We study string breaking in the three-dimensional SU(2) Higgs model, using values of the gauge coupling for which the confinementlike and Higgs-like regions of the phase diagram are separated just by a smooth crossover. We show that even in the presence of string breaking, the confining part of the interquark potential is well described by the effective string theory and that also the fine details of the effective string, like the higher order terms of the Nambu-Goto action or the boundary correction, can be precisely extracted from the fits and agree with the effective string predictions. We comment on the implications of these results for QCD simulations with dynamical quarks.

We calculate gluon and ghost propagators in Yang-Mills theory in linear covariant gauges. To that end, we utilize Nielsen identities with Landau gauge propagators and vertices as the starting point. We present and discuss numerical results for the gluon and ghost propagators for values of the gauge parameter $0<\xi \le 5$. Extrapolating the propagators to $\xi \to \infty$, we find the expected qualitative behavior. We provide arguments that our results are quantitatively reliable at least for values $\xi \lesssim 1/2$ of the gauge-fixing parameter. It is shown that the correlation functions, and, in particular, the ghost propagator, change significantly with increasing gauge parameter. In turn, the ghost-gluon running coupling as well as the position of the zero crossing of the Schwinger function of the gluon propagator remain within the uncertainties of our calculation unchanged.

The Electron-Ion Collider (EIC) at Brookhaven National Laboratory will be a precision quantum chromodynamics machine that will enable a vast physics program with electron+proton/ion collisions across a broad center-of-mass range. Measurements of hard probes such as heavy flavor in deep inelastic scatterings will be an essential component to the EIC physics program and are one of the detector R&D driving aspects. In this paper we study the projected statistical precision of open charm hadron production through exclusive hadronic channel reconstruction with a silicon detector concept currently being developed using a pythia-based simulation. We further study the impact of possible intrinsic charm in the proton on projected data, and estimate the constraint on the nuclear gluon parton distribution function (PDF) from the charm structure functions $F_2^{c\overline{c}}$ in $e+\mathrm{Au}$ collisions using a Bayesian PDF reweighting technique. Our studies show the EIC will be capable of delivering an unprecedented measurement of charm hadron production across a broad kinematic region and will provide strong constraints to both intrinsic charm and nuclear gluon PDFs.

The observation by BESIII and LHCb of states with hidden charm and open strangeness ($c\overline{c}q\overline{s}$) presents new opportunities for the development of a global model of heavy-quark exotics. Here we extend the dynamical diquark model to encompass such states, using the same values of Hamiltonian parameters previously obtained from the nonstrange and hidden-strange sectors. The large mass splitting between $Z_{cs}(4000)$ and $Z_{cs}(4220)$ suggests substantial ${\mathrm{SU}(3)}_{\text{flavor}}$ mixing between all $J^P=1^{+}$ states, while their average mass compared to that of other sectors offers a direct probe of flavor octet-singlet mixing among exotics. We also explore the inclusion of $\eta$-like exchanges within the states, and find their effects to be quite limited. In addition, using the same diquark-mass parameters, we find $P_c(4312)$ and $P_{cs}(4459)$ to fit well as corresponding nonstrange and open-strange pentaquarks.

The problem of time in quantum gravity calls for a relational solution. Using quantum reduction maps, we establish a previously unknown equivalence between three approaches to relational quantum dynamics: (1) relational observables in the clock-neutral picture of Dirac quantization, (2) Page and Wootters’ (PW) Schrödinger picture formalism, and (3) the relational Heisenberg picture obtained via symmetry reduction. Constituting three faces of the same dynamics, we call this equivalence the trinity. In the process, we develop a quantization procedure for relational Dirac observables using covariant positive operator-valued measures which encompass nonideal clocks and resolve the nonmonotonicity issue of realistic quantum clocks reported by Unruh and Wald. The quantum reduction maps reveal this procedure as the quantum analog of gauge-invariantly extending gauge-fixed quantities. We establish algebraic properties of these relational observables. We extend a recent “clock-neutral” approach to changing temporal reference frames, transforming relational observables and states, and demonstrate a clock dependent temporal nonlocality effect. We show that Kuchař’s criticism, alleging that the conditional probabilities of the PW formalism violate the constraint, is incorrect. They are a quantum analog of a gauge-fixed description of a gauge-invariant quantity and equivalent to the manifestly gauge-invariant evaluation of relational observables in the physical inner product. The trinity furthermore resolves a previously reported normalization ambiguity and clarifies the role of entanglement in the PW formalism. The trinity finally permits us to resolve Kuchař’s criticism that the PW formalism yields wrong propagators by showing how conditional probabilities of relational observables give the correct transition probabilities. Unlike previous proposals, our resolution does not invoke approximations, ideal clocks or ancilla systems, is manifestly gauge invariant, and easily extends to an arbitrary number of conditionings.

