Using data samples with a total integrated luminosity of $20.1{\mathrm{fb}}^{-1}$ collected by the BESIII detector operating at the BEPCII collider, the cross section of the process $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}\psi (3686)$ is measured at center-of-mass energies between 4.0076 and 4.6984 GeV. The measured cross section is consistent with previous results, and with much improved precision. A fit to the measured energy-dependent cross section, which includes three Breit-Wigner functions and a nonresonant contribution, confirms the existence of the charmonium-like states $Y(4220)$, $Y(4390)$, and $Y(4660)$. This is the first observation of the $Y(4660)$ at the BESIII experiment.

A search is presented for long-lived particles produced in pairs in proton-proton collisions at the LHC operating at a center-of-mass energy of $13\mathrm{TeV}$. The data were collected with the CMS detector during the period from 2015 through 2018, and correspond to a total integrated luminosity of $140{\mathrm{fb}}^{-1}$. This search targets pairs of long-lived particles with mean proper decay lengths between 0.1 and $100\mathrm{mm}$, each of which decays into at least two quarks that hadronize to jets, resulting in a final state with two displaced vertices. No significant excess of events with two displaced vertices is observed. In the context of $R$-parity violating supersymmetry models, the pair production of long-lived neutralinos, gluinos, and top squarks is excluded at 95% confidence level for cross sections larger than 0.08 fb, masses between 800 and 3000 GeV, and mean proper decay lengths between 1 and 25 mm.

We analyze dynamics of chiral gauge theories based on the $SU(N)$ gauge group with one antisymmetric tensor $A$ and ($N-4$) antifundamentals $F_i$ when $N$ is odd. Based on the continuity to the supersymmetric gauge theories with anomaly-mediated supersymmetry breaking, we claim that the global $SU(N-4)$ symmetry is spontaneously broken to $Sp(N-5)$. There are $N-5$ massless fermions as a fundamental representation of $Sp(N-5)$, and another massless fermion, together saturating the anomaly matching conditions. When $N$ is even, the unbroken flavor symmetry is $Sp(N-4)$ while there are no massless fermions. Our result is different from the dynamics suggested by tumbling where the full $SU(N-4)$ symmetry is unbroken, but the tumbling picture can be modified via the addition of a second condensate to produce the symmetry breaking pattern predicted from our method.

An efficient algorithm is developed for compactly weaving all the Lorentz-covariant three-point vertices in relation to the decay of a massive particle $X$ of mass $m_X$ and spin $J$ into two particles $M_{1,2}$ with equal mass $m$ and spin $s$. The closely related equivalence between the helicity formalism and the covariant formulation is utilized so as to identify the basic building blocks for constructing the covariant three-point vertex corresponding to each helicity combination explicitly. The massless case with $m=0$ is worked out straightforwardly and the (anti)symmetrization of the three-point vertex required by the spin statistics of identical particles is made systematically. We show that the off-shell electromagnetic photon coupling to the states $M_1$ and $M_2$ can be accommodated in this framework. The power of the algorithm is demonstrated with a few typical examples with specific $J$ and $s$ values.

