The results of the recent unpolarized target experiments on the reaction ${\pi }^{-}\overrightarrow{p}{\pi }^0{\pi }^{0}n$ performed at KEK, BNL, IHEP, and CERN are analyzed in detail. In practice, the unpolarized data allow information on $\pi \pi$ scattering to be obtained under the assumption of the dominance of the one-pion exchange mechanism. In this way, for the $I=0\mathrm{}\pi \pi S$ wave phase shift ${\delta }_0^0$ and inelasticity ${\eta }_0^0$ a few sets of values are obtained up to about 1.64 GeV. These sets correspond to the ambiguous solutions found for the partial wave amplitudes. The difficulties emerging when using the physical solutions for the ${\pi }^0{\pi }^0$ S and D wave amplitudes extracted with partial wave analyses are discussed. Attention is drawn to the fact that, for the ${\pi }^0{\pi }^0$ invariant mass m above 1 GeV, the other solutions, in principle, are found to be preferred to the physical ones. To clarify the situation and further study the $f_0\mathrm{}\left(980\right)\mathrm{}$ resonance, thorough experimental investigations of the reaction ${\pi }^{-}\overrightarrow{p}{\pi }^0{\pi }^{0}n$ in the m region near the $K\overline{K}$ threshold are required.

Within the Wilson integral formalism, we discuss the structure of nonperturbative corrections to the quark form factor at large momentum transfer analyzing the infrared renormalon and instanton effects. We show that the nonperturbative effects determine the initial value for the perturbative evolution of the quark form factor and attribute their general structure to the renormalon ambiguities of the perturbative series. It is demonstrated that the instanton contributions result in the finite renormalization of the next-to-leading perturbative result and numerically are characterized by a small factor reflecting the diluteness of the QCD vacuum within the instanton liquid model.

We investigate the importance of final state interactions in weak nonleptonic hyperon decays within a relativistic chiral unitary approach based on coupled channels. The effective potentials for meson-baryon scattering are derived from a chiral effective Lagrangian and iterated in a Bethe-Salpeter equation, which generates the low-lying baryon resonances dynamically. The inclusion of final state interactions decreases the discrepancy between theory and experiment for both s and p waves. Our study indicates that contributions from higher-order terms of the weak effective Lagrangian may play an important role in these decays.

The models of large extra compact dimensions, as suggested by Arkani-Hamed, Dimopoulos, and Dvali, predict exciting phenomenological consequences with gravitational interactions becoming strong at the TeV scale. Such theories can be tested at the existing and future colliders. In this paper, we study the contribution of virtual Kaluza-Klein excitations (both spin-0 and 2) in the process $e^{+}{e}^{-}\to \mathrm{HHZ}$ and $e^{+}{e}^{-}\to \mathrm{HH}\gamma$ at a future linear collider (NLC). We find that the virtual exchange KK gravitons can modify the cross section $\sigma {(e}^{+}{e}^{-}\to HHZ)$ significantly from its standard model value and will allow the effective string scale to be probed up to 6.6 TeV. The second process is absent at the tree level in the standard model, and can therefore be used to put limits on the effective string scale of 7.4 TeV.

The deconfinement phase transition in SU(2) Yang-Mills theory is reexamined in the vortex picture. Defining the world sheets of the confining vortices by maximal center projection, the percolation properties of the vortex lines in the hypercube consisting of the time axis and two spatial axes are studied. Using the percolation cumulant, the temperature for the percolation transition is found to be in good agreement with the critical temperature of the thermal transition. The finite size scaling function for the cumulant is obtained. The critical index of the finite size scaling function is consistent with the index of the 3D Ising model.

Smooth-throat wormholes are treated as possessing quantum fluctuation energy with a scalar massive field as its source. The heat kernel coefficients of the Laplace operator are calculated in the background of the arbitrary-profile throat wormhole with the help of the zeta-function approach. Two specific profiles are considered. Some arguments are given that wormholes may exist. It serves as a solution of semiclassical Einstein equations in the range of specific values of the length, a certain radius of the wormhole’s throat, and a constant of nonminimal connection.

