Inflation and Dark Matter in the Higgs Portal of Classically Scale Invariant Standard Model

Abstract: We consider a minimal classically scale-invariant extension of the Standard Model. In this theory, the Higgs mechanism is triggered and the electroweak symmetry breaking is generated radiatively by the Coleman-Weinberg sector which is coupled to the SM Higgs. We extend the Higgs portal interactions of the theory to include an additional singlet which is also non-minimally coupled to gravity. This generates a single-field slow-roll inflation mechanism in the effective field theory formulation which is robust up to Planck scales. Our approach does not require integrating in any additional new physics degrees of freedom to unitarise the theory in the sub-Planckian regime where inflation happens. As a result, no large threshold corrections appear in our approach to inflation so that the electroweak scale and the SM Higgs mass are not affected. The singlet field responsible for inflation also gives a viable dark matter candidate in our model. We also discuss the relation between classical scale-invariance of the effective theory and the possible local scale invariance of the full theory and comment on the naturalness of the electroweak scale.