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, $T_n \ll T_c$, which can significantly alter the usual phase-transition pattern in 2HD models with $T_n \approx T_c$. 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 ($\sim 2$).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 $\tan\beta$, $m_h$, the critical temperature, and the up-squark mass parameter $m_U$. In contrast, the DR results are consistent with 2\lsim\tan\beta\lsim 4, $m_h<80$ GeV, and $m_U$ 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