909 research outputs found
Baryogenesis from Mixing of Lepton Doublets
It is shown that the mixing of lepton doublets of the Standard Model can
yield sizeable contributions to the lepton asymmetry, that is generated through
the decays of right-handed neutrinos at finite temperature in the early
Universe. When calculating the flavour-mixing correlations, we account for the
effects of Yukawa as well as of gauge interactions. We compare the freeze-out
asymmetry from lepton-doublet mixing to the standard contributions from the
mixing and direct decays of right-handed neutrinos. The asymmetry from lepton
mixing is considerably large when the mass ratio between the right-handed
neutrinos is of order of a few, while it becomes Maxwell-suppressed for larger
hierarchies. For an intermediate range between the case of degenerate
right-handed neutrinos (resonant Leptogenesis) and the hierarchical case,
lepton mixing can yield the main contribution to the lepton asymmetry.Comment: 25 page
Spectator Effects during Leptogenesis in the Strong Washout Regime
By including spectator fields into the Boltzmann equations for Leptogenesis,
we show that partially equilibrated spectator interactions can have a
significant impact on the freeze-out value of the asymmetry in the strong
washout regime. The final asymmetry is typically increased, since partially
equilibrated spectators "hide" a part of the asymmetry from washout. We study
examples with leptonic and non-leptonic spectator processes, assuming thermal
initial conditions, and find up to 50% enhanced asymmetries compared to the
limit of fully equilibrated spectators. Together with a comprehensive overview
of the equilibration temperatures for various Standard Model processes, the
numerical results indicate the ranges when the limiting cases of either fully
equilibrated or negligible spectator fields are applicable and when they are
not. Our findings also indicate an increased sensitivity to initial conditions
and finite density corrections even in the strong washout regime.Comment: 23 pages, 4 figure
Phenomenology of Baryogenesis from Lepton-Doublet Mixing
Mixing lepton doublets of the Standard Model can lead to lepton flavour
asymmetries in the Early Universe. We present a diagrammatic representation of
this recently identified source of violation and elaborate in detail on
the correlations between the lepton flavours at different temperatures. For a
model where two sterile right-handed neutrinos generate the light neutrino
masses through the see-saw mechanism, the lower bound on reheat temperatures in
accordance with the observed baryon asymmetry turns out to be \gsim 1.2\times
10^9\,{\rm GeV}. With three right-handed neutrinos, substantially smaller
values are viable. This requires however a tuning of the Yukawa couplings, such
that there are cancellations between the individual contributions to the masses
of the light neutrinos.Comment: 28 page
Perturbative and Nonperturbative Contributions to a Simple Model for Baryogenesis
Single field baryogenesis, a scenario for Dirac leptogenesis sourced by a
time-dependent scalar condensate, is studied. We compare the creation of the
charge asymmetry by the perturbative decay of the condensate with the
nonperturbative decay, a process of particle production commonly known in the
context of inflation as preheating. The nonperturbative channel dominates when
the coupling of the scalar field to leptons is sufficiently large.Comment: 11 pages, 3 figure
Combining Experimental and Cosmological Constraints on Heavy Neutrinos
We study experimental and cosmological constraints on the extension of the
Standard Model by three right handed neutrinos with masses between those of the
pion and W boson. We combine for the first time direct, indirect and
cosmological constraints in this mass range. This includes experimental
constraints from neutrino oscillation data, neutrinoless double decay,
electroweak precision data, lepton universality, searches for rare lepton
decays, tests of CKM unitarity and past direct searches at colliders or fixed
target experiments. On the cosmological side, big bang nucleosynthesis has the
most pronounced impact. Our results can be used to evaluate the discovery
potential of searches for heavy neutrinos at LHCb, BELLE II, SHiP, ATLAS, CMS
or a future lepton collider.Comment: 64 pages, 22 figures. Matches published versio
Green's function method for handling radiative effects on false vacuum decay
We introduce a Green's function method for handling radiative effects on
false vacuum decay. In addition to the usual thin-wall approximation, we
achieve further simplification by treating the bubble wall in the planar limit.
As an application, we take the theory, extended with
additional heavier scalars, wherein we calculate analytically both the
functional determinant of the quadratic fluctuations about the classical
soliton configuration and the first correction to the soliton configuration
itself.Comment: 19 pages, 5 figures, revtex format; references extended, Section III
A and Appendix C corrected and further clarifications added; version accepted
for publication Physical Review
Slow Roll during the Waterfall Regime: The Small Coupling Window for SUSY Hybrid Inflation
It has recently been pointed out that a substantial amount of e-folds can
occur during the waterfall regime of hybrid inflation. Moreover, Kodama et.al.
have derived analytic approximations for the trajectories of the inflaton and
of the waterfall fields. Based on these, we derive here the consequences for F-
and D-term SUSY hybrid inflation: A substantial amount of e-folds may occur in
the waterfall regime, provided kappa << M^2/M_P^2, where kappa is the
superpotential coupling, M the scale of symmetry breaking and M_P the reduced
Planck mass. When this condition is amply fulfilled, a number of e-folds much
larger than N_e\approx60 can occur in the waterfall regime and the scalar
spectral index is then given by the expression found by Kodama et.al.
n_s=1-4/N_e. This value may be increased up to unity, if only about N_e e-folds
occur during the waterfall regime, such that the largest observable scale
leaves the horizon close to the critical point of hybrid inflation, what can be
achieved for kappa\approx10^(-13) and M\approx5x10^(12) GeV in F-term
inflation. Imposing the normalization of the power spectrum leads to a lower
bound on the scale of symmetry breaking.Comment: 14 pages, 4 figures, minor corrections, references added, accepted
for publication in Phys.Rev.
F_D-Term Hybrid Inflation with Electroweak-Scale Lepton Number Violation
We study F-term hybrid inflation in a novel supersymmetric extension of the
SM with a subdominant Fayet-Iliopoulos D-term. We call this particular form of
inflation, in short, F_D-term hybrid inflation. The proposed model ties the
mu-parameter of the MSSM to an SO(3)-symmetric Majorana mass m_N, through the
vacuum expectation value of the inflaton field. The late decays of the
ultraheavy particles associated with the extra U(1) gauge group, which are
abundantly produced during the preheating epoch, could lower the reheat
temperature even up to 1 TeV, thereby avoiding the gravitino overproduction
problem. The baryon asymmetry in the Universe can be explained by thermal
electroweak-scale resonant leptogenesis, in a way independent of any
pre-existing lepton- or baryon-number abundance. Further cosmological and
particle-physics implications of the F_D-term hybrid model are briefly
discussed.Comment: 20 pages, 1 eps figure, comments added to conclusion
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