# A String Theory of Flavor and CP

## TL;DR

This paper introduces a systematic method to compute unified flavor symmetries in string theory, revealing how modular transformations unify CP and flavor symmetries and lead to local flavor unification phenomena.

## Contribution

It provides a novel, systematic approach to determine the low-energy flavor symmetry, incorporating string dualities and modular transformations, and uncovers the concept of local flavor unification.

## Key findings

- Unified flavor group is non-universal in moduli space.
- Modular transformations unify CP with flavor symmetries.
- Different sectors can have distinct flavor structures.

## Abstract

Modular transformations of string theory (including the well-known stringy dualities) play a crucial role in the discussion of discrete flavor symmetries in the Standard Model. They are at the origin of CP transformations and provide a unification of CP with traditional flavor symmetries. Here, we present a novel, fully systematic method to reliably compute the unified flavor symmetry of the low-energy effective theory, including enhancements from the modular transformations of string theory. The unified flavor group is non-universal in moduli space and exhibits the phenomenon of "Local Flavor Unification" where different sectors of the theory can be subject to different flavor structures.