A taste of dark portals

Abstract

Overwhelming evidence on all cosmological scales points to the inevitable existence of Dark Matter (DM), constituting approximately 85% of all matter in the Universe. The different evidence have one thing in common: they all depend on indirect, gravitational effects arising from the presence of DM. The particle nature of DM remains unknown. While the Weakly Interacting Massive Particle (WIMP) has been a promising candidate to DM, extensive direct detection searches has not yet found a conclusive signal. A possibility is that DM does not interact directly with the Standard Model (SM) but rather through an unstable mediator particle, scenarios commonly referred to as dark portals. A way to probe such models is through flavour changing rare decays of mesons, which are heavily suppressed in the SM, but receive contributions from dark portal models. In this work I consider a model where spin-1 DM is realised as a hidden U(1) symmetry, spontaneously broken by a singlet scalar that acts as the mediator and mixes with the SM Higgs field. This extension induces contributions to the branching fractions B0 s,d ! `+`− where the particular ones B0 s ! μ+μ− and B0 ! μ+μ− have been measured experimentally. The contributions were found to be primarily dependent on the mixing angle and the mediator mass MH1 . I find that while the most likely combination of fundamental parameters lies on the straight line sin2 /M2H 1 = 0.001 where sin 2 [10−3, 1] and MH1 2 [100.5, 101.5] GeV, a large region below this line possess a flat, intermediate likelihood. This is due to the effects of H1’s presence is heavily suppressed by its mass. At the moment the analysis of constraints on spin-1 DM by rare meson decays is largely