mp }{H}^{\pm }{W}^{\mp }\to [\tau \nu ][\tau \nu ]WW$, and (iii) $pp\to H^{+}{H}^{-}\to [b\overline{b}W][b\overline{b}W]$. Based on sophisticated signal-background analyses including detector simulation, we show that the significance of the first final state is large and that of the second one is marginal (around 3), but that the third one suffers from enormous $t\overline{t}$ related backgrounds.

We investigate the potential of the 100 TeV future circular collider (FCC-hh) to probe heavy neutrinos. We concentrate in particular on heavy neutrino production via a $U(1{)}_{B-L}$ $Z^{\prime }$ gauge boson and contrast the resulting limits with that mediated by Standard Model weak currents. We consider heavy neutrino decays to semileptonic as well as fully leptonic final states, particularly with muon flavor, and we show the importance of considering searches both in prompt and displaced decays of the heavy neutrinos. For prompt final states, semileptonic modes are more promising due to smaller background and larger yields, and TeV-scale heavy neutrinos with active-sterile mixing compatible with light neutrino mass generation in a seesaw scenario can be probed for a 5 TeV $Z^{\prime }$ and gauge coupling as low as $g_{B-L}={10}^{-2}$. Displaced vertex searches can extend this range to heavy neutrino masses as low as 10 GeV.

We consider the effects of nonminimal couplings to curvature of the form ${\xi }_S{S}^{2}R$ for three types of scalars: the Higgs boson, the inflaton, and a scalar dark matter candidate. We compute the abundance of dark matter produced by these nonminimal couplings to gravity and compare to similar results with minimal couplings. We also compute the contribution to the radiation bath during reheating. The main effect is a potential augmentation of the maximum temperature during reheating. A model independent limit of $\mathcal{O}({10}^{12})\mathrm{GeV}$ is obtained. For couplings ${\xi }_S\gtrsim \mathcal{O}(1)$, these dominate over minimal gravitational interactions.

The knowledge of the Higgs potential is crucial for understanding the origin of mass and the thermal history of our Universe. We show how collider measurements and observations of stochastic gravitational wave signals can complement each other to explore the multiform scalar potential in the two Higgs doublet model (2HDM). Accounting for theoretical and current experimental constraints, we analyze the key ingredients in the shape of the Higgs potential triggering the transmutation in phase transition, from the smooth crossover to the strong first-order phase transition (${\xi }_c>1$), focusing on the barrier formation and the upliftment of the true vacuum. In particular, we observe that the ${\xi }_c>1$ regime is favored for lower scalar masses, rendering strong extra motivation for collider searches. We contrast the dominant collider signals at the HL-LHC (high-luminosity LHC) with observable gravitational wave signals at LISA. We obtain that the HL-LHC will be able to cover a vast range of the ${\xi }_c>1$ parameter space, with scalar decays to heavy fermions $(H,A,H^{\pm }\to tt,tb)$ being the most promising smoking gun signature of a strong first-order electroweak phase transition in the 2HDM.

We compute the Standard Model semileptonic vector and axial-vector form factors for $B_s\to D_s^{*}$ decay across the full $q^2$ range using lattice QCD. We use the highly improved staggered quark (HISQ) action for all valence quarks, enabling us to normalize weak currents nonperturbatively. Working on second-generation MILC ensembles of gluon field configurations which include $u$, $d$, $s$, and $c$ HISQ sea quarks and HISQ heavy quarks with masses from that of the $c$ mass up to that of the $b$ on the ensemble with the smallest lattice spacing, allows us to map out the heavy quark mass dependence of the form factors, and to constrain the associated discretization effects. We can then determine the physical form factors at the $b$ mass. We use these to construct the differential and total rates for $\mathrm{\Gamma }(B_s^0\to D_s^{*-}{\ell }^{+}{\nu }_{\ell })$ and find ${\mathrm{\Gamma }}_{\ell =e}/|{\eta }_{\mathrm{EW}}{V}_{cb}{|}^2=2.07(17{)}_{\mathrm{latt}}(2{)}_{\mathrm{EM}}\times {10}^{13}{\mathrm{s}}^{-1}$, ${\mathrm{\Gamma }}_{\ell =\mu }/|{\eta }_{\mathrm{EW}}{V}_{cb}{|}^2=2.06(16{)}_{\mathrm{latt}}(2{)}_{\mathrm{EM}}\times {10}^{13}{\mathrm{s}}^{-1}$, and ${\mathrm{\Gamma }}_{\ell =\tau }/|{\eta }_{\mathrm{EW}}{V}_{cb}{|}^2=5.14(37{)}_{\mathrm{latt}}(5{)}_{\mathrm{EM}}\times {10}^{12}{\mathrm{s}}^{-1}$, where ${\eta }_{\mathrm{EW}}$ contains the short-distance electroweak correction to $G_F$, the first uncertainty is from our lattice calculation, and the second allows for long-distance QED effects. The ratio $R(D_s^{*-})\equiv {\mathrm{\Gamma }}_{\ell =\tau }/{\mathrm{\Gamma }}_{\ell =\mu }=0.2490(60{)}_{\mathrm{latt}}(35{)}_{\mathrm{EM}}$. We also obtain a value for the ratio of decay rates ${\mathrm{\Gamma }}_{\ell =\mu }(B_s\to D_s)/{\mathrm{\Gamma }}_{\ell =\mu }(B_s\to D_s^{*})=0.443(40{)}_{\mathrm{latt}}(4{)}_{\mathrm{EM}}$, which agrees well with recent LHCb results. We can determine $V_{cb}$ by combining our lattice results across the full kinematic range of the decay with experimental results from LHCb and obtain $|V_{cb}|=42.2(1.5{)}_{\mathrm{latt}}(1.7{)}_{\exp }(0.4{)}_{\mathrm{EM}}\times {10}^{-3}$. A comparison of our lattice results for the shape of the differential decay rate to the binned, normalized differential decay rate from LHCb shows good agreement. We also test the impact of new physics couplings on angular observables and ratios which are sensitive to lepton flavor universality violation.

