The radiative decays of the phi meson are known to be a good source of information about the $a_0(980)$ and $f_0(980)$ scalar mesons. We discuss these decays starting from a nonlinear model Lagrangian which maintains the (broken) chiral symmetry for the pseudoscalar (P), scalar (S) and vector (V) nonets involved. The characteristic feature is derivative coupling for the SPP interaction. In an initial approximation which models all the scalar nonet radiative processes together with the help of a pointlike vertex, it is noted that the derivative coupling prevents the $a_0$ and $f_0$ resonance peaks from getting washed out (by falling phase space). However, the shapes of the invariant two final PP mass distributions do not agree well with the experimental ones. For improving the situation we verify that inclusion of the charged $K$ meson loop diagrams in the model does reproduce the experimental spectrum shapes in the resonance region. The derivative coupling introduces quadratic as well as logarithmic divergences in this calculation. Using dimensional regularization we show in detail that these divergences actually cancel out among the four diagrams, as expected from gauge invariance. We point out the features which are expected to be important for further work on this model and for learning more about the puzzling scalar mesons.

The decay modes $J/\psi \to \gamma {\pi }^0$, $\gamma \eta$ and $\gamma {\eta }^{\prime }$ are analyzed using a data sample of $58\times {10}^6$ $J/\psi$ decays collected with the BESII detector at the BEPC. The branching fractions are determined to be: $Br(J/\psi \to \gamma {\pi }^0)=({3.13}_{-0.47}^{+0.65})\times {10}^{-5}$, $Br(J/\psi \to \gamma \eta )=(11.23\pm 0.89)\times {10}^{-4}$, and $Br(J/\psi \to \gamma {\eta }^{\prime })=(5.55\pm 0.44)\times {10}^{-3}$, where the errors are combined statistical and systematic errors. The ratio of partial widths $\Gamma (J/\psi \to \gamma {\eta }^{\prime })/\Gamma (J/\psi \to \gamma \eta )$ is measured to be $4.94\pm 0.40$, and the singlet-octet pseudoscalar mixing angle of $\eta -{\eta }^{\prime }$ system is determined.

We study the metric solutions for the gravitational equations in Modified Gravity Models (MGMs). In models with negative powers of the scalar curvature, we show that the Newtonian Limit (NL) is well defined as a limit at intermediate energies, in contrast with the usual low energy interpretation. Indeed, we show that the gravitational interaction is modified at low densities or low curvatures.

The generalized Chaplygin gas (GCG) is a candidate for the unification of dark energy and dark matter, and is parametrized by an exotic equation of state given by $p_{\mathrm{ch}}=-A/{\rho }_{\mathrm{ch}}^{\alpha }$, where $A$ is a positive constant and $0<\alpha \le 1$. In this paper, exact solutions of spherically symmetric traversable wormholes supported by the GCG are found, possibly arising from a density fluctuation in the GCG cosmological background. To be a solution of a wormhole, the GCG equation of state imposes the following generic restriction $A<(8\pi r_0^2{)}^{-(1+\alpha )}$, where $r_0$ is the wormhole throat radius, consequently violating the null energy condition. The spatial distribution of the exotic GCG is restricted to the throat neighborhood, and the physical properties and characteristics of these Chaplygin wormholes are further analyzed. Four specific solutions are explored in some detail, namely, that of a constant redshift function, a specific choice for the form function, a constant energy density, and finally, isotropic pressure Chaplygin wormhole geometries.

We investigate signatures of neutrino scattering in the cosmic microwave background (CMB) and matter power spectra, and the extent to which present cosmological data can distinguish between a free-streaming or tightly coupled fluid of neutrinos. If neutrinos have strong nonstandard interactions, for example, through the coupling of neutrinos to a light boson, they may be kept in equilibrium until late times. We show how the power spectra for these models differ from more conventional neutrino scenarios, and use CMB and large scale structure data to constrain these models. CMB polarization data improves the constraints on the number of massless neutrinos, while the Lyman-$\alpha$ power spectrum improves the limits on the neutrino mass. Neutrino mass limits depend strongly on whether some or all of the neutrino species interact and annihilate. The present data can accommodate a number of tightly coupled relativistic degrees of freedom, and none of the interacting-neutrino scenarios considered are ruled out by current data—although considerations regarding the age of the Universe disfavor a model with three annihilating neutrinos with very large neutrino masses.

