We analyze the exclusive charmonium $J/\psi +{\eta }_c$ pair production in $e^{+}{e}^{-}$ annihilation using the nonfactorized perturbative QCD and the light-front quark model (LFQM) that goes beyond the peaking approximation. We effectively include all orders of higher twist terms in the leading order of QCD coupling constant and compare our nonfactorized analysis with the usual factorized analysis in the calculation of the cross section. We also calculate the quark distribution amplitudes, the Gegenbauer moments, and the decay constants for $J/\psi$ and ${\eta }_c$ mesons using our LFQM. Our nonfactorized result enhances the nonrelativistic QCD result by a factor of $3\sim 4$ at $\sqrt{s}=10.6\mathrm{GeV}$.

We present measurements of the time-dependent $CP$-violating asymmetries in $B^0\to K_S^0{K}_S^0{K}_S^0$ decays based on $384\times {10}^6$ ${\rm Y}(4S)\to B\overline{B}$ decays collected with the BABAR detector at the PEP-II asymmetric-energy $B$ Factory at SLAC. We obtain the $CP$ asymmetry parameters $C=0.02\pm 0.21\pm 0.05$ and $S=-0.71\pm 0.24\pm 0.04$, where the first uncertainties are statistical and the second systematic. These results are consistent with standard model expectations.

We study the application of AdS/CFT duality to longitudinal boost-invariant Bjorken expansion of QCD matter produced in ultrarelativistic heavy ion collisions. As the exact $(1+4)$-dimensional bulk solutions for the $(1+3)$-dimensional boundary theory are not known, we investigate in detail the $(1+1)$-dimensional boundary theory, where the bulk is ${\mathrm{AdS}}_3$ gravity. We find an exact bulk solution, show that this solution describes part of the spinless Bañados-Teitelboim-Zanelli black hole with the angular dimension unwrapped, and use the thermodynamics of the Bañados-Teitelboim-Zanelli hole to recover the time-dependent temperature and entropy density on the boundary. After separating from the holographic energy-momentum tensor a vacuum contribution, given by the extremal black hole limit in the bulk, we find that the boundary fluid is an ideal gas in local thermal equilibrium. Including angular momentum in the bulk gives a boundary flow that is boost invariant but has a nonzero longitudinal velocity with respect to the Bjorken expansion.

We show that the correct entropy, temperature (and absorption probability) of nonextremal black $p$-brane can be reproduced by a certain thermodynamical model when maximizing its entropy. We show that the form of the model is related to the geometrical similarity of nonextremal and near extremal black $p$-brane at near horizon region, and argue about the appropriateness of the model.

We propose a scenario in which the dark components of the Universe are manifestations of a single bulk viscous fluid. Using dynamical system methods, a qualitative study of the homogeneous, isotropic background scenario is performed in order to determine the phase space of all possible solutions. The specific model which we investigate shares similarities with a generalized Chaplygin gas in the background but is characterized by nonadiabatic pressure perturbations. This model is tested against supernova type Ia and matter power spectrum data. Different from other unified descriptions of dark matter and dark energy, the matter power spectrum is well behaved, i.e., there are no instabilities or oscillations on small perturbation scales. The model is competitive in comparison with the currently most popular proposals for the description of the cosmological dark sector.

Weakly interacting massive particles with electroweak scale masses (neutralinos, etc.) remain in kinetic equilibrium with other particle species until temperatures approximately in the range of 10 MeV to 1 GeV, leading to the formation of dark matter substructure with masses as small as ${10}^{-4}{M}_{\odot }$ to ${10}^{-12}{M}_{\odot }$. However, if dark matter consists of particles with MeV scale masses, as motivated by the observation of 511 keV emission from the galactic bulge, such particles are naturally expected to remain in kinetic equilibrium with the cosmic neutrino background until considerably later times. This would lead to a strong suppression of small scale structure with masses below about ${10}^7{M}_{\odot }$ to ${10}^4{M}_{\odot }$. This cutoff scale has important implications for present and future searches for faint local group satellite galaxies and for the missing satellites problem. We also summarize current constraints on the MeV dark matter scenario.

