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Nicolas Couchoud

Publications and source records attributed to Nicolas Couchoud.

4 recordsLinked to original sources
arXiv2004

D-branes et orientifolds dans des espaces courbes ou dependant du temps

In this thesis we study string theory with D-branes and possibly orientifolds in curved or time-dependent spaces. Our study aims at understanding some aspects of curved and time-dependent spaces, notably because of their importance in cosmology. The first chapter introduces some bases of string theory. The second chapter studies non-oriented strings on compact groups SU(2) and SO(3): after reviewing known results about D-branes in such spaces, we present our results on the position of orientifolds and their interaction with open and closed strings. The third chapter studies D-branes in certain backgrounds of Ramond-Ramond type, using S-duality, which links them with backgrounds of Neveu-Schwarz type, where calculations can be done. The last chapter considers strings on a D-brane embedded with a plane wave, and introduces tools which allow to study interactions in such a background.

hep-th↗
arXiv2002

D-branes and orientifolds of SO(3)

We study branes and orientifolds on the group manifold of SO(3). We consider particularly the case of the equatorial branes, which are projective planes. We show that a Dirac-Born-Infeld action can be defined on them, although they are not orientable. We find that there are two orientifold projections with the same spacetime action, which differ by their action on equatorial branes.

hep-th↗
arXiv2001

Orientifolds of the 3-sphere

We study the geometry of orientifolds in the SU(2) WZW model. They correspond to the two inequivalent, orientation-reversing involutions of $S^3$, whose fixed-point sets are: the north and south poles (O0), or the equator two-sphere (O2). We show how the geometric action of these involutions leads unambiguously to the previously obtained algebraic results for the Klein bottle and Moebius amplitudes. We give a semiclassical derivation of the selection rules and signs in the crosscap couplings, paying particular attention to discrete B-fluxes. A novel observation, which does not follow from consistency of the one-loop vacuum diagrams, is that in the case of the O0 orientifolds only integer- or only half-integer-spin Cardy states may coexist.

hep-th↗