126 research outputs found
Precise Nucleosynthesis Limits on Neutrino Masses
A computation of nucleosynthesis bounds on the masses of long-lived Dirac and
Majorana neutrinos is reviewed. In particular an explicit treatment of the
``differential heating'' of the \nue and \bnue ensembles due to the
residual out-of-equilibrium annihilations of decoupled heavy neutrinos is
included. The effect is found to be considerably weaker than recently reported
by Dolgov et al. For example, the bounds for a Dirac tau neutrino are \mnt <
0.37 MeV or \mnt > 25 MeV (for \dNu > 1), whereas the present laboratory
bound is \mnt < 23.1 MeV.Comment: 6 pages, 2 eps-figures. Talk at Neutrino 9
Dark matter from unification
We consider a minimal extension of the Standard Model (SM), which leads to
unification of the SM coupling constants, breaks electroweak symmetry
dynamically by a new strongly coupled sector and leads to novel dark matter
candidates. In this model, the coupling constant unification requires the
existence of electroweak triplet and doublet fermions singlet under QCD and new
strong dynamics underlying the Higgs sector. Among these new matter fields and
a new right handed neutrino, we consider the mass and mixing patterns of the
neutral states. We argue for a symmetry stabilizing the lightest mass
eigenstates of this sector and determine the resulting relic density. The
results are constrained by available data from colliders and direct and
indirect dark matter experiments. We find the model viable and outline briefly
future research directions.Comment: 30 pages, 7 figure
Naturality, unification and dark matter
We consider a model where electroweak symmetry breaking is driven by
Technicolor dynamics with minimal particle content required for walking
coupling and saturation of global anomalies. Furthermore, the model features
three additional Weyl fermions singlet under Technicolor interactions, which
provide for a one-loop unification of the Standard Model gauge couplings. Among
these extra matter fields exists a possible candidate for weakly interacting
dark matter. We evaluate the relic densities and find that they are sufficient
to explain the cosmological observations and avoid the experimental limits from
earth-based searches. Hence, we establish a non-supersymmetric framework where
hierarchy and naturality problems are solved, coupling constant unification is
achieved and a plausible dark matter candidate exists
Baryogenesis in the two doublet and inert singlet extension of the Standard Model
We investigate an extension of the Standard Model containing two Higgs
doublets and a singlet scalar field (2HDSM). We show that the model can have a
strongly first-order phase transition and give rise to the observed baryon
asymmetry of the Universe, consistent with all experimental constraints. In
particular, the constraints from the electron and neutron electric dipole
moments are less constraining here than in pure two-Higgs-doublet model (2HDM).
The two-step, first-order transition in 2HDSM, induced by the singlet field,
may lead to strong supercooling and low nucleation temperatures in comparison
with the critical temperature, , which can significantly alter the
usual phase-transition pattern in 2HD models with .
Furthermore, the singlet field can be the dark matter particle. However, in
models with a strong first-order transition its abundance is typically but a
thousandth of the observed dark matter abundance.Comment: 25 pages, 8 figures; minor changes to match the published versio
Diffusion and Debye Screening Near Expanding Domain Walls
We study the effect of Debye screening of hypercharge when a net fermion
number is reflected from a domain wall during a first order phase transition,
which may be relevant for electroweak baryogenesis. We give a simple method for
computing the effect of screening within the diffusion approximation, whose
results are compatible with those of a more elaborate treatment based on the
Boltzmann equation. Our formalism takes into account the differences in
mobility of different particle species. We believe it is conceptually simpler
than other accounts of screening that have appeared in this context. Somewhat
surprisingly, we find that Debye screening can actually {\it enhance}
electroweak baryogenesis by a modest factor ().Comment: 11 pp. latex, uses epsf.tex, 1 uuencoded figur
Supersymmetric Electroweak Phase Transition: Dimensional Reduction versus Effective Potential
We compare two methods of analyzing the finite-temperature electroweak phase
transition in the minimal supersymmetric standard model: the traditional
effective potential (EP) approach, and the more recently advocated procedure of
dimensional reduction (DR). The latter tries to avoid the infrared
instabilities of the former by matching the full theory to an effective theory
that has been studied on the lattice. We point out a limitation of DR that
caused a large apparent disagreement with the effective potential results in
our previous work. We also incorporate wave function renormalization into the
EP, which is shown to decrease the strength of the phase transition. In the
regions of parameter space where both methods are expected to be valid, they
give similar results, except that the EP is significantly more restrictive than
DR for the range of baryogenesis-allowed values of , , the
critical temperature, and the up-squark mass parameter . In contrast, the
DR results are consistent with 2\lsim\tan\beta\lsim 4, GeV, and
sufficiently large to have universality of the squark soft-breaking
masses at the GUT scale, in a small region of parameter space. We suggest that
the differences between DR and EP are due to higher-order perturbative
corrections rather than infrared effects.Comment: 19 pages, Latex, 7 figures, uses epsf.te
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