Sources for Electroweak Baryogenesis

I review a computation of the baryon asymmetry arising from a first order electroweak phase transition in the Minimal Supersymmetric Standard model by classical force mechanism (CFM). I focus on CP violation provided by the charginos and show that it is the usually neglected sum of the two Higgsino fields, H_1+H_2, which gives a larger contribution to the baryon asymmetry than does the combination H_1-H_2. In fact, the latter contribution is exactly zero in CFM, because it is associated with a phase transformation of the fields. Baryogenesis is found to be most effective in MSSM CFM when only $\tilde t_R$ is light, which lends independent support for the "light stop scenario", and it remains viable for CP-violating phases as small as \delta_\mu \sim {\it few} \times 10^{-3}.Comment: 7 pages 1 figure; plenary talk at COSMO-99, Trieste, Italy, Sep 27 - Oct 2, 199

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

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

Supersymmetric Electroweak Baryogenesis in the WKB approximation

We calculate the baryon asymmetry generated at the electroweak phase transition in the minimal supersymmetric standard model, treating the particles in a WKB approximation in the bubble wall background. A set of diffusion equations for the particle species relevant to baryon generation, including source terms arising from the CP violation associated with the complex phase $\delta$ of the $\mu$ parameter, are derived from Boltzmann equations, and solved. The conclusion is that $\delta$ must be \gsim 0.1 to generate a baryon asymmetry consistent with nucleosynthesis. We compare our results to several other recent computations of the effect, arguing that some are overestimates.Comment: 12 pages, 1 figure, corrected some criticisms of hep-ph/9702409; to appear in Phys. Lett.

Creation of large spatial fluctuations in neutrino asymmetry by neutrino oscillations

We consider active-sterile neutrino oscillations in the early universe in an inhomogeneous isocurvature background. We show that very small initial baryonic seed-inhomogeneities can trigger a growth of very large amplitude spatial fluctuations in lepton asymmetry. Domains of varying asymmetry are observed to persist for a long time despite dissipative effects. The space dependent asymmetry profiles give rise to MSW-resonances within the domain boundaries, enhancing dramatically the equilibration of the sterile neutrino species. According to our one-dimensional toy-model, the effect is so strong that almost the entire parameter space where exponential growth of asymmetry occurs would be ruled out by nucleosynthesis.Comment: 1+21 pages, 3 figure

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

The Quantum Boltzmann Equation in a Nontrivial Background

This talk is a status report on our study of quantum transport equations relevant for baryogenesis computations. Our main finding is that, as a consequence of localization in space, the quasiparticle picture of the plasma dynamics breaks down at first non-trivial order in gradient expansion. While in this talk we focus on bosons, we expect that a similar picture holds for fermions. We then argue that the quasiparticle picture is recovered in the adiabatic limit of frequent scattering.Comment: 7 pages, 2 figures, macro sprocl.sty, plenary talk given by T. Prokopec at COSMO-99, Trieste, Italy, Sep 27 - Oct 2, 199

Connection between dense gas mass fraction, turbulence driving, and star formation efficiency of molecular clouds

We examine the physical parameters that affect the accumulation of gas in molecular clouds to high column densities where the formation of stars takes place. In particular, we analyze the dense gas mass fraction (DGMF) in a set of self-gravitating, isothermal, magnetohydrodynamic turbulence simulations including sink particles to model star formation. We find that the simulations predict close to exponential DGMFs over the column density range N(H2) = 3-25 x 10^{21} cm^{-2} that can be easily probed via, e.g., dust extinction measurements. The exponential slopes correlate with the type of turbulence driving and also with the star formation efficiency. They are almost uncorrelated with the sonic Mach number and magnetic-field strength. The slopes at early stages of cloud evolution are steeper than at the later stages. A comparison of these predictions with observations shows that only simulations with relatively non-compressive driving (b ~< 0.4) agree with the DGMFs of nearby molecular clouds. Massive infrared dark clouds can show DGMFs that are in agreement with more compressive driving. The DGMFs of molecular clouds can be significantly affected by how compressive the turbulence is on average. Variations in the level of compression can cause scatter to the DGMF slopes, and some variation is indeed necessary to explain the spread of the observed DGMF slopes. The observed DGMF slopes can also be affected by the clouds' star formation activities and statistical cloud-to-cloud variations.Comment: 7 pages, 7 figures, accepted to A&A Letter

Supersymmetric Electroweak Baryogenesis

We re-examine the generation of the baryon asymmetry in the minimal supersymmetric standard model (MSSM) during the electroweak phase transition. We find that the dominant source for baryogenesis arises from the chargino sector. The CP-violation comes from the complex phase in the mu parameter, which provides CP-odd contributions to the particle dispersion relations. This leads to different accelerations for particles and antiparticles in the wall region which, combined with diffusion, leads to the separation of Higgsinos and their antiparticles in the front of the wall. These asymmetries get transported to produce perturbations in the left-handed chiral quarks, which then drive sphaleron interactions to create the baryon asymmetry. We present a complete derivation of the semiclassical WKB formalism, including the chargino dispersion relations and a self-consistent derivation of the diffusion equations starting from semiclassical Boltzmann equations for WKB-excitations. We stress the advantages of treating the transport equations in terms of the manifestly gauge invariant physical energy and kinetic momentum, rather than in the gauge variant canonical variables used in previous treatments. We show that a large enough baryon asymmetry can be created for the phase of the complex mu parameter as small as ~ 0.001, which is consistent with bounds from the neutron electric dipole moment.Comment: 54 pages, 3 figure