The Type II Dirac Seesaw Portal to the mirror sector: Connecting neutrino masses and a solution to the strong CP problem

TL;DR

This paper introduces a novel Type II Seesaw model with a mirror sector that explains small Dirac neutrino masses, addresses the strong CP problem via a discrete symmetry, and explores phenomenological and cosmological implications.

Contribution

It proposes a new gauge extension with a mirror sector and a bidoublet scalar to generate small Dirac neutrino masses and solve the strong CP problem simultaneously.

Findings

Model predicts charged scalar particles similar to Type II Seesaw.

Mirror sector cancels contributions to the strong CP phase.

Discusses potential for Dirac leptogenesis and cosmological effects.

Abstract

We present a version of the Type II Seesaw mechanism for parametrically small Dirac neutrino masses. Our model starts from an $\text{SU}(2)_\text{L} \otimes \text{SU}(2)'\otimes \text{U}(1)_\text{X}$ gauge extension of the Standard Model involving a sector of mirror fermions. A bidoublet scalar with a very small vacuum expectation value connects the SM leptons with their mirror counterparts and we can identify the mirror neutrino with the right-handed neutrino. Similar to the conventional Type II Seesaw, our particle spectrum features singly- and doubly-charged scalars. The strong CP problem is solved by a discrete exchange symmetry between the two sectors that forces the contributions of quarks and mirror quarks to the strong CP phase to cancel each other. We discuss the low-energy phenomenology, comment on the cosmological implications of this scenario and indicate how to realize successful Dirac leptogenesis.