We compute correlation functions of closed strings in Misner space, which is a big crunch/big bang universe. We develop a general method for correlators with twist fields, which are relevant for the investigation of the condensation of winding tachyons. We propose to compute the correlation functions by performing an analytic continuation of the results in the $\mathbb{C}/{\mathbb{Z}}_N$ Euclidean orbifold. In particular, we obtain a finite result for a general four point function of twist fields, which might be important for the interpretation as the quartic term of the tachyon potential. Three point functions are read off through the factorization.

We study the general deformed conformal-Poincaré (Galilean) symmetries consistent with relativistic (nonrelativistic) canonical noncommutative spaces. In either case we obtain deformed generators, containing arbitrary free parameters, which close to yield new algebraic structures. We show that a particular choice of these parameters reproduces the undeformed algebra. The modified coproduct rules and the associated Hopf algebra are also obtained. Finally, we show that for the choice of parameters leading to the undeformed algebra, the deformations are represented by twist functions.

The averaging problem in cosmology is of fundamental importance. When applied to study cosmological evolution, the theory of macroscopic gravity (MG) can be regarded as a long-distance modification of general relativity. In the MG approach to the averaging problem in cosmology, the Einstein field equations on cosmological scales are modified by appropriate gravitational correlation terms. We study the averaging problem within the class of spherically symmetric cosmological models. That is, we shall take the microscopic equations and effect the averaging procedure to determine the precise form of the correlation tensor in this case. In particular, by working in volume-preserving coordinates, we calculate the form of the correlation tensor under some reasonable assumptions on the form for the inhomogeneous gravitational field and matter distribution. We find that the correlation tensor in a Friedmann-Lemaître-Robertson-Walker (FLRW) background must be of the form of a spatial curvature. Inhomogeneities and spatial averaging, through this spatial curvature correction term, can have a very significant dynamical effect on the dynamics of the Universe and cosmological observations; in particular, we discuss whether spatial averaging might lead to a more conservative explanation of the observed acceleration of the Universe (without the introduction of exotic dark matter fields). We also find that the correlation tensor for a non-FLRW background can be interpreted as the sum of a spatial curvature and an anisotropic fluid. This may lead to interesting effects of averaging on astrophysical scales. We also discuss the results of averaging an inhomogeneous Lemaître-Tolman-Bondi solution as well as calculations of linear perturbations (that is, the backreaction) in an FLRW background, which support the main conclusions of the analysis.

The relativistic five-quark equations are found in the framework of the dispersion relation technique. The five-quark amplitudes for the low-lying exotic baryons including the $u$, $d$ quarks are calculated. The poles of the five-quark amplitudes determine the masses and the widths of $uuuu\overline{d}$ and $dddd\overline{u}$ states (isospin $I=5/2$). The mass spectrum of the $E^{+++}$ exotic baryons with $J^P=\frac{1^{+}}{2}$, $\frac{3^{+}}{2}$, $\frac{5^{+}}{2}$ is calculated.

The interacting instanton liquid model (IILM) is used to explore the role of instanton-induced dynamics in hadron structure. To support the validity of this model in the chiral regime, the quark mass dependencies of several properties are shown to agree with chiral perturbation theory, including the density of eigenmodes of the Dirac operator and the mass of the pion. A quark mass $m^{*}=80\mathrm{MeV}$ emerging naturally from the model is shown to specify the mass scale above which the fermion determinant is suppressed, the zero modes become subdominant, and the density of quasizero modes become independent of the quark mass.

We present a measurement of the branching fraction of invisible ${\rm Y}(1S)$ decays, using $1.2{\mathrm{fb}}^{-1}$ of data collected at the ${\rm Y}(2S)$ resonance with the CLEO III detector at CESR. After subtracting expected backgrounds from events that pass selection criteria for invisible ${\rm Y}(1S)$ decay in ${\rm Y}(2S)\to {\pi }^{+}{\pi }^{-}{\rm Y}(1S)$, we deduce a 90% C.L. upper limit of $\mathcal{B}[{\rm Y}(1S)\to \mathrm{\text{invisible}}]<0.39\%$.

