Abstract
The flavor-changing neutral current decay processes of the $B$ and $B_c$ mesons with the final states involving spin-$1/2$ particles are investigated. By considering the background of the Standard Model where $\nu\bar\nu$ contributes the missing energy and the experimental upper bounds for the branching fractions, we get the constraints of the coupling constants of the quark-antiquark and the assumed invisible particles $\chi\bar\chi$. The constraints of the coupling constants are then used to study the similar processes of the $B_c$ meson. At some specific region of $m_\chi$, the upper limit of BR($B_c\to D_{(s)}\chi\bar\chi$) is of the order of $10^{-6}$, while for BR($B_c\to D^\ast_{(s)}\chi\bar\chi$), it is $10^{-5}$. The possibility of distinguishing $\chi$ to be a Majorana or Dirac fermion by the differential branching fractions is also discussed.
Highlights
As the freeze-out mechanism [1,2] can naturally interpret the observed dark matter abundance in our Universe, the weakly interacting massive particle (WIMP) is considered to be one of the most promising dark matter candidates
We studied the flavor-changing neutral current (FCNC) processes of the B meson decaying to the invisible spin-1=2 fermions
By comparing the theoretical predictions of BRðB → DððÃsÞÞννÞ and the experimental upper bounds for BRðB → DððÃsÞÞ=EÞ, we derived the constraints of the effective coupling constants
Summary
As the freeze-out mechanism [1,2] can naturally interpret the observed dark matter abundance in our Universe, the weakly interacting massive particle (WIMP) is considered to be one of the most promising dark matter candidates. Missing energy signals [11] in flavor-changing neutral current (FCNC) processes of heavy mesons provide a possible way to probe light WIMP. There are many models involving the fermionic dark matter particles, such as sterile neutrino [14], neutralino [17,18], Higgs-portal [19,20], Z-portal [21], and singlet-doublet [22,23,24,25,26] It can be either a Majorana or a Dirac fermion, as it is electrically neutral. We will further study the spin-1=2 invisible particles in B and Bc meson FCNC decays.
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