A taste of dark portals
Typ
Examensarbete för masterexamen
Program
Publicerad
2021
Författare
Åstrand, Emil
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
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
Beskrivning
Ämne/nyckelord
dark matter , flavour physics , B-meson , higgs portal , rare decays