We study a family of classical string solutions with large spins on ${\mathbb{R}}_{\mathrm{t}}\times {\mathrm{S}}^3$ subspace of ${\mathrm{AdS}}_5\times {\mathrm{S}}^5$ background, which are related to Complex sine-Gordon solitons via Pohlmeyer’s reduction. The equations of motion for the classical strings are cast into Lamé equations and Complex sine-Gordon equations. We solve them under periodic boundary conditions, and obtain analytic profiles for the closed strings. They interpolate two kinds of known rigid configurations with two spins: on one hand, they reduce to folded or circular spinning/rotating strings in the limit where a soliton velocity goes to zero, while on the other hand, the dyonic giant magnons are reproduced in the limit where the period of a kink-array goes to infinity.

We investigate lattice simulations of scalar and non-Abelian gauge fields in Minkowski space-time. For $SU(2)$ gauge-theory expectation values of link variables in $3+1$ dimensions are constructed by a stochastic process in an additional (5th) “Langevin-time.” A sufficiently small Langevin step size and the use of a tilted real-time contour leads to converging results in general. All fixed point solutions are shown to fulfil the infinite hierarchy of Dyson-Schwinger identities, however, they are not unique without further constraints. For the non-Abelian gauge theory the thermal equilibrium fixed point is only approached at intermediate Langevin-times. It becomes more stable if the complex time path is deformed towards Euclidean space-time. We analyze this behavior further using the real-time evolution of a quantum anharmonic oscillator, which is alternatively solved by diagonalizing its Hamiltonian. Without further optimization stochastic quantization can give accurate descriptions if the real-time extent of the lattice is small on the scale of the inverse temperature.

Scalar form factor of the nucleon is calculated in the framework of light-cone QCD sum rules, using the most general form of the baryon current. Using the result on scalar form factor of the nucleon, the nucleon-scalar $\sigma$ and $a_0$ meson coupling constants are estimated. Our results on these couplings are in good agreement with the prediction of the external-field QCD sum rules method.

We consider the classical equations of the Einstein-Yang-Mills model in five space-time dimensions and in the presence of a cosmological constant. We assume that the fields do not depend on the extra dimension and that they are spherically symmetric with respect to the three standard space dimensions. The equations are then transformed into a set of ordinary differential equations that we solve numerically. We construct new types of regular (resp. black holes) solutions which, close to the origin (resp. the event horizon) resemble the 4-dimensional gravitating monopole (resp. non-Abelian black hole) but exhibit an unexpected asymptotic behavior.

The interaction of a Reissner-Nordström black hole and a charged massive particle is studied in the framework of perturbation theory. The particle backreaction is taken into account, studying the effect of general static perturbations of the hole following the approach of Zerilli. The solutions of the combined Einstein-Maxwell equations for both perturbed gravitational and electromagnetic fields to first order of the perturbation are exactly reconstructed by summing all multipoles, and are given explicit closed form expressions. The existence of a singularity-free solution of the Einstein-Maxwell system requires that the charge-to-mass ratios of the black hole and of the particle satisfy an equilibrium condition which is in general dependent on the separation between the two bodies. If the black hole is undercritically charged (i.e. its charge-to-mass ratio is less than one), the particle must be overcritically charged, in the sense that the particle must have a charge-to-mass ratio greater than one. If the charge-to-mass ratios of the black hole and of the particle are both equal to one (so that they are both critically charged, or ‘‘extreme”), the equilibrium can exist for any separation distance, and the solution we find coincides with the linearization in the present context of the well-known Majumdar-Papapetrou solution for two extreme Reissner-Nordström black holes. In addition to these singularity-free solutions, we also analyze the corresponding solution for the problem of a massive particle at rest near a Schwarzschild black hole, exhibiting a strut singularity on the axis between the two bodies. The relations between our perturbative solutions and the corresponding exact two-body solutions belonging to the Weyl class are also discussed.

