The axial form factor as well as the axial charges and radii of octet $N$, $\mathrm{\Sigma }$, and $\mathrm{\Xi }$ baryons are studied in the perturbative chiral quark model with the quark wave functions predetermined by fitting the theoretical results of the proton charge form factor to experimental data. The theoretical results are found, based on the predetermined quark wave functions, in good agreement with experimental data and lattice values. This may indicate that the electric charge and axial charge distributions of the constituent quarks are the same. The study reveals that the meson cloud plays an important role in the axial charge of octet baryons, contributing 30%–40% to the total values, and strange sea quarks have a considerable contribution to the axial charges of the $\mathrm{\Sigma }$ and $\mathrm{\Xi }$.

This paper presents a detailed account of the evaluation of the electron anomalous magnetic moment $a_e$ which arises from a gauge-invariant set, called Set V, consisting of 6354 tenth-order Feynman diagrams without closed lepton loops. The latest value of the sum of Set V diagrams evaluated by the Monte Carlo integration routine VEGAS is 8.726 $(336)(\alpha /\pi {)}^5$, which replaces the very preliminary value reported in 2012. Combining it with 6318 previously published tenth-order diagrams, we obtain 7.795 $(336)(\alpha /\pi {)}^5$ as the complete mass-independent tenth-order term. Together with the improved value of the eighth-order term this leads to $a_e(\text{theory})=1159652181.643(25)(23)(16)(763)\times 10^{-12}$, where the first three uncertainties are from the eighth-order, tenth-order, and hadronic and elecroweak terms. The fourth and largest uncertainty is from ${\alpha }^{-1}=137.035999049(90)$, the fine-structure constant derived from the rubidium recoil measurement. Thus, $a_e(\text{experiment})-a_e(\text{theory})=-0.91(0.82)\times 10^{-12}$. Assuming the validity of the standard model, we obtain the fine-structure constant ${\alpha }^{-1}(a_e)=137.0359991570(29)(27)(18)(331)$, where uncertainties are from the eighth-order, tenth-order, and hadronic and electroweak terms, and the measurement of $a_e$. This is the most precise value of $\alpha$ available at present and provides a stringent constraint on possible theories beyond the standard model.

It is shown that the causal structure associated to stringlike solutions of the Faddeev-Niemi model is described by an effective metric. Remarkably, the surfaces characterizing the causal replacement depend on the energy momentum tensor of the background soliton and carry implicitly a topological invariant ${\pi }_3({\mathbb{S}}^2)$. As a consequence, it follows that the preimage curves in ${\mathbb{R}}^3$ nontrivially define directions where the cones remain unchanged. We expect that these early results may be of importance in understanding time dependent solutions (collisions/scatterings) numerically or analytically.

We study the symmetries of nonrelativistic systems with an emphasis on applications to the fractional quantum Hall effect. A source for the energy current of a Galilean system is introduced and the nonrelativistic diffeomorphism invariance studied in previous work is enhanced to a full spacetime symmetry, allowing us to derive a number of Ward identities. These symmetries are smooth in the massless limit of the lowest Landau level. We develop a formalism for Newton-Cartan geometry with torsion to write these Ward identities in a covariant form. Previous results on the connection between Hall viscosity and Hall conductivity are reproduced.

In the framework of the functional renormalization group method, it is shown that the phase structure of the two-dimensional sine-Gordon model possesses a nontrivial UV fixed point which makes the model asymptotically safe. The fixed point exhibits strong singularity similar to the scaling found in the vicinity of the infrared fixed point. The singularity signals the upper energy-scale limit to the validity of the model. We argue that the sine-Gordon model with a momentum-dependent wave-function renormalization is in a dual connection with the massive sine-Gordon model.

We reexamine the gravitational collapse of rotating neutron stars to black holes by new $3+1$ numerical relativity simulations employing the Z4c formulation of Einstein equations, the moving puncture gauge conditions, and a conservative mesh refinement scheme for the general relativistic hydrodynamics. The end state of the collapse is compared to the vacuum spacetime resulting from the evolution of spinning puncture initial data. Using a local analysis for the metric fields, we demonstrate that the two spacetimes actually agree. Gravitational waveforms are analyzed in some detail. We connect the emission of radiation to the collapse dynamics using simplified spacetime diagrams, and discuss the similarity of the waveform structure with the one of black hole perturbation theory.

We discuss how a background bath of gravitons can induce decoherence of quantum systems. The mechanism is dephasing, the loss of phase coherence due to quantum geometry fluctuations caused by the gravitons. This effect is illustrated in a simple analog model of quantum particles in a cavity whose walls undergo position fluctuations, and create the same effect expected from spacetime geometry fluctuations. We obtain an explicit result for the decoherence rate in the limit where the graviton wavelength is large compared to the size of the quantum system, and make some estimates for this rate.

