641 research outputs found
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 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 . 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 and the size
of the observable universe 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 regardless of their distance measured with the use of the induced
metric on the brane. In an intermediate distance regime
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 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
, 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 is
consistent with the mechanism being the source of the baryon asymmetry of our
universe provided the violating processes have an efficiency of order
.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
- …