The current status of electroweak radiative corrections to the muon anomalous magnetic moment is discussed. Asymptotic expansions for some important electroweak two-loop top quark triangle diagrams are illustrated and extended to higher order. Results are compared with the more general integral representation solution for generic fermion triangle loops coupled to pseudoscalar and scalar bosons of arbitrary mass. Excellent agreement is found for a broader than expected range of mass parameters.

We propose a new approach to circumvent the sign problem in which the integration path is optimized to control the sign problem. We give a trial function specifying the integration path in the complex plane and tune it to optimize the cost function which represents the seriousness of the sign problem. We call it the path optimization method. In this method, we do not need to solve the gradient flow required in the Lefschetz-thimble method and then the construction of the integration-path contour arrives at the optimization problem where several efficient methods can be applied. In a simple model with a serious sign problem, the path optimization method is demonstrated to work well; the residual sign problem is resolved and precise results can be obtained even in the region where the global sign problem is serious.

The decays of ${\chi }_{c2}\to K^{+}{K}^{-}{\pi }^0$, $K_S{K}^{\pm }{\pi }^{\mp }$, and ${\pi }^{+}{\pi }^{-}{\pi }^0$ are studied with the $\psi (3686)$ data samples collected with the Beijing Spectrometer (BESIII). For the first time, the branching fractions of ${\chi }_{c2}\to K^{*}\overline{K}$, ${\chi }_{c2}\to a_2^{\pm }(1320){\pi }^{\mp }/a_2^0(1320){\pi }^0$, and ${\chi }_{c2}\to \rho (770{)}^{\pm }{\pi }^{\mp }$ are measured. Here, $K^{*}\overline{K}$ denotes both $K^{*\pm }{K}^{\mp }$ and its isospin-conjugated process $K^{*0}{\overline{K}}^0+\mathrm{c}.\mathrm{c}.$, and $K^{*}$ denotes the resonances $K^{*}(892)$, $K_2^{*}(1430)$, and $K_3^{*}(1780)$. The observations indicate a strong violation of the helicity selection rule in ${\chi }_{c2}$ decays into vector and pseudoscalar meson pairs. The measured branching fractions of ${\chi }_{c2}\to K^{*}(892)\overline{K}$ are more than ten times larger than the upper limit of ${\chi }_{c2}\to \rho (770{)}^{\pm }{\pi }^{\mp }$, which is so far the first direct observation of a significant $U$-spin symmetry breaking effect in charmonium decays.

The collision of black holes and the emission of gravitational radiation in higher-dimensional spacetimes are of interest in various research areas, including the gauge-gravity duality, the TeV gravity scenarios evoked for the explanation of the hierarchy problem, and the large-dimensionality limit of general relativity. We present numerical simulations of head-on collisions of nonspinning, unequal-mass black holes starting from rest in general relativity with $4\le D\le 10$ spacetime dimensions. We compare the energy and linear momentum radiated in gravitational waves with perturbative predictions in the extreme mass ratio limit, demonstrating the strength and limitations of black-hole perturbation theory in this context.

The next generation of CMB experiments (CMB Stage-4) will produce a Sunyaev-Zel’dovich (SZ) cluster catalog containing $\sim {10}^5$ objects, two orders of magnitudes more than currently available. In this paper, we discuss the detectability of the polarized signal generated by scattering of the CMB quadrupole on the cluster electron gas using this catalog. We discuss the possibility of using this signal to measure the relationship between cluster optical depth and mass. We find that the area of observation of S4 maximizes the signal-to-noise (S/N) on the polarized signal but that this S/N is extremely small for an individual cluster, of order 0.5% for a typical cluster in our catalog, the main source of noise being the residual primordial E-mode signal. However, we find that the signal could be detected using the full cluster catalog and that the significance of the result will increase linearly with the size of the CMB S4 telescope mirror.