We investigate hadronic unquenching effects in light quarks and mesons. Within the nonperturbative continuum framework of Schwinger-Dyson and Bethe-Salpeter equations we quantify the strength of the back reaction of the pion onto the quark-gluon interaction. To this end we add a Yang-Mills part of the interaction such that unquenched lattice results for various current quark masses are reproduced. We find considerable effects in the quark mass function at low momenta as well as for the chiral condensate. The quark wave function is less affected. The Gell-Mann-Oakes-Renner relation is valid to good accuracy up to pion masses of 400–500 MeV. As a by-product of our investigation we verify the Coleman theorem, that chiral symmetry cannot be broken spontaneously when QCD is reduced to $1+1$ dimensions.

We show that the shear viscosity of $\lambda {\varphi }^4$ theory is sensitive at next-to-leading order to soft physics, which gives rise to subleading corrections suppressed by only a half power of the coupling, $\eta =\frac{(3033.54+1548.3\sqrt{(N+2)\lambda /72})N{T}^3}{\frac{N+2}{3}{\lambda }^2}$. The series appears to converge about as well as the series for the pressure.

The density of states of Yang-Mills integrals in the supersymmetric case is characterized by power-law tails whose decay is independent of $N$, the rank of the gauge group. It is believed that this has no counterpart in matrix models, but we construct a matrix model that exactly exhibits this property. In addition, we show that the eigenfunctions employed to construct the matrix model are invariant under the collinear subgroup of conformal transformations, $SL(2,\mathbb{R})$. We also show that the matrix model itself is invariant under a fractional linear transformation. The wave functions of the model appear in the trigonometric Rosen-Morse potential and in free relativistic motion on anti-de Sitter space.

We first study the temporal Wilson loop in the finite-temperature noncommutative dipole field theory from the string/gauge correspondence. The associated dual supergravity background is constructed from the near-horizon geometry of near-extremal D branes, after applying T duality and smeared twist. We investigate the string configuration therein and find that while the temperature produces a maximum distance $L_{\max }$ in the interquark distance the dipole in there could produce a minimum distance $L_{\min }$. The quark boundary pair therefore could be found only if their distance is between $L_{\min }$ and $L_{\max }$. We also show that, beyond a critical temperature the quark pair becomes totally free due to screening by thermal bath. We next study the spatial Wilson loop and find the confining nature in the zero temperature 3D and 4D nonsupersymmetry dipole gauge theory. The string tension of the linear confinement potential is obtained and found to be a decreasing function of the dipole field. We also investigate the associated t’Hooft loop and determine the corresponding monopole antimonopole potential. The conventional screening of magnetic charge which indicates the confinement of the electric charge is replaced by a strong repulsive however. Finally, we show that the dual string which is rotating along the dipole deformed $S^5$ will behave as a static one without dipole field, which has no minimum distance and has larger energy than a static one with dipole field. We discuss the phase transition between these string solutions.

We report a calculation in $\mathcal{N}=4$ Yang-Mills of the four-loop term $g^{(4)}$ in the collinear anomalous dimension $g(\lambda )$ which governs the universal subleading infrared structure of gluon scattering amplitudes. Using the method of obstructions to extract this quantity from the $1/ϵ$ singularity in the four-gluon iterative relation at four loops, we find $g^{(4)}=-1240.9$ with an estimated numerical uncertainty of 0.02%. We also analyze the implication of our result for the strong coupling behavior of $g(\lambda )$, finding support for the string theory prediction computed recently by Alday and Maldacena using AdS/CFT.