We show that phantom dark energy, if it is described by a $k$-essence theory, has three fundamental problems: first, its Hamiltonian is unbounded from below. Second, classical stability precludes the equation of state from crossing the “Lambda-barrier,” $w_{\Lambda }=-1$. Finally, both the equation of state and the sound speed are unbounded—the first, from below, the second, from above—if the kinetic term is not bounded by dynamics.

The structure of the dark energy equation of state phase plane holds important information on the nature of the physics. We explain the bounds of the freezing and thawing models of scalar field dark energy in terms of the tension between the steepness of the potential vs the Hubble drag. Additionally, we extend the phase plane structure to modified gravity theories, examine trajectories of models with certain properties, and categorize regions in terms of scalar field hierarchical parameters, showing that dark energy is generically not a slow roll phenomenon.

We combine the constraints on the pion quark structure available from perturbative QCD, nonperturbative QCD (nonlocal QCD sum rules and light-cone sum rules) with the analysis of current data on $F_{\pi \gamma {\gamma }^{*}}(Q^2)$, including recent high-precision lattice calculations of the second moment of the pion’s distribution amplitude. We supplement these constraints with those extracted from the renormalon approach by means of the twist-four contributions to the pion distribution amplitude in order to further increase stability with respect to related theoretical uncertainties. We show which regions in the space of the first two nontrivial Gegenbauer coefficients $a_2$ and $a_4$ of all these constraints overlap, tagging this way the pion structure to the highest degree possible at present.

We study the sensitivity of testing the anomalous gauge couplings $g_{HVV}$’s of the Higgs boson in the formulation of linearly realized gauge symmetry via the processes $\gamma \gamma \to ZZ$ and $\gamma \gamma \to WWWW$ at polarized and unpolarized photon colliders based on $e^{+}{e}^{-}$ linear colliders of c.m. energies 500 GeV, 1 TeV, and 3 TeV. Signals beyond the standard model (SM) and SM backgrounds are carefully studied. We propose certain kinematic cuts to suppress the standard model backgrounds. For an integrated luminosity of $1{\mathrm{ab}}^{-1}$, we show that (a) $\gamma \gamma \to ZZ$ can provide a test of $g_{H\gamma \gamma }$ to the $3\sigma$ sensitivity of $O({10}^{-3}–{10}^{-2}){\mathrm{TeV}}^{-1}$ at a 500 GeV ILC, and $O({10}^{-3}){\mathrm{TeV}}^{-1}$ at a 1 TeV ILC and a 3 TeV CLIC, and (b) $\gamma \gamma \to WWWW$ at a 3 TeV CLIC can test all the anomalous couplings $g_{HVV}$’s to the $3\sigma$ sensitivity of $O({10}^{-3}–{10}^{-2}){\mathrm{TeV}}^{-1}$.

We compute from quenched lattice QCD the ground state masses of the charmed hybrid mesons $\overline{c}cg$, with exotic quantum numbers $J^{PC}=1^{-+}$, $0^{+-}$ and $0^{--}$. The $0^{--}$ hybrid meson spectrum has never been provided by lattice simulations due to the difficulties to extract high gluonic excitations from noise. We employ improved gauge and fermion actions on the anisotropic lattice, which reduce greatly the lattice artifacts, and lead to very good signals. The data are extrapolated to the continuum limit, with finite size effects under well control. For $1^{-+}$ and $0^{+-}$ hybrid mesons, the ground state masses are 4.405(38) GeV and 4.714(52) GeV. We predict for the first time from lattice QCD, the ground state mass of $0^{--}$ to be 5.883(146) GeV.

