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Register a new userBaryogenesis: A small review of the big picture
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Authors
Csaba Balazs
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I schematically, and very lightly, review some ideas that fuel model building in the field of baryogenesis. Due to limitations of space, and my expertise, this mini-review is incomplete and biased toward particle physics, especially supersymmetry.
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We explore the possibility of an Ekpyrotic contraction phase harbouring a mechanism for Baryogenesis. A Chern-Simons coupling between the fast-rolling Ekpyrotic scalar and the Standard Model Hypercharge gauge field enables the generation of a non-zero helicity during the contraction phase. The baryon number subsequently produced at the Electroweak Phase Transition is consistent with observation for a range of couplings and bounce scales. Simultaneously, the gauge field production during the contraction provides the seeds for galactic magnetic fields and sources gravitational waves, which may provide additional avenues for observational confirmation.
We explore a simple model which naturally explains the observed baryon asymmetry of the Universe. In this model the strong coupling is promoted to a dynamical quantity, which evolves through the vacuum expectation value of a singlet scalar field that mixes with the Higgs field. In the resulting cosmic history, QCD confinement and electroweak symmetry breaking initially occur simultaneously close to the weak scale. The early confinement triggers the axion to roll toward its minimum, which creates a chemical potential between baryons and antibaryons through the interactions of the $eta$ meson, resulting in spontaneous baryogenesis. The electroweak sphalerons are sharply switched off after confinement and the baryon asymmetry is frozen in. Subsequently, evolution of the Higgs vacuum expectation value (which is modified in the confined phase) triggers a relaxation to a Standard Model-like vacuum. We identify viable regions of parameter space, and describe various experimental probes, including current and future collider constraints, and gravitational wave phenomenology.
A novel mechanism, catalyzed baryogenesis, is proposed to explain the observed baryon asymmetry in our universe. In this mechanism, the motion of a ball-like catalyst provides the necessary out-of-equilibrium condition, its outer wall has CP-violating interactions with the Standard Model particles, and its interior has baryon number violating interactions. We use the electroweak-symmetric ball model as an example of such a catalyst. In this model, electroweak sphalerons inside the ball are active and convert baryons into leptons. The observed baryon number asymmetry can be produced for a light ball mass and a large ball radius. Due to direct detection constraints on relic balls, we consider a scenario in which the balls evaporate, leading to dark radiation at testable levels.
We re-evaluate the status of supersonic electroweak baryogenesis using a generalized fluid Ansatz for the non-equilibrium distribution functions. Instead of truncating the expansion to first order in momentum, we allow for higher order terms as well, including up to 21 fluctuations. The collision terms are computed analytically at leading-log accuracy. We also point out inconsistencies in the standard treatments of transport in electroweak baryogenesis, arguing that one cannot do without specifying an Ansatz for the distribution function. We present the first analysis of baryogenesis using the fluid approximation to higher orders. Our results support the recent findings that baryogenesis may indeed be possible even in the presence of supersonic wall velocities.
A personal summary of the discussions which took place at the informal meeting in Amirim, Israel from June 1-4 2000, concerning the dipole picture of small-$x$ physics is presented. The broad aim of the meeting was to address the question ``Has HERA reached a new QCD regime (at small $x$) ?. The new regime in question is the high-density, but weak-coupling, limit of perturbative QCD.
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