Decay Modes of Intersecting Fluxbranes

Just as the single fluxbrane is quantum mechanically unstable to the nucleation of a locally charged spherical brane, so intersecting fluxbranes are unstable to various decay modes. Each individual element of the intersection can decay via the nucleation of a spherical brane, but uncharged spheres can also be nucleated in the region of intersection. For special values of the fluxes, however, intersecting fluxbranes are supersymmetric, and so are expected to be stable. We explicitly consider the instanton describing the decay modes of the two--element intersection (an F5-brane in the string theory context), and show that in dimensions greater than four the action for the decay mode of the supersymmetric intersection diverges. This observation allows us to show that stable intersecting fluxbranes should also exist in type 0A string theory.Comment: 19 pages, 6 figures. References adde

Entropy in the RST Model

The RST Model is given boundary term and Z-field so that it is well-posed and local. The Euclidean method is described for general theory and used to calculate the RST intrinsic entropy. The evolution of this entropy for the shockwave solutions is found and obeys a second law.Comment: 10 pages, minor revisions, published version in Late

New twist field couplings from the partition function for multiply wrapped D-branes

We consider toroidal compactifications of bosonic string theory with particular regard to the phases (cocycles) necessary for a consistent definition of the vertex operators, the boundary states and the T-duality rules. We use these ingredients to compute the planar multi-loop partition function describing the interaction among magnetized or intersecting D-branes, also in presence of open string moduli. It turns out that unitarity in the open string channel crucially depends on the presence of the cocycles. We then focus on the 2-loop case and study the degeneration limit where this partition function is directly related to the tree-level 3-point correlators between twist fields. These correlators represent the main ingredient in the computation of Yukawa couplings and other terms in the effective action for D-brane phenomenological models. By factorizing the 2-loop partition function we are able to compute the 3-point couplings for abelian twist fields on generic non-factorized tori, thus generalizing previous expressions valid for the 2-torus.Comment: 36 pages, 1 figure; v2: typos corrected, proof in the Appendix improve

Two-dimensional quantum-corrected black hole in a finite size cavity

We consider the gravitation-dilaton theory (not necessarily exactly solvable), whose potentials represent a generic linear combination of an exponential and linear functions of the dilaton. A black hole, arising in such theories, is supposed to be enclosed in a cavity, where it attains thermal equilibrium, whereas outside the cavity the field is in the Boulware state. We calculate quantum corrections to the Hawking temperature $T_{H}$, with the contribution from the boundary taken into account. Vacuum polarization outside the shell tend to cool the system. We find that, for the shell to be in the thermal equilibrium, it cannot be placed too close to the horizon. The quantum corrections to the mass due to vacuum polarization vanish in spite of non-zero quantum stresses. We discuss also the canonical boundary conditions and show that accounting for the finiteness of the system plays a crucial role in some theories (e.g., CGHS), where it enables to define the stable canonical ensemble, whereas consideration in an infinite space would predict instability.Comment: 21 pages. In v.2 misprints corrected. To appear in Phys. Rev.

A New Cosmological Scenario in String Theory

We consider new cosmological solutions with a collapsing, an intermediate and an expanding phase. The boundary between the expanding (collapsing) phase and the intermediate phase is seen by comoving observers as a cosmological past (future) horizon. The solutions are naturally embedded in string and M-theory. In the particular case of a two-dimensional cosmology, space-time is flat with an identification under boost and translation transformations. We consider the corresponding string theory orbifold and calculate the modular invariant one-loop partition function. In this case there is a strong parallel with the BTZ black hole. The higher dimensional cosmologies have a time-like curvature singularity in the intermediate region. In some cases the string coupling can be made small throughout all of space-time but string corrections become important at the singularity. This happens where string winding modes become light which could resolve the singularity. The new proposed space-time casual structure could have implications for cosmology, independently of string theory.Comment: 28 pages, 3 figures; v2: Added new subsection relating two-dimensional model to BTZ black hole, typos corrected and references added; v3: minor corrections, PRD versio

Glueballs of Super Yang-Mills from Wrapped Branes

In this paper we study qualitative features of glueballs in N=1 SYM for models of wrapped branes in IIA and IIB backgrounds. The scalar mode, 0++ is found to be a mixture of the dilaton and the internal part of the metric. We carry out the numerical study of the IIB background. The potential found exhibits a mass gap and produces a discrete spectrum without any cut-off. We propose a regularization procedure needed to make these states normalizable.Comment: 22 pages plus a appendixes, 2 figure

On unquenched N=2 holographic flavor

The addition of fundamental degrees of freedom to a theory which is dual (at low energies) to N=2 SYM in 1+3 dimensions is studied. The gauge theory lives on a stack of Nc D5 branes wrapping an S^2 with the appropriate twist, while the fundamental hypermultiplets are introduced by adding a different set of Nf D5-branes. In a simple case, a system of first order equations taking into account the backreaction of the flavor branes is derived (Nf/Nc is kept of order 1). From it, the modification of the holomorphic coupling is computed explicitly. Mesonic excitations are also discussed.Comment: 25 pages, 4 figure

N=1* in 5 dimensions: Dijkgraaf-Vafa meets Polchinski-Strassler

One of the powerful techniques to analyze the 5 dimensional Super Yang Mills theory with a massive hypermultiplet (N=1*) is provided by the AdS/CFT correspondence. It predicts that, for certain special values of the hypermultiplet mass, this theory develops nonperturbative branches of the moduli space as well as new light degrees of freedom. We use the higher dimensional generalization of the matrix model/gauge theory correspondence and recover all the prediction of the supergravity analysis. We construct the map between the four dimensional holomorphic superpotential and the five dimensional action and explicitly show that the superpotential is flat along the nonperturbative branches. This is the first instance in which the Dijkgraaf-Vafa method is used to analyze intrinsically higher dimensional phenomena.Comment: 28 pages, Late

Rotating and Orbiting Strings in the Near-Horizon Brane Backgrounds

Using the Schwarzschild-type coordinates in stead of the global ones we reconstruct the classical rotating closed string solutions in the AdS*5 x S*5 backgrounds. They are explicitly described by the Jacobi elliptic and trigonometrical functions of worldsheet coordinates. We study the orbiting closed string configurations in the near-horizon geometries of Dp, NS1 and NS5 branes, and derive the energy and spin of them, whose relation takes a simple form for short strings. Specially in the D5 and NS5 backgrounds we have a linear relation that the energy of the point-like string is proportional to the spin, which is associated with the spectrum of strings in the pp-wave geometries obtained by taking a special Penrose limit on the D5 and NS5 backgrounds.Comment: 15 pages, LaTeX, no figure

Strings in Gravimagnetic Fields

We provide a complete solution of closed strings propagating in Nappi-Witten space. Based on the analysis of geodesics we construct the coherent wavefunctions which approximate as closely as possible the classical trajectories. We then present a new free field realization of the current algebra using the gamma, beta ghost system. Finally we construct the quantum vertex operators, for the tachyon, by representing the wavefunctions in terms of the free fields. This allows us to compute the three- and four-point amplitudes, and propose the general result for N-point tachyon scattering amplitude.Comment: final version, 29 pages + 4 app