We consider a phenomenological model for the dynamics of Wilson loops in pure $SU(N)$ QCD where the expectation value of the loop is the average over an interacting diffusion process on the group manifold $SU(N)$. The interaction is provided by an arbitrary potential that generates the transition from the Casimir scaling regime into the screening phase of the four-dimensional gauge theory. The potential is required to respect the underlying center symmetry of the gauge theory, and this predicts screening of arbitrary $SU(N)$ representations to the corresponding antisymmetric representations of the same $N$-ality. The stable strings before the onset of screening are therefore the $k$ strings. In the process we find a nontrivial but solvable modification of the ${\mathrm{QCD}}_2$ matrix model that involves an arbitrary potential.

It is pointed out that if the molecular interpretation of the recently observed resonance $X(3872)$ is valid, then nature may have prepared a good laboratory for us to examine the phenomenon of superradiance and subradiance of Dicke. The superradiance and supradiance factors are evaluated and the effects on the electromagnetic radiative decay of $X(3872)$ are discussed. Our results using coordinate space representation is similar to the momentum space results of Voloshin.

Rapidity, azimuthal and multiplicity dependence of mean transverse momentum and transverse momentum correlations of charged particles is studied in ${\pi }^{+}\mathrm{p}$ and ${\mathrm{K}}^{+}\mathrm{p}$ collisions at $250\mathrm{GeV}/c$ incident beam momentum. For the first time, it is found that the rapidity dependence of the two-particle transverse momentum correlation is different from that of the mean transverse momentum, but both have similar multiplicity dependence. In particular, the transverse momentum correlations are boost invariant. This is similar to the recently found boost invariance of the charge balance function. A strong azimuthal dependence of the transverse momentum correlations originates from the constraint of energy-momentum conservation. The results are compared with those from the PYTHIA Monte Carlo generator. The similarities to and differences with the results from current heavy ion experiments are discussed.

We consider the generation of thick brane configurations in a pure geometric Weyl integrable 5D spacetime which constitutes a non-Riemannian generalization of Kaluza-Klein (KK) theory. In this framework, we show how 4D gravity can be localized on a scalar thick brane which does not necessarily respect reflection symmetry, generalizing in this way several previous models based on the Randall-Sundrum (RS) system and avoiding both, the restriction to orbifold geometries and the introduction of the branes in the action by hand. We first obtain a thick brane solution that preserves 4D Poincaré invariance and breaks $Z_2$-symmetry along the extra dimension which, indeed, can be either compact or extended, and supplements brane solutions previously found by other authors. In the noncompact case, this field configuration represents a thick brane with positive energy density centered at $y=c_2$, whereas pairs of thick branes arise in the compact case. Remarkably, the Weylian scalar curvature is nonsingular along the fifth dimension in the noncompact case, in contraposition to the RS thin brane system. We also recast the wave equations of the transverse traceless modes of the linear fluctuations of the classical background into a Schrödinger’s equation form with a volcano potential of finite bottom in both the compact and the extended cases. We solve Schrödinger equation for the massless zero mode $m^2=0$ and obtain a single bound wave function which represents a stable 4D graviton. We also get a continuum gapless spectrum of KK states with $m^2>0$ that are suppressed at $y=c_2$ and turn asymptotically into plane waves.

We present a class of higher-dimensional solutions to Gauss-Bonnet-Maxwell equations in $2k+2$ dimensions with a $U(1)$ fibration over a $2k$-dimensional base space $\mathcal{B}$. These solutions depend on two extra parameters, other than the mass and the Newman-Unti-Tamburino charge, which are the electric charge $q$ and the electric potential at infinity $V$. We find that the form of metric is sensitive to geometry of the base space, while the form of electromagnetic field is independent of $\mathcal{B}$. We investigate the existence of Taub-Newman-Unti-Tamburino/bolt solutions and find that in addition to the two conditions of uncharged Newman-Unti-Tamburino solutions, there exist two other conditions. These two extra conditions come from the regularity of vector potential at $r=N$ and the fact that the horizon at $r=N$ should be the outer horizon of the black hole. We find that for all nonextremal Newman-Unti-Tamburino solutions of Einstein gravity having no curvature singularity at $r=N$, there exist Newman-Unti-Tamburino solutions in Gauss-Bonnet-Maxwell gravity. Indeed, we have nonextreme Newman-Unti-Tamburino solutions in $2+2k$ dimensions only when the $2k$-dimensional base space is chosen to be ${\mathbb{C}\mathbb{P}}^{2k}$. We also find that the Gauss-Bonnet-Maxwell gravity has extremal Newman-Unti-Tamburino solutions whenever the base space is a product of 2-torii with at most a 2-dimensional factor space of positive curvature, even though there a curvature singularity exists at $r=N$. We also find that one can have bolt solutions in Gauss-Bonnet-Maxwell gravity with any base space. The only case for which one does not have black hole solutions is in the absence of a cosmological term with zero curvature base space.

