Conformal Standard Model with an extended scalar sector

TL;DR

This paper proposes an extended Conformal Standard Model with an enlarged scalar sector and a new global symmetry, addressing vacuum stability, dark matter candidates, and leptogenesis, while maintaining consistency up to the Planck scale.

Contribution

It introduces a novel scalar sector and global symmetry in the Conformal Standard Model, ensuring vacuum stability and providing dark matter candidates without disrupting the model's simplicity.

Findings

The model achieves a stable, positive effective potential up to the Planck scale.

Pseudo-Goldstone bosons serve as natural dark matter candidates.

The Yukawa matrix structure supports leptogenesis.

Abstract

We present an extended version of the Conformal Standard Model (characterized by the absence of any new intermediate scales between the electroweak scale and the Planck scale) with an enlarged scalar sector coupling to right-chiral neutrinos. The scalar potential and the Yukawa couplings involving only right-chiral neutrinos are invariant under a new global symmetry SU(3)$_N$ that complements the standard U(1)$_{B-L}$ symmetry, and is broken explicitly only by the Yukawa interaction, of order $10^{-6}$, coupling right-chiral neutrinos and the electroweak lepton doublets. We point out four main advantages of this enlargement, namely: (1) the economy of the (non-supersymmetric) Standard Model, and thus its observational success, is preserved; (2) thanks to the enlarged scalar sector the RG improved one-loop effective potential is everywhere positive with a stable global minimum, thereby avoiding the notorious instability of the Standard Model vacuum; (3) the pseudo-Goldstone bosons resulting from spontaneous breaking of the SU(3)$_N$ symmetry are natural Dark Matter candidates with calculable small masses and couplings; and (4) the Majorana Yukawa coupling matrix acquires a form naturally adapted to leptogenesis. The model is made perturbatively consistent up to the Planck scale by imposing the vanishing of quadratic divergences at the Planck scale (`softly broken conformal symmetry'). Observable consequences of the model occur mainly via the mixing of the new scalars and the standard model Higgs boson.