arXiv subjects

Robert G. Leigh

Publications and source records attributed to Robert G. Leigh.

114 records · Page 7Linked to original sources

arXiv1997

D-Branes, Moduli and Supersymmetry

We study toroidal compactifications of Type II string theory with D-branes and nontrivial antisymmetric tensor moduli and show that turning on these fields modifies the supersymmetry projections imposed by D-branes. These modifications are seen to be necessary for the consistency of T-duality. We also show the existence of unusual BPS configurations of branes at angles that are supersymmetric because of conspiracies between moduli fields. Analysis of the problem from the point of view of the effective field theory of massless modes shows that the presence of a 2-form background must modify the realization of supersymmetry on the brane. In particular, the appropriate supersymmetry variation of the physical gaugino vanishes in any constant field strength background. These considerations are relevant for the $E_7$-symmetric counting of states of 4-dimensional black holes in Type II string theory compactified on $T^6$.

hep-th↗

arXiv1996

Accidental Symmetries and N=1 Duality in Supersymmetric Gauge Theory

We note that the accidental symmetries which are present in some examples of duality imply the existence of continuously infinite sets of theories with the same infrared behavior. These sets interpolate between theories of different flavors and colors; the change in color and flavor is compensated by interactions (often non-perturbative) induced by operators in the superpotential. As an example we study the behavior of SU(2) gauge theories with 2\nf doublets; these are dual to SU(\nf-2) gauge theories whose ultraviolet flavor symmetry is SU(\nf)xSU(\nf)xU(1) but whose flavor symmetry is SU(2\nf) in the infrared. The infrared SU(2\nf) flavor symmetry is implemented in the ultraviolet as a non-trivial transformation on the Lagrangian and matter content of the magnetic theory, involving (generally non-renormalizable) baryon operators and non-perturbative dynamics. We discuss various implications of this fact, including possible new chiral fixed points and interesting examples of dangerously irrelevant operators.

hep-th↗

arXiv1996

Branes Intersecting at Angles

We show that configurations of multiple D-branes related by SU(N) rotations will preserve unbroken supersymmetry. This includes cases in which two D-branes are related by a rotation of arbitrarily small angle, and we discuss some of the physics of this. In particular, we discuss a way of obtaining 4D chiral fermions on the intersection of D-branes. We also rephrase the condition for unbroken supersymmety as the condition that a `generalized holonomy group' associated with the brane configuration and manifold is reduced, and relate this condition (in Type IIA string theory) to a condition in eleven dimensions.

hep-th↗

arXiv1996

Anomalies, Dualities, and Topology of D=6 N=1 Superstring Vacua

We consider various aspects of compactifications of the Type I/heterotic $Spin(32)/\Z_2$ theory on K3. One family of such compactifications includes the standard embedding of the spin connection in the gauge group, and is on the same moduli space as the compactification of the heterotic $E_8\times E_8$ theory on K3 with instanton numbers (8,16). Another class, which includes an orbifold of the Type I theory recently constructed by Gimon and Polchinski and whose field theory limit involves some topological novelties, is on the moduli space of the heterotic $E_8\times E_8$ theory on K3 with instanton numbers (12,12). These connections between $Spin(32)/\Z_2$ and $E_8\times E_8$ models can be demonstrated by T duality, and permit a better understanding of non-perturbative gauge fields in the (12,12) model. In the transformation between $Spin(32)/\Z_2$ and $E_8\times E_8$ models, the strong/weak coupling duality of the (12,12) $E_8\times E_8$ model is mapped to T duality in the Type I theory. The gauge and gravitational anomalies in the Type I theory are canceled by an extension of the Green-Schwarz mechanism.

hep-th↗

arXiv1995

Supersymmetry, Finite Temperature and Gravitino Production in the Early Universe

We reconsider post-inflation gravitino production, in the context of hidden sector supergravity models. We discuss the possible role of supersymmetry breaking from finite temperature effects in enhancing the rate for gravitino production and argue that there is no such enhancement. Our conclusion is based on a simple decoupling argument, which is independent of temperature. We also characterize the properties of goldstino-like hydrodynamic fluctuations that arise in supersymmetric models at finite temperature. We show that they cannot lead to enhanced gravitino emission via infrared divergences. We comment on an analogy with axion emission from hadronic matter.

hep-ph↗

arXiv1995

Exactly Marginal Operators and Duality in Four Dimensional N=1 Supersymmetric Gauge Theory

We show that manifolds of fixed points, which are generated by exactly marginal operators, are common in N=1 supersymmetric gauge theory. We present a unified and simple prescription for identifying these operators, using tools similar to those employed in two-dimensional N=2 supersymmetry. In particular we rely on the work of Shifman and Vainshtein relating the $\bt$-function of the gauge coupling to the anomalous dimensions of the matter fields. Finite N=1 models, which have marginal operators at zero coupling, are easily identified using our approach. The method can also be employed to find manifolds of fixed points which do not include the free theory; these are seen in certain models with product gauge groups and in many non-renormalizable effective theories. For a number of our models, S-duality may have interesting implications. Using the fact that relevant perturbations often cause one manifold of fixed points to flow to another, we propose a specific mechanism through which the N=1 duality discovered by Seiberg could be associated with the duality of finite N=2 models.

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