The space based gravitational wave detector LISA (Laser Interferometer Space Antenna) is expected to observe a large population of Galactic white dwarf binaries whose collective signal is likely to dominate instrumental noise at observational frequencies in the range ${10}^{-4}$ to ${10}^{-3}\mathrm{Hz}$. The motion of LISA modulates the signal of each binary in both frequency and amplitude—the exact modulation depending on the source direction and frequency. Starting with the observed response of one LISA interferometer and assuming only Doppler modulation due to the orbital motion of LISA, we show how the distribution of the entire binary population in frequency and sky position can be reconstructed using a tomographic approach. The method is linear and the reconstruction of a delta-function distribution, corresponding to an isolated binary, yields a point spread function (psf). An arbitrary distribution and its reconstruction are related via smoothing with this psf. Exploratory results are reported demonstrating the recovery of binary sources, in the presence of white Gaussian noise.

Radiative transitions between charmonium states offer an insight into the internal structure of heavy-quark bound states within QCD. We compute, for the first time within lattice QCD, the transition form factors of various multipolarities between the lightest few charmonium states. In addition, we compute the experimentally unobservable, but physically interesting vector form factors of the ${\eta }_c$, $J/\psi$, and ${\chi }_{c0}$. To this end we apply an ambitious combination of lattice techniques, computing three-point functions with heavy domain-wall fermions on an anisotropic lattice within the quenched approximation. With an anisotropy $\xi =3$ at $a_s\sim 0.1\mathrm{fm}$ we find a reasonable gross spectrum and a hyperfine splitting $\sim 90\mathrm{MeV}$, which compares favorably with other improved actions. In general, after extrapolation of lattice data at nonzero $Q^2$ to the photopoint, our results agree within errors with all well-measured experimental values. Furthermore, results are compared with the expectations of simple quark models where we find that many features are in agreement; beyond this we propose the possibility of constraining such models using our extracted values of physically unobservable quantities such as the $J/\psi$ quadrupole moment. We conclude that our methods are successful and propose to apply them to the problem of radiative transitions involving hybrid mesons, with the eventual goal of predicting hybrid meson photoproduction rates at the GlueX experiment.

In this paper, we discuss a decoupling of the Goldstone bosons from highly excited hadrons in relation to the restoration of chiral symmetry in such hadrons. We use a generalized Nambu-Jona-Lasinio model with the interaction between quarks in the form of an instantaneous Lorentz-vector confining potential. This model is known to provide spontaneous breaking of chiral symmetry in the vacuum via the standard self-energy loops for valence quarks. For highly excited hadrons, where the typical momentum of valence quarks is large, the loop contributions represent only a small correction to the chiral-invariant classical contributions and asymptotically vanish. Consequently, the chiral symmetry violating Lorentz-scalar dynamical mass of quarks vanishes. Then the conservation of the axial-vector current in the chiral limit requires, via the Goldberger-Treiman relation, that the valence quarks decouple from the Goldstone boson. As a consequence, the whole hadron decouples from the Goldstone boson as well, which implies that its axial constant also vanishes.

We investigate the threshold-enhanced QCD corrections to the cross sections for direct top quark productions induced by model-independent flavor changing neutral current couplings at hadron colliders. We use the soft-collinear effective theory to describe the incoming massless partons and use the heavy quark effective theory to treat the top quark. Then we construct the flavor changing operator based on the above effective theories, and resum the large logarithms near threshold arising from soft gluon emission. Our results show that the resummed QCD corrections further enhance the next-to-leading order cross sections significantly. Moreover, the resummation effects vastly reduce the dependence of the cross sections on the renormalization and factorization scales, especially in cases where the next-to-leading order results behave worse than the leading order results. Our results are more sensitive to the new physics effects. If signals of direct top quark production are found in future experiments, it is more appropriate to use our results as the theoretical inputs for extracting the anomalous couplings.

We present the full $\mathcal{O}({\alpha }_{\mathrm{ew}})$ electroweak radiative corrections to the Higgs-boson production in association with $Z^0$-boson pair at an electron-positron linear collider (LC) in the standard model. We analyze the dependence of the full one-loop corrections on the Higgs-boson mass $m_H$ and colliding energy $\sqrt{s}$. We find that the corrections significantly suppress the Born cross section, and the $\mathcal{O}({\alpha }_{\mathrm{ew}})$ electroweak radiative corrections are generally between 1.0% and $-15\%$ in our chosen parameter space, which should be taken into consideration in the future precise experiments.

We present a numerical study of the lattice Landau gluon and ghost propagators in three-dimensional pure $SU(2)$ gauge theory. Data have been obtained using asymmetric lattices ($V={20}^2\times 40$, ${20}^2\times 60$, $8^2\times 64$, $8^2\times 140$, ${12}^2\times 140$, and ${16}^2\times 140$) for the lattice coupling $\beta =3.4$ in the scaling region. We find that the gluon (respectively, ghost) propagator is suppressed (respectively, enhanced) at small momenta in the limit of large lattice volume $V$. By comparing these results with data obtained using symmetric lattices ($V={20}^2,{60}^3,\mathrm{\text{and}}{140}^3$), we find that both propagators suffer from systematic effects in the infrared region ($p\lesssim 650\mathrm{MeV}$). In particular, the gluon (ghost) propagator is less IR suppressed (enhanced) than in the symmetric case. We discuss possible implications of the use of asymmetric lattices.

