Neutrino mass with large $SU(2{)}_L$ multiplet fields

We propose an extension of the standard model introducing large $SU(2{)}_L$ multiplet fields which are quartet and septet scalars and quintet Majorana fermions. These multiplets can induce the neutrino masses via interactions with the $SU(2)$ doublet leptons. We then find the neutrino masses are suppressed by a small vacuum expectation value of the quartet/septet and an inverse of the quintet fermion mass, relaxing the Yukawa hierarchies among the standard model fermions. We also discuss collider physics at the Large Hadron Collider, considering the production of charged particles in these multiplets, and due to the effects of violating the custodial symmetry, some specific signatures can be found. Then, we discuss the detectability of these signals.

Figure 1

Left: Tree level contribution to neutrino masses. Right: Contribution to neutrino masses at a one-loop level.

Figure 2

The running of $g$ and $g_Y$ in terms of a reference energy of $\mu$.

Figure 3

(a) The cross section for a pair production process $pp\to Z/\gamma \to {\phi }^{++}{\phi }^{--}$ and $pp\to Z/\gamma \to {\phi }_1^{+}{\phi }_1^{-}+pp\to Z/\gamma \to {\phi }_2^{+}{\phi }_2^{-}$ as a function of quartet mass $M_4$. (b) The cross section for the pair production process $pp\to Z/\gamma \to {\varphi }^{+4}{\varphi }^{-4}$ as a function of a septet mass $M_7$.

Figure 4

The cross section for a pair production process $pp\to Z/\gamma \to {\mathrm{\Sigma }}^{++}{\mathrm{\Sigma }}^{--}$ as a function of the ${\mathrm{\Sigma }}^{\pm \pm }$ mass.