First, the ideas introduced in the wormhole research field since the work of Morris and Thorne are reviewed, namely, the issues of energy conditions, wormhole construction, stability, time machines and astrophysical signatures. Then, spherically symmetric and static traversable Morris-Thorne wormholes in the presence of a generic cosmological constant $\Lambda$ are analyzed. A matching of an interior solution to the unique exterior vacuum solution is done using directly the Einstein equations. The structure as well as several physical properties and characteristics of traversable wormholes due to the effects of the cosmological term are studied. Interesting equations appear in the process of matching. For instance, one finds that for asymptotically flat and anti–de Sitter spacetimes the surface tangential pressure $\mathcal{P}$ of the thin shell, at the boundary of the interior and exterior solutions, is always strictly positive, whereas for de Sitter spacetime it can take either sign as one would expect, being negative (tension) for relatively high $\Lambda$ and high wormhole radius, positive for relatively high mass and small wormhole radius, and zero in between. Finally, some specific solutions with $\Lambda ,$ based on the Morris-Thorne solutions, are provided.

The spectrum of the Dirac Hamiltonian in the background of crossing vortices is studied. To exploit the index theorem, and in analogy with the lattice, the space-time manifold is chosen to be the four-torus $T^4.$ For the sake of simplicity we consider two idealized cases: infinitely fat and thin transversally intersecting vortices. The time-dependent spectrum of the Dirac Hamiltonian is calculated and in particular the influence of the vortex crossing on the quark spectrum is investigated. For the infinitely fat intersecting vortices it is found that zero modes of the four-dimensional Dirac operator can be expressed in terms of those eigenspinors of the Euclidean time-dependent Dirac Hamiltonian which cross zero energy. For thin intersecting vortices the time gradient of the spectral flow of the Dirac Hamiltonian is steepest at the time at which the vortices cross each other.

We consider combining two important methods for constructing quasiequilibrium initial data for binary black holes: the conformal thin-sandwich formalism and the puncture method. The former seeks to enforce stationarity in the conformal three-metric and the latter attempts to avoid internal boundaries, like minimal surfaces or apparent horizons. We show that these two methods make partially conflicting requirements on the boundary conditions that determine the time slices. In particular, it does not seem possible to construct slices that are quasistationary and that avoid physical singularities while simultaneously are connected by an everywhere positive lapse function, a condition which must be obtained if internal boundaries are to be avoided. Some relaxation of these conflicting requirements may yield a soluble system, but some of the advantages that were sought in combining these approaches will be lost.

We present a high statistics study of the light hadron spectrum and quark masses in QCD with two flavors of dynamical quarks. Numerical simulations are carried out using the plaquette gauge action and the O(a)-improved Wilson quark action at $\beta =5.2,$ where the lattice spacing is found to be $a=0.0887\mathrm{}\left(11\right)\mathrm{}\mathrm{fm}$ from the $\rho$ meson mass, on a ${20}^3\times 48$ lattice. At each of five sea quark masses corresponding to $m_{\mathrm{PS}}{/m}_{\mathrm{V}}\simeq 0.8–0.6,$ we generate 12 000 trajectories using a symmetrically preconditioned Hybrid Monte Carlo algorithm. Finite spatial volume effects are investigated employing ${12}^3\times 48,$ ${16}^3\times 48$ lattices. We also perform a set of simulations in quenched QCD with the same lattice actions at a similar lattice spacing to those for the full QCD runs. In the meson sector we find clear evidence of sea quark effects. The J parameter increases for lighter sea quark masses, and the full QCD meson masses are systematically closer to experiment than in quenched QCD. Careful finite-size studies are made to ascertain that these are not due to finite-size effects. Evidence of sea quark effects is less clear in the baryon sector due to larger finite-size effects. We also calculate light quark masses and find $m_{\mathrm{ud}}^{\overline{\mathrm{MS}}}\left(2\mathrm{}\mathrm{GeV}{)=3.223(}_{-0.069}^{+0.046\mathrm{}}\right)\mathrm{MeV}$ and $m_s^{\overline{\mathrm{MS}}}\left(2\mathrm{}\mathrm{GeV}{)=84.5(}_{-1.7}^{+12.0\mathrm{}}\right)\mathrm{MeV}$ which are about 20% smaller than in quenched QCD.