The strong $CP$ problem is known to be solved by imposing Peccei-Quinn (PQ) symmetry. However, the domain wall problem caused by the spontaneous breaking of its remnant discrete subgroup could make models invalid in many cases. We propose a model in which the PQ charge is assigned quarks so as to escape this problem without introducing any extra colored fermions. In the low energy effective model resulting after the PQ symmetry breaking, both the quark mass hierarchy and the CKM mixing could be explained through Froggatt-Nielsen mechanism. If the model is combined with the lepton sector supplemented by an inert doublet scalar and right-handed neutrinos, the effective model reduces to the scotogenic neutrino mass model in which both the origin of neutrino masses and dark matter are closely related. The strong $CP$ problem could be related to the quark mass hierarchy, neutrino masses, and dark matter through the PQ symmetry.

We entertain the possibility that neutrino masses and dark matter (DM) originate from a common composite dark sector. A minimal effective theory can be constructed based on a dark $SU(3{)}_D$ interaction with three flavors of massless dark quarks; electroweak symmetry breaking gives masses to the dark quarks. By assigning a ${\mathbb{Z}}_2$ charge to one flavor, a stable “dark kaon” can provide a good thermal relic DM candidate. We find that “dark neutrons” may be identified as right handed Dirac neutrinos. Some level of “neutron-anti-neutron” oscillation in the dark sector can then result in non-zero Majorana masses for light standard model neutrinos. A simple ultraviolet completion is presented, involving additional heavy $SU(3{)}_D$-charged particles with electroweak and lepton Yukawa couplings. At our benchmark point, there are “dark pions” that are much lighter than the Higgs and we expect spectacular collider signals arising from the UV framework. This includes the decay of the Higgs boson to $\tau \tau \ell {\ell }^{\prime }$, where $\ell ({\ell }^{\prime })$ can be any lepton, with displaced vertices. We discuss the observational signatures of this UV framework in dark matter searches and primordial gravitational wave experiments; the latter signature is potentially correlated with the $H\to \tau \tau \ell {\ell }^{\prime }$ decay.

We present an analysis of strong two-body decays of the $a_1(1420)$ with $J^{PC}=1^{++}$ recently reported by the COMPASS Collaboration at CERN. Following the interpretation of the COMPASS Collaboration that the $a_1$ is an unusual state with a four-quark $q\overline{q}s\overline{s}$ structure we consider two possible configurations for this state—hadronic molecular and color diquark-antidiquark structures. We find that the dominant decay mode of the $a_1$ is the decay into $K$ and $K^{*}$. In particular, we calculate that the four decay modes $a_1\to VP$ with $VP=K^{*\pm }{K}^{\mp }$, $K^{*0}{\overline{K}}^0$, ${\overline{K}}^{*0}{K}^0$ together give a dominant contribution to the measured total width of about 150 MeV. The observational mode $a_1\to f_0(980)+{\pi }^0$ is significantly suppressed by one order of magnitude.

Using the data samples of $(1310.6\pm 7.2)\times {10}^{6}J/\psi$ events and $(448.1\pm 2.9)\times {10}^6\psi (3686)$ events collected with the BESIII detector, we search for the rare decays $J/\psi \to D^0{e}^{+}{e}^{-}+\mathrm{c}.\mathrm{c}.$ and $\psi (3686)\to D^0{e}^{+}{e}^{-}+\mathrm{c}.\mathrm{c}.$ No significant signals are observed and the corresponding upper limits on the branching fractions at the 90% confidence level are determined to be $\mathcal{B}(J/\psi \to D^0{e}^{+}{e}^{-}+\mathrm{c}.\mathrm{c}.)<8.5\times {10}^{-8}$ and $\mathcal{B}(\psi (3686)\to D^0{e}^{+}{e}^{-}+\mathrm{c}.\mathrm{c}.)<1.4\times {10}^{-7}$, respectively. Our limit on $\mathcal{B}(J/\psi \to D^0{e}^{+}{e}^{-}+\mathrm{c}.\mathrm{c}.)$ is more stringent by 2 orders of magnitude than the previous results, and $\mathcal{B}(\psi (3686)\to D^0{e}^{+}{e}^{-}+\mathrm{c}.\mathrm{c}.)$ is measured for the first time.