The spectrum of energy density fluctuations, baryon asymmetry, and coherent large-scale magnetic fields are the three observables that provide crucial information on physics at very high energies. Inflation can only provide a mechanism to explain the density perturbations, and the origin of primordial magnetic fields and baryon asymmetry require physics beyond the standard models of cosmology and particle physics. In this work, we show that the mechanism that leads to primordial helical fields also leads to baryogenesis at the beginning of the radiation-dominated epoch. The model we consider here consists of mass dimension 6 operators that include Riemann coupling between gravity and electromagnetic field without extending the Standard Model of particle physics. We explicitly show that the generation of primordial helical magnetic fields leads to baryogenesis. We further show that the model predicts the observed amount of baryon asymmetry of the Universe for a range of reheating temperatures consistent with the observations.

We study a possibility of a strong first-order phase transition taking place below the electroweak scale in the context of a $U(1{)}_D$ gauge extension of the standard model. As pointed out recently by the NANOGrav Collaboration, gravitational waves from such a phase transition with appropriate strength and nucleation temperature can explain their 12.5 yr data. We first find the parameter space of this minimal model consistent with NANOGrav findings by considering only a complex singlet scalar and $U(1{)}_D$ vector boson. The existence of a singlet fermion charged under $U(1{)}_D$ can give rise to dark matter in this model, preferably of nonthermal type, while incorporating additional fields can also generate light neutrino masses through typical low-scale seesaw mechanisms like a radiative or inverse seesaw.

The leptophilic weakly interacting massive particle (WIMP) is realized in a minimal renormalizable model scenario where scalar mediators with lepton number establish the WIMP interaction with the standard model leptons. We perform a comprehensive analysis for such a WIMP scenario for two distinct cases with an SU(2) doublet or singlet mediator, considering all of the relevant current theoretical, cosmological, and experimental constraints. We show that monophoton searches at near-future lepton collider experiments (ILC, FCC-ee, CEPC, etc.) can play a significant role in probing the yet unexplored parameter range allowed by the WIMP relic density constraint. This will complement the search prospects at the near-future hadron collider experiment HL-LHC. Furthermore, we discuss the combined model scenario including both the doublet and singlet mediators. The combined model is capable of explaining the long-standing muon $g-2$ anomaly, which is an additional advantage. We demonstrate that the region allowed by the latest muon ($g-2$) result, which has been updated very recently at Fermi National Accelerator Laboratory, can also be probed at future colliders and thus will be a simultaneous authentication of the model scenario.

We study the probability distribution of the number of particle and antiparticle pairs produced via the Schwinger effect when a uniform but time-dependent electric field is applied to noninteracting scalars or spinors initially at a thermodynamic equilibrium. We derive the formula for the characteristic function by employing techniques in mesoscopic physics, reflecting a close analogy between the Schwinger effect and mesoscopic tunneling transports. In particular, we find that the pair production in a medium is enhanced (suppressed) for scalars (spinors) due to the Bose stimulation (Pauli blocking). Furthermore, in addition to the production of accelerated pairs by the electric field, the annihilation of decelerated pairs is found to take place in a medium. Our formula allows us to extract the probability distributions in various situations, such as those obeying the generalized trinomial statistics for spin-momentum resolved counting and the bidirectional Poisson statistics for spin-momentum unresolved counting.

We study celestial amplitudes in (super) Yang-Mills theory using a parametrization of the spinor helicity variables where their overall phase is not fixed by the little group action. In this approach the spin constraint $h-\overline{h}=J$ for celestial conformal primaries emerges naturally from a new Mellin transform, and the action of conformal transformations on celestial amplitudes is derived. Applying this approach to $\mathcal{N}=4$ super Yang-Mills, we show how the appropriate definition of on-shell superspace coordinates leads naturally to a formulation of chiral celestial superamplitudes and a representation of the generators of the four-dimensional superconformal algebra on the celestial sphere, which by construction annihilate all tree-level celestial superamplitudes.

