Natural electroweak symmetry breaking from scale invariant Higgs mechanism

Abstract

We construct a minimal viable extension of the standard model (SM) with classical scale symmetry. Its scalar sector contains a complex singlet in addition to the SM Higgs doublet. The scale-invariant and CP-symmetric Higgs potential generates radiative electroweak symmetry breakingà la Coleman-Weinberg, and gives a natural solution to the hierarchy problem, free from fine-tuning. Besides the 125 GeV SM-like Higgs particle, it predicts a new CP-even Higgs (serving as the pseudo-Nambu-Goldstone boson of scale symmetry breaking) and a CP-odd scalar singlet (providing the dark matter candidate) at weak scale. We systematically analyze experimental constraints from direct LHC Higgs searches and electroweak precision tests, as well as theoretical bounds from unitarity, triviality and vacuum stability. We demonstrate the viable parameter space, and discuss implications for new Higgs and dark matter (DM) searches at the upcoming LHC runs and for the on-going direct detections of DM. 1 After the SM is extended with singlet right-handed neutrinos, their dimension-3 heavy Majorana mass-term provides another soft breaking of scale invariance. Our present construction will naturally generate this Majorana mass term via spontaneous symmetry breaking. 2 The SM Higgs sector with a 125 GeV Higgs boson is free from triviality bound, but suffers a vacuum stability bound at the scale µ 10 12 GeV [8]. We will analyze both triviality and vacuum stability bounds for the present model.

Very light dilaton and naturally light Higgs boson

“…At low energy our model contains only the standard model with very light dilaton, which is therefore different from previous models [14][15][16][17][18][19][20][21] that attempt to solve the naturalness problem by imposing the scale invariance in the Higgs sector, not broken spontaneously. We also show that the light dilaton of our model abundantly constitutes the dark matter in our universe once it is non-thermally produced at early universe by the vacuum misalignment of the dilaton field.…”

Classically scale invariant inflation, supermassive WIMPs, and adimensional gravity

“…In order to account for the gravitational effects, the described model is, subsequently, embedded within a scale-symmetric renormalizable framework of gravity, the Adimensional gravity (Agravity) [9], in which all scalars couple non-minimally to the curvature. Interestingly, the CP -symmetry of the action protects the pseudoscalar component of the complex singlet from decaying [2], rendering it a stable dark matter candidate.…”

“…The most general form of the scalar potential, satisfying the scale-and CP -symmetry, is composed of the following six operators [2] …”

“…We shall report the one-loop β-functions of all relevant running couplings, calculated within the MS-scheme. The SM couplings' β-functions are analytically known up to two-loops within the literature [27], those of our extended scalar sector and the right-handed Majorana neutrinos were first calculated in [2], and all gravitational contributions 13 are deduced from the Agravity framework [9]. 14 Let us begin by discussing the gauge couplings' β-functions.…”

“…It has been previously demonstrated [2] that, within such an extended scalar sector, the ColemanWeinberg mechanism [3] may be successfully realized, while accommodating the discovered 125 GeV Higgs-like state [4], and, therefore, remedy the failure of the mechanism within the ordinary SM scalar sector. In particular, the dynamical generation of a nonzero vacuum expectation value (VEV) for the CP -even component of the complex singlet scalar via this mechanism can be transmitted to the electroweak sector via the Higgs portal operators, inducing the nonzero VEV for the SM Higgs boson, and, thereby, giving rise to a successful spontaneous breaking of the electroweak symmetry.…”