CP violation effects in the diphoton spectrum of heavy scalars

Abstract

In a class of new physics models, an extended Higgs sector and new CP-violating sources are simultaneously present in order to explain the baryon asymmetry in the Universe. The aim of this work is to study the implications of beyond the Standard Model (SM) CP violation for the searches of heavy scalars at the LHC. In particular, we focus on the diphoton channel searches in the CP-violating two-Higgs-doublet model (CPV 2HDM). To have a sizable CPV in the scalar sector, the two heavy neutral scalars in 2HDM tend to be nearly degenerate. The theoretical constraints of unitarity, perturbativity and vacuum stability are considered, which requires that the heavy scalars M-H less than or similar to 1 TeV in a large region of the parameter space. The experimental limits are also taken into account, including the direct searches for heavy neutral scalars in the final state of the SM h, W and Z bosons; the differential (tt) over bar data; those from the charged scalar sector which is implied by the oblique T parameter; and the precise measurements of the electric dipole moments of electrons and mercury. The quantum interference effects between the resonances and the SM background are crucially important for the diphoton signals, and the CPV mixing of the quasidegenerate heavy scalars could enhance significantly the resonance peak. With an integrated luminosity of 3000 fb(-1) at the LHC, almost the whole parameter space of CPV 2HDM could be probed in the diphoton channel, and the CPV could also be directly detected via the diphoton spectrum.