Double Beta Decay Constraint on Composite Neutrinos

Abstract

Neutrinoless double beta decay occurs through the magnetic coupling of dimension five, $λ_W/m_{ν*}$, among the excited electron neutrino $ν^*$, electron and $W$ boson if $ν^*$ is a massive Majorana neutrino. (λ_W m_W / m_{ν*}^2 |\frac{(m_*/m_W) +2}{(m_*/m_W +1)^2} -0.129{m_*/m_W} | <2.13\times 10^{-2}, where $λ_W$ is the relative strength, $m_{ν*}$ is the composite scale and $m_*$ is the mass of excited neutrino. If the coupling is not small, i.e., $λ_W>1$ and $m_{ν*}=m_*$, we find $m_*>3.4 m_W$.