Neutrino Masses and Conformal Electro-Weak Symmetry Breaking

TL;DR

This paper investigates how classically conformal electroweak symmetry breaking via dimensional transmutation can naturally generate neutrino masses. It formulates model-building rules that forbid explicit mass terms and require masses to arise from Yukawa couplings to scalars whose VEVs are dynamically produced, often through a Higgs portal to a Hidden Sector. A comprehensive catalogue of viable models is presented, including SM-gauge extended theories and Hidden Sector constructions that realize left-handed Majorana, pseudo-Dirac, sub-TeV seesaw, and inverse seesaw neutrino masses, frequently with TeV-scale spectra and a radiative symmetry-breaking mechanism. The phenomenology section assesses compatibility with oscillation data, LFV and EWPO constraints, and highlights four viable regimes with distinctive collider signatures and potential Dark Matter connections, offering concrete pathways for experimental tests at the LHC and beyond.

Abstract

Dimensional transmutation in classically conformal invariant theories may explain the electro-weak scale and the fact that so far nothing but the Standard Model (SM) particles have been observed. We discuss in this paper implications of this type of symmetry breaking for neutrino mass generation.

Figures (4)

• Figure 1: The phenomenlogically allowed mass region in the simplest neutrino mass model with RSSB, a Higgs mass of $125$ GeV, a higgs portal mixing compatible with the bound $\sin \theta < 0.37$, perturbative potential parameters and no low scale Landau pole. Here $M_N$ is the mass of the heaviest right handed neutrino, $M_\Phi$ is the heavy scalar dominating the spectrum and $M_S$ is the mass of the PGB.
• Figure 2: The lepton number violating decay as a collider signature for the Sub-TeV and multi TeV see-saw with a heavy Majorana Neutrino decay.
• Figure 3: The dominant collider signature for the ISS scenario with the trilepton plus missing energy signature.
• Figure 4: The phenomenologically allowed regions on the Mass Map are displayed. The averaged right handed scale normalized to the TeV scale of symmetry breaking is shown on the x-axis and the averaged EW Dirac mass is shown on the y-axis. Two regions are zoomed in and shown as insets. In the left upper corner the blow up shows the region around the TeV right handed scale, the color coding represents the non-unitartity of the active mixing matrix. In the right lower corner the region of sub-dominant Majorana masses is shown, the color code indicates the maximal expected effective electron neutrino mass for $0\nu\beta\beta$ decays. The experimental constraints are the limits on the rare decay $\mu \rightarrow e + \gamma$, shown as the magenta line, the lepton universality, shown as the blue line and the $0\nu\beta\beta$ decay, leading to the red exclusion line. The points allowed only in the inverse see-saw are shown in grey-green. The most universal bounds come from non-unitarity constraints, shown as a brown line with gradient one in the log-plot. The see-saw relation explains the lower boundary of the allowed region, it has gradient one-half in the log-plot. I is a fraction of parameter space without a see-saw relation, it is the Pseudo-Dirac region. Here neutrinos come in pairs of strongly mixed left and right particles, with mass splitting induced by Majorana mass fraction. II Yukawa see-saw with the upper bound- Scale 1- set by the requirement of perturbative couplings. III ISS allows perturbative couplings and at the same time the right handed mass up to Scale 2. The most natural parameter choice in the ISS scenario leads to considerable active-sterile mixing of states at the TeV scale and a significantly improved $\chi^2$ of the Electro-Weak fit w.r.t the standard model (light blue points).