Branching ratios and polarization amplitudes for $B$ decaying to all allowed pseudoscalar, vector, axial-vector, scalar and tensor combinations of $D_s$ and $D$ mesons are calculated in the Isgur Scora Grinstein Wise (ISGW) quark model after assuming factorization. We find good agreement with other models in the literature and the limited experimental data and make predictions for as yet unseen decay modes. Lattice QCD results in this area are very limited. We make phenomenological observations on decays in to $D_s(2317)$ and $D_s(2460)$ and propose tests for determining the status and mixings of the axial mesons. We use the same approach to calculate branching ratios and polarization fraction for decays in to two $D$ type mesons.

The top quark antiquark production system in the dilepton decay channel is described by a set of equations which is nonlinear in the unknown neutrino momenta. Its most precise and least time consuming solution is of major importance for measurements of top quark properties like the top quark mass and $t\overline{t}$ spin correlations. The initial system of equations can be transformed into two polynomial equations with two unknowns by means of elementary algebraic operations. These two polynomials of multidegree two can be reduced to one univariate polynomial of degree four by means of resultants. The obtained quartic equation is solved analytically.

We consider a search for the $CP$-violating angle ${\delta }_{CP}$ in long baseline neutrino oscillation experiments. We show that the subleading ${\delta }_{CP}$-dependent terms in the ${\nu }_{\mu }\to {\nu }_{\mathrm{e}}$ oscillation probability can be easily obscured by the ambiguity of the leading term which depends on $|\delta m_{31}^2|$. It is thus necessary to determine the value of $\delta m_{31}^2$ with a sufficient accuracy. The ${\nu }_{\mu }$ survival events, which can be accumulated simultaneously with the ${\nu }_{\mathrm{e}}$ appearance events, can serve for this purpose owing to its large statistics. Therefore, the combined analysis of ${\nu }_{\mathrm{e}}$ appearance and ${\nu }_{\mu }$ survival events is crucial to provide a restrictive constraint on ${\delta }_{CP}$. Taking a test experimental setup, we demonstrate in the ${\delta }_{CP}\mathrm{\text{−}}\delta m_{31}^2$ plane that the analysis of ${\nu }_{\mathrm{e}}$ appearance events leads to less restrictive constraints on the value of ${\delta }_{CP}$ due to the ambiguity of $\delta m_{31}^2$ and that the combined analysis efficiently improves the constraints.

Motivated by the recent developments about the Hartle-Hawking wave function associated to black holes, we formulate an entropy functional on the moduli space of Calabi-Yau compactifications. We find that the maximization of the entropy is correlated with the appearance of asymptotic freedom in the effective field theory. The points where the entropy is maximized correspond to points on the moduli which are maximal intersection points of walls of marginal stability for Bogomolnyi-Prasad-Sommerfield states. We also find an intriguing link between extremizing the entropy functional and the points on the moduli space of Calabi-Yau three folds which admit a “quantum deformed“ complex multiplication.

Using the recent observations of the relation between the Hartle-Hawking wave function and the topological string partition function, we propose a wave function for scalar metric fluctuations on ${\mathbf{S}}^3$ embedded in a Calabi-Yau manifold. This problem maps to a study of noncritical bosonic string propagating on a circle at the self-dual radius. This can be viewed as a stringy toy model for a quantum cosmology.

