1,146 research outputs found
Excited Dark Matter versus PAMELA/Fermi
Excitation of multicomponent dark matter in the galactic center has been
proposed as the source of low-energy positrons that produce the excess 511 keV
gamma rays that have been observed by INTEGRAL. Such models have also been
promoted to explain excess high-energy electrons/positrons observed by the
PAMELA, Fermi/LAT and H.E.S.S. experiments. We investigate whether one model
can simultaneously fit all three anomalies, in addition to further constraints
from inverse Compton scattering by the high-energy leptons. We find models that
fit both the 511 keV and PAMELA excesses at dark matter masses M < 400 GeV, but
not the Fermi lepton excess. The conflict arises because a more cuspy DM halo
profile is needed to match the observed 511 keV signal than is compatible with
inverse Compton constraints at larger DM masses.Comment: 4 pages, presented at Moriond Cosmology 201
Is electroweak baryogenesis dead?
Electroweak baryogenesis is severely challenged in its traditional settings:
the Minimal Supersymmetric Standard Model, and in more general two Higgs
doublet models. Fine tuning of parameters is required, or large couplings
leading to a Landau pole at scales just above the new physics introduced. The
situation is somewhat better in models with a singlet scalar coupling to the
Higgs so as to give a strongly first order phase transition due to a tree-level
barrier, but even in this case no UV complete models had been demonstrated to
give successful baryogenesis. Here we point out some directions that overcome
this limitation, by introducing a new source of CP violation in the couplings
of the singlet field. A model of electroweak baryogenesis requiring no fine
tuning and consistent to scales far above 1 TeV is demonstrated, in which dark
matter plays the leading role in creating a CP asymmetry that is the source of
the baryon asymmetry.Comment: 10 pages, 7 figures. Talk presented at Moriond Electroweak (24 Mar.
2017) and Higgs Cosmology workshop, Kavli Royal Society Centre, Chichley
Hall, UK (28 Mar. 2017); v2: added discussion of bubble wall shape and
velocity and references; published versio
Quintessence, Cosmological Horizons, and Self-Tuning
We point out that quintessence with an exponential potential V_0 exp(- beta
phi / 3^{1/2} M_p) can account for the present observed acceleration of the
universe, without necessarily leading to eternal acceleration. This occurs for
2.4 < beta < 2.8. Thus a cosmological horizon, which is supposed to be
problematic within the context of string theory, can be avoided. We argue that
this class of models is not particularly fine-tuned. We further examine this
question in the context of a modified Friedmann equation, H^2 ~ rho + p, which
is suggested by higher dimensional self-tuning approaches to the cosmological
constant problem. It is shown that the self-tuning case can also be consistent
with observations, if 1.8 < beta < 2.4. Future observations of high-z
supernovae will be able to test whether beta lies in the desired range.Comment: 13 pp., 5 figures; references adde
Predictions for SUSY Particle Masses from Electroweak Baryogenesis
In collaboration with G.D. Moore, the electroweak phase transition in the
minimal supersymmetric standard model is studied using the two-loop effective
potential. We make a comprehensive search of the MSSM parameter space
consistent with electroweak baryogenesis, taking into account various factors:
the latest experimental constraints on the Higgs boson mass and the rho
parameter, the possibility of significant squark and Higgs boson mixing, and
the exact rate of bubble nucleation and sphaleron transitions. Most of the
baryogenesis-allowed regions of parameter space will be probed by LEP 200,
hence the Higgs boson is likely to be discovered soon if the baryon asymmetry
was indeed created during the electroweak phase transition.Comment: 5pp, 12 figures, uses psfig and ltwol2e2.sty (included); invited talk
presented at ICHEP `98, Vancouve
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