The effective potential $V$ is a massless self-coupled scalar theory, and massless scalar electrodynamics is considered. Both the $\overline{\mathrm{MS}}$ and Coleman-Weinberg renormalization schemes are examined. The renormalization scheme dependence of $V$ is determined. Upon summing all of the logarithmic contributions to $V$, it is shown that the implicit and explicit dependence on the renormalization scale $\mu$ cancels. In addition, if there is spontaneous symmetry breaking, then the dependence on the background field $\mathrm{\Phi }$ cancels, leaving $V$ flat but with nonperturbative contributions. The quartic scalar coupling in the Coleman-Weinberg renormalization scheme consequently vanishes.

When binary systems of neutron stars merge, a very small fraction of their rest mass is ejected, either dynamically or secularly. This material is neutron-rich and its nucleosynthesis provides the astrophysical site for the production of heavy elements in the Universe, together with a kilonova signal confirming neutron-star mergers as the origin of short gamma-ray bursts. We perform full general-relativistic simulations of binary neutron-star mergers employing three different nuclear-physics equations of state (EOSs), considering both equal- and unequal-mass configurations, and adopting a leakage scheme to account for neutrino radiative losses. Using a combination of techniques, we carry out an extensive and systematic study of the hydrodynamical, thermodynamical, and geometrical properties of the matter ejected dynamically, employing the WinNet nuclear-reaction network to recover the relative abundances of heavy elements produced by each configurations. Among the results obtained, three are particularly important. First, we find that, within the sample considered here, both the properties of the dynamical ejecta and the nucleosynthesis yields are robust against variations of the EOS and masses. Second, using a conservative but robust criterion for unbound matter, we find that the amount of ejected mass is $\lesssim {10}^{-3}{M}_{\odot }$, hence at least one order of magnitude smaller than what normally assumed in modelling kilonova signals. Finally, using a simplified and gray-opacity model we assess the observability of the infrared kilonova emission finding, that for all binaries the luminosity peaks around $\sim 1/2$ day in the $H$-band, reaching a maximum magnitude of $-13$, and decreasing rapidly after one day.

We present an exact solution in Einstein-Maxwell-dilaton gravity describing a spacetime with an anisotropic Kasner-type singularity and Lifshitz asymptotics. This configuration can also be supported by a phantom scalar while still satisfying the null energy condition. For certain parameters of this solution, null geodesics can have an infinitely deep effective potential, thus trapping photons in a finite region along the radial direction. Some examples of periodic null geodesics are obtained. A particularly interesting special case of this solution is a regular, soliton-type metric that retains its Lifshitz scaling in the time coordinate.

Stability analysis of interacting dark-energy models generally divides its parameters space into two regions, (i) $w_x\ge -1$ and $\xi \ge 0$ and (ii) $w_x\le -1$ and $\xi \le 0$, where $w_x$ is the dark-energy equation of state and $\xi$ is the coupling strength of the interaction. Because of this separation, crucial information about the cosmology and phenomenology of these models may be lost. In a recent study, it has been shown that one can unify the two regions with a coupling function that depends on the dark-energy equation of state. In this work, we introduce a new coupling function that also unifies the two regions of the parameter space and generalizes the previous proposal. We analyze this scenario considering the equation of state of dark energy to be either constant or dynamical. We study the cosmology of such models and constrain both scenarios with the use of the latest astronomical data from both the background evolution as well as large-scale structures. Our analysis shows that a nonzero value of the coupling parameter $\xi$ as well as the dark-energy equation of state other than $-1$ are allowed. However, within $1\sigma$ confidence level, $\xi =0$ and the dark-energy equation of state equal to $-1$ are compatible with the current data. In other words, the observational data allow a very small but nonzero deviation from the $\mathrm{\Lambda }$ cosmology; however, within the $1\sigma$ confidence region, the interacting models can mimic the $\mathrm{\Lambda }$ cosmology. In fact, we observe that the models both at the background and perturbative levels are very hard to distinguish from each other and from $\mathrm{\Lambda }$ cosmology as well. Finally, we offer a rigorous analysis on the current tension on $H_0$, allowing different regions of the dark-energy equation of state, which shows that interacting dark-energy models reasonably solve the current tension on $H_0$.

