Conformal complex singlet extension of the Standard Model: scenario for dark matter and a second Higgs boson

Abstract

We consider a conformal complex singlet extension of the Standard Model with a Higgs portal interaction. The global U(1) symmetry of the complex singlet can be either broken or unbroken and we study each scenario. In the unbroken case, the global U(1) symmetry protects the complex singlet from decaying, leading to an ideal cold dark matter candidate with approximately 100 GeV mass along with a significant proportion of thermal relic dark matter abundance. In the broken case, we have developed a renormalization-scale optimization technique to significantly narrow the parameter space and in some situations, provide unique predictions for all the model's couplings and masses. We have found there exists a second Higgs boson with a mass of approximately 550 GeV that mixes with the known 125 GeV Higgs with a large mixing angle sin θ ≈ 0.47 consistent with current experimental limits. The imaginary part of the complex singlet in the broken case could provide axion dark matter for a wide range of models. Upon including interactions of the complex scalar with an additional vector-like fermion, we explore the possibility of a diphoton excess in both the unbroken and the broken cases. In the unbroken case, the model can provide a natural explanation for diphoton excess if extra terms are introduced providing extra contributions to the singlet mass. In the broken case, we find a set of coupling solutions that yield a second Higgs boson of mass 720 GeV and an 830 GeV extra vector-like fermion F , which is able to address the 750 GeV LHC diphoton excess. We 1 Corresponding author.Open Access, c The Authors. Article funded by SCOAP 3 .doi:10.1007/JHEP08(2016)065 JHEP08(2016)065also provide criteria to determine the symmetry breaking pattern in both the Higgs and hidden sectors.

Accidental scale-invariant Majorana dark matter in leptoquark-Higgs portals

“…In terms of the one-loop VEV ν, effective potential along the flat direction is given by 12) and the scalon mass will be…”

“…This mechanism works only if extra bosonic degrees of freedom are added to SM with sizable couplings. Scale-invariant extensions of SM are also a generic feature of many DM models with bosonic [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] and fermionic [20][21][22][23][24][25][26] DM candidates.…”

Gravitational waves from scale-invariant vector dark matter model: probing below the neutrino-floor

“…Scale-invariant extensions of the SM can also provide a DM candidate (for recent papers see e.g. [70][71][72][73][74][75][76][77][78][79][80]). Particle nature of the DM is another important puzzle in particle cosmology [81].…”

Phase transition and gravitational wave phenomenology of scalar conformal extensions of the Standard Model

“…Phase transitions which directly or indirectly result in the generation of the electroweak scale have also been analysed within the framework of classically conformal (or scale invariant) models [30,[32][33][34][35][36][37], often in connection to other open problems of contemporary physics such as the origins of Dark Matter (DM) and the inflationary dynamics [31,32,[38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57]. An important feature of classically conformal models is that the phase transition associated to the insurgence of the electroweak scale is generally of the first order and very strong.…”