A basis independent formulation of quark-lepton complementarity is implemented at a high scale for quasidegenerate Majorana neutrinos. It is shown that even with the renormalization group evolution in the minimal supersymmetric standard model, the scenario can be consistent with the data provided a nontrivial role is played by the Majorana phases. Correlated constraints are found on these phases and the neutrino mass scale using the current data. We also indicate how future accurate measurements of the mixing angles can serve as tests of this scenario and restrict the values of the Majorana phases.

We investigate vortices on a cylinder in supersymmetric non-Abelian gauge theory with hypermultiplets in the fundamental representation. We identify moduli space of periodic vortices and find that a pair of wall-like objects appears as the vortex moduli is varied. Usual domain walls also can be obtained from the single vortex on the cylinder by introducing a twisted boundary condition. We can understand these phenomena as a $T$ duality among D-brane configurations in type II superstring theories. Using this $T$-duality picture, we find a one-to-one correspondence between the moduli space of non-Abelian vortices and that of kinky D-brane configurations for domain walls.

The quantization of the family of linearly polarized Gowdy $T^3$ spacetimes is discussed in detail, starting with a canonical analysis in which the true degrees of freedom are described by a scalar field that satisfies a Klein-Gordon type equation in a fiducial time-dependent background. A time-dependent canonical transformation, which amounts to a change of the basic (scalar) field of the model, brings the system to a description in terms of a Klein-Gordon equation on a background that is now static, although subject to a time-dependent potential. The system is quantized by means of a natural choice of annihilation and creation operators. The quantum time evolution is considered and shown to be unitary, so that both the Schrödinger and Heisenberg pictures can be consistently constructed. This has to be contrasted with previous treatments for which time evolution failed to be implementable as a unitary transformation. Possible implications for both canonical quantum gravity and quantum field theory in curved spacetime are noted.

We propose a program for counting microstates of four-dimensional BPS black holes in $\mathcal{N}\ge 2$ supergravities with symmetric-space valued scalars by exploiting the symmetries of timelike reduction to three dimensions. Inspired by the equivalence between the four-dimensional attractor flow and geodesic flow on the three-dimensional scalar manifold, we radially quantize stationary, spherically symmetric BPS geometries. Connections between the topological string amplitude, attractor wave function, the Ooguri-Strominger-Vafa conjecture and the theory of automorphic forms suggest that black hole degeneracies are counted by Fourier coefficients of modular forms for the three-dimensional $U$-duality group, associated to special unipotent representations which appear in the supersymmetric Hilbert space of the quantum attractor flow.

We show that a recent claim that matter wave interferometers have a much higher sensitivity than laser interferometers for a comparable physical setup is unfounded. We point out where the mistake in the earlier analysis is made. We also disprove the claim that only a description based on the geodesic deviation equation can produce the correct physical result. The equations for the quantum dynamics of nonrelativistic massive particles in a linearly perturbed spacetime derived here are useful for treating a wider class of related physical problems. A general discussion on the use of atom interferometers for the detection of gravitational waves is also provided.

The impact of the leading quantum gravity effects on the dynamics of the Hawking evaporation process of a black hole is investigated. Its spacetime structure is described by a renormalization group improved Vaidya metric. Its event horizon, apparent horizon, and timelike limit surface are obtained by taking the scale dependence of Newton’s constant into account. The emergence of a quantum ergosphere is discussed. The final state of the evaporation process is a cold, Planck size remnant.

The main challenge faced by Higgsless models of electroweak symmetry breaking is to reconcile the experimental constraints imposed by the precision electroweak data and the top quark phenomenology with the unitarity constraints imposed by longitudinal gauge boson scattering amplitudes. In this paper we expand on previous work, giving details of how delocalized fermions can be used to adjust the $S$ parameter to zero, while keeping the $T$ and $U$ parameters naturally suppressed. We also show that it is possible to obtain the top quark mass, without affecting the delay of unitarity violation of the $W^{+}{W}^{-}\to W^{+}{W}^{-}$ scattering amplitude, by separating the mass scales of the fermion sector ($1/R_f$) from that of the gauge sector ($1/R_g$). The fermion sector scale $1/R_f$ is only weakly constrained by unitarity of the $t\overline{t}\to W^{+}{W}^{-}$ scattering amplitude; thus the ratio $R_g/R_f$ can be quite large, and the top mass can be achieved easily. Anomalous right-handed couplings involving the third generation quarks also avoid constraints from experimental data if $1/R_f$ is sufficiently large.

We discuss how experiments measuring $B\to \pi \pi$ and $B\to \rho \rho$ may be used to search for a $\Delta I=5/2$ amplitude component. This component could be the explanation for a recent (albeit very tentative) hint from $B(\overline{B})\to \rho \rho$ decays that the isospin triangles do not close.