Proton decay from quark and lepton compositeness

TL;DR

This paper explores proton decay implications in a chiral $SU(15)$ preon model, estimating the compositeness scale and suggesting potential observable decay modes in current neutrino detectors.

Contribution

It introduces a specific $SU(15)$ preon model and estimates the proton decay scale, linking it to experimental constraints and potential observable decay channels.

Findings

Proton decay operators are likely induced at the compositeness scale.

Lower limit on the compositeness scale is between 3,000 and 50,000 TeV.

Exotic decay modes could be detected by Super-Kamiokande or DUNE.

Abstract

Within a chiral $SU(15)$ gauge theory in which the Standard Model fermions are bound states of massless preons, we show that proton-decay operators are likely induced at the compositeness scale, $\Lambda_{\rm pre}$. Our estimate of the limit imposed by searches for proton decays is $\Lambda_{\rm pre} > 10^4 \, {\rm TeV}^{1/2} \, C_8^{1/4} \, m_{\cal Q}^{1/2}$, where $C_8$ is a rescaled coefficient of an 8-prebaryon operator induced by $SU(15)$ dynamics, and $m_{\cal Q}$ is the mass of a composite vectorlike quark. The latter has a lower limit related to the mass of a composite vectorlike lepton, which in turn is required by LHC searches to be above 1 TeV. For $C_8$ in the $10^{-5} - 1$ range, the lower limit on $\Lambda_{\rm pre}$ varies between $3 \times 10^3$ TeV and $5 \times 10^4$ TeV. We point out that exotic proton decay modes, into a $\pi^+$ and a heavy right-handed neutrino, could be observed using the Super-Kamiokande or DUNE detectors.