We present the first results for the masses of positive and negative parity excited baryons calculated in lattice QCD using an ${O(a}^2)$-improved gluon action and a fat-link irrelevant clover (FLIC) fermion action in which only the irrelevant operators are constructed with APE-smeared links. The results are in agreement with earlier calculations of $N^{*}$ resonances using improved actions and exhibit a clear mass splitting between the nucleon and its chiral partner. A correlation matrix analysis reveals two low-lying $J^P={\frac{1}{2}}^{-}$ states with a small mass splitting. The study of different $\Lambda$ interpolating fields suggests a similar splitting between the lowest two $\Lambda {\frac{1}{2}}^{-}$ octet states. However, the empirical mass suppression of the ${\Lambda }^{*}\mathrm{}\left(1405\right)\mathrm{}$ is not evident in these quenched QCD simulations, suggesting a potentially important role for the meson cloud of the ${\Lambda }^{*}\mathrm{}\left(1405\right)\mathrm{}$ and/or a need for more exotic interpolating fields.

We discuss simulations with different lattice Dirac operators for sea and valence quarks. A goal of such a “mixed” action approach is to probe deeper the chiral regime of QCD by enabling simulations with light valence quarks. This is achieved by using chiral fermions as valence quarks while computationally inexpensive fermions are used in the sea sector. Specifically, we consider Wilson sea quarks and Ginsparg-Wilson valence quarks. The local Symanzik action for this mixed theory is derived to $\mathcal{O}\mathrm{}\left(a\right),$ and the appropriate low energy chiral effective Lagrangian is constructed, including the leading $\mathcal{O}\mathrm{}\left(a\right)\mathrm{}$ contributions. Using this Lagrangian one can calculate expressions for physical observables and determine the Gasser-Leutwyler coefficients by fitting them to the lattice data.

Octet and decuplet baryon magnetic moments have been formulated within the chiral quark model $\left(\chi \mathrm{QM}\right)$ with configuration mixing incorporating the sea quark polarizations and their orbital angular momentum through a generalization of the Cheng-Li mechanism. When the parameters of the $\chi \mathrm{QM}$ without configuration mixing are fixed by incorporating the latest data pertaining to $ū-\overline{d}$ asymmetry (E866) and the spin polarization functions, in the case of octet magnetic moments the results not only show improvement over the nonrelativistic quark model results but also give a nonzero value for the right hand side of the Coleman-Glashow sum rule, usually zero in most of the models. In the case of decuplet magnetic moments, we obtain a good overlap for ${\Delta }^{++},$ ${\Omega }^{-},$ and the transition magnetic moment $\Delta N$ for which data are available. In the case of the octet, the predictions of the $\chi \mathrm{QM}$ with the generalized Cheng-Li mechanism show remarkable improvements in general when the effects of configuration mixing and “mass adjustments” due to confinement are included, specifically in the case of p, ${\Sigma }^{+},$ ${\Xi }^0,$ and the $\Sigma \Lambda$ transition magnetic moment and in the violation of the Coleman-Glashow sum rule an almost perfect agreement with data is obtained. When the above analysis is repeated with the earlier NMC data, a similar level of agreement is obtained; however, the results in the case of E866 look to be better. In this case, we incorporate in our analysis the gluon polarization $\Delta g,$ found phenomenologically through the relation $\Delta \Sigma {(Q}^2)=\Delta \Sigma -[3{\alpha }_s{(Q}^2)/2\mathrm{}\pi ]\Delta {g(Q}^2);$ not only do we obtain an improvement in the quark spin distribution functions and magnetic moments, but also the value of $\Delta g$ comes out in good agreement with certain recent measurements as well as theoretical estimates.

