Conformal vector dark matter and strongly first-order electroweak phase transition

Seyed Yaser Ayazi,Ahmad Mohamadnejad

doi:10.1007/jhep03(2019)181

Abstract

We study a conformal version of the Standard Model (SM), which apart from SM sector, containing a UD(1) dark sector with a vector dark matter candidate and a scalar field (scalon). In this model the dark sector couples to the SM sector via a Higgs portal. The theory is scale-invariant in lowest order, therefore the spontaneous symmetry breaking of scale invariance entails the existence of a scalar particle, scalon, with vanishing zeroth-order mass. However, one-loop corrections break scale invariance, so they give mass to the scalon. Because of the scale invariance, our model is subjected to constraints which remove many of the free parameters. We put constraints to the two remaining parameters from the Higgs searches at the LHC, dark matter relic density and dark matter direct detection limits by PandaX-II. The viable mass region for dark matter is about 1–2 TeV. We also obtain the finite temperature one-loop effective potential of the model and demonstrate that finite temperature effects, for the parameter space constrained by dark matter relic density, induce a strongly first-order electroweak phase transition.

Highlights

There are plenty astronomical and cosmological evidences that around 27 percent of the Universe is made of DM
We study a conformal version of the Standard Model (SM), which apart from SM sector, containing a UD(1) dark sector with a vector dark matter candidate and a scalar field
The theory is scale-invariant in lowest order, the spontaneous symmetry breaking of scale invariance entails the existence of a scalar particle, scalon, with vanishing zerothorder mass

Summary

The model

We introduce a complex scalar field φ which has unit charge under a dark UD(1) gauge symmetry with a vector field Vμ. Since at the minimum of the one-loop effective potential V tree 0 and Ve1ff−loop < 0, the minimum of Ve1ff−loop along the flat direction (where V tree = 0) is a global minimum of the full potential, spontaneous symmetry breaking occurs and we should substitute h1 → ν1 + h1 and h2 → ν2 + h2 This breaks the electroweak symmetry with vacuum expectation value ν1 = 246 GeV. Note that according to (2.18) and (2.12), MH2 is completely determined by the independent parameters of the model, i.e., vector DM mass MV and the coupling g. These constraints are due to the scale invariance conditions which were imposed to the model. We check the validity of our model against DM relic density, and direct detection experimental data

Relic density via freeze-out

Direct detection

One-loop effective potential at finite temperature

Results

Conclusion