In this work, the ${\mathrm{\Omega }}_c$-like molecular states are systematically investigated in a quasipotential Bethe-Salpeter equation approach. The relevant interactions ${\mathrm{\Xi }}_c^{({*,}^{\prime })}{\overline{K}}^{(*)}$, ${\mathrm{\Xi }}^{(*)}{D}^{(*)}$, and ${\mathrm{\Omega }}_c^{(*)}(\pi /\eta /\rho /\omega )$ are described by light meson exchanges with the help of the effective Lagrangians with SU(3), chiral, and heavy quark symmetries. The obtained potential kernels of considered interactions are inserted into the quasipotential Bethe-Salpeter equation, and coupled-channel calculations are performed to find possible molecular states and its couplings to the channels considered. The results suggest that an isoscalar state can be produced from the ${\mathrm{\Xi }}_c^{*}\overline{K}$ interaction with spin parity $3/2^{-}$, which can be related to state ${\mathrm{\Omega }}_c(3120)$. And its isoscalar partner is predicted with a dominant decay in the ${\mathrm{\Omega }}_c^{*}\pi$ channel. The isoscalar and isovector states with $1/2^{-}$ can be produced from the ${\mathrm{\Xi }}_c^{\prime }\overline{K}$ interaction with a threshold close to the mass of the ${\mathrm{\Omega }}_c(3050)$ and ${\mathrm{\Omega }}_c(3065)$. Their couplings to the ${\mathrm{\Xi }}_c\overline{K}$ channel are very weak, and the isovector one has strong coupling to ${\mathrm{\Omega }}_c\pi$. High-precision measurement is helpful to confirm or search such molecular states. Experimental search of states with higher masses generated from interactions ${\mathrm{\Xi }}_c^{({*,}^{\prime })}{\overline{K}}^{*}$ and ${\mathrm{\Xi }}^{*}{D}^{(*)}$ are also suggested by the current results.

We present a framework that resums threshold enhanced large logarithms to all orders in perturbation theory for the production of a pair of leptons in the Drell-Yan process and of the Higgs boson in gluon fusion as well as in bottom quark annihilation. We restrict ourselves to contributions from diagonal partonic channels. These logarithms include the distributions $((1-z{)}^{-1}{\ln }^i(1-z){)}_{+}$ resulting from soft plus virtual (SV) and the logarithms ${\ln }^i(1-z)$ from next-to-SV contributions. We use collinear factorization and renormalization group invariance to achieve this. The former allows one to define a soft-collinear (SC) function that encapsulates soft and collinear dynamics of the perturbative results to all orders in the strong coupling constant. The logarithmic structure of these results is governed by universal infrared anomalous dimensions and process-dependent functions of the Sudakov differential equation that the SC satisfies. The solution to the differential equation is obtained by proposing an all-order ansatz in dimensional regularization, owing to several state-of-the-art perturbative results available to third order. The $z$ space solutions thus obtained provide an integral representation to sum up large logarithms originating from both soft and collinear configurations, conveniently in Mellin $N$ space. We show that in $N$ space, the tower of logarithms $a_s^n/N^{\alpha }{\ln }^{2n-\alpha }(N),a_s^n/N^{\alpha }{\ln }^{2n-1-\alpha }(N)\cdots$ for $\alpha =0$, 1 is summed to all orders in $a_s$.

