Smallness of neutrino masses and leptogenesis in 331 composite Higgs model

TL;DR

This work analyzes a 331-inspired composite Higgs model (CHM3) in which a strongly coupled sector with global $SU(3)_C \times SU(3) \times U(1)_6$ symmetry breaks to the SM gauge group at $f \sim 5$–$10\ \mathrm{TeV}$, producing a Higgs as a pseudo-Nambu–Goldstone boson. It demonstrates that approximate $U(1)_L$ and a discrete $Z_2$ symmetry can yield naturally small left-handed neutrino masses via $M^{\nu}_{ij} = - \dfrac{\varkappa_{ij}}{2f} s_{2i} s_{2j} v^2$, while predicting light composite leptons with masses around $1$–$2\ \mathrm{TeV}$ that could be probed at the LHC. Leptogenesis is achieved through out-of-equilibrium decays of an extra Majorana fermion $n$ with mass $\sim 10\ \mathrm{TeV}$, generating a CP asymmetry $\varepsilon_{0}$ from loop effects and a baryon asymmetry $Y_{\Delta B}$ that can match observations for modest washout ($\eta_{0} \sim 0.01$) and small Yukawa couplings $|h_{10}|$. Overall, CHM3 links neutrino mass generation to leptogenesis within a unified TeV-scale composite framework and yields distinctive collider signatures from light lepton-sector composites.

Abstract

We consider 331 composite Higgs model (CHM3) in which the Lagrangian of the strongly coupled sector is invariant with respect to global SU(3)_C \times SU(3)\times U(1)_6 symmetry that can originate from SU(6) subgroup of E_6 and contains the gauge group of the standard model (SM) as a subgroup. The breakdown of the approximate SU(3)\times U(1)_6 symmetry down to SU(2)_W\times U(1)_Y subgroup around the scale f\sim 10 TeV results in a set of pseudo--Nambu--Goldstone bosons (pNGBs) that, in particular, involves Higgs doublet. The generation of the masses of the SM fermions in the CHM3 is discussed. We argue that approximate U(1)_L and discrete Z_2 symmetries may give rise to tiny masses of the left--handed neutrinos and several composite fermions with masses 1-2 TeV. The lepton and baryon asymmetries can be generated within the CHM3 via the out--of equilibrium decays of extra Majorana particle into the Higgs doublet and these composite fermions.

Figures (1)

• Figure 1: Logarithm (base 10) of the absolute values of the efficiency factor $\eta_0$ ( Left) and decay asymmetry $\varepsilon_{0}$ ( Right) for $h_{20}=h_{30}=0$. The absolute value of $\eta_0$ is given as a function of logarithm (base 10) of $|h_{10}|$ for $M_{n}=10\,\hbox{TeV}$ (solid line) and $M_{n}=15\,\hbox{TeV}$ (dashed line). The absolute value of $\varepsilon_{0}$ is presented as a function of logarithm (base 10) of $\Delta\varphi_{1}=\Delta\varphi_{2}=\Delta\varphi_{3}=\Delta\varphi$ for $M_{n}=10\,\hbox{TeV}$, $M_{1}=12\,\hbox{TeV}$, $M_{2}=14\,\hbox{TeV}$, $M_{3}=16\,\hbox{TeV}$, $|h_{11}|=|h_{12}|=|h_{13}|=|h|$, $|h|=0.1$ (solid line) and $|h|=0.3$ (dashed line).