Dark $Z$ Implication for Flavor Physics

TL;DR

This paper explores how a dark $Z$ boson influences flavor physics, providing exact calculations of new penguin diagrams and analyzing experimental data to constrain dark matter models.

Contribution

It introduces an exact calculation of $Z'$-induced penguin diagrams and assesses their impact on flavor physics observables, offering a novel approach to dark matter studies.

Findings

The $Z'$ coupling constant is constrained to be of order 1.

Flavor physics measurements limit the parameter space of dark $Z$ models.

The new penguin diagrams modify standard flavor decay processes.

Abstract

Dark $Z$/dark photon ($Z'$) is one candidate of dark force carrier, which helps to interpret the properties of dark matter (DM). Other than traditional studies of DM including direct detection, indirect detection and collider simulation, in this work we take flavor physics as a complementary approach to investigate the features of dark matter. We give an exact calculation of the new type of penguin diagram induced by $Z'$ which further modifies the well-known $X, Y, Z$ functions in penguin-box expansion. The measurement of rare decays $B\to K^{(*)}\mu^+\mu^-$ and $B_s\to \mu^+\mu^-$ at LHC, together with direct CP violation $\varepsilon'/\varepsilon$ in $K\to\pi \pi$ as well as $K_L\to\mu^+\mu^-$, are used to determine the parameter space. The size of coupling constant, however, is found to be $\mathcal{O}(1)$ which is much weaker than the known constraints.