Taking as a starting point a Lorentz and CPT noninvariant Chern-Simons-like model defined in $1+3$ dimensions, we proceed to realize its dimensional reduction to $D=1+2.\mathrm{}$ One then obtains a new planar model, composed by the Maxwell-Chern-Simons (MCS) sector, a Klein-Gordon massless scalar field, and a coupling term that mixes the gauge field to the external vector $v^{\mu }.$ In spite of breaking Lorentz invariance in the particle frame, this model may preserve CPT symmetry for a single particular choice of $v^{\mu }.$ Analyzing the dispersion relations, one verifies that the reduced model exhibits stability, but the causality can be jeopardized by some modes. The unitarity of the gauge sector is assured without any restriction, while the scalar sector is unitary only in the spacelike case.

We discuss the modal properties of the r modes of relativistic superfluid neutron stars, taking account of the entrainment effects between superfluids. In this paper, the neutron stars are assumed to be filled with neutron and proton superfluids and the strength of the entrainment effects between the superfluids are represented by a single parameter $\eta .$ We find that the basic properties of the r modes in a relativistic superfluid star are very similar to those found for a Newtonian superfluid star. The r modes of a relativistic superfluid star are split into two families: ordinary fluid-like r modes ${(r}^o$ mode) and superfluid-like r modes ${(r}^s$ mode). The two superfluids counter-move for the $r^s$ modes, while they co-move for the $r^o$ modes. For the $r^o$ modes, the quantity $\kappa \equiv \sigma /\Omega +m$ is almost independent of the entrainment parameter $\eta ,$ where m and $\sigma$ are the azimuthal wave number and the oscillation frequency observed by an inertial observer at spatial infinity, respectively. For the $r^s$ modes, on the other hand, $\kappa$ almost linearly increases with increasing $\eta .$ It is also found that the radiation driven instability due to the $r^s$ modes is much weaker than that of the $r^o$ modes because the matter current associated with the axial parity perturbations almost completely vanishes.

Quintessence models leading to a constant equation of state are studied in hyperbolic universes. The general properties of the quintessence potentials $V\left(\phi \right)$ are discussed, and for some special cases also the exact analytic expressions for these potentials are derived. It is shown that the observed angular power spectrum of the cosmic microwave background is in excellent agreement with some of the quintessence models even in cases with negative curvature. It is emphasized that due to a ${(w}_{\phi },{\Omega }_{\phi },{\Omega }_{\mathrm{c}})$ degeneracy a universe with a negative spatial curvature cannot be excluded.

Rapid progress has been made in observations of the temperature anisotropies of the cosmic microwave background (CMB). These observations have enabled cosmologists to characterize the state of the universe at recombination, and observational efforts are now being directed towards obtaining the polarization map of the CMB. Here we draw an analogy between the CMB polarization map and nematic liquid crystals, pointing out that the two have similar defects. Making use of known results in the theory of defect formation we predict the statistical distribution of defects in the CMB polarization map and provide a novel tool for probing the CMB at large angular scales.

We study superstring theories on the Penrose limit of the enhançon geometry realized by $\mathrm{D}\mathrm{}(p+4\mathrm{})\mathrm{}$-branes wrapped on a $K3\mathrm{}$ surface. We first examine the null geodesics with a fixed radius in general brane backgrounds, which give solvable superstring theories with constant masses. In most cases, the superstring theories contain negative mass-squared. We clarify a condition that the world-sheet free fields have positive mass-squared. We then apply this condition to the enhançon geometry and find that the null geodesics with a fixed radius exist only for the $p=0\mathrm{}$ case. They define superstring theories with positive mass-squared. For the $p>\mathrm{}0\mathrm{}$ case, we show that there is no null geodesic with a fixed radius. We also discuss the decoupling limit which gives the dual geometry of super Yang-Mills theory with 8 supercharges. We discuss the $K3\mathrm{}$-volume dependence of the superstring spectrum.