We propose a $SU(5)\times U(1{)}_X\times U(1{)}_{\mathrm{PQ}}$ model, where $U(1{)}_X$ is the generalization of the $B-L$ (baryon minus lepton number) gauge symmetry and $U(1{)}_{\mathrm{PQ}}$ is the global Peccei-Quinn (PQ) symmetry. There are four fermions families in $\overline{\mathbf{5}}+\mathbf{10}$ representations of $SU(5)$, a mirror family in $\mathbf{5}+\overline{\mathbf{10}}$ representations, and three $SU(5)$ singlet Majorana fermions. The $U(1{)}_X$ related anomalies all cancel in the presence of the Majorana neutrinos. The $SU(5)$ symmetry is broken at $M_{\mathrm{GUT}}\simeq (6–9)\times {10}^{15}\mathrm{GeV}$ and the proton lifetime ${\tau }_p$ is estimated to be well within the expected sensitivity of the future hyper-Kamiokande experiment, ${\tau }_p\lesssim 1.3\times {10}^{35}\mathrm{years}$. The $SU(5)$ breaking also triggers the breaking of the PQ symmetry, resulting in axion dark matter (DM), with the axion decay constant $f_a$ of order $M_{\mathrm{GUT}}$ or somewhat larger. The CASPEr experiment can search for such an axion DM candidate. The Hubble parameter during inflation must be low, $H_{\inf }\lesssim {10}^9\mathrm{GeV}$, in order to successfully resolve the axion domain wall, axion DM isocurvature and $SU(5)$ monopole problems. With the identification of the $U(1{)}_X$ breaking Higgs field with the inflaton field, we implement inflection-point inflation, which is capable of realizing the desired value for $H_{\inf }$. The vectorlike fermions in the model are essential for achieving successful unification of the SM gauge couplings as well as the phenomenological viability of both axion DM and inflation scenario.

Bayesian parameter inference techniques require a choice of prior distribution, which can strongly impact the statistical conclusions drawn. We discuss the construction of least-informative priors for neutrinoless double beta decay searches. Such priors attempt to be objective by maximizing the information gain from an experimental setup. In a parametrization using the lightest neutrino mass $m_l$ and an effective Majorana phase parameter $\mathrm{\Phi }$, we construct such a prior using two different approaches and compare them with the standard flat and logarithmic priors in $m_l$.

Effective field theory arguments suggest that if beyond the standard model (BSM) sectors contain new sources of $CP$ violation that couple to QCD, these sources will renormalize the $\theta$ term and frustrate ultraviolet solutions to the strong $CP$ problem. Simultaneously, they will generate distinctive patterns of low-energy electric dipole moments in hadronic, nuclear, atomic, and molecular systems. Observing such patterns thus provides evidence that strong $CP$ is solved by an infrared relaxation mechanism. We illustrate the renormalization of $\theta$ and the collections of electric dipole moments generated in several models of BSM physics, confirming effective field theory expectations, and demonstrate that measurements of ratios of electric dipole moments at planned experiments can provide valuable input on the resolution of the strong $CP$ problem.

Pulsar magnetospheres admit nonstationary vacuum gaps that are characterized by nonvanishing $\mathbf{E}·\mathbf{B}$. The vacuum gaps play an important role in plasma production and electromagnetic wave emission. We show that these gaps generate axions whose energy is set by the gap oscillation frequency. The density of axions produced in a gap can be several orders of magnitude greater than the ambient dark matter density. In the strong pulsar magnetic field, a fraction of these axions may convert to photons, giving rise to broadband radio signals. We show that dedicated observations of nearby pulsars with radio telescopes (FAST) and interferometers (SKA) can probe axion-photon couplings that are a few orders of magnitude lower than current astrophysical bounds.

We study the localization properties of the eigenmodes of the staggered Dirac operator in finite-temperature ${\mathbb{Z}}_2$ pure gauge theory on the lattice in $2+1$ dimensions. We find that the low modes turn from delocalized to localized as the system crosses over from the confined to the deconfined phase in the “physical” sector (positive average Polyakov loop) selected by external fermionic probes, while they remain delocalized in the “unphysical” sector (negative average Polyakov loop). This confirms that the close connection between deconfinement and localization of the low Dirac modes in the physical sector, already observed in other models, holds also in the simplest gauge theory displaying a deconfinement transition. We also observe a clear correlation of localized modes with fluctuations of the Polyakov loop away from the ordered value, as expected according to the “sea/islands” picture of localization, and with clusters of negative plaquettes. A novel finding is the presence of localized modes at the high end of the Dirac spectrum in all phases/sectors of the theory.

