Wrapped Magnetized Branes: Two Alternative Descriptions?

We discuss two inequivalent ways for describing magnetized D-branes wrapped N times on a torus T^2. The first one is based on a non-abelian gauge bundle U(N), while the second one is obtained by means of a Narain T-duality transformation acting on a theory with non-magnetized branes. We construct in both descriptions the boundary state and the open string vertices and show that they give rise to different string amplitudes. In particular, the description based on the gauge bundle has open string vertex operators with momentum dependent Chan-Paton factors.Comment: 60 pages, LaTe

The twisted open string partition function and Yukawa couplings

We use the operator formalism to derive the bosonic contribution to the twisted open string partition function in toroidal compactifications. This amplitude describes, for instance, the planar interaction between g+1 magnetized or intersecting D-branes. We write the result both in the closed and in the open string channel in terms of Prym differentials on the appropriate Riemann surface. Then we focus on the g=2 case for a 2-torus. By factorizing the twisted partition function in the open string channel we obtain an explicit expression for the 3-twist field correlator, which is the main ingredient in the computation of Yukawa couplings in D-brane phenomenological models. This provides an alternative method for computing these couplings that does not rely on the stress-energy tensor technique.Comment: 32 pages, 5 figures, Latex; v2: typos correcte

Spacetime Superalgebra in AdS_4 \times S^7 via Supermembrane Probe

The spacetime superalgebra via the supermembrane probe in the background of AdS_4 \times S^7 is discussed to the lowest order in the spinor coordinate \t. To obtain the correct spacetime superalgebras, all \t^2 order corrections for supervielbein and super 3-form gauge potential have to be included. The central extension of the superalgebra OSp(8|4) of the super isometries for AdS_4 \times S^7 is found.Comment: 8 pages, Latex, minor corrections, final version to appear in Phys. Rev.

Quantization of Superstrings in Ramond-Ramond Backgrounds

We present a perturbative study of Ramond-Ramond backgrounds in the NSR formalism. We show how to perform sigma-model computations and discuss in detail the structure of the BRST charge and picture-changing operators. Contact terms play a vital role in the analysis. We also give evidence for a two loop non-renormalization theorem for the background beta functions.Comment: 29 pages, 1 figure; uses LaTeX, epsf, hyperref packages; references adde

AdS and pp-wave D-particle superalgebras

We derive anticommutators of supercharges with a brane charge for a D-particle in AdS(2) x S(2) and pp-wave backgrounds. A coset GL(2|2)/(GL(1))^4 and its Penrose limit are used with the supermatrix-valued coordinates for the AdS and the pp-wave spaces respectively. The brane charges have position dependence, and can be absorbed into bosonic generators by shift of momenta which results in closure of the superalgebras.Comment: 15 page

Strings in an arbitrary constant magnetic field with arbitrary constant metric and stringy form factors

We quantize the open string in an arbitrary constant magnetic field with a non factorized metric on a torus. We then discuss carefully the vertexes which describe the emission of dipole open strings and closed strings in the non compact limit. Finally we compute various stringy form factors which in the compact case induces a Kaehler and complex structure dependence and suppression of some amplitudes with KK states.Comment: 45 page

Duality and Superconvergence Relation in Supersymmetric Gauge Theories

We investigate the phase structures of various N=1 supersymmetric gauge theories including even the exceptional gauge group from the viewpoint of superconvergence of the gauge field propagator. Especially we analyze in detail whether a new type of duality recently discovered by Oehme in $SU(N_c)$ gauge theory coupled to fundamental matter fields can be found in more general gauge theories with more general matter representations or not. The result is that in the cases of theories including matter fields in only the fundamental representation, Oehme's duality holds but otherwise it does not. In the former case, superconvergence relation might give good criterion to describe the interacting non-Abelian Coulomb phase without using some information from dual magnetic theory.Comment: 20 pages, 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

Nondegenerate Super-Anti-de Sitter Algebra and a Superstring Action

We construct an Anti-de Sitter(AdS) algebra in a nondegenerate superspace. Based on this algebra we construct a covariant kappa-symmetric superstring action, and we examine its dynamics: Although this action reduces to the usual Green-Schwarz superstring action in flat limit, the auxiliary fermionic coordinates of the nondegenerate superspace becomes dynamical in the AdS background.Comment: Latex, 12 pages, explanations added, version to be published in Phys. Rev.