2,417 research outputs found
The nuMSM, leptonic asymmetries, and properties of singlet fermions
We study in detail the mechanism of baryon and lepton asymmetry generation in
the framework of the MSM (an extension of the Standard Model by three
singlet fermions with masses smaller than the electroweak scale). We elucidate
the issue of CP-violation in the model and define the phase relevant for
baryogenesis. We clarify the question of quantum-mechanical coherence,
essential for the lepton asymmetry generation in singlet fermion oscillations
and compute the relevant damping rates. The range of masses and couplings of
singlet leptons which can lead to successful baryogenesis is determined. The
conditions which ensure survival of primordial (existing above the electroweak
temperatures) asymmetries in different leptonic numbers are analysed. We
address the question whether CP-violating reactions with lepton number
non-conservation can produce leptonic asymmetry {\em below} the sphaleron
freeze-out temperature. This asymmetry, if created, leads to resonant
production of dark matter sterile neutrinos. We show that the requirement that
a significant lepton asymmetry be produced puts stringent constraints on the
properties of a pair of nearly degenerate singlet fermions, which can be tested
in accelerator experiments. In this region of parameters the MSM provides
a common mechanism for production of baryonic matter and dark matter in the
universe. We analyse different fine-tunings of the model and discuss possible
symmetries of the MSM Lagrangian that can lead to them.Comment: 56 pages, 16 figures. Many clarifications added, published versio
Some Two-Loop Corrections to the Finite Temperature Effective Potential in the Electroweak Theory
Perturbation theory at finite temperature suffers from well-known infrared
problems. In the standard model, as a result, one cannot calculate the
effective potential for arbitrarily small values of , the Higgs
expectation value. Because the Higgs field is now known not to be extremely
light, it is necessary to determine whether perturbation theory is a reliable
guide to properties of the weak phase transition. In this note, we evaluate the
most singular contributions to the potential at two loops as well as the
leading strong interaction contributions. Above the critical temperature, the
strong interaction corrections are reasonably small, while the weak corrections
are about 10\%, even for rather small values of the Higgs field. At the
critical temperature, the weak corrections have a more substantial effect,
rendering the transition significantly more first order, but not significantly
changing the upper bound on the Higgs mass required for baryogenesis.Comment: 13 pages, figures available on request, SCIPP 92/4
On the High Phase Transition in the Gauged Higgs Model
We study the effective field theory of a weakly coupled 3+1d gauged
type model at high temperature. Our model has real scalars
( complex Higgs doublets) and a gauge group which is spontaneously
broken by a nonzero scalar field at zero temperature.
We find, for sufficiently large , that the transition from the high
temperature symmetry restoring phase to the low temperature phase can be either
first order or second order depending on the ratio of the gauge coupling to the
scalar self coupling.Comment: 16 pages. 1 Figure, not include
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
Quantum scale invariance, cosmological constant and hierarchy problem
We construct a class of theories which are scale invariant on quantum level
in all orders of perturbation theory. In a subclass of these models scale
invariance is spontaneously broken, leading to the existence of a massless
dilaton. The applications of these results to the problem of stability of the
electroweak scale against quantum corrections, to the cosmological constant
problem and to dark energy are discussed.Comment: 6 pages, replaced with journal versio
- …