Composite Neutrinos and Double Beta Decay

Abstract

Neutrinoless double beta decay $(\b\b)_{0ν}$ occurs through the magnetic coupling of dimension five, ${\lambda }_W^{(\nu \ast )}/m_{\nu \ast }$, among the excited electron neutrino ${\nu }^{\ast }$, electron and $W$ boson if ${\nu }^{\ast }$ is a massive Majorana neutrino. If the coupling is not small, i.e., ${\lambda }_W^{(\nu \ast )}>1$ the mass of the excited neutrino must not be gless than the $Z$ boson mass, $m_Z$. Since ${\nu }^{\ast }$ contributes in the $(\b\b)_{0ν}$ decay as a vertual state, this decay will give an oppotunity to explore the much heavier mass region of ${\nu }^{\ast }$. In this paper, we present the decay formula of $(\b\b)_{0ν}$ decay through the ${\nu }^{\ast }$ exchange and discuss the constraint on the coupling constant and the mass of the excited neutrino. By comparing the recent data for ${}^{76}$Ge, we find ${\lambda }_W^{(\nu \ast )}(1\mathrm{TeV}/m_{\nu \ast }))(m_N/1\mathrm{TeV}{)}^{\frac{1}{2}}<4.1\cdot 10^{-3}$ where $m_N$ is the Majorana mass of the excited electron neutrino. If $m_N=m_{\nu \ast }$ and ${\lambda }_W^{(\nu \ast )}>1$, we find the mass bound for the excited Majorana neutrino as $m_{{\nu }^{\ast }}>5.9\cdot 10^4$TeV. In order to obtain the constraint on the composite scale $\Lambda$, we have to specify the model. For the mirror type and the homodoublet type models, ${\lambda }_W^{(\nu \ast )}/m_{\nu \ast }=f/(\sqrt{2}\Lambda )$ where $f$ is the relative strength of gauge couplings. Then, we obtain $\Lambda >170f(m_N/1\mathrm{TeV}{)}^{\frac{1}{2}}$TeV. For the sequential type model, $\lambda /m_{\nu \ast }=fv/(\sqrt{2}{\Lambda }^2)$ where $v$ is the vacuum expectation value of the dopublet Higgs boson, i.e., $v=$250GeV. In this model, we find $\Lambda >6.6f^{\frac{1}{2}}(m_N/1\mathrm{TeV}{)}^{\frac{1}{4}}$TeV.

Cited by in corpus (5)

• Neutrinoless Double Beta Decay and Physics Beyond the Standard Model
• Hunting for heavy composite Majorana neutrinos at the LHC
• Neutrinoless Double Beta Decay with Composite Neutrinos
• Leptogenesis and composite heavy neutrinos with gauge mediated interactions
• Like-sign dileptons with mirror type composite neutrinos at the HL-LHC