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

Sterile neutrinos in cosmology and how to find them in the lab

A number of observed phenomena in high energy physics and cosmology lack their resolution within the Standard Model of particle physics. These puzzles include neutrino oscillations, baryon asymmetry of the universe and existence of dark matter. We discuss the suggestion that all these problems can be solved by new physics which exists only below the electroweak scale. The dedicated experiments that can confirm or rule out this possibility are discussed.Comment: Invited talk at XXIII Int. Conf. on Neutrino Physics and Astrophysics, May 25-31, Christchurch, New Zealan

An all-order discontinuity at the electroweak phase transition

We define a non-local gauge-invariant Green's function which can distinguish between the symmetric (confinement) and broken (Higgs) phases of the hot SU(2)xU(1) electroweak theory to all orders in the perturbative expansion. It is related to the coupling of the Chern-Simons number to a massless Abelian gauge field. The result implies either that there is a way to distinguish between the phases, even though the macroscopic thermodynamical properties of the system have been observed to be smoothly connected, or that the perturbative Coleman-Hill theorem on which the argument is based, is circumvented by non-perturbative effects. We point out that this question could in principle be studied with three-dimensional lattice simulations.Comment: 9 pages; misprint corrected, reference and small clarifications added; to appear in Phys.Lett.

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

Strong Sphalerons and Electroweak Baryogenesis

We analyze the spontaneous baryogenesis and charge transport mechanisms suggested by Cohen, Kaplan and Nelson for baryon asymmetry generation in extended versions of electroweak theory. We find that accounting for non-perturbative chirality-breaking transitions due to strong sphalerons reduces the baryonic asymmetry by the factor $(m_t/\pi T)^2$ or $\alpha_W$, provided those processes are in thermal equilibrium.Comment: CERN-TH.7080/9

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

On the Decoupling of Heavy Modes in Kaluza-Klein Theories

In this paper we examine the 4-dimensional effective theory for the light Kaluza-Klein (KK) modes. Our main interest is in the interaction terms. We point out that the contribution of the heavy KK modes is generally needed in order to reproduce the correct predictions for the observable quantities involving the light modes. As an example we study in some detail a 6-dimensional Einstein-Maxwell theory coupled to a charged scalar and fermions. In this case the contribution of the heavy KK modes are geometrically interpreted as the deformation of the internal space.Comment: 38 pages, 1 figur

Asymptotic safety of gravity and the Higgs-boson mass

Abtract: If gravity is asymptotically safe, then the ultimate theory might be just the standard model (minimally supplemented by a few light particles to accommodate neutrino masses and oscillations, dark matter, and the baryon asymmetry of the Universe) plus gravity. If this is indeed the case, then the Higgs-boson mass can be predicted (m H = m min ≃ 130 GeV with an uncertainty of only a few GeV) or constrained to be in the interval m min < m H < m max ≃ 174 Ge