Discrete gauge symmetries in string theory
Mikel Berasaluce González (Universidad Autónoma de Madrid)

In particle physics model building discrete symmetries are often invoked for phenomenological reasons, like forbidding unwanted or dangerous couplings, or explaining and reproducing the matrices of masses and mixings of fermions in flavour physics. While these discrete symmetries do their phenomenological job, they are poorly motivated at a fundamental level in the context of field theory. Moreover, there are arguments suggesting that discrete global symmetries are expected to be violated in consistent theories of quantum gravity; therefore, any exact symmetry of the theory should be gauge. This motivates the study of discrete gauge symmetries in string theory, which is one of the most promising candidates for a complete theory of quantum gravity. In this talk we will study different mechanisms that give rise to discrete gauge symmetries in string theory, specially in compactifications to four dimensions, although we also explore several generalizations, like compactifications to a number of dimensions different from four, or supercritical string theories.