In this paper we discuss on the phenomenological viability of nonmetricity theories of gravity which are based in the class of generalized Weyl spacetimes—denoted by $W_4$—where arbitrary nonmetricity is allowed. This class of geometry includes the so called teleparallel spaces $Z_4$, which are the geometric bases of the symmetric teleparallel theories. The guiding principle in our discussion is Weyl gauge symmetry, which is a manifest symmetry of $W_4$ spaces. Here we derive the master equation that drives the gauge-invariant variations of the length of vectors during parallel transport in $W_4$. This is the mathematical basis of the second clock effect (SCE). We are able to give qualitative and quantitative estimates for the SCE, as well as for the perihelion shift, in the coincident gauge of $Z_4$ space. We conclude that generalized Weyl spaces do not represent phenomenologically viable descriptions of nature due to the SCE and, also to their predictions for the perihelion shift. All of the present results are based on the assumption of: (i) a gauge invariant parallel transport law, and (ii) a consistency hypothesis which enables identifying hypothetical vectors and tensors defined in $W_4$, with related physical vectors and tensors arising in the given gravitational theory. Our discussion is mostly geometrical without relying on specific theories of gravity, unless it is absolutely necessary.

We investigate the motion of massive charged and spinning test particles around a charged dyonic black hole surrounded by perfect fluid scalar dark matter field. We obtain the equations of motion and find the expressions for the four-velocity for the case of a charged particle and four-momentum components for the case of a spinning particle. The trajectories for various values of electric $Q_e$ and magnetic $Q_m$ charges are investigated under the influence of dark matter field $\lambda$. We study in detail the properties of innermost stable circular orbits (ISCOs) in the equatorial plane. We show that, in addition to the particle’s spin, the dark matter field parameter $\lambda$ and black hole charges ($Q_m$ and $Q_e$) have significant influence on the ISCOs of spinning particles. We find that if the spin is parallel to the total angular momentum $J$ (i.e., $\mathcal{S}>0$), the ISCO parameters (i.e., $r_{\mathrm{ISCO}},L_{\mathrm{ISCO}}$, and $E_{\mathrm{ISCO}}$) of a spinning particle are smaller than those of a nonspinning particle, whereas if the spin is antiparallel to total angular momentum $J$ (i.e., $\mathcal{S}<0$), the value of the ISCO parameters is greater than that of the nonspinning particle. We also show that for the corresponding values of spin parameter S, the behavior of Keplerian angular frequency $\mathrm{\Omega }$ at the ISCO is opposite that of $r_{\mathrm{ISCO}},L_{\mathrm{ISCO}}$, and $E_{\mathrm{ISCO}}$. As an astrophysical application, the study of ISCOs may play a significant role as ISCOs can be used to set the inner edge of the accretion disk around a black hole as well as the initial condition of the binary black hole mergers.

As first noted by Robert Wagoner in the 1970s, if a scalar field is nonminimally coupled to the Ricci scalar and propagates at subluminal speeds, then there exists the possibility of scalar Čerenkov radiation from a moving particle. The mere observation of high-energy cosmic rays could in principle rule out the existence of such scalar fields since any particle moving faster than scalar perturbations would lose energy in the form of scalar waves until it moves slower than those. We compute in detail the energy loss to scalar waves and find that it scales with the square of the ultraviolet (UV) cutoff frequency of the effective field theory (EFT) of gravity. For dark-energy-motivated EFTs, the UV cutoff can be low, in which case that energy loss could always be negligible. In contrast, if viewed as a covariant theory valid at all scales or as an EFT valid at higher energies, perhaps even all the way up to the Planck scale, as may be the case if motivated by quantum-gravity perspectives, then the energy loss to scalar waves may diverge or become dramatically large. In this case, high-energy cosmic rays of extragalactic origin stringently constrain any conformally coupled scalar fields with noncanonical kinetic terms, although a minimum scalar phase velocity is required to trust the EFT.

We demonstrate the existence of Q-balls in nonminimally coupled inflation models with a complex inflaton in the Palatini formulation of gravity. We show that there exist Q-ball solutions which are compatible with inflation and we derive a window in the inflaton mass squared for which this is the case. In particular, we confirm the existence of Q-ball solutions with $\varphi \sim {10}^{17}–{10}^{18}\mathrm{GeV}$, consistent with the range of field values following the end of slow-roll Palatini inflation. We study the Q-balls and their properties both numerically and in an analytical approximation. The existence of such Q-balls suggests that the complex inflaton condensate can fragment into Q-balls, and that there may be an analogous process for the case of a real inflaton with fragmentation to neutral oscillons. We discuss the possible postinflationary cosmology following the formation of Q-balls, including an early Q-ball matter domination (eMD) period and the effects of this on the reheating dynamics of the model, gravitational wave signatures which may be detectable in future experiments, and the possibility that Q-balls could lead to the formation of primordial black holes (PBHs). In particular, we show that Palatini Q-balls with field strengths typical of inflaton condensate fragmentation can directly form black holes with masses around 500 kg or more when the self-coupling is $\lambda =0.1$, resulting in very low (less than 100 GeV) reheating temperatures from black hole decay, with smaller black hole masses and larger reheating temperatures possible for smaller values of $\lambda$. Q-ball dark matter from nonminimally coupled Palatini inflation may also be a direction for future work.