We systematically calculate the mass spectrum of the higher excited fully charmed tetraquark $cc\overline{c}\overline{c}$ states including the $S$-wave radial excitations and the $P$-wave states with a nonrelativistic quark model. The quark model is composed of a vector one-gluon-exchange and a scalar linear confinement interaction with the parameters determined by the charmonium spectrum. In the calculation, we consider both the $3_c-{\overline{3}}_c$ and the $6_c-{\overline{6}}_c$ color representations. For the $cc\overline{c}\overline{c}$ state, the $6_c-{\overline{6}}_c$ component is located lower than the ${\overline{3}}_c-3_c$ one because of the stronger attractive interactions between the diquark and antidiquark. We focus on two excited modes and their properties for the $P$-wave tetraquarks. The mass splitting for the $\rho$-mode excitations with different color configurations is large. The low-lying $6_c-{\overline{6}}_c$ $\rho$-mode component helps to explain the small mass gap between the ground $S$-wave and the $P$-wave tetraquark states. The recently observed $X(6900)$ state may be the candidate of the first radially excited tetraquarks with $J^{PC}=0^{++}$ or $2^{++}$, or the $1^{+-}$ or $2^{-+}$ $P$-wave states based on the mass spectrum. Moreover, the lowest $T_c$ states with the exotic $J^{PC}$ quantum numbers $0^{--}$ and $1^{-+}$ may decay into the $P$-wave ${\eta }_{c}J/\psi$ and di-$J/\psi$ modes, respectively. The future experimental search of these $T_c$ states will enrich the hadronic spectrum.

Enhanced dynamically assisted pair production in frequency chirped spatially inhomogeneous electric fields is studied using the Dirac-Heisenberg-Wigner formalism. The effects of the chirp parameter on the reduced momentum spectrum and the total particle yield are investigated in detail for the single field or the dynamically assisted combined fields at various spatial scales. For the single high frequency field and the combined fields, the interference effect of momentum spectrum becomes more and more remarkable with the increasing chirp, meanwhile, in the chirped dynamically assisted case, the reduced total yield is enhanced significantly when chirping of two fields are present. Specifically, in the assisted case, the reduced particle number is increased by more than one order of magnitude at the small spatial scale, while it is enhanced about two times at the large spatial scale. We also obtain some optimal chirp and spatial scale parameters for the total yield and the enhancement factor for various scenarios.

The presence of nonstandard neutrino interactions (NSI) has a large effect on the precision measurements at next generation neutrino oscillation experiments. Other type of experiments are needed to constrain the NSI parameter space. We study the constraints on NSI with electrons from current and future $e^{+}{e}^{-}$ collider experiments including Belle II, STCF, and CEPC. We find that Belle II and STCF will provide competitive and complementary bounds on electron-type NSI parameters as compared to the current global analysis, and strong improvements in the constraints on tau-type NSI. In addition, CEPC alone will impose stringent constraints on the parameter space of NSI with electrons. We find that the degeneracy between the left-handed (vector) and right-handed (axial-vector) NSI parameters can be lifted by combining the data from three different running modes at CEPC, and the limits on ${\epsilon }_{ee}^{eL}$ (${\epsilon }_{ee}^{eV}$) and ${\epsilon }_{ee}^{eR}$ (${\epsilon }_{ee}^{eA}$) can reach 0.002 at CEPC even if both the left- and right-handed NSI parameters are present.

We propose a leptoquark model simultaneously to explain anomalies of muon anomalous magnetic dipole moment and $b\to s\mu \overline{\mu }$ in light of experimental reports very recently. Here, we satisfy several stringent constraints such as $\mu \to e\gamma$ and meson mixings. In addition, we find these leptoquarks also play an role in generating tiny neutrino masses at one-loop level without introducing any additional symmetries. We have numerical analysis and show how degrees our parameter space is restricted.

We discuss the minimal theory for quark-lepton unification at the low scale. In this context, the quarks and leptons are unified in the same representations and neutrino masses are generated through the inverse seesaw mechanism. The properties of the leptoquarks predicted in this theory are discussed in detail, and we investigate the predictions for the leptonic and semileptonic decays of mesons. We study the possibility to explain the current value of ${\mathcal{R}}_K$ reported by the LHCb Collaboration and the value of the muon anomalous magnetic moment reported by the Muon $g-2$ experiment at Fermilab.