We discuss the implications of a possible quasinuclear DK bound state at 2.32 GeV. Evidence for such a state was recently reported in $D_s^{+}{\pi }^0$ by the BaBar Collaboration. We first note that a conventional quark model $c\overline{s}$ assignment is implausible, and then consider other options involving multiquark systems. An $I=0\mathrm{}$ $c\overline{s}n\mathrm{n̄}$ baryonium assignment is one possibility. We instead favor a DK meson molecule assignment, which can account for the mass and quantum numbers of this state. The higher-mass scalar $c\overline{s}$ state expected at 2.48 GeV is predicted to have a very large DK coupling, which would encourage formation of an $I=0\mathrm{}$ DK molecule. Isospin mixing is expected in hadron molecules, and a dominantly $I=0\mathrm{}$ DK state with some $I=1\mathrm{}$ admixture could explain both the narrow total width of the 2.32 GeV state as well as the observed decay to $D_s^{+}{\pi }^0.$ Additional measurements that can be used to test this and related scenarios are discussed.

We elaborate in more detail why the lattice calculation by Kolanovic et al., Phys. Rev. D 62, 025021 (2000), was done correctly and argue that increasing the number of sites is not expected to change our conclusions about the mass spectrum.

It is shown that the continuum limit of the spin 1/2 Heisenberg XYZ model is far from sufficient for the site number of 16. Therefore the energy spectrum of the XYZ model obtained by Kolanovic et al. has nothing to do with the massive Thirring model, but it shows only the spectrum of the finite size effects.

We discuss the relation between the dual formulations of type IIB supergravity emphasizing the differences between the Lorentz and Euclidean signature. We demonstrate how the SL(2,R) symmetry of the usual action is manifested in the solution of the equations of motion with Euclidean signature for the dual theory.

We discuss the computation of the leading corrections to D-brane solutions due to higher derivative terms in the corresponding low energy effective action. We develop several alternative methods for analyzing the problem. In particular, we derive an effective one-dimensional action from which the field equations for spherically symmetric two-block brane solutions can be derived, show how to obtain first order equations, and discuss a few other approaches. We integrate the equations for extremal branes and obtain the corrections in terms of integrals of the evaluation of the higher derivative terms on the lowest order solution. To obtain completely explicit results one would need to know all leading higher derivative corrections which at present are not available. One of the known higher derivative terms is the $R^4$ term, and we obtain the corrections to the D3-brane solution due to this term alone. We note, however, that (unknown at present) higher terms depending on $F_5$ are expected to modify our result. We analyze the thermodynamics of brane solutions when such quantum corrections are present. We find that the $R^4$ term induces a correction to the tension and the electric potential of the D3-brane but not to its charge, and the tension is still proportional to the electric potential times the charge. In the near-horizon limit the corrected solution becomes ${\mathrm{AdS}}_5\times {\mathrm{S}}^5$ with the same cosmological constant as the lowest order solution but a different value of the (constant) dilaton.

Recently, it was pointed out that quantum orders and the associated projective symmetry groups can produce and protect massless gauge bosons and massless fermions in local bosonic models. In this paper, we demonstrate that a state with such kinds of quantum order can be viewed as a condensed state of nets of strings. The emergent gauge bosons and fermions in local bosonic models can be regarded as a direct consequence of string-net condensation. The gauge bosons are fluctuations of large closed string nets. The ends of open strings are the charged particles of the corresponding gauge field. For certain types of strings, the ends of open strings can even be fermions. According to the string-net picture, fermions always carry gauge charges. This suggests the existence of a new discrete gauge field that couples to neutrinos and neutrons. We also discuss how chiral symmetry that protects massless Dirac fermions can emerge from the projective symmetry of quantum order.

