Clockwork for Neutrino Masses and Lepton Flavor Violation

TL;DR

This paper explores how the clockwork mechanism can generate small neutrino masses and induce lepton flavor violation, deriving formulas and analyzing different mass scenarios with implications for experimental constraints.

Contribution

It provides analytic formulas for neutrino masses and couplings in a clockwork framework, including Dirac and Majorana mass scenarios, and discusses experimental constraints.

Findings

Zero mode forms a Dirac pair with active neutrino when Majorana masses vanish.

Neutrino masses can be generated via seesaw mechanism with non-zero Majorana masses.

Constraints from $oldsymbol{ ext{μ→eγ}}$ decay limit the clockwork fermion mass scale.

Abstract

We investigate the generation of small neutrino masses in a clockwork framework which includes Dirac mass terms as well as Majorana mass terms for the new fermions. We derive analytic formulas for the masses of the new particles and for their Yukawa couplings to the lepton doublets, in the scenario where the clockwork parameters are universal. When the Majorana masses all vanish, the zero mode of the clockwork sector forms a Dirac pair with the active neutrino, with a mass which is in agreement with oscillations experiments for a sufficiently large number of clockwork gears. On the other hand, when the Majorana masses do not vanish, neutrino masses are generated via the seesaw mechanism. In this case, and due to the fact that the effective Yukawa couplings of the higher modes can be sizable, neutrino masses can only be suppressed by postulating a large Majorana mass for all the gears. Finally, we discuss the constraints on the mass scale of the clockwork fermions from the non-observation of the rare leptonic decay $\mu\rightarrow e\gamma$.