The firewall paradox states that an observer falling into an old black hole must see a violation of unitarity, locality, or the equivalence principle. Motivated by this remarkable conflict, we analyze the causal structure of black hole spacetimes in order to determine whether all the necessary ingredients for the paradox fit within a single observer’s causal patch. We particularly focus on the question of whether the interior partner modes of the outgoing Hawking quanta can, in principle, be measured by an infalling observer. Since the relevant modes are spread over the entire sphere, we answer a simple geometrical question: can any observer see an entire sphere behind the horizon? We find that for all static black holes in $3+1$ and higher dimensions, with any value of the cosmological constant, no single observer can see both the early Hawking radiation and the interior modes with low angular momentum. We present a detailed description of the causal patch geometry of the Schwarzschild black hole in $3+1$ dimensions, where an infalling observer comes closest to being able to measure the relevant modes.

We investigate the slowly rotating general relativistic superfluid neutron stars including the entrainment effect in a two-fluid model, where one fluid represents the superfluid neutrons and the other is the charge-neutral fluid, called the proton fluid, made of protons and electrons. The equation of state and the entrainment effect between the superfluid neutrons and the proton fluid are computed using a relativistic mean field (RMF) model where baryon-baryon interaction is mediated by the exchange of $\sigma$, $\omega$, and $\rho$ mesons, and scalar self-interactions are also included. The equations governing rotating neutron stars in the slow rotation approximation are second order in rotational velocities of neutron and proton fluids. We explore the effects of the isospin dependent entrainment and the relative rotation between two fluids on the global properties of rotating superfluid neutron stars such as mass, shape, and the mass-shedding (Kepler) limit within the RMF model with different parameter sets. It is observed that for the global properties of rotating superfluid neutron stars in particular, the Kepler limit is modified compared with the case that does not include the contribution of $\rho$ mesons in the entrainment effect.

Recent perturbative studies have shown the existence of long-lived, quasistationary configurations of scalar fields around black holes. In particular, such configurations have been found to survive for cosmological time scales, which is a requirement for viable dark matter halo models in galaxies based on such types of structures. In this paper we perform a series of numerical relativity simulations of dynamical nonrotating black holes surrounded by self-gravitating scalar fields. We solve numerically the coupled system of equations formed by the Einstein and the Klein-Gordon equations under the assumption of spherical symmetry using spherical coordinates. Our results confirm the existence of oscillating, long-lived, self-gravitating scalar field configurations around nonrotating black holes in highly dynamical spacetimes with a rich scalar field environment. Our numerical simulations are long-term stable and allow for the extraction of the resonant frequencies to make a direct comparison with results obtained in the linearized regime. A by-product of our simulations is the existence of a degeneracy in plausible long-lived solutions of Einstein equations that would induce the same motion of test particles, either with or without the existence of quasibound states.

In this paper, we develop a new method that is different from the Schwinger proper time method to deduce the fermion propagator with a constant external magnetic field. In the NJL model, we use this method to find the gap equation at zero and nonzero temperature and give the numerical results and phase diagram between the magnetic field and temperature. Additionally, we introduce the current mass to study the susceptibilities because there is a new parameter (the strength of the external magnetic field) in this problem. Corresponding to this new parameter, we define a new susceptibility ${\chi }_B$ to compare with the other two susceptibilities ${\chi }_c$ (chiral susceptibility) and ${\chi }_T$ (thermal susceptibility). All three susceptibilities show that when the current mass is not zero, the phase transition is a crossover, while for comparison, in the chiral limit, the susceptibilities show a second order phase transition. Last, we give the critical coefficients of different susceptibilities in the chiral limit.

Computations at next-to-leading order in the Standard Model offer new technical challenges in the presence of higher dimensional operators. We introduce a framework that, starting from the top-quark effective field theory at dimension six, allows one to make predictions for cross sections as well as distributions in a fully automatic way. As an application, we present the first complete results at next-to-leading order in QCD for flavor-changing neutral interactions including parton shower effects, for $tZ$, $th$, $t\gamma$ associated production at the LHC.

We propose a method to introduce Sudakov effects to the unintegrated gluon density, promoting it to be hard scale dependent. The advantage of the approach is that it guarantees that the gluon density is positive definite and that the Sudakov effects cancel on the integrated level. As a case study, we apply the method to calculate angular correlations and the $R_{pA}$ ratio for $\mathrm{p}+\mathrm{p}$ vs $\mathrm{p}+\mathrm{Pb}$ collision in the production of forward-forward dijets.

