Sub-GeV Right-Handed Neutrino as a Probe of Neutrino Mass Generation in the Minimal Left-Right Symmetric Model

TL;DR

This work investigates the sub-GeV right-handed neutrino in the minimal left-right symmetric model (mLRSM) within the type-II seesaw limit and without left-right mixing. By combining collider bounds, meson decays, SN1987A cooling and energy deposition, cosmology (BBN/CMB), and a state-of-the-art EFT treatment of neutrinoless double beta decay, the authors map the viable parameter space and identify a region with $m_{\nu_4}$ in the range of 700 MeV to 1 GeV and $M_{W_R}$ just below 20 TeV that remains consistent with all current constraints. This region is uniquely accessible to future tonne-scale $0\nu\beta\beta$ decay experiments, offering a concrete test of the mLRSM origin of neutrino masses. The analysis highlights the complementary roles of high-energy colliders, low-energy precision experiments, astrophysical observations, and cosmology in probing the neutrino mass generation mechanism. The study also notes that including potential W_L–W_R mixing could strengthen the bounds, further constraining the parameter space.

Abstract

The minimal left-right symmetric model (mLRSM) provides an elegant and testable framework for addressing the origin of neutrino masses. We examine the constraints on the sub-GeV right-handed (RH) neutrino in the type-II seesaw scenario of the mLRSM without left-right mixing, taking limits from collider searches, meson decays, supernovae, neutrinoless double beta ($0νββ$) decay and cosmology. Specifically, we derive the $0νββ$ decay constraints using the advanced effective field theory approach and up-to-date nuclear matrix element calculations. Besides, we update the SN1987A cooling bound with the state-of-the-art simulations, provide new constraints from the energy deposition in the supernova ejecta, and incorporate the stringent RH neutrino lifetime upper limit $τ\lesssim 0.023\text{ s}$ from the big bang nucleosynthesis. Our results identify the parameter region compatible with all current experimental and observational constraints, where the RH neutrino mass lies between 700 MeV and 1 GeV and the RH $W$ boson mass is slightly below 20 TeV. This region is exclusively probed by the future tonne-scale $0νββ$ decay experiments, providing a unique window to test the mLRSM and the possible origin of neutrino masses.

Figures (2)

• Figure 1: Constraints on $M_{W_R}$ from the SN1987A cooling (blue), SN energy deposition (green), $0\nu\beta\beta$ decay (purple), BBN (red), meson decays (gray, taken from Ref. Alves:2023znq) and LHC searches (black) for various $m_{\nu_4}$. Two variations are considered for the SN energy deposition constraint, one of which (solid green) ignores the $\nu_4$ scattering absorption among the sources, while the other (dashed green) has it included. The top-left inset panel zooms into the region enclosed by the black square.
• Figure 2: An illustration on the geometry of $\nu_4$'s photonic decay.