The isospin doublet scalar field with hypercharge $3/2$ is introduced in some new physics models such as tiny neutrino masses. Detecting the doubly charged scalar bosons from the doublet field can be a good probe of such models. However, their collider phenomenology has not been examined sufficiently. We investigate collider signatures of the doubly and singly charged scalar bosons at the LHC for the high-luminosity upgraded option (HL-LHC) by looking at transverse mass distributions etc. With the appropriate kinematical cuts we demonstrate the background reduction in the minimal model in the following two cases depending on the mass of the scalar bosons. (1) The main decay mode of the singly charged scalar bosons is the tau lepton and missing (as well as charm and strange quarks). (2) That is into a top bottom pair. In the both cases, we assume that the doubly charged scalar boson is heavier than the singly charged ones. We conclude that the scalar doublet field with $Y=3/2$ is expected to be detectable at the HL-LHC unless the mass is too large.

Using an artificial neural network, we explore the parameter space of supergravity grand unified models consistent with the combined Fermilab E989 and Brookhaven E821 data on $(g-2{)}_{\mu }$. Within an extended mSUGRA model with nonuniversal gaugino masses, the analysis indicates that the region favored by the data is the one generated by gluino-driven radiative breaking of the electroweak symmetry ($\tilde{g}\mathrm{SUGRA}$). This region naturally leads to a split sparticle spectrum with light sleptons and weakinos but heavy squarks, with the stau and the chargino as the lightest charged particles. We show that if the entire deviation from the Standard Model $(g-2{)}_{\mu }$ arises from supersymmetry, then supersymmetry is discoverable at HL-LHC and HE-LHC via production and decay of sleptons and sneutrinos within the optimal integrated luminosity of HL-LHC and with a smaller integrated luminosity at HE-LHC. The effect of $CP$ phases on the muon anomaly is investigated, and the parameter space of $CP$ phases excluded by the Fermilab constraint is exhibited.

We show how one may classify all semisimple algebras containing the $\mathfrak{s}\mathfrak{u}(3)\oplus \mathfrak{s}\mathfrak{u}(2)\oplus \mathfrak{u}(1)$ symmetry of the Standard Model and acting on some given matter sector, enabling theories beyond the Standard Model with unification (partial or total) of symmetries (gauge or global) to be cataloged. With just a single generation of Standard Model fermions plus a singlet neutrino, the only gauge symmetries correspond to the well-known algebras $\mathfrak{su}(5)$, $\mathfrak{so}(10)$, and $\mathfrak{su}(4)\oplus \mathfrak{su}(2)\oplus \mathfrak{su}(2)$, but with two or more generations a limited number of exotic symmetries mixing flavor, color, and electroweak degrees of freedom become possible. We provide a complete catalog in the case of three generations or fewer and outline how our method generalizes to cases with additional matter.

Partial quenching allows one to consider correlation functions and amplitudes that do not arise in the corresponding unquenched theory. For example, physical $s$-wave pion scattering can be decomposed into $I=0$ and 2 amplitudes, while, in a partially-quenched extension, the larger symmetry group implies that there are more than two independent scattering amplitudes. It has been proposed that the finite-volume quantization condition of Lüscher holds for the correlation functions associated with each of the two-particle amplitudes that arise in partially-quenched theories. Using partially-quenched chiral perturbation theory, we show that this proposal fails for those correlation functions for which the corresponding one-loop amplitudes do not satisfy $s$-wave unitarity. For partially-quenched amplitudes that, while being unphysical, do satisfy one-loop $s$-wave unitarity, we argue that the proposal is plausible. Implications for previous work are discussed.

We study the chiral separation effect (CSE) in two-color and two-flavor QCD to delineate quasiparticle pictures in dense matter from low to high temperatures. Both massless and massive quarks are discussed. We particularly focus on the high density domain where diquarks form a color-singlet condensate with the electric charge $1/3$. The condensate breaks the baryon number and $U(1{)}_A$ axial symmetry, and induces the electromagnetic Meissner effects. Within a quark quasiparticle picture, we compute the chiral separation conductivity at one-loop. We have checked that Nambu-Goldstone modes, which should appear in the improved vertices as required by the Ward-Takahashi identities, do not contribute to the chiral-separation conductivity due to their longitudinal natures. In the static limit, the destructive interferences in the particle-hole channel, as in the usual Meissner effects, suppress the conductivity (in the chiral limit, to $1/3$ of that of the normal phase). This locally breaks the universality of the CSE coefficients, provided quasiparticle pictures are valid in the bulk matter.