We investigate some issues regarding quantum corrections for de Sitter branes in a bulk ${\mathrm{AdS}}_5$ spacetime. The one-loop effective action for a Majorana spinor field is evaluated and compared with the scalar field result. We also evaluate the cocycle function for various boundary conditions, finding that the quantum corrections naturally induce higher order curvature terms in the original action and, in general, it is not possible to eliminate the cocycle function by renormalization. In the one brane limit care must be taken on how one extracts physical results. The effective potential is found to be zero on the conformally related cylinder. However, using the actual metric, the contribution from the cocycle function is nonzero and must be included. Subtleties with any zero modes are also discussed.

In the framework of chiral perturbation theory we demonstrate the equivalence of the supersymmetric and the replica methods in the symmetry breaking classes of Dyson indices $\beta =1\mathrm{}$ and $\beta =4.\mathrm{}$ Schwinger-Dyson equations are used to derive a universal differential equation for the finite volume partition function in sectors of fixed topological charge, $\nu .$ All dependence on the symmetry breaking class enters through the Dyson index $\beta .$ We utilize this differential equation to obtain Virasoro constraints in the small mass expansion for all $\beta$ and in the large mass expansion for $\beta =2\mathrm{}$ with arbitrary $\nu .$ Using quenched chiral perturbation theory we calculate the first finite volume correction to the chiral condensate demonstrating how, for all $\beta ,$ there exists a region in which the two expansion schemes of quenched finite volume chiral perturbation theory overlap.

String theory gives rise to various mechanisms to generate primordial inflation, of which “brane inflation” is one of the most widely considered. In this scenario, inflation takes place while two branes are approaching each other, and the modulus field representing the separation between the branes plays the role of the inflaton field. We study the phase space of initial conditions which can lead to a sufficiently long period of cosmological inflation, and find that taking into account the possibility of nonvanishing initial momentum can significantly change the degree of fine-tuning of the required initial conditions.

We investigate the nature of ordinary cosmic vortices in some scalar-tensor extensions of gravity. We find solutions for which the dilaton field condenses inside the vortex core. These solutions can be interpreted as raising the degeneracy between the eigenvalues of the effective stress-energy tensor, namely, the energy per unit length U and the tension T, by picking a privileged spacelike or timelike coordinate direction; in the latter case, a phase frequency threshold occurs that is similar to what is found in ordinary neutral current-carrying cosmic strings. We find that the dilaton contribution for the equation of state, once averaged along the string worldsheet, vanishes, leading to an effective Nambu-Goto behavior of such a string network in cosmology, i.e.on very large scales. It is found also that on small scales, the energy per unit length and tension depend on the string internal coordinates in such a way as to permit the existence of centrifugally supported equilibrium configuration, also known as vortons, whose stability, depending on the very short distance (unknown) physics, can lead to catastrophic consequences on the evolution of the Universe.

The ekpyrotic and cyclic universe scenarios have revived the idea that the density perturbations apparent in today’s universe could have been generated in a “presingularity” epoch before the big bang. These scenarios provide explicit mechanisms whereby a scale invariant spectrum of adiabatic perturbations may be generated without the need for cosmic inflation, albeit in a phase preceding the hot big bang singularity. A key question they face is whether there exists a unique prescription for following perturbations through the bounce, an issue which is not yet definitively settled. The goal of this paper is more modest, namely, to study a bouncing universe model in which neither general relativity nor the weak energy condition is violated. We show that a perturbation which is a pure growing mode before the bounce does not match to a pure decaying mode perturbation after the bounce. Analytical estimates of when the comoving curvature perturbation varies around the bounce are given. It is found that in general it is necessary to evaluate the evolution of the perturbation through the bounce in detail rather than using matching conditions.

The differential rates and emissivities of neutrino pairs from an equilibrium plasma are calculated for the wide range of density and temperature encountered in astrophysical systems. New analytical expressions are derived for the differential emissivities which yield total emissivities in full agreement with those previously calculated. The photon and plasmon pair production and absorption kernels in the source term of the Boltzmann equation for neutrino transport are provided. The appropriate Legendre coefficients of these kernels, in forms suitable for multi-group flux-limited diffusion schemes are also computed.