A recently proposed approximate large-$n$ ground state solution of the $U_L(n)\times U_R(n)$ symmetric linear sigma model is investigated at finite temperature. We study the coupled evaporation of two condensates corresponding to the symmetry breaking pattern $U_L(3)\times U_R(3)\to U_V(2)$, realized by the ground state in certain parts of the coupling space. The region of the fluctuation induced first order transitions and its second order boundary is mapped out. The existence of a tricritical point is conjectured.

The quark-mass dependence of the $\eta$ in the Schwinger model, which—like the ${\eta }^{\prime }$ in QCD—becomes massive through the axial anomaly, is studied on the lattice with $N_f=0$, 1, 2. Staggered quarks are used, with a rooted determinant for $N_f=1$. In the chiral limit the Schwinger mass is reproduced, which suggests that the anomaly is being treated correctly.

There is great interest in numerical relativity simulations involving matter due to the likelihood that binary compact objects involving neutron stars will be detected by gravitational wave observatories in the coming years, as well as to the possibility that binary compact object mergers could explain short-duration gamma-ray bursts. We present a code designed for simulations of hydrodynamics coupled to the Einstein field equations targeted toward such applications. This code has recently been used to study eccentric mergers of black hole-neutron star binaries. We evolve the fluid conservatively using high-resolution shock-capturing methods, while the field equations are solved in the generalized-harmonic formulation with finite differences. In order to resolve the various scales that may arise, we use adaptive mesh refinement (AMR) with grid hierarchies based on truncation error estimates. A noteworthy feature of this code is the implementation of the flux correction algorithm of Berger and Colella to ensure that the conservative nature of fluid advection is respected across AMR boundaries. We present various tests to compare the performance of different limiters and flux calculation methods, as well as to demonstrate the utility of AMR flux corrections.

There is a high level of interest in black hole-neutron star binaries, not only because their mergers may be detected by gravitational wave observatories in the coming years, but also because of the possibility that they could explain a class of short duration gamma-ray bursts. We study black hole-neutron star mergers that occur with high eccentricity as may arise from dynamical capture in dense stellar regions such as nuclear or globular clusters. We perform general relativistic simulations of binaries with a range of impact parameters, three different initial black hole spins (zero, aligned and antialigned with the orbital angular momentum), and neutron stars with three different equations of state. We find a rich diversity across these parameters in the resulting gravitational wave signals and matter dynamics, which should also be reflected in the consequent electromagnetic emission. Before tidal disruption, the gravitational wave emission is significantly larger than perturbative predictions suggest for periapsis distances close to effective innermost stable separations, exhibiting features reflecting the zoom-whirl dynamics of the orbit there. Guided by the simulations, we develop a simple model for the change in orbital parameters of the binary during close-encounters. Depending upon the initial parameters of the system, we find that mass transfer during nonmerging close-encounters can range from essentially zero to a sizable fraction of the initial neutron star mass. The same holds for the amount of material outside the black hole post-merger, and in some cases roughly half of this material is estimated to be unbound. We also see that nonmerging close-encounters generically excite large oscillations in the neutron star that are qualitatively consistent with $f$-modes.

We present the first steps needed for an analysis of the perturbations that occur in the cosmology associated with the conformal gravity theory. We discuss the implications of conformal invariance for perturbative coordinate gauge choices and show that in the conformal theory the trace of the metric fluctuation kinematically decouples from the first-order gravitational fluctuation equations. We determine the equations that describe first-order metric fluctuations around the illustrative conformal to flat de Sitter background. Via a conformal transformation, we show that such fluctuations can be constructed from fluctuations around a flat background, even though the fluctuations themselves are associated with a perturbative geometry that is not itself conformal to flat. We extend the analysis to fluctuations around other cosmologically relevant backgrounds, such as the conformal to flat Robertson-Walker background, and find tensor fluctuations that grow far more rapidly than those that occur in the analogous standard case. We show that while the standard gravity tensor fluctuations around a de Sitter background are also fluctuation solutions in the conformal theory, in the conformal case they do not carry energy.