Starting from the free Polyakov action of an open 2-brane, we obtain the solutions to the Euler-Lagrange equation. By relating the normal modes to the raising and lowering operators and defining the vacuum state, we achieve the spectrum of the open 2-brane at different levels. Interestingly, there are two kinds of tachyon states appearing as scalar states and vector states, respectively. Besides, the graviton fields, Kalb-Ramond fields, dilaton, and photon states appear at the same level in the open 2-brane model.

We study the symmetry breaking phenomenon in the standard model during the electroweak phase transition in the presence of a constant hypermagnetic field. We compute the finite temperature effective potential up to the contribution of ring diagrams in the weak field, high temperature limit and show that under these conditions, the phase transition becomes stronger first order.

Minimal universal extra dimensions (mUED) is often thought to predict that the lightest Kaluza-Klein particle (LKP) is the Kaluza-Klein gauge boson $B^1$, leading to conventional missing energy signals at colliders and weakly interacting massive particle (WIMP) dark matter. In fact, the implications of mUED are far richer: the $B^1$, charged Higgs boson $H^{\pm 1}$, and graviton $G^1$ are all possible LKPs, leading to many different phases with distinct signatures. Considering the complete phase diagram, we find predictions for charged or neutral particles with decay lengths of microns to tens of meters; WIMP, superWIMP, or charged relic particles; metastable particles with lifetimes of the order of or in excess of the age of the Universe; and scenarios combining two or more of these phenomena. In the cosmologically preferred region, the Higgs boson mass is between 180 and 245 GeV, the LKP mass is between 810 and 1400 GeV, and the maximal splitting between first Kaluza-Klein modes is less than 320 GeV. This region predicts a variety of exotic collider signals, such as slow charged particles, displaced vertices, tracks with nonvanishing impact parameters, track kinks, and even vanishing charged tracks, all of which provide early discovery possibilities at the Large Hadron Collider.

We study elastic pion-pion scattering in global linear moose models and apply the results to a variety of Higgsless models in flat and anti-de Sitter (AdS) space using the equivalence theorem. In order to connect the global moose to Higgsless models, we first introduce a block-spin transformation which corresponds, in the continuum, to the freedom to perform coordinate transformations in the Higgsless model. We show that it is possible to make an “$f$-flat” deconstruction in which all of the $f$-constants $f_j$ of the linear moose model are identical; the phenomenologically relevant $f$-flat models are those in which the coupling constants of the groups at either end of the moose are small—corresponding to the global linear moose. In studying pion-pion scattering, we derive various sum rules, including one analogous to the Kawarabayashi-Suzuki-Riazuddin-Fayyazuddin (KSRF) relation, and use them in evaluating the low-energy and high-energy forms of the leading elastic partial-wave scattering amplitudes. We obtain elastic unitarity bounds as a function of the mass of the lightest $KK$ mode and discuss their physical significance.

In supersymmetric models where the magnitude of the GUT scale gaugino mass parameter $M_3$ is suppressed relative to $M_1$ and $M_2$, the lightest neutralino can be a mixed higgsino-bino state with a thermal relic abundance in agreement with the WMAP central value for ${\Omega }_{\mathrm{CDM}}{h}^2$ and consistent with all other phenomenological constraints. In these models, the gluino can be as light as 200 GeV without conflicting with the LEP2 bounds on the chargino mass. Thus, gluino pair production can be accessible at the Fermilab Tevatron at high rates. In this framework, gluinos decay radiatively with a large branching fraction to a gluon plus a neutralino. We find that experiments at the Fermilab Tevatron, with $5{\mathrm{fb}}^{-1}$ of integrated luminosity, will be sensitive to $\tilde{g}\tilde{g}$ production in the $m_{\tilde{g}}\sim 200–350\mathrm{GeV}$ range via the $\mathrm{\text{multi-jet}}+E_T^{\mathrm{miss}}$ and $\mathrm{\text{multi-jet}}+{\ell }^{+}{\ell }^{-}+E_T^{\mathrm{miss}}$ channels at the $5\sigma$ level, while trilepton signatures are expected to be below this level of detectability. Dilepton mass edges from both ${\tilde{Z}}_2$ and ${\tilde{Z}}_3$ decays may be measurable in the $\mathrm{\text{dilepton}}+\mathrm{\text{multi-jet}}+E_T^{\mathrm{miss}}$ channel.

