6,578 research outputs found
Bounds on Heavy-to-Heavy Weak Decay Form Factors
We provide upper and lower bounds on the semileptonic weak decay form factors
for and decays by utilizing inclusive
heavy quark effective theory sum rules. These bounds are calculated to second
order in and first order in . The corrections to the bounds at zero recoil are also presented.Comment: 3 pages, talk given at DPF 2000, Columbus, OH, August 9, 2000;
reference adde
3.5-keV X-ray line from nearly-degenerate WIMP dark matter decays
The unidentified emission line at the energy of 3.5~keV observed in
X-rays from galaxy clusters may originate from a process involving a dark
matter particle. On the other hand, a weakly interacting massive particle
(WIMP) has been an attractive dark matter candidate, due to its well-understood
thermal production mechanism and its connection to physics at the TeV scale. In
this paper, we pursue the possibility that the 3.5-keV X-ray arises from a late
time decay of a WIMP dark matter into another WIMP dark matter, both of which
have the mass of ~GeV and whose mass splitting is about 3.5~keV. We
focus on the simplest case where there are two Majorana dark matter particles
and two charged scalars that couple with a standard model matter particle. By
assuming a hierarchical structure in the couplings of the two dark matter
particles and two charged scalars, it is possible to explain the 3.5-keV line
and realize the WIMP dark matter scenario at the same time. Since the effective
coupling of the two different Majorana dark matter particles and one photon
violates CP symmetry, the model always contains a new source of CP violation,
so the model's connection to the physics of electric dipole moments is
discussed. The model's peculiar signatures at the LHC are also studied. We show
the prospect of detecting the charged scalars through a detailed collider
simulation
Electroweak Phase Transition in Georgi-Machacek Model
The Georgi-Machacek model extends the standard model Higgs sector by adding
two isospin triplet scalar fields and imposing global SU(2) symmetry on
them. A feature of the model is that the triplets can acquire a large vacuum
expectation value without conflicting with the current experimental bound on
the parameter. We investigate the electroweak phase transition in the
Georgi-Machacek model by evaluating the finite-temperature effective potential
of the Higgs sector. The electroweak phase transition can be sufficiently
strong in a large parameter space when the triplets acquire a vacuum
expectation value of GeV, opening a possibility to realize successful
electroweak baryogenesis
On gauge dependence of gravitational waves from a first-order phase transition in classical scale-invariant models
We study gauge dependence of gravitational waves produced from a first-order
phase transition in classical scale-invariant models. Accidental gauge
independence of the one-loop effective potential in this class of models is
spoiled by including thermal resummation. The gauge artifact in the resummed
effective potential propagates to the gravitational wave spectrum and results
in one order of magnitude uncertainties in the prediction under a specific
gauge choice.Comment: 12 pages, 1 figure; v2: updated to match version published in PL
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