We investigate wide-angle photo- and electroproduction of pions within the handbag mechanism in which the ${\gamma }^{(*)}N\to \pi N^{\prime }$ amplitudes factorize into hard partonic subprocess amplitudes, ${\gamma }^{(*)}q\to \pi q^{\prime }$, and form factors representing $1/x$-moments of generalized parton distributions (GPDs). The subprocess is calculated to twist-3 accuracy taking into account the 2- and 3-body Fock components of the pion. Both components are required for achieving gauge invariance in QED and QCD. The twist-2 and twist-3 distribution amplitudes (DAs) of the pion as well as the form factors are taken from our study of ${\pi }^0$ photoproduction. Extensive results on photoproduction of charged pions are presented and compared to experiment. Predictions on electroproduction of pions as well as on spin effects are also given. As a byproduct of our analysis we also obtain the complete twist-3 subprocess amplitudes contributing to deeply virtual electroproduction of pions.

We investigate the impact of soft gluon resummation on the azimuthal angle correlation between the total and relative momenta of two energetic final-state particles (jets). We show that the initial and final-state radiations induce sizable $\cos (\varphi )$ and $\cos (2\varphi )$ asymmetries in single jet and dijet events, respectively. We numerically evaluate the magnitude of these asymmetries for a number of processes in collider experiments, including diffractive dijet and dilepton production in ultraperipheral $pA$ and $AA$ collisions, inclusive and diffractive dijet production at the electron-ion collider, and inclusive dijet production in $pp$ collisions at the LHC. In particular, the $\cos (2\varphi )$ asymmetry of perturbative origin can dominate over the primordial asymmetry due to the linearly polarized gluon distribution.

Two decades after its unexpected discovery, the properties of the $X(3872)$ exotic resonance are still under intense scrutiny. In particular, there are doubts about its nature as an ensemble of mesons or having any other internal structure. We use a diffusion Monte Carlo method to solve the many-body Schrödinger equation that describes this state as a $c\overline{c}n\overline{n}$ ($n=u$ or $d$ quark) system. This approach accounts for multiparticle correlations in physical observables avoiding the usual quark-clustering assumed in other theoretical techniques. The most general and accepted pairwise Coulomb + linear-confining + hyperfine spin-spin interaction, with parameters obtained by a simultaneous fit of around 100 masses of mesons and baryons, is used. The $X(3872)$ contains light quarks whose constituent masses are given by the dynamical breaking of chiral symmetry. The same mechanism gives rise to Goldstone-boson exchange interactions between light quarks whose contribution, derived from a well extended chiral quark model, has been included in this analysis but plays a marginal role. It appears that a meson-meson molecular configuration is preferred but, contrary to the usual assumption of $D^0{\overline{D}}^{*0}$ molecule for the $X(3872)$, our formalism produces $\omega J/\psi$ and $\rho J/\psi$ clusters as the most stable ones, which could explain in a natural way all the observed features of the $X(3872)$.

We study the scattering of open-beauty mesons and Goldstone bosons as predicted by the chiral SU(3) Lagrangian. The impact of subleading-order chiral interactions to systems with $J^P=0^{+}$ and $J^P=1^{+}$ quantum numbers is worked out. We estimate the relevant low-energy coefficients from the open-charm sector, for which their values have been determined previously from sets of QCD lattice data. The leading-order heavy-quark symmetry-breaking effects are estimated by matching the $B$-meson ground-state chiral mass formula to the mass formula from the heavy-quark effective theory. We make refined predictions for the flavor antitriplet and sextet resonances that are generated dynamically by coupled-channel interactions.