An updated version of the PNJL model is used to study the thermodynamics of $N_f=2$ quark flavors interacting through chiral four-point couplings and propagating in a homogeneous Polyakov loop background. Previous PNJL calculations are extended by introducing explicit diquark degrees of freedom and an improved effective potential for the Polyakov loop field. The mean field equations are treated under the aspect of accommodating group theoretical constraints and issues arising from the fermion sign problem. The input is fixed exclusively by selected pure-gauge lattice QCD results and by pion properties in vacuum. The resulting $(T,\mu )$ phase diagram is studied with special emphasis on the critical point, its dependence on the quark mass and on Polyakov loop dynamics. We present successful comparisons with lattice QCD thermodynamics expanded to finite chemical potential $\mu$.

We calculate contributions to $B_s\mathrm{\text{−}}{\overline{B}}_s$ mixing through tree-level sneutrino exchange in the framework of the minimal supersymmetric standard model with $R$-parity violation, including the next-to-leading-order QCD corrections. We compare our results with the updated bounds on the $B_s\mathrm{\text{−}}{\overline{B}}_s$ mass difference reported by CDF collaborations and present new constraints on the relevant combinations of parameters of the minimal supersymmetric standard model with $R$-parity violation. Our results show that upper bound on the relevant combination of couplings of $B_s\mathrm{\text{−}}{\overline{B}}_s$ mixing is of the order ${10}^{-9}$. We also calculate the $B_d^0\mathrm{\text{−}}{\overline{B}}_d^0$ and $K^0\mathrm{\text{−}}{\overline{K}}^0$ mass differences and show that the upper bounds on the relevant combinations of couplings are 2 and 4 orders of magnitude stronger than ones reported in the literatures, respectively. We also discuss the case of complex couplings and show that how the relevant combinations of couplings are constrained by the updated experiment data of $B_s\mathrm{\text{−}}{\overline{B}}_s$, $B_d\mathrm{\text{−}}{\overline{B}}_d$ mixing and time-dependent $CP$ asymmetry $S_{J/\psi K_s}$, and future possible observations of $S_{J/\psi \varphi }$ at the Large Hadron Collider beauty experiment (LHCb), respectively.

A search for a manifestly exotic $S=-2$ baryon state decaying to ${\mathit{\Xi }}^{-}{\pi }^{-}$, and its neutral partner decaying to ${\mathit{\Xi }}^{-}{\pi }^{+}$, has been performed using $220{\mathrm{pb}}^{-1}$ of $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ collected by the Collider Detector at Fermilab. The ${\mathit{\Xi }}^{-}$ trajectories were measured in a silicon tracker before their decay, resulting in a sample with low background and excellent position resolution. No evidence was found for $S=-2$ pentaquark candidates in the invariant mass range of $1600–2100\mathrm{MeV}/c^2$. Upper limits on the product of pentaquark production cross section times its branching fraction to ${\mathit{\Xi }}^{-}{\pi }^{+,-}$, relative to the cross section of the well-established $\mathit{\Xi }(1530)$ resonance, are presented for neutral and doubly negative candidates with $p_T>2\mathrm{GeV}/c$ and $|y|<1$ as a function of pentaquark mass. At $1862\mathrm{MeV}/c^2$, these upper limits for neutral and doubly negative final states were found to be 3.2% and 1.7% at the 90% confidence level, respectively.