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

Abstract

In this work we consider a real scalar dark matter $S$ interacting only with $SU(2{)}_L$ singlet Up-type quarks $U_i=u_R,c_R,t_R$ via a vector-like fermion $\ddot{I}ˆ$ which has the same quantum number as $U_i$. The DM-nucleon scattering can proceed through both $h$-mediated Higgs portal (HP) and $\ddot{I}ˆ$-mediated vector-like portal (VLP), in which HP can receive sizable radiative corrections through the new fermions. We first study the separate constraints on the new Yukawa couplings $y_i$ and find that the constraints of XENON1T results are strong on $y_1$ from VLP scattering and on $y_3$ from its radiative contributions to HP scattering. Since both DM-light quark interactions and HP have been well studied in the existing literature, we move forward to focus on DM-heavy quark interactions. Since there is no valence $c,t$ quark inside nucleons at $\hat{I}{¼}_{\mathrm{had}}\sim 1$ GeV, $y_2,y_3$ interactions are manifested in DM-gluon scattering at loop level. We find that renormalization group equation (RGE) and heavy quark threshold effects are important if one calculates the DM-nucleon scattering rate $\ddot{I}{ƒ}_p^{\mathrm{SI}}$ at $\hat{I}{¼}_{\mathrm{had}}\sim 1\mathrm{GeV}$ while constructing the effective theory at $\hat{I}{¼}_{\mathrm{EFT}}\sim m_Z$. For the benchmarks $y_3=0.5,y_2=0.5,1,3$, combined results from $\hat{I}{\text{c◯}}_{\mathrm{DM}}{h}^2\simeq 0.12$, XENON1T, Fermi-LAT, 13 TeV LHC data have almost excluded $m_S<m_t/2$ when only DM-$\{c,t\}$ interactions are considered. FCNC of top quark can be generated at both tree level $t\to \ddot{I}{ˆ}^{(\ast )}S\to cSS$ and loop level $t\to c+{\hat{I}}^3/g/Z$, of which the branching fractions are typically below $10^{-9}$ after passing the other constraints, which are still safe from the current top quark width measurements.

30 pages, 11 figures, JCAP published version