Realizing dark matter and Higgs inflation in light of LHC diphoton excess

LHC Run-2 has provided intriguing di-photon signals of a new resonance around 750GeV, which, if not due to statistical fluctuations, must call for new physics beyond the standard model (SM) at TeV scale. We propose a minimal extension of the SM with a complex singlet scalar SS and a doublet of vector-like quarks. The scalar sector respects CP symmetry, with its CP-odd imaginary component χ   providing a natural dark matter (DM) candidate. The real component of SS serves as the new resonance (750GeV) and explains the diphoton excess of the LHC Run-2. The new scalar degrees of freedom of SS help to stabilize the Higgs vacuum, and can realize the Higgs inflation around GUT scale, consistent with the current cosmological observations. We construct two representative samples A and B of our model for demonstration. We study the mono-jet signals of DM production from invisible decays Re(S)→χχRe(S)→χχ at the LHC Run-2. We further derive the DM relic density bound, and analyze constraints from the direct and indirect DM detections.