In this work we revisit Wald’s cosmic no-hair theorem [R. M. Wald, Phys. Rev. D 28, 2118 (1983).] in the context of accelerating Bianchi cosmologies for a generic cosmic fluid with nonvanishing anisotropic stress tensor and when the fluid energy-momentum tensor is of the form of a cosmological constant term plus a piece which does not respect strong or dominant energy conditions. Such a fluid is the one appearing in inflationary models. We show that for such a system anisotropy may grow, in contrast to the cosmic no-hair conjecture. In particular, for a generic inflationary model we show that there is an upper bound on the growth of anisotropy. For slow-roll inflationary models, our analysis can be refined further and the upper bound is found to be of the order of slow-roll parameters. We examine our general discussions and our extension of Wald’s theorem for three classes of slow-roll inflationary models, generic multiscalar field driven models, anisotropic models involving U(1) gauge fields and the gauge-flation scenario.

We reexamine the scale dependence of the Efremov-Teryaev-Qiu-Sterman twist-3 matrix element that has been studied already by the four different groups with conflicting results [Z.-B. Kang and J.-W. Qiu, Phys. Rev. D 79, 016003 (2009); J. Zhou, F. Yuan, and Z.-T. Liang, Phys. Rev. D 79, 114022 (2009); W. Vogelsang and F. Yuan, Phys. Rev. D 79, 094010 (2009); and V. M. Braun, A. N. Manashov, and B. Pirnay, Phys. Rev. D 80, 114002 (2009)]. We find that we can in fact reproduce the results of V. M. Braun, A. N. Manashov, and B. Pirnay, Phys. Rev. D 80, 114002 (2009) with the methods of J. Zhou, F. Yuan, and Z.-T. Liang, Phys. Rev. D 79, 114022 (2009) when we treat some subtleties with greater care, thus easing the mentioned conflict.

We study the implications of the searches based on $H\to {\tau }^{+}{\tau }^{-}$ by the ATLAS and CMS collaborations on the parameter space of the two-Higgs-doublet model (2HDM). In the 2HDM, the scalars can decay into a tau pair with a branching ratio larger than the SM one, leading to constraints on the 2HDM parameter space. We show that in model II, values of $\tan \beta >1.8$ are definitively excluded if the pseudoscalar is in the mass range $110\mathrm{GeV}<m_A<145\mathrm{GeV}$. We have also discussed the implications for the 2HDM of the recent dimuon search by the ATLAS collaboration for a $CP$-odd scalar in the mass range 4–12 GeV.

We study the scattering of a single parton state with a multiparton state to derive the complete results of perturbative coefficient functions at leading order, which appear in the collinear factorization for single transverse-spin asymmetry (SSA) in Drell-Yan processes with a transversely polarized hadron in the initial state. We find that the factorization formula of SSA contains hard-pole, soft-quark-pole, and soft-gluon-pole contributions. It is interesting to note that the leading-order perturbative coefficient functions of soft-quark-pole and soft-gluon-pole contributions are extracted from parton-scattering amplitudes at one-loop, while the functions of hard-pole contributions are extracted from the tree-level amplitudes at tree-level. Our method to derive the factorization of SSA is different than the existing one in literature. A comparison of our results with those obtained by other methods is made here.

We investigate the quark orbital angular momentum of the nucleon in the absence of gauge-field degrees of freedom, by using the concept of the Wigner distribution and the light-cone wave functions of the Fock-state expansion of the nucleon. The quark orbital angular momentum is obtained from the phase-space average of the orbital angular momentum operator weighted with the Wigner distribution of unpolarized quarks in a longitudinally polarized nucleon. We also derive the light-cone wave-function representation of the orbital angular momentum. In particular, we perform an expansion in the nucleon Fock-state space and decompose the orbital angular momentum into the $N$-parton state contributions. Explicit expressions are presented in terms of the light-cone wave functions of the three-quark Fock state. Numerical results for the up and down quark orbital angular momenta of the proton are shown in the light-cone constituent quark model and the light-cone chiral quark-soliton model.

The use of the vacuum lepton pair production process ($\nu \to \nu e^{-}{e}^{+}$), a viable reaction for superluminal neutrinos, to put constraints on Lorentz violations requires a dynamical framework. Different choices of dynamical matrix elements and modified dispersion relations for neutrinos, leading to numerical factors differing by 1 order of magnitude in the results for the pair production decay width, are used to show the uncertainties on these constraints.