The perturbative evaluation of the effective action can be expanded in powers of derivatives of the external field. We apply the renormalization group equation to the term in the effective action that is second order in the derivatives of the external field and all orders in a constant external field, considering both massless scalar ${\varphi }_4^4$ model and massless scalar electrodynamics. A so-called “on shell” renormalization scheme permits one to express this “kinetic term” for the scalar field entirely in terms of the renormalization group functions appropriate for this scheme. These renormalization group functions can be related to those associated with minimal subtraction.

We present arguments for the existence of charged, rotating black holes with equal magnitude angular momenta in $d=5$ Einstein-Yang-Mills theory with negative cosmological constant. These solutions possess a regular horizon of spherical topology and approach asymptotically the anti-de Sitter spacetime background. The black hole solutions have also an electric charge and a nonvanishing magnetic flux through the sphere at infinity. Different from the static case, no regular solution with a nonvanishing angular momenta is found for a vanishing event horizon radius.

We analyze the general features of localization of fermions and scalars in smoothed field-theoretical versions of the type 2 Randall-Sundrum braneworld model. A scalar field domain wall forms the brane, inducing warped gravity, and we study the mass spectra of the matter fields in the dimensionally reduced theory. We demonstrate explicitly that both scalar and fermion fields exhibit a continuum of properly normalizable modes starting at zero mass. If discrete bound modes are present in the gravity-free case, these become resonances in the continuum, while off-resonant modes are highly suppressed on the brane. We describe briefly how another scalar field can be used to break a symmetry on the domain wall while leaving it unbroken far from the wall, as has already been done in the flat space case. Finally we present numerical calculations for a toy model which demonstrates the decoupling of continuum modes at low energies, so the theory becomes four dimensional.

The generalized Chaplygin gas provides an interesting candidate for the present accelerated expansion of the universe. We explore a geometrical explanation for the generalized Chaplygin gas within the context of brane world theories where matter fields are confined to the brane by means of the action of a confining potential. We obtain the modified Friedmann equations, deceleration parameter, and age of the universe in this scenario and show that they are consistent with the present observational data.

The production of a sterile species via active-sterile mixing in a thermal medium is studied in an exactly solvable model. The exact time evolution of the sterile distribution function is determined by the dispersion relations and damping rates ${\Gamma }_{1,2}$ for the quasiparticle modes. These depend on $\tilde{\gamma }={\Gamma }_{aa}/2\Delta E$, with ${\Gamma }_{aa}$ the interaction rate of the active species in absence of mixing and $\Delta E$ the oscillation frequency in the medium without damping. $\tilde{\gamma }\ll 1$, $\tilde{\gamma }\gg 1$ describe the weak and strong damping limits, respectively. For $\tilde{\gamma }\ll 1$, ${\Gamma }_1={\Gamma }_{aa}{cos}^2{\theta }_m$; ${\Gamma }_2={\Gamma }_{aa}{sin}^2{\theta }_m$ where ${\theta }_m$ is the mixing angle in the medium and the sterile distribution function does not obey a simple rate equation. For $\tilde{\gamma }\gg 1$, ${\Gamma }_1={\Gamma }_{aa}$ and ${\Gamma }_2={\Gamma }_{aa}{sin}^{2}2{\theta }_m/4{\tilde{\gamma }}^2$, is the sterile production rate. In this regime sterile production is suppressed and the oscillation frequency vanishes at an Mikheyev-Smirnov-Wolfenstein (MSW) resonance, with a breakdown of adiabaticity. These are consequences of quantum Zeno suppression. For active neutrinos with standard model interactions the strong damping limit is only available near an MSW resonance if $\sin 2\theta \ll {\alpha }_w$ with $\theta$ the vacuum mixing angle. The full set of quantum kinetic equations for sterile production for arbitrary $\tilde{\gamma }$ are obtained from the quantum master equation. Cosmological resonant sterile neutrino production is quantum Zeno suppressed relieving potential uncertainties associated with the QCD phase transition.