General relativistic magnetohydrodynamic (GRMHD) simulations represent a fundamental tool to probe various underlying mechanisms at play during binary neutron star (BNS) and neutron star (NS)—black hole (BH) mergers. Contemporary flux-conservative GRMHD codes numerically evolve a set of conservative equations based on “conserved” variables which then need to be converted back into the fundamental (“primitive”) variables. The corresponding conservative-to-primitive variable recovery procedure, based on root-finding algorithms, constitutes one of the core elements of such GRMHD codes. Recently, a new robust, accurate and efficient recovery scheme called RePrimAnd was introduced, which has demonstrated the ability to always converge to a unique solution. The scheme provides fine-grained error policies to handle invalid states caused by evolution errors, and also provides analytical bounds for the error of all primitive variables. In this work, we describe the technical aspects of implementing the RePrimAnd scheme into the GRMHD code spritz. To check our implementation as well as to assess the various features of the scheme, we perform a number of GRMHD tests in three dimensions. Our tests, which include critical cases such as a NS collapse to a BH as well as the early evolution ($\sim 50\mathrm{ms}$) of a Fishbone-Moncrief BH-accrection disk system, show that RePrimAnd is able to support magnetized, low density environments with magnetic-to-fluid pressure ratios as high as ${10}^4$, in situations where the previously used recovery scheme fails.

An observation of gravitational waves is a trigger of the multimessenger search of an astronomical event. A combination of the data from two or three gravitational wave detectors indicates the location of a source and low-latency data analysis is key to transferring the information to other detectors sensitive at different wavelengths. In contrast to the current method, which relies on the matched-filtering technique, we proposed the use of machine learning that is much faster and possibly more accurate than matched filtering. Our machine-learning method is a combination of the method proposed by Chatterjee et al. and a method using the temporal convolutional network. We demonstrate the sky localization of a gravitational-wave source using four detectors; LIGO H1, LIGO L1, Virgo, and KAGRA, and compare the result in the case without KAGRA to examine the positive influence of having the fourth detector in the global gravitational-wave network.

Using a trapped quintessence model, a series of time-of-flight (TOF) experiments with different frequencies of probe light are designed and performed. The varying-frequency TOF (VFTOF) experiments demonstrate that the free-fall acceleration of test atoms is dependent on the detuning of the probe light frequency with respect to the atomic transition frequency. In appropriately designed experiments, if the scalar field in the model accounts for the accelerated expansion of the Universe entirely, the field will result in an observable fifth force. Meanwhile, the trapped quintessence model still satisfies all experimental bounds on deviations from general relativity due to both the saturation effect and the short interaction range of the scalar field. The scalar saturates at a value corresponding to the cosmological constant when the microscopic nonrelativistic matter density is large enough. The interaction range of the scalar is inversely proportional to the square root of the microscopic nonrelativistic matter density. The interaction range has been estimated to be several $\mu \mathrm{m}$ in the current cosmic density $\sim {10}^{-27}\mathrm{kg}/{\mathrm{m}}^3$. The Universe is assumed to be permeated with fuzzy dark matter, which means that the microscopic nonrelativistic matter density defined through the quantum wave functions of the ultralight particles can be used on the cosmic scale. In an almost completely empty space between atoms of a dilute atomic gas in an ultrahigh vacuum chamber, the interaction range of the scalar field may approach the order of $\sim 1\mu \mathrm{m}$ in the presence of dark matter; then, the scalar field might be detected in laboratories. Since the trapped quintessence model hypothesizes that the scalar strongly couples to nonrelativistic matter but cannot couple to radiation, the source for generating the fifth force is experimentally set up by the laser-irradiated background atoms in the ultrahigh vacuum chamber. The mass density of the source is altered by detuning the frequency of the probe laser light from the atomic resonance transition. The test atoms are prepared by the laser cooling technique and located initially above the probe light. When the test atoms are released from their initial positions, they are able to pass through the region of the source that generates the fifth force to be measured. Thus, if the scalar field exists, the corresponding fifth force might be sensed by the test atoms even if the interaction range is extremely short. By measuring the free-fall acceleration of the test atoms with the TOF method step by step in the detuning frequency domain of the probe light, we derive the dispersion curves of the measured acceleration versus the frequency detuning of the probe light. When the nonrelativistic matter density of the source increases due to the energy gained from the laser light, the test atoms are pulled to the center of the source, and vice versa. If the trapped quintessence model is correct, the observed detuning-dependent acceleration in the VFTOF scheme suggests a closed Universe, i.e., a positive spatial curvature of the Universe.