We study the distribution of color electric flux of the three-quark system in quenched and full QCD (with $N_f=2$ flavors of dynamical quarks) at zero and finite temperature. To reduce ultraviolet fluctuations, the calculations are done in the Abelian projected theory fixed to the maximally Abelian gauge. In the confined phase we find clear evidence for a $\mathrm{Y}$-shape flux tube surrounded and formed by the solenoidal monopole current, in accordance with the dual superconductor picture of confinement. In the deconfined, high temperature phase monopoles cease to condense, and the distribution of the color electric field becomes Coulomb-like.

We calculate the spectrum of the charm-beauty mesons using the relativized quark model. Using the wave functions from this model we compute the radiative widths of excited $c\overline{b}$ states. The hadronic transition rates between $c\overline{b}$ states are estimated using the Kuang-Yan approach and are combined with the radiative widths to give estimates of the relative branching ratios. These results are combined with production rates at the Tevatron and the LHC to suggest promising signals for excited $B_c$ states. Our results are compared with other models to gauge the reliability of the predictions and point out differences.

This work is devoted to the study of the nonperturbative contributions in nonleptonic hyperon decays. We show that the instanton-induced 't Hooft interaction can naturally explain the $\Delta I=1/2$ rule, by generating quark-diquark clustering inside octet baryons. We compute $P$-wave and $S$-wave amplitudes in the instanton liquid model, and find good agreement with experiment. We propose a model-independent procedure to test on the lattice if the leading quark-quark attraction in the $0^{+}$ antitriplet channel responsible for diquark structures in hadrons is originated by the interaction generated by quasiclassical fields or if it is predominantly due to other perturbative and/or confining forces.

In the framework of the type II seesaw mechanism we propose two simple but instructive ansätze for neutrino mixing and leptogenesis. In each ansatz, the effective Majorana neutrino mass matrix is composed of two parts—the part with ${\mathrm{Z}}_{\mathrm{2}}$ symmetry arises from the ordinary type I seesaw mechanism and the part with ${\mathrm{S}}_{\mathrm{3}}$ symmetry arises from an additional Higgs triplet vacuum expectation value. The two ansätze can simultaneously account for the current neutrino oscillation data and the cosmological baryon number asymmetry via leptogenesis.

The ultrahigh energy neutrino-nucleon cross sections are computed taking into account different phenomenological implementations of the nonlinear QCD dynamics. Based on the color dipole framework, the results for the saturation model supplemented by the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) evolution as well as for the Balitskii-Fadin-Kuraev-Lipatov (BFKL) formalism in the geometric scaling regime are presented. They are contrasted with recent calculations using next-to-leading order DGLAP and unified BFKL-DGLAP formalisms.

It is shown that extremely strong electric fields may be generated at the surface of strange quark matter in the color-flavor locked phase because of the surface effects. Some properties of strange stars made of this matter are briefly discussed.

We explore the possibility of obtaining de Sitter vacua in strongly coupled heterotic models by adding various corrections to the supergravity potential energy. We show that, in a generic compactification scenario, Fayet-Iliopoulos terms can generate a de Sitter vacuum. The cosmological constant in this vacuum can be fine tuned to be consistent with observation. We also study moduli potentials in nonsupersymmetric compactifications of $E_8\times E_8$ theory with anti five-branes and $E_8\times {\overline{E}}_8$ theory. We argue that they can be used to create a de Sitter vacuum only if some of the Kahler structure moduli are stabilized at values much less than the Calabi-Yau scale.

We find explicit probe D3-brane solutions in the infrared of the Maldacena-Nuñez background. The solutions describe deformed baryon vertices: $q$ external quarks are separated in spacetime from the remaining $N-q$. As the separation is taken to infinity we recover known solutions describing infinite confining strings in $\mathcal{N}=1$ gauge theory. We present results for the mass of finite confining strings as a function of length. We also find probe D2-brane solutions in a confining type IIA geometry, the reduction of a $G_2$ holonomy M theory background. The relation between these deformed baryons and confining strings is not as straightforward.

We extend a recently discovered, nonsingular 6-dimensional brane, solution to $D=4+n$ dimensions. As with the previous 6D solution the present solution provides a gravitational trapping mechanism for fields of spin 0, $\frac{1}{2}$, 1, and 2. There is an important distinction between two extra dimensions and $n$ extra dimensions that makes this more than a trivial extension. In contrast to gravity in $n>2$ dimensions, gravity in $n=2$ dimensions is conformally flat. The stress-energy tensor required by this solution has reasonable physically properties, and for $n=2$ and $n=3$ can be made to asymptotically go to zero as one moves away from the brane.

We present a formulation of $\mathcal{N}=(1,1)$ super Yang-Mills theory in $1+1$ dimensions at finite-temperature. The partition function is constructed by finding a numerical approximation to the entire spectrum. We solve numerically for the spectrum using supersymmetric discrete light-cone quantization (SDLCQ) in the large-$N_c$ approximation and calculate the density of states. We find that the density of states grows exponentially and the theory has a Hagedorn temperature, which we extract. We find that the Hagedorn temperature at infinite resolution is slightly less than one in units of $\sqrt{g^2{N}_{\mathrm{c}}/\pi }$. We use the density of states to also calculate a standard set of thermodynamic functions below the Hagedorn temperature. In this temperature range, we find that the thermodynamics is dominated by the massless states of the theory.

The gauge dependence of the complex fermion quasiparticle poles corresponding to soft collective excitations is studied in hot gauge theories at one-loop order and next-to-leading order in the high-temperature expansion, with a view towards going beyond the leading order hard thermal loops and resummations thereof. We find that for collective excitations of momenta $k\sim eT$ the dispersion relations are gauge independent, but the corresponding damping rates are gauge dependent. For $k\ll eT$ and in the $k\to 0$ limit, both the dispersion relations and the damping rates are found to be gauge dependent. The gauge dependence of the position of the complex quasiparticle poles signals the need for resummation. Possible cancellation of the leading gauge dependence at two-loop order in the case of QED is briefly discussed.