In order to check the validity of the auxiliary field method in the Nambu–Jona-Lasinio model, the one-loop (= quantum) effects of auxiliary fields on the gap equation are considered with N-component fermion models in four and three dimensions. N is not assumed very large but is regarded as a loop expansion parameter. To overcome infrared divergences caused by the Nambu-Goldstone bosons, an intrinsic fermion mass is assumed. It is shown that the loop expansion can be justified by this intrinsic mass whose lower limit is also given. It is found that due to quantum effects, chiral symmetry breaking (χSB) is restored in $D=4\mathrm{}$ and $D=3\mathrm{}$ when the four-Fermi coupling is large. However, χSB is enhanced in a small coupling region in $D=3.\mathrm{}$

We show that in applications of variational theory to quantum field theory it is essential to account for the correct Wegner exponent $\omega$ governing the approach to the strong coupling, or scaling, limit. Otherwise the procedure does not converge at all or to the wrong limit. This casts doubt on all papers applying the so-called $\delta$ expansion to quantum field theory.

We discuss the treatment of squeezed states as excitations in the Euclidean vacuum of de Sitter space. A comparison with the treatment of these states as candidate no-particle states, or alpha vacua, shows important differences already in the free theory. At the interacting level alpha vacua are inconsistent, but squeezed state excitations seem perfectly acceptable. Indeed, matrix elements can be renormalized in the excited states using precisely the standard local counterterms of the Euclidean vacuum. Implications for inflationary scenarios in cosmology are discussed.

The generalized covariant entropy bound is the conjecture that for any null hypersurface which is generated by geodesics with nonpositive expansion starting from a spacelike 2-surface B and ending in a spacelike 2-surface $B^{\prime },$ the matter entropy on that hypersurface will not exceed one quarter of the difference in areas, in Planck units, of the two spacelike 2-surfaces. We show that this bound can be derived from the following phenomenological assumptions: (i) matter entropy can be described in terms of an entropy current $s_a;$ (ii) the gradient of the entropy current is bounded by the energy density, in the sense that $|k^a{k}^b{\nabla }_a{s}_b|<~2\pi T_{\mathrm{ab}}{k}^a{k}^b/ħ$ for any null vector $k^a$ where $T_{\mathrm{ab}}$ is the stress energy tensor; and (iii) the entropy current $s_a$ vanishes on the initial 2-surface B. We also show that the generalized Bekenstein bound—the conjecture that the entropy of a weakly gravitating isolated matter system will not exceed a constant times the product of its mass and its width—can be derived from our assumptions. Though we note that any local description of entropy has intrinsic limitations, we argue that our assumptions apply in a wide regime. We closely follow the framework of an earlier derivation, but our assumptions take a simpler form, making their validity more transparent in some examples.

We test approximate approaches to solving a neutrino transport problem that presents itself in the analysis of some accretion-disk models. Approximation No. 1 consists of replacing the full, angular-dependent, distribution function by a two-stream simulation, where the streams are respectively outwardly and inwardly directed, with angles $\cos \theta =\pm 1/\sqrt{3}$ to the vertical. In this approximation the full energy dependence of the distribution function is retained, as are the energy and temperature dependences of the scattering rates. Approximation No. 2, used in recent works on the subject, replaces the distribution function by an intensity function and the scattering rates by temperature-energy-averaged quantities. We compare the approximations to the results of solving the full Boltzmann equation. Under some interesting conditions, approximation No. 1 passes the test; approximation No. 2 does not. We utilize the results of our analysis to construct a toy model of a disk at a temperature and density such that relativistic particles are more abundant than nucleons, and dominate both the opacity and pressure. The nucleons will still provide most of the energy density. In the toy model we take the rate of heat generation (which drives the radiative transfer problem) to be proportional to the nucleon density. The model allows the simultaneous solution of the neutrino transport and hydrostatic equilibrium problems in a disk in which the nucleon density decreases approximately linearly as one moves from the median plane of the disk upwards, reaching zero on the upper boundary.