Three-dimensional simulations for the merger of binary neutron stars are performed in the framework of full general relativity. We pay particular attention to the black hole formation case and to the resulting mass of the surrounding disk for exploring the possibility for formation of the central engine of short-duration gamma-ray bursts (SGRBs). Hybrid equations of state are adopted mimicking realistic, stiff nuclear equations of state (EOSs), for which the maximum allowed gravitational mass of cold and spherical neutron stars, $M_{\mathrm{sph}}$, is larger than $2M_{\odot }$. Such stiff EOSs are adopted motivated by the recent possible discovery of a heavy neutron star of mass $\sim 2.1\pm 0.2M_{\odot }$. For the simulations, we focus on binary neutron stars of the ADM mass $M\gtrsim 2.6M_{\odot }$. For an ADM mass larger than the threshold mass $M_{\mathrm{thr}}$, the merger results in prompt formation of a black hole irrespective of the mass ratio $Q_M$ with $0.65\lesssim Q_M\le 1$. The value of $M_{\mathrm{thr}}$ depends on the EOSs and is approximately written as $1.3–1.35M_{\mathrm{sph}}$ for the chosen EOSs. For the black hole formation case, we evolve the space-time using a black hole excision technique and determine the mass of a quasistationary disk surrounding the black hole. The disk mass steeply increases with decreasing the value of $Q_M$ for given ADM mass and EOS. This suggests that a merger with small value of $Q_M$ is a candidate for producing central engine of SGRBs. For $M<M_{\mathrm{thr}}$, the outcome is a hypermassive neutron star of a large ellipticity. Because of the nonaxisymmetry, angular momentum is transported outward. If the hypermassive neutron star collapses to a black hole after the long-term angular momentum transport, the disk mass may be $\gtrsim 0.01M_{\odot }$ irrespective of $Q_M$. Gravitational waves are computed in terms of a gauge-invariant wave extraction technique. In the formation of the hypermassive neutron star, quasiperiodic gravitational waves of frequency between 3 and 3.5 kHz are emitted irrespective of EOSs. The effective amplitude of gravitational waves can be $\gtrsim 5\times {10}^{-21}$ at a distance of 50 Mpc, and hence, it may be detected by advanced laser-interferometers. For the black hole formation case, the black hole excision technique enables a long-term computation and extraction of ring-down gravitational waves associated with a black hole quasinormal mode. It is found that the frequency and amplitude are $\approx 6.5–7\mathrm{kHz}$ and $\sim {10}^{-22}$ at a distance of 50 Mpc for the binary of mass $M\approx 2.7–2.9M_{\odot }$.

Gravity in five-dimensional braneworld backgrounds often exhibits problematic features, including kinetic ghosts, strong coupling, and the van Dam-Veltman-Zakharov (vDVZ) discontinuity. These problems are an obstacle to producing and analyzing braneworld models with interesting and potentially observable modifications of 4d gravity. We examine these problems in a general ${\mathrm{AdS}}_5/{\mathrm{AdS}}_4$ setup with two branes and localized curvature from arbitrary brane kinetic terms. We use the interval approach and an explicit straight gauge-fixing. We compute the complete quadratic gauge-fixed effective 4d action, as well as the leading cubic order corrections. We compute the exact Green’s function for gravity as seen on the brane. In the full parameter space, we exhibit the regions which avoid kinetic ghosts and tachyons. We give a general formula for the strong coupling scale, i.e., the energy scale at which the linearized treatment of gravity breaks down, for relevant regions of the parameter space. We show how the vDVZ discontinuity can be naturally but nontrivially avoided by ultralight graviton modes. We present a direct comparison of warping versus localized curvature in terms of their effects on graviton mode couplings. We exhibit the first example of Dvali-Gabadadze-Porrati (DGP)-like crossover behavior in a general warped setup.

We analyze the order ${\alpha }_s^2$ corrections to the single inclusive jet cross section in lepton-nucleon deep inelastic scattering. The full calculation is done analytically, in the small cone approximation, obtaining finite NLO partonic level cross sections for these processes. A detailed study of the different underlying partonic reactions is presented focusing in the size of the corrections they get at NLO accuracy, their relative weight, and the residual scale uncertainty they leave in the full cross section depending on the kinematical region explored. In agreement with what has already been found in forward production of ${\pi }^0$, we show that the dominant partonic process in very forward jet production is found to start at order ${\alpha }_s^2$, being effectively a lowest order estimate, with the consequent large factorization scale uncertainty, and the likelihood of non-negligible corrections at the subsequent order in perturbation theory.

We consider a class of seven-dimensional $\mathcal{N}=1$ supersymmetric orbifold GUTs in which the standard model (SM) gauge couplings and one of the Yukawa couplings (top quark, bottom quark or tau lepton) are unified, without low-energy supersymmetry, at $M_{\mathrm{GUT}}\simeq 4\times {10}^{16}\mathrm{GeV}$. With gauge-top quark Yukawa coupling unification the SM Higgs boson mass is estimated to be $135\pm 6\mathrm{GeV}$, which increases to $144\pm 4\mathrm{GeV}$ for gauge-bottom quark (or gauge-tau lepton) Yukawa coupling unification.