The study of heavy quarkonium suppression in heavy-ion collisions represents an important source of information about the properties of the quark-gluon plasma produced in such collisions. In a previous paper, we have considered how to model the evolution of a quarkonium in such a way that the solution of the resulting equations evolves toward the correct thermal equilibrium distribution for a homogeneous and static medium. We found that it is crucial to take into account the energy gap between singlet and octet configurations when the temperature is not much greater than this energy gap. In this paper, we explore in more detail the phenomenological consequences of this observation in the more realistic situation of an expanding system. We consider two different scenarios, based on the same approximation scheme, but on different choices of parameters. In the first case, we rely on a Hard Thermal Loop approximation, while the second case is based on a recent determination of the static potential in lattice QCD. In both cases, we compute the decay width and the nuclear modification factor, both taking the energy gap into account and ignoring it. We find that the impact on the predictions is as large in the expanding medium as it is in the static case. Our conclusion is that this energy gap should be taken into account in phenomenological studies.

We compute two-loop corrections to the vector current matching coefficient involving two heavy quark masses. The result is applied to the computation of the $\mathrm{\Upsilon }(1S)$ decay width into an electron or muon pair. We complement the next-to-next-to-next-to-leading order corrections of M. Beneke, et al. [Phys. Rev. Lett. 112, 151801 (2014)] by charm quark mass effects up to second order in perturbation theory. Furthermore, we apply the formalism to $\mathrm{\Gamma }(J/\mathrm{\Psi }\to {\ell }^{+}{\ell }^{-})$ and compare to the experimental data.

We present a computation of the global soft function for single inclusive hadronic jet production at next-to-next-to-leading order in the strong coupling constant involving four lightlike Wilson lines. Our soft function belongs to ${\mathrm{SCET}}_{\mathrm{I}}$ observables, which are not sensitive the rapidity divergences and obey the non-Abelian exponentiation theorem. We provide the calculation of the soft function involving four collinear light-cone directions for all $2\to 2$ processes extending the previous result. We perform the threshold resummation for these processes at the next-to-next-to-leading logarithmic accuracy and present the corresponding numerical results.

Future precision measurements of Higgs boson decays will determine the branching fraction for the decay into two photons with a precision at the one percent level. To fully exploit such measurements, equally precise theoretical predictions need to be available. To this end we compute four-loop QCD corrections in the large top quark mass expansion to the Higgs boson–photon form factor, which enter the two-photon decay width at next-to-next-to-next-to-leading order. Furthermore we obtain corrections to the two-photon decay width stemming from the emission of additional gluons, which contribute for the first time at next-to-next-to-leading order. Finally, we combine our results with other available perturbative corrections and estimate the residual uncertainty due to missing higher-order contributions.

We present a precise and efficient computation of the two-loop amplitudes entering the Higgs boson pair production process via gluon fusion. Our approach is based on the small-Higgs-mass expansion while keeping the full dependence on the top quark mass and other kinematic invariants. We compare our results to the up-to-date predictions based on a combination of sector decomposition and high-energy expansion. We find that our method provides precision numeric predictions in the entire phase space, while at the same time is highly efficient as the computation can be easily performed on a normal desktop or laptop computer. Our method is valuable for practical phenomenological studies of the Higgs boson pair production process, and can also be applied to other similar processes.

Ultralight axionlike particles are well-motivated dark matter candidates that are the target of numerous direct detection efforts. In the vicinity of the Solar System, such particles can be treated as oscillating scalar fields. The velocity dispersion of the Milky Way determines a coherence time of about ${10}^6$ oscillations, beyond which the amplitude of the axion field fluctuates stochastically. Any analysis of data from an axion direct detection experiment must carefully account for this stochastic behavior to properly interpret the results. This is especially true for experiments sensitive to the gradient of the axion field that are unable to collect data for many coherence times. Indeed, the direction, in addition to the amplitude, of the axion field gradient fluctuates stochastically. We present the first complete stochastic treatment for the gradient of the axion field, including multiple computationally efficient methods for performing likelihood-based data analysis, which can be applied to any axion signal, regardless of coherence time. Additionally, we demonstrate that ignoring the stochastic behavior of the gradient of the axion field can potentially result in failure to discover a true axion signal.