Speaker
Description
We propose a novel solution to the strong CP problem based on modular invariance. The latter is inherent to toroidal compactifications in string theory. We show that modular invariance allows for simple effective theories of flavour and CP where (i) the QCD angle vanishes, (ii) the CKM phase is large, (iii) quark and lepton masses and mixings can be reproduced up to order one coefficients. This solution is further extended to incorporate features that appear in string compactifications: quarks with mostly positive modular weights and non-trivial gauge kinetic functions. This requires assuming that singularities and zeroes only appear at special points in the moduli space, such as decompactification limits. We discuss the impact of these assumptions on string gauge unification.