Motivated by the alpha-magnetic-spectrometer (AMS) project, we assume that after the big bang or inflation epoch, antimatter was repelled onto one brane which is separated from our brane where all the observational matter resides. It is suggested that $CP$ may be spontaneously broken, the two branes would correspond to ground states for matter and antimatter, respectively. Generally a complex scalar field which is responsible for the spontaneous $CP$ violation, exists in the space between the branes. The matter and antimatter on the two branes attract each other via gravitational force, meanwhile the scalar field causes a Casimir effect to result in a repulsive force against the gravitation. We find that the Casimir force is much stronger than the gravitational force, as long as the separation of the two branes is small. Thus at early epoch after the big bang, the two branes were closer and then have been separated by the Casimir repulsive force from each other. The trend will continue until the separation is sufficiently large and then the gravitational force observed in our four-space would obviously deviate from the Newton’s universal gravitational law. We suppose that there is a potential barrier at the brane boundary, which is similar to the surface tension for a water membrane. The barrier prevents the matter (antimatter) particles from entering the space between two branes and jump from one brane to another. However, by the quantum tunneling, a sizable antimatter flux may come to our brane and be observed by the AMS. In this work by considering two possible models, i.e. the naive flat space-time and Randall-Sundrum models, and using the observational data on the visible matter in our universe as inputs, we derive the antimatter flux which comes to our detector in the nonrelativistic approximation and make a rough numerical estimate of possible numbers of antihelium at AMS.

With sufficiently light up and down quarks the isovector ($a_0$) and isosinglet ($f_0$) scalar meson propagators are dominated at large distance by two-meson states. In the staggered-fermion formulation of lattice quantum chromodynamics, taste-symmetry breaking causes a proliferation of two-meson states that further complicates the analysis of these channels. Many of them are unphysical artifacts of the lattice approximation. They are expected to disappear in the continuum limit. The staggered-fermion fourth-root procedure has its purported counterpart in rooted staggered chiral perturbation theory ($\mathrm{rS}\chi \mathrm{PT}$). Fortunately, the rooted theory provides a strict framework that permits the analysis of scalar meson correlators in terms of only a small number of low-energy couplings. Thus the analysis of the point-to-point scalar meson correlators in this context gives a useful consistency check of the fourth-root procedure and its proposed chiral realization. Through numerical simulation we have measured correlators for both the $a_0$ and $f_0$ channels in the “Asqtad” improved staggered-fermion formulation in a lattice ensemble with lattice spacing $a=0.12\mathrm{fm}$. We analyze those correlators in the context of $\mathrm{rS}\chi \mathrm{PT}$ and obtain values of the low-energy chiral couplings that are reasonably consistent with previous determinations.

We find membrane configurations in ${\mathrm{AdS}}_4\times S^7$, which correspond to the continuous limit of the $SU(2)$ integrable spin chain, considered as a limit of the $SU(3)$ spin chain, arising in $\mathcal{N}=4$ SYM in four dimensions, dual to strings in ${\mathrm{AdS}}_5\times S^5$. We also discuss the relationship with the Neumann-Rosochatius integrable system at the level of Lagrangians, comparing the string and membrane cases.

We present the conformal windows of SU(N) supersymmetric and nonsupersymmetric gauge theories with vectorlike matter transforming according to higher irreducible representations of the gauge group. We determine the fraction of asymptotically free theories expected to develop an infrared fixed point and find that it does not depend on the specific choice of the representation. This result is exact in supersymmetric theories while it is an approximate one in the nonsupersymmetric case. The analysis allows us to size the unparticle world related to the existence of underlying gauge theories developing an infrared stable fixed point. We find that exactly 50% of the asymptotically free theories can develop an infrared fixed point while for the nonsupersymmetric theories it is circa 25%. When considering multiple representations, only for the nonsupersymmetric case, the conformal regions quickly dominate over the nonconformal ones. For four representations, 70% of the asymptotically free space is filled by the conformal region. According to our theoretical landscape survey the unparticle physics world occupies a sizable amount of the particle world, at least in theory space, and before mixing it (at the operator level) with the nonconformal one.