We compute the production rate of a lepton pair by static photons at finite temperature at two-loop order. We treat the infrared region of the gluon phase space carefully by using a hard thermal loop gluon propagator. The result is free of infrared and collinear divergences and exhibits an enhancement which produces a result of the order of $\sim e^2{g}^3$ instead of $\sim e^2{g}^4,$ as would be expected from ordinary perturbation theory.

We present a quenched lattice calculation of $f_V^{\perp }{/f}_V,$ the coupling of vector mesons to the tensor current normalized by the vector meson decay constant. The chirally improved lattice Dirac operator, which allows us to reach small quark masses, is used. We put emphasis on analyzing the quark mass dependence of $f_V^{\perp }{/f}_V$ and find only a rather weak dependence. Our results at the $\rho$ and $\phi$ masses agree well with QCD sum rule calculations and those from previous lattice studies.

We argue that high gluon density effects at small x are important for the calculation of ultrahigh energy neutrino-nucleon cross sections due to the phenomenon of geometric scaling. We calculate the cross section for $\nu \overrightarrow{N}\mu X,$ including high gluon density effects, using the all twist formalism of McLerran and Venugopalan and show that it can be related to the dipole nucleon cross section measured in deep inelastic scattering experiments. For neutrino energies of $E_{\nu }\sim {10}^{12}\mathrm{GeV},$ the geometric scaling region extends all the way up to $Q^2\sim M_W^2.$ We show that geometric scaling can lead to an enhancement of the neutrino-nucleon total cross section by an order of magnitude compared to the leading twist cross section and discuss the implications for neutrino observatories. At extremely high energies, gluon saturation effects suppress the neutrino-nucleon total cross section and lead to its unitarization.

Recently a version of Lorentz-conserving noncommutative field theory (NCFT) has been suggested. The underlying Lie algebra of the theory is the same as that of Doplicher, Fredenhagen, and Roberts. In Lorentz-conserving NCFT the matrix parameter ${\theta }^{\mu \nu }$ which characterizes the canonical NCFT’s is promoted to an operator ${\hat{\theta }}^{\mu \nu }$ that transforms as a Lorentz tensor. In this paper, we calculate the phenomenological consequences of the QED version of this theory by looking at various collider processes. In particular we calculate modifications to Møller scattering, Bhabha scattering, $e^{+}{e}^{-}\to {\mu }^{+}{\mu }^{-}$ and $e^{+}{e}^{-}\to \gamma \gamma .$ We obtain bounds on the noncommutativity scale from the existing experiments at CERN LEP and make predictions for what may be seen in future collider experiments.

We calculate the CP-averaged branching ratios and CP-violating asymmetries of two-body charmless hadronic decays of $B_s\to PP,PV$ with the QCD factorization approach (here P and V denote pseudoscalar and vector mesons, respectively), including contributions from the chirally enhanced power corrections and weak annihilations. Only several decay modes, such as $B_s\to K^{\left(*\right)}K,$ $K^{\left(*\right)\pm }{\pi }^{\mp },$ $K^{\pm }{\rho }^{\mp },$ ${\eta }^{(\prime )}{\eta }^{(\prime )},$ have large branching ratios, which may be observed in the near future. We also discuss $B_s\to K^{+}{K}^{-},$ $K^0{K}^0$ decays which could overconstrain the penguin-to-tree ratio $|P_{\pi \pi }{/T}_{\pi \pi }|$ of $\overrightarrow{B}{\pi }^{+}{\pi }^{-}$ decays and give a bound on the Cabibbo-Kobayashi-Maskawa angle $\gamma .$