133 research outputs found
Baryon and lepton numbers in two scenarios of leptogenesis
Baryon and lepton numbers of the Universe in leptogenesis with Dirac neutrino
and leptogenesis with Majorana neutrino scenarios are considered. It is shown
that despite quite different features of Dirac and Majorana fermions both
scenarios yield the same relation among the initial lepton and the final baryon
asymmetries. Moreover right-handed neutrinos in the leptogenesis with Dirac
neutrino scenario have very little impact on the effective number of
relativistic degrees of freedom, constrained by BBN. Thus the two scenarios are
similar from the cosmological point of view. It is also pointed out that in
thermal equilibrium the 3B+L sum is zero for left-handed fermions.Comment: 9 pages, 4 figure
Basis invariant measure of CP-violation and renormalization
We analyze, in the context of a simple toy model, for which renormalization
schemes the CP-properties of bare Lagrangian and its finite part coincide. We
show that this is the case for the minimal subtraction and on-shell schemes.
The CP-properties of the theory can then be characterized by CP-odd basis
invariants expressed in terms of renormalized masses and couplings. For the
minimal subtraction scheme we furthermore show that in CP-conserving theories
the CP-odd basis invariants are zero at any scale but are not renormalization
group invariant in CP-violating ones.Comment: 5 page
Leptogenesis in crossing and runaway regimes
We study the impact of effective thermal masses and widths on resonant
leptogenesis. We identify two distinct possibilities which we refer to as
crossing and runaway regimes. In the runaway regime the mass difference grows
monotonously with temperature, whereas it initially decreases in the crossing
regime, such that the effective masses become equal at some temperature.
Following the conventional logic the source of the asymmetry would vanish in
the latter case. Using non-equilibrium quantum field theory, we analytically
demonstrate that the vanishing of the difference of the effective masses does
however neither imply a suppression nor a strong enhancement of the source for
the lepton asymmetry. In the vicinity of the crossing point the asymmetry
calculated in an (improved) Boltzmann limit develops a spurious peak, which
signals the breakdown of the quasiparticle approximation. In the exact result
this spurious enhancement is compensated by coherent transitions between the
two mass shells. Despite the breakdown of the quasiparticle approximation
off-shell contributions remain negligibly small even at the crossing point.Comment: 41 pages, 9 figures, figures 3 and 6 are animation
Medium corrections to the CP-violating parameter in leptogenesis
In two recent papers, arXiv:0909.1559 and arXiv:0911.4122, it has been
demonstrated that one can obtain quantum corrected Boltzmann kinetic equations
for leptogenesis using a top-down approach based on the
Schwinger-Keldysh/Kadanoff-Baym formalism. These "Boltzmann-like" equations are
similar to the ones obtained in the conventional bottom-up approach but differ
in important details. In particular there is a discrepancy between the
CP-violating parameter obtained in the first-principle derivation and in the
framework of thermal field theory. Here we demonstrate that the two approaches
can be reconciled if causal n-point functions are used in the thermal field
theory approach. The new result for the medium correction to the CP-violating
parameter is qualitatively different from the conventional one. The analogy to
a toy model considered earlier enables us to write down consistent quantum
corrected Boltzmann equations for thermal leptogenesis in the Standard Model
(supplemented by three right-handed neutrinos) which include quantum
statistical terms and medium corrected expressions for the CP-violating
parameter.Comment: 13 pages, 9 figure
Universal description of three two-component fermions
A quantum mechanical three-body problem for two identical fermions of mass
and a distinct particle of mass in the universal limit of zero-range
two-body interaction is studied. For the unambiguous formulation of the problem
in the interval ( and ) an additional parameter determining the wave function near
the triple-collision point is introduced; thus, a one-parameter family of
self-adjoint Hamiltonians is defined. The dependence of the bound-state
energies on and in the sector of angular momentum and parity is calculated and analysed with the aid of a simple model
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