Browsing by Author "Sharpe, E"

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    D-branes and Spinc structures
    (Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 1999-12-01) Sharpe, E; Bryant, RL
    It was recently pointed out by E. Witten that for a D-brane to consistently wrap a submanifold of some manifold, the normal bundle must admit a Spinc structure. We examine this constraint in the case of type II string compactifications with vanishing cosmological constant, and argue that in all such cases, the normal bundle to a supersymmetric cycle is automatically Spinc. © 1999 Published by Elsevier Science B.V. All rights reserved.
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    Elusive Worldsheet Instantons in Heterotic String Compactifications
    (STRING-MATH 2011, 2012-01-01) Aspinwall, Paul S; Plesser, M Ronen
    We compute the spectrum of massless gauge singlets in some heterotic string compactifications using Landau-Ginzburg, orbifold and non-linear sigma-model methods. This probes the worldsheet instanton corrections to the quadratic terms in the spacetime superpotential. Previous results predict that some of these states remain massless when instanton effects are included. We find vanishing masses in many cases not covered by these predictions. However, we discover that in the case of the Z-manifold the corrections do not vanish. Despite this, in all the examples studied, we find that the massless spectrum in the orbifold limit agrees with the nonlinear sigma-model computation.