Probing flavor-diagonal couplings of doubly-charged scalar at low and high energies

TL;DR

This paper explores how a TeV-scale doubly-charged scalar in left-right symmetric models can be detected through various high-energy collider experiments and low-energy precision tests, revealing its flavor-diagonal couplings to electrons and muons.

Contribution

It provides a comprehensive analysis of the phenomenology of a TeV-scale doubly-charged scalar, combining collider and low-energy experimental constraints to identify detectable parameter regions.

Findings

Couplings as small as 10^{-2} are accessible for scalar masses 1-3 TeV.

Multiple collider and low-energy experiments can probe the scalar's flavor-diagonal couplings.

Detection could support the type-I seesaw mechanism in left-right symmetric models.

Abstract

We investigate the phenomenology of a TeV-scale doubly-charged scalar from the right-handed sector within the framework of left-right symmetric models. Focusing on its flavor-diagonal couplings to right-handed electrons and muons, we assess probes from both high-energy colliders and low-energy precision experiments. High-energy processes include Bhabha scattering at LEP and future circular electron-positron colliders (CEPC/FCC-ee), direct production at the LHC, and dedicated searches and precision measurements at proposed muon colliders and $\mu$TRISTAN. Low-energy observables encompass parity-violating M{\o}ller scattering, muon anomalous magnetic moment, and muonium-antimuonium oscillations. Our combined analysis indicates that for a doubly-charged scalar in the $1$-$3$ TeV range, the flavor-diagonal Yukawa couplings to electrons and muons as small as $10^{-2}$ are accessible. Observations of such a doubly-charged scalar would potentially point toward the type-I seesaw mechanism of neutrino masses in the left-right symmetric model with $D$-parity breaking.