In this work, we study the isospin conserved hidden bottomonium decay of $X_b\to \mathrm{\Upsilon }(1S)\omega$, where $X_b$ is taken to be the counterpart of the famous $X(3872)$ in the bottomonium sector as a candidate for the meson-meson molecule. Since it is likely that the $X_b$ is below the $B{\overline{B}}^{*}$ threshold and the mass difference between the neutral and charged bottom meson is small compared to the binding energy of the $X_b$, the isospin violating decay mode $X_b\to \mathrm{\Upsilon }(nS){\pi }^{+}{\pi }^{-}$ would be greatly suppressed. We use the effective Lagrangian based on the heavy quark symmetry to explore the rescattering mechanism of $X_b\to \mathrm{\Upsilon }(1S)\omega$ and calculate the partial widths. Our results show that the partial width for the $X_b\to \mathrm{\Upsilon }(1S)\omega$ is about tens of keVs. Taking into account the fact that the total width of $X_b$ may be smaller than a few MeV like $X(3872)$, the calculated branching ratios may reach to orders of ${10}^{-2}$. These hidden bottomonium decay modes are of great importance in the experimental search for the $X_b$ particularly at the hadron collider. Also, the associated studies of hidden bottomonium decays $X_b\to \mathrm{\Upsilon }(nS)\gamma$, $\mathrm{\Upsilon }(nS)\omega$, and $B\overline{B}\gamma$ may help us investigate the structure of $X_b$ deeply. The experimental observation of $X_b$ will provide us with further insight into the spectroscopy of exotic states and is helpful to probe the structure of the states connected by the heavy quark symmetry.

A mechanism for determining fermion masses in four spacetime dimensions is presented, which uses a scalar-field domain wall extending in a fifth spacelike dimension and a special choice of Yukawa coupling constants. A bounded and discrete fermion mass spectrum is obtained analytically for spinors localized in the fifth dimension. These particular mass values depend on a combination of the absolute value of the Yukawa coupling constant and the parameters of the scalar potential. A similar mechanism for a finite mass spectrum may apply to $(1+1)$-dimensional fermions relevant to condensed matter physics.

We study a Skyrme-type model with a potential term motivated by Bose–Einstein condensates (BECs), which we call the BEC Skyrme model. We consider two flavors of the model: the first is the Skyrme model, and the second has a sixth-order derivative term instead of the Skyrme term, both with the added BEC-motivated potential. The model contains toroidally shaped Skyrmions, and they are characterized by two integers $P$ and $Q$, representing the winding numbers of two complex scalar fields along the toroidal and poloidal cycles of the torus, respectively. The baryon number is $B=PQ$. We find stable Skyrmion solutions for $P=1,2,3,4,5$ with $Q=1$, while for $P=6$ and $Q=1$, it is only metastable. We further find that configurations with higher $Q>1$ are all unstable and split into $Q$ configurations with $Q=1$. Finally we discover a phase transition, possibly of first order, in the mass parameter of the potential under study.

In a recent proposal using the group field theory approach, a spatially homogeneous (generally anisotropic) universe is described as a quantum gravity condensate of “atoms of space,” which allows the derivation of an effective cosmological Friedmann equation from the microscopic quantum gravity dynamics. Here we take a first step towards the study of cosmological perturbations over the homogeneous background. We consider a state in which a single “atom” is added to an otherwise homogeneous condensate. Backreaction of the perturbation on the background is negligible and the background dynamics can be solved separately. The dynamics for the perturbation takes the form of a quantum cosmology Hamiltonian for a “wave function,” depending on background and perturbations, of the product form usually assumed in a Born-Oppenheimer approximation. We show that the perturbation we consider corresponds to a spatially homogeneous metric perturbation, and for this case derive the usual procedures in quantum cosmology from fundamental quantum gravity.

We study the Hubble parameter $H(z)$ in perturbed Friedmann universe and obtain an expression of the perturbed Hubble parameter $H(z,\mathbf{n})$. We derive the Hubble parameter power spectrum by using the initial spectrum during inflation and the Bardeen transfer function. We obtain a semianalytical expression in the case of cold dark matter universe. Similar with luminosity distance, the Hubble parameter spectrum is suggested to be a useful observational tool to determine some cosmological parameters. In addition, we show that the Hubble parameter power spectrum could be used to check whether the expansion is accelerated by the second order small scale fluctuation.

We consider a Bohmian approach to the Wheeler-DeWitt quantization of the Friedmann-Lemaître-Robertson-Walker model and investigate the question of whether or not there are singularities, in the sense that the Universe reaches zero volume. We find that for generic wave functions (i.e., nonclassical wave functions), there is a nonzero probability for a trajectory to be nonsingular. This should be contrasted to the consistent histories approach for which it was recently shown by Craig and Singh that there is always a singularity. This result illustrates that the question of singularities depends much on which version of quantum theory one adopts. This was already pointed out by Pinto-Neto et al., albeit with a different Bohmian approach. Our current Bohmian approach agrees with the consistent histories approach by Craig and Singh for single-time histories, unlike the one studied earlier by Pinto-Neto et al. Although the trajectories are usually different in the two Bohmian approaches, their qualitative behavior is the same for generic wave functions.