Heavy quark-philic scalar dark matter with a vector-like fermion portal

Abstract

The absence of confirmed signal in dark matter (DM) direct detection (DD) may suggest weak interactions of DM with gluons and light quarks. In this work we consider a real scalar dark matter $S$ interacting dominantly with $U_i=c_R,t_R$ via a vector-like fermion $\psi$ and new couplings $y_i$ with $i=2,3$ being flavor index. DM-nucleon scattering proceed through both Higgs portal (HP) and vector-like portal (VLP), in which HP can receive sizable radiative corrections from VLP. DM-heavy quark ($c_R,t_R$) interactions generate DM-gluon scattering via loop, in which we include renormalization group equation and heavy quark threshold effects. For $y_3=0.5, y_2=0.5, 1, 3$, DM relic abundance, XENON1T, Fermi-LAT and 13 TeV LHC data can exclude most of $m_S<m_t/2$. FCNC of top quark exist at both tree and loop level and the branch ratios are typically below $10^{-7}$ and safe from the current measurements.