We study the behavior of dark energy (DE) in the scope of anisotropic Bianchi type V (BV) spacetime. First, we derive Friedmann-like equations, then we compare the dark energy equation of state (EoS) parameter for viscous and nonviscous dark energy and make a correspondence between DE and quintessence and phantom descriptions of nonviscous and viscous dark energy and reconstruct the potential of these two scalar fields. The late time behavior of the EoS parameter through a thermodynamical study has also been investigated. Finally, we investigate the conditions under which BV spacetime can be mapped into the Friedmann-Robertson-Walker and how the bulk viscose coefficient may affect the dark energy EoS parameter of our $\omega \mathrm{BV}$ model with constraints from 28 Hubble parameter, $H(z)$, measurements at intermediate redshifts $0.07\le z\le 2.3$.

If the very early Universe is dominated by the nonminimally coupled Higgs field and Starobinsky’s curvature-squared term together, the potential diagram would mimic the landscape of a valley, serving as a cosmological attractor. The inflationary dynamics along this valley is studied, model parameters are constrained against observational data, and the effect of isocurvature perturbation is estimated.

The discovery of extraterrestrial neutrinos in the $\sim 30\mathrm{TeV}–\mathrm{PeV}$ energy range by IceCube provides new constraints on high energy astrophysics. An important background to the signal are the prompt neutrinos which originate from the decay of charm hadrons produced by high energy cosmic-ray particles interacting in the Earth’s atmosphere. It is conventional to use the calculations of charm hadroproduction using gluon splitting $g\to c\overline{c}$ alone. However, QCD predicts an additional “intrinsic" component of the heavy quark distribution which arises from diagrams where heavy quarks are multiply connected to the proton’s valence quarks. We estimate the prompt neutrino spectrum due to intrinsic charm. We find that the atmospheric prompt neutrino flux from intrinsic charm is comparable to those calculated using QCD computations not including intrinsic charm, once we normalize the intrinsic charm differential cross sections to the ISR and the LEBC-MPS collaboration data. In the future, IceCube will constrain the intrinsic charm content of the proton and will contribute to one of the major questions in high energy physics phenomenology.

In this article, we provide analytical expressions for the photon polarization tensor in pulsed Hermite- and Laguerre-Gaussian laser beams. Our results are based on a locally constant field approximation of the one-loop Heisenberg-Euler effective Lagrangian for quantum electrodynamics. Hence, by construction they are limited to slowly varying electromagnetic fields, varying on spatial and temporal scales significantly larger than the Compton wavelength/time of the electron. The latter criterion is fulfilled by all laser beams currently available in the laboratory. Our findings will, e.g., be relevant for the study of vacuum birefringence experienced by probe photons brought into collision with a high-intensity laser pulse which can be represented as a superposition of either Hermite- or Laguerre-Gaussian modes.

The dynamical diquark picture asserts that exotic hadrons can be formed from widely separated colored diquark or triquark components. We use the Born-Oppenheimer (BO) approximation to study the spectrum of states thus constructed, both in the basis of diquark spins and in the basis of heavy quark-antiquark spins. We develop a compact notation for naming these states, and use the results of lattice simulations for hybrid mesons to predict the lowest expected BO potentials for both tetraquarks and pentaquarks. We then compare to the set of exotic candidates with experimentally determined quantum numbers, and find that all of them can be accommodated. Once decay modes are also considered, one can develop selection rules of both exact ($J^{PC}$ conservation) and approximate (within the context of the BO approximation) types and test their effectiveness. We find that the most appealing way to satisfy both sets of selection rules requires including additional low-lying BO potentials, a hypothesis that can be checked on the lattice.

The very high precision of current measurements and theory predictions of spectral lines in few-electron atoms allows us to efficiently probe the existence of exotic forces between electrons, neutrons and protons. We investigate the sensitivity to new spin-independent interactions in transition frequencies (and their isotopic shifts) of hydrogen, helium and some heliumlike ions. We find that present data probe new regions of the force-carrier couplings to electrons and neutrons around the MeV mass range. We also find that, below few keV, the sensitivity to the electron coupling in precision spectroscopy of helium and positronium is comparable to that of the anomalous magnetic moment of the electron. Finally, we interpret our results in the dark-photon model where a new gauge boson is kinetically mixed with the photon. There, we show that helium transitions, combined with the anomalous magnetic moment of the electron, provide the strongest indirect bound from laboratory experiments above 100 keV.