303 research outputs found
CP violation in the mass matrix of heavy neutrinos
We discuss the question of CP-violation in the effective Hamiltonian approach
in models of leptogenesis through heavy right handed neutrino decays. We first
formulate the problem in four component notation and then point out that before
the heavy neutrinos have decayed away, the universe becomes CP-asymmetric in
the heavy neutrinos. However, the lepton asymmetry generated after they
completely decay are independent of this asymmetry.Comment: 9 pages latex file, minor change
Leptogenesis from Additional Higgs Doublets
Leptogenesis may be induced by the mixing of extra Higgs doublets with
experimentally accessible masses. This mechanism relies on diagrammatic cuts
that are kinematically forbidden in the vacuum but contribute at finite
temperature. A resonant enhancement of the asymmetry occurs generically
provided the dimensionless Yukawa and self-interactions are suppressed compared
to those of the Standard Model Higgs field. This is in contrast to typical
scenarios of Resonant Leptogenesis, where the asymmetry is enhanced by imposing
a degeneracy of singlet neutrino masses.Comment: 12 pages; more phenomenological details adde
Leptogenesis with Majorana neutrinos
I review the origin of the lepton asymmetry which is converted to a baryon
excess at the electroweak scale. This scenario becomes more attractive if we
can relate it to other physical phenomena. For this reason I elaborate on the
conditions of the early universe which lead to a sizable lepton asymmetry. Then
I describe methods and models which relate the low energy parameters of
neutrinos to the high energy (cosmological) CP-violation and to neutrinoless
double beta-decay.Comment: Contributed to 1st Workshop on Neutrino - Nucleus Interactions in the
Few GeV Region (NuInt01), Tsukuba, Japan, 13-16 Dec 2001. 6 pages, 6 figure
Leptogenesis with "Fuzzy Mass Shell" for Majorana Neutrinos
We study the mixing of elementary and composite particles. In quantum field
theory the mixing of composite particles originates in the couplings of the
constituent quarks and for neutrinos in self-energy diagrams. In the event that
the incoming and outgoing neutrinos have different masses, the self-energy
diagrams vanish because energy is not conserved but the finite decaying widths
make the mixing possible. We can consider the neutrinos to be "fuzzy" states on
their mass shell and the mixing is understood as the overlap of two
wavefunctions. These considerations restrict the mass difference to be
approximately equal to or smaller than the largest of the two widths: abs(M_i -
M_j) lessorequal max(Gamma_i, Gamma_j).Comment: 11 pages, 1 figur
Soft Leptogenesis
We study ``soft leptogenesis'', a new mechanism of leptogenesis which does
not require flavour mixing among the right-handed neutrinos. Supersymmetry
soft-breaking terms give a small mass splitting between the CP-even and CP-odd
right-handed sneutrino states of a single generation and provide a CP-violating
phase sufficient to generate a lepton asymmetry. The mechanism is successful if
the lepton-violating soft bilinear coupling is unconventionally (but not
unnaturally) small. The values of the right-handed neutrino masses predicted by
soft leptogenesis can be low enough to evade the cosmological gravitino
problem.Comment: 13 pages, 5 figures, uses axodraw.st
Leptogenesis: The Other Cuts
For standard leptogenesis from the decay of singlet right-handed neutrinos,
we derive source terms for the lepton asymmetry that are present in a finite
density background but absent in the vacuum. These arise from cuts through the
vertex correction to the decay asymmetry, where in the loop either the Higgs
boson and the right-handed neutrino or the left-handed lepton and the
right-handed neutrino are simultaneously on shell. We evaluate the source terms
numerically and use them to calculate the lepton asymmetry for illustrative
points in parameter space, where we consider only two right-handed neutrinos
for simplicity. Compared to calculations where only the standard cut through
the propagators of left-handed lepton and Higgs boson is included, sizable
corrections arise when the masses of the right-handed neutrinos are of the same
order, but the new sources are found to be most relevant when the decaying
right-handed neutrino is heavier than the one in the loop. In that situation,
they can yield the dominant contribution to the lepton asymmetry.Comment: 22 pages, 4 figure
Baryon Asymmetry, Neutrino Mixing and Supersymmetric SO(10) Unification
The baryon asymmetry of the universe can be explained by the
out-of-equilibrium decays of heavy right-handed neutrinos. We analyse this
mechanism in the framework of a supersymmetric extension of the Standard Model
and show that lepton number violating scatterings are indispensable for
baryogenesis, even though they may wash-out a generated asymmetry. By assuming
a similar pattern of mixings and masses for neutrinos and up-type quarks, as
suggested by SO(10) unification, we can generate the observed baryon asymmetry
without any fine tuning, if is broken at the unification scale
GeV and, if m_{\n_\m} \sim 3\cdot 10^{-3} eV as
preferred by the MSW solution to the solar neutrino deficit.Comment: latex2e, 39 pages, 15 figures, uses epsfig and pstricks. Additional
contribution to the CP-asymmetry added, conclusions unchanged. Final version,
to appear in Nucl.Phys.
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