22 research outputs found
Fermion number violating effects in low scale leptogenesis
The existence of baryon asymmetry and dark matter in the Universe may be
related to CP-violating reactions of three heavy neutral leptons (HNLs) with
masses well below the Fermi scale. The dynamical description of the lepton
asymmetry generation, which is the key ingredient of baryogenesis and of dark
matter production, is quite complicated due to the presence of many different
relaxation time scales and the necessity to include quantum-mechanical coherent
effects in HNL oscillations. We derive kinetic equations accounting for fermion
number violating effects missed so far and identify one of the domains of HNL
masses that can potentially lead to large lepton asymmetry generation boosting
the sterile neutrino dark matter production.Comment: 10 pages, 10 figures, Journal version with corrected misprint
Neutrinoless double decay and low scale leptogenesis
The extension of the Standard Model by right handed neutrinos with masses in
the GeV range can simultaneously explain the observed neutrino masses via the
seesaw mechanism and the baryon asymmetry of the universe via leptogenesis. It
has previously been claimed that the requirement for successful baryogenesis
implies that the rate of neutrinoless double decay in this scenario is
always smaller than the standard prediction from light neutrino exchange alone.
In contrast, we find that the rate for this process can also be enhanced due to
a dominant contribution from heavy neutrino exchange. In a small part of the
parameter space it even exceeds the current experimental limit, while the
properties of the heavy neutrinos are consistent with all other experimental
constraints and the observed baryon asymmetry is reproduced. This implies that
neutrinoless double decay experiments have already started to rule out
part of the leptogenesis parameter space that is not constrained by any other
experiment, and the lepton number violation that is responsible for the origin
of baryonic matter in the universe may be observed in the near future.Comment: Discussion extended, figures added; 16 pages, 5 figures; identical to
published version up to minor text correction
Parameter space of baryogenesis in the MSM
The Standard Model accompanied with two right-handed neutrinos with the
masses below the weak scale can explain the observed baryon asymmetry of the
Universe. Moreover, this model is at least partially testable in the
forthcoming experiments such as NA62, SHiP, and MATHUSLA. The remarkable
progress in understanding of various rates entering the kinetic equations
describing the asymmetry generation along with considerable improvements of the
numerical procedures allow us to perform a comprehensive analysis of the
parameter space of the model. We find that the region of parameters leading to
the successful baryogenesis is notably larger than it was previously obtained.
Our results are presented in a way that they can be readily used for studies of
sensitivity of various experiments searching for the right-handed neutrinos
responsible for the baryon asymmetry of the Universe. We also present a
detailed comparison with the studies by other groups.Comment: 42 pages, 14 figures, 5 tables, additional data files could be found
at https://doi.org/10.5281/zenodo.1407071; published versio
Heavy neutrino search in accelerator-based experiments
We explore the feasibility of detecting heavy neutrinos by the existing
facilities of neutrino experiments. A heavy neutrino in the mass range 1 MeV <
M < 500 MeV is produced by pion or kaon decay, and decays to charged particles
which leave signals in neutrino detectors. Taking the T2K experiment as a
typical example, we estimate the heavy neutrino flux produced in the neutrino
beam line. Due to massive nature of the heavy neutrino, the spectrum of the
heavy neutrino is significantly different from that of the ordinary neutrinos.
While the ordinary neutrinos are emitted to various directions in the
laboratory frame due to their tiny masses, the heavy neutrinos tend to be
emitted to the forward directions and frequently hit the detector.The
sensitivity for the mixing parameters is studied by evaluating the number of
signal events in the near detector ND280. For the electron-type mixing, the
sensitivity of T2K at 10^{21} POT is found to