Finite temperature effective theories

Lecture Notes, Summer School on Effective Theories and Fundamental Interactions, Erice, July 1996. I describe the construction of effective field theories for equilibrium high-temperature plasma of elementary particles.Comment: 24 pages, Latex, 5 eps figure

Einstein static universe as a brane in extra dimensions

We present a brane-world scenario in which two regions of $AdS_5$ space-time are glued together along a 3-brane with constant positive curvature such that {\em all} spatial dimensions form a compact manifold of topology $S^4$. It turns out that the induced geometry on the brane is given by Einstein's static universe. It is possible to achieve an anisotropy of the manifold which allows for a huge hierarchy between the size of the extra dimension $R$ and the size of the observable universe $R_U$ at present. This anisotropy is also at the origin of a very peculiar property of our model: the physical distance between {\em any two points} on the brane is of the order of the size of the extra dimension $R$ regardless of their distance measured with the use of the induced metric on the brane. In an intermediate distance regime $R \ll r \ll R_U$ gravity on the brane is shown to be effectively 4-dimensional, with corresponding large distance corrections, in complete analogy with the Randall-Sundrum II model. For very large distances $r \sim R_U$ we recover gravity in Einstein's static universe. However, in contrast to the Randall-Sundrum II model the difference in topology has the advantage of giving rise to a geodesically complete space.Comment: 45 pages, 3 figure

Supersymmetric Electroweak Baryogenesis Via Resonant Sfermion Sources

We calculate the baryon asymmetry produced at the electroweak phase transition by quasi-degenerate third generation sfermions in the minimal supersymmetric extension of the Standard Model. We evaluate constraints from Higgs searches, from collider searches for supersymmetric particles, and from null searches for the permanent electric dipole moment (EDM) of the electron, of the neutron and of atoms. We find that resonant sfermion sources can in principle provide a large enough baryon asymmetry in various corners of the sfermion parameter space, and we focus, in particular, on the case of large $\tan\beta$, where third-generation down-type (s)fermions become relevant. We show that in the case of stop and sbottom sources, the viable parameter space is ruled out by constraints from the non-observation of the Mercury EDM. We introduce a new class of CP violating sources, quasi-degenerate staus, that escapes current EDM constraints while providing large enough net chiral currents to achieve successful "slepton-mediated" electroweak baryogenesis.Comment: 35 pages, 9 figures; v2: several revisions, but conclusions unchanged. Matches version published in PR

Electroweak Baryon Number Non-Conservation in the Early Universe and in High Energy Collisions

We review recent progress in the study of the anomalous baryon number non-conservation at high temperatures and in high energy collisions. Recent results on high temperature phase transitions are described, and applications to electroweak baryogenesis are considered. The current status of the problem of electroweak instanton-like processes at high energies is outlined. This paper is written on the occasion of Sakharov's 75th anniversary and will appear in the memorial volume of Uspekhi (Usp. Fiz. Nauk, volume 166, No 5, May 1996).Comment: Minor modifications. A number of new references added. Final version to appear in Uspekhi (Usp. Fiz. Nauk 166 (May, 1996) No 5). 100 pages and 16 eps figure

The Electroweak Phase Transition in Ultra Minimal Technicolor

We unveil the temperature-dependent electroweak phase transition in new extensions of the Standard Model in which the electroweak symmetry is spontaneously broken via strongly coupled, nearly-conformal dynamics achieved by the means of multiple matter representations. In particular, we focus on the low energy effective theory introduced to describe Ultra Minimal Walking Technicolor at the phase transition. Using the one-loop effective potential with ring improvement, we identify regions of parameter space which yield a strong first order transition. A striking feature of the model is the existence of a second phase transition associated to the electroweak-singlet sector. The interplay between these two transitions leads to an extremely rich phase diagram.Comment: 38 RevTeX pages, 9 figure

Beyond MSSM Baryogenesis

Taking the MSSM as an effective low-energy theory, with a cut-off scale of a few TeV, can make significant modifications to the predictions concerning the Higgs and stop sectors. We investigate the consequences of such a scenario for electroweak baryogenesis. We find that the window for MSSM baryogenesis is extended and, most important, can be made significantly more natural. Specifically, it is possible to have one stop lighter than the top and the other significantly lighter than TeV simultaneously with the Higgs mass above the LEP bound. In addition, various aspects concerning CP violation are affected. Most notably, it is possible to have dynamical phases in the bubble walls at tree level, providing CP violating sources for Standard Model fermions.Comment: 20 pages, 2 figures; v2: added reference

Generating the Baryon Asymmetry of the Universe in Split Fermion Models

The origin of the matter-antimatter asymmetry of the universe is one of the major unsolved problems in cosmology and particle physics. In this paper, we investigate the recently proposed possibility that split fermion models -- extra dimensional models where the standard model fermions are localized to different points around the extra dimension -- could provide a means to generate this asymmetry during the phase transition of the localizing scalars. After setting up the scenario that we consider, we use a single fermion toy model to estimate the reflection coefficients for scattering off the phase boundary using a more realistic scalar profile than previous work resulting in a different Kaluza Klein spectrum. The value we calculate for $n_B/s$ is consistent with the mechanism being the source of the baryon asymmetry of our universe provided the $B-L$ violating processes have an efficiency of order $10^{-5}$.Comment: 17 pages, 3 figures; References added; Minor changes, Accepted for publication in Phys. Rev.

Numerical Approach to Multi Dimensional Phase Transitions

We present an algorithm to analyze numerically the bounce solution of first-order phase transitions. Our approach is well suited to treat phase transitions with several fields. The algorithm consists of two parts. In the first part the bounce solution without damping is determined, in which case energy is conserved. In the second part the continuation to the physically relevant case with damping is performed. The presented approach is numerically stable and easily implemented.Comment: 18 pages, 8 figures; some comments, a reference and a table adde

Electroweak bubbles and sphalerons

We consider non-perturbative solutions of the Weinberg-Salam model at finite temperature. We employ an effective temperature-dependent potential yielding a first order phase transition. In the region of the phase transition, there exist two kinds of static, spherically symmetric solutions: sphalerons and bubbles. We analyze these solutions as functions of temperature. We consider the most general spherically symmetric fluctuations about the two solutions and construct the discrete modes in the region of the phase transition. Sphalerons and bubbles both possess a single unstable mode. We present simple approximation formulae for these levels.Comment: 14 pages, plain tex, 9 figures appended as postscript files at the end of the paper. THU-93/0