Searches for a nucleon decay into a charged antilepton ($e^{+}$ or ${\mu }^{+}$) plus a light meson (${\pi }^0$, ${\pi }^{-}$, $\eta$, ${\rho }^0$, ${\rho }^{-}$, $\omega$) were performed using the Super-Kamiokande I and II data. Twelve nucleon decay modes were searched for. The total exposure is $140.9\mathrm{kiloton}·\mathrm{years}$, which includes a $91.7\mathrm{kiloton}·\mathrm{year}$ exposure (1489.2 live days) of Super-Kamiokande-I and a $49.2\mathrm{kiloton}·\mathrm{year}$ exposure (798.6 live days) of Super-Kamiokande II. The number of candidate events in the data was consistent with the atmospheric neutrino background expectation. No significant evidence for a nucleon decay was observed in the data. Thus, lower limits on the nucleon partial lifetime at 90% confidence level were obtained. The limits range from $3.6\times {10}^{31}$ to $8.2\times {10}^{33}\mathrm{years}$, depending on the decay modes.

By application of the “geometric spectral inversion” technique, which we have recently generalized to accommodate also singular interaction potentials, we construct from spectral data emerging from the solution of the Minkowski-space formulation of the homogeneous Bethe–Salpeter equation describing bound states of two spinless particles a Schrödinger approach to such states in terms of nonrelativistic potential models. This spectrally equivalent modeling of bound states yields their qualitative features (masses, form factors, etc.) without having to deal with the more involved Bethe–Salpeter formalism.

The study of the Dyson-Schwinger equations of Landau gauge Yang-Mills theory has revealed two types of solutions for the gluon and ghost propagators, with a scaling and a massive (decoupling) behavior in the extreme infrared, respectively. We show that both types of solutions are quantitatively reproduced by applying renormalization group equations of Callan-Symanzik type in an epsilon expansion to the infrared limit of Landau gauge Yang-Mills theory when a mass term for the gluons is added to the action. Only the decoupling solution corresponds to an infrared-stable fixed point in three and four space-time dimensions and is hence expected to be physically realized, in agreement with the results of recent lattice calculations.

We study the lepton flavor models with the flavor symmetry $(Z_N\times Z_N\times Z_N)⋊Z_3$. Our models lead nonvanishing discrete values of ${\theta }_{13}$ as well as ${\theta }_{12}$ and ${\theta }_{23}$ depending on $N$. For certain values, our models realize the tribimaximal mixing angles with ${\theta }_{13}=0$. For other values, our models provide discrete deviation from the tribimaximal mixing angles.

In this paper, we describe the perturbative generation of the higher-derivative Lorentz-breaking terms for the gauge field, that is, the Myers-Pospelov term and the higher-derivative Carroll-Field-Jackiw term. These terms are explicitly calculated in the one-loop approximation and shown to be finite and ambiguous.

A general way of interpreting odd-dimensional models as a doublet of chiral models is discussed. Based on the equations of motion this dual composition is illustrated. Examples from quantum mechanics, field theory and gravity are considered. Specially the recently advocated topologically massive gravity is analyzed in some details.

Scattering theory in the Gell-Mann and Goldberger formulation is slightly extended to render a Hamiltonian quantum-mechanical description of the neutrino oscillations.

We propose a new scenario for the bouncing universe in a simple five-dimensional braneworld model in the framework of Einstein-Gauss-Bonnet gravity, which works even with ordinary matter on the brane. In this scenario, the so-called branch singularity located at a finite physical radius in the bulk spacetime plays an essential role. We show that a three-brane moving in the bulk may reach and pass through it in spite of the fact that it is a curvature singularity. The bulk spacetime is extended beyond the branch singularity in the $C^0$ sense and then the branch singularity is identified as a massive thin shell. From the bulk point of view, this process is the collision of the three-brane with the shell of branch singularity. From the point of view on the brane, this process is a sudden transition from the collapsing phase to the expanding phase of the universe. The present result opens a completely new possibility to achieve the bouncing brane universe as a higher-curvature effect.