74 research outputs found
Effects of an extra gauge boson on the top quark decay
The effects of an extra gauge boson with family nonuniversal fermion
couplings on the rare top quark decay gamma10^{-8}m_{Z'}=500Z'B(t --> c
\gamma)\sim 10^{-6}m_{Z'}=1$ TeV.Comment: New paragraphs included to clarify our results, conclusion remains
unchange
Rare top quark decay t --> u_1 \bar{u}_2 u_2 in the standard model
The one-loop induced top quark decay () is
calculated in the context of the standard model. The dominant contribution to
this top quark decay arises from the Feynman diagrams induced by the off-shell
vertex, whereas the box diagrams are negligibly small. In contrast
with the on-shell vertex, which only gives rise to a pure dipolar
effect, the off-shell coupling also involves a monopolar term, which
gives a larger contribution than the dipolar one. It is found that the
branching ratio for the three-body decay is about of the
same order of magnitude of the two-body decay , the latter being
slightly larger, which stems from the fact that the three-body decay is
dominated by a monopolar term.Comment: 8 pages, 3 figures, branching ratio is evaluated using the running
quark masses at the top quark mass scale, results and conclusion changes
slightly, new results agree with those presented in hep-ph/0601151, missing
references are adde
CP violating scalar Dark Matter
We study an extension of the Standard Model (SM) in which two copies of the SM scalar SU(2) doublet which do not acquire a Vacuum Expectation Value (VEV), and hence are inert, are added to the scalar sector. We allow for CP-violation in the inert sector, where the lightest inert state is protected from decaying to SM particles through the conservation of a Z(2) symmetry. The lightest neutral particle from the inert sector, which has a mixed CP-charge due to CP-violation, is hence a Dark Matter (DM) candidate. We discuss the new regions of DM relic density opened up by CP-violation, and compare our results to the CP-conserving limit and the Inert Doublet Model (IDM). We constrain the parameter space of the CP-violating model using recent results from the Large Hadron Collider (LHC) and DM direct and indirect detection experiments.Peer reviewe
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