Bounds on Neutrino-Scalar Yukawa Coupling

TL;DR

This paper derives new bounds on neutrino-scalar Yukawa couplings using meson decay and heavy neutrino searches, significantly improving existing limits especially for scalar masses below 300 MeV.

Contribution

It provides the first constraints on neutrino-scalar couplings for scalar masses up to 300 MeV, extending previous bounds to a broader mass range.

Findings

Limits on $|g_e|^2$ and $|g_bc|^2$ for massless scalars.

First constraints on couplings for scalar masses below 300 MeV.

Enhanced bounds for scalar masses between below 1 MeV and 300 MeV.

Abstract

General neutrino-scalar couplings appear in many extensions of Standard Model. We can probe these neutrino-scalar couplings by leptonic decay of mesons and from heavy neutrino search. Our analysis improves the present limits to $|g_e|^2<1.9\times 10^{-6}$ and $|g_\mu|^2<1.9\times 10^{-7}$ at 90\% C.L. for massless scalars. For massive scalars we found for the first time the constraints for $g^2_{\alpha}$ couplings to be $10^{-6}-10^{-1}$ respectively for scalar masses between below 1 MeV and for 300 MeV.