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Aspects of D-brane geometry and boundary superspace

Friday, 21 September, 2007 - 15:30
Campus: Brussels Humanities, Sciences & Engineering campus
Faculty: Science and Bio-engineering Sciences
Alexander Wijns
phd defence

String theory is a candidate theory for describing gravity at the quantum level and for unifying all known fundamental interactions of nature. In many of the successes of string theory, certain solitonic objects known as D-branes play a crucial role. We study D-branes and their geometry from two points of view: the nonlinear sigma-model action on the world-sheet of an open string ending on the brane and the effective world-volume action for gauge fields living on the brane. In particular, we develop an N=2 boundary superspace formulation of the sigma-model for when only chiral or twisted chiral superfields are needed. This enables us to give a concrete world- sheet description of A and B branes on Kaehler manifolds. This includes the coisotropic A branes recently found to be important for a consistent formulation of mirror symmetry. The N=2 superspace formulation of B branes also leads to a relatively simple setting for obtaining derivative corrections to the Born-Infeld action by computing the beta-function corresponding to the boundary coupling to the gauge field to higher loop order. In this way, we successfully derive the complete four derivative correction to the Born-Infeld action by performing a three-loop beta-fuction calculation.