Publications (3)0 Total impact
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ABSTRACT: In particle physics model building discrete symmetries are often invoked to
forbid unwanted or dangerous couplings. A classical example is the R-parity of
the MSSM, which guarantees the absence of dimension four baryon- and
lepton-number violating operators. Although phenomenologically useful, these
discrete symmetries are, in the context of field theory, poorly motivated at a
more fundamental level. Moreover, discrete {\em global} symmetries are expected
to be violated in consistent couplings to quantum gravity, while their {\em
gauged} versions are expected to actually exist. In this paper we study
discrete gauge symmetries in brane models in string theory, and argue that they
are fairly generic in this framework. In particular we study the appearance of
discrete gauge symmetries in (MS)SM brane constructions in string theory, and
show that a few discrete ${Z_N}$ gauge symmetries, including R-parity and {\it
baryon triality}, appear naturally as remnants of continuous U(1) gauge
symmetries with St\"uckelberg $N(B\wedge F)$ couplings. Interestingly, they
correspond to the simplest anomaly-free discrete symmetries of the MSSM as
classified in the early 90's. We provide a number of examples based on type IIA
intersecting brane constructions with a (MS)SM spectrum. We also study the
appearance of discrete generalizations of R-parity in unified SU(5) type IIA
orientifolds and local F-theory SU(5) GUTs.
06/2011;
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ABSTRACT: We study non-perturbative D(-1)-instanton corrections to quartic gauge and curvature couplings in 8d type IIB orientifolds, in terms of a one-loop computation of BPS D0-branes in T-dual type I' models. The complete perturbative and non-perturbative results are determined by the BPS multiplicities of perturbative open strings and D0-brane bound states in the 9d type I' theory. Its modular properties admit a geometric interpretation by lifting to Horava-Witten theory. We use the type I' viewpoint to motivate a proper interpretation of 8d and 4d polyinstanton effects, consistent with heterotic - type II orientifold duality. Comment: 37 pages, 2 figures, clarifications and references added
01/2010;
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ABSTRACT: We argue that the Gopakumar-Vafa interpretation of the topological string partition function can be used to compute and resum certain non-perturbative brane instanton effects of type II CY compactifications. In particular the topological string A-model encodes the non-perturbative corrections to the hypermultiplet moduli space metric from general D1/D(-1)-brane instantons in 4d N=2 IIB models. We also discuss the reduction to 4d N=1 by fluxes and/or orientifolds and/or D-branes, and the prospects to resum brane instanton contributions to non-perturbative superpotentials. We argue that the connection between non-perturbative effects and the topological string underlies the continuity of non-perturbative effects across lines of BPS stability. We also confirm this statement in mirror B-model matrix model examples, relating matrix model instantons to non-perturbative D-brane instantons. The computation of non-perturbative effects from the topological string requires a 3d circle compactification and T-duality, relating effects from particles and instantons, reminiscent of that involved in the physical derivation of the Kontsevich-Soibelmann wall-crossing formula. Comment: 44 pages, 5 figures. Major revisions, new results added, previous results unchanged, refs added
04/2009;
