Spontaneous CP Violation and Horizontal Symmetry in the MSSM: Toward Lepton Flavor Naturalness

Understand

We study the contributions of supersymmetric models with a $U(1)$ horizontal symmetry and only spontaneous CP breaking to various lepton flavor observables, such as $\mu \to e\gamma$ and the electron electric dipole moment.

• We show that both a horizontal symmetry and a lack of explicit CP violation can alleviate the existing bounds from such observables.
• The undetermined $\mathcal{O}(1)$ coefficients in such mass matrix models muddle the interpretation of the bounds from various flavor observables.
• To overcome this, we define a new fine-tuning measure for different observables in such setups.