We consider static axially symmetric solutions of SU(2) Yang-Mills-Higgs theory. The simplest such solutions represent monopoles, multimonopoles and monopole-antimonopole pairs. In general such solutions are characterized by two integers, the winding number $m$ of their polar angle, and the winding number $n$ of their azimuthal angle. For solutions with $n=1$ and $n=2$, the Higgs field vanishes at $m$ isolated points along the symmetry axis, which are associated with the locations of $m$ monopoles and antimonopoles of charge $n$. These solutions represent chains of $m$ monopoles and antimonopoles in static equilibrium. For larger values of $n$, totally different configurations arise, where the Higgs field vanishes on one or more rings, centered around the symmetry axis. We discuss the properties of such monopole-antimonopole chains and vortex rings, in particular, their energies and magnetic dipole moments, and we study the influence of a finite Higgs self-coupling constant on these solutions.

We study the Brownian motion of a charged test particle coupled to electromagnetic vacuum fluctuations near a perfectly reflecting plane boundary. The presence of the boundary modifies the quantum fluctuations of the electric field, which in turn modifies the motion of the test particle. We calculate the resulting mean squared fluctuations in the velocity and position of the test particle. In the case of directions transverse to the boundary, the results are negative. This can be interpreted as reducing the quantum uncertainty which would otherwise be present.

We discuss space-time evolution of ultrarelativistic quantum dipole in QED. We show that the space-time evolution can be described, in a certain approximation, by means of a regularized wave function, whose parameters are determined by the process of the dipole creation by a local current. Using these wave functions, we derive the dipole expansion law that is found to coincide parametrically in the leading order with the one suggested by G. R. Farrar et al. (G. R. Farrar, H. Liu, L. Frankfurt and M. Strikman, Phys. Rev. Lett, Vol. 61, p. 686, 1988).

The late-time tail behavior of massive Dirac fields is investigated in the Schwarzschild black-hole geometry and the result is compared with that of the massive scalar fields. It is shown that in the intermediate late times there are three kinds of differences between the massive Dirac and scalar fields: (i) The asymptotic behavior of massive Dirac fields is dominated by a decaying tail without any oscillation, but the massive scalar field by a oscillatory inverse power-law decaying tail; (ii) the dumping exponent for the massive Dirac field depends not only on the multiple number of the wave mode but also on the mass of the Dirac field, while that for the massive scalar field depends on the multiple number only; and (iii) the decay of the massive Dirac field is slower than that of the massive scalar field.

We study the stability of new neutral and electrically charged four-dimensional black hole solutions of Einstein’s equations with a positive cosmological constant and conformally coupled scalar field [C. Martinez, R. Troncoso, and J. Zanelli, Phys. Rev. D 67, 024008 (2003).]. The neutral black holes are always unstable. The charged black holes are also shown analytically to be unstable for the vast majority of the parameter space of solutions, and we argue using numerical techniques that the configurations corresponding to the remainder of the parameter space are also unstable.

We analyze the creation of particles in two dimensions under the action of conformal transformations. We focus our attention on Mobius transformations and compare the usual approach, based on the Bogoliubov coefficients, with an alternative but equivalent viewpoint based on correlation functions. In the latter approach the absence of particle production under full Mobius transformations is manifest. Moreover, we give examples, using the moving-mirror analogy, to illustrate the close relation between the production of quanta and energy.

The low energy regime of cosmological BPS-brane configurations with a bulk scalar field is studied. We construct a systematic method to obtain five-dimensional solutions to the full system of equations governing the geometry and dynamics of the bulk. This is done for an arbitrary bulk scalar field potential and taking into account the presence of matter on the branes. The method, valid in the low energy regime, is a linear expansion of the system about the static vacuum solution. Additionally, we develop a four-dimensional effective theory describing the evolution of the system. At the lowest order in the expansion, the effective theory is a biscalar tensor theory of gravity. One of the main features of this theory is that the scalar fields can be stabilized naturally without the introduction of additional mechanisms, allowing satisfactory agreement between the model and current observational constraints. The special case of the Randall-Sundrum model is discussed.

It is unlikely that uniqueness theorem holds for stationary black holes in higher dimensional spacetimes. However, we will examine the possibility that the higher multipole moments classify vacuum solutions uniquely. Especially, we compute the potentials associated with rotational Killing vectors and look at the dependence on the total mass $M$ and angular momentum $J$. Consequently, there is a potential $\sigma$ which we cannot write down in terms of integer power of $M$ and $J$ explicitly. This may be regarded as an evidence for the uniqueness using multipole moments generated by $\sigma$.

A lower bound on the size of a Lorentzian wormhole can be obtained by semiclassically introducing the Planck cutoff on the magnitude of tidal forces (Horowitz-Ross constraint). Also, an upper bound is provided by the quantum field theoretic constraint in the form of the Ford-Roman Quantum Inequality for massless minimally coupled scalar fields. To date, however, exact static solutions belonging to this scalar field theory have not been worked out to verify these bounds. To fill this gap, we examine the wormhole features of two examples from the Einstein frame description of the vacuum low energy string theory in four dimensions which is the same as the minimally coupled scalar field theory. Analyses in this paper support the conclusion of Ford and Roman that wormholes in this theory can have sizes that are indeed only a few order of magnitudes larger than the Planck scale. It is shown that the two types of bounds are also compatible. In the process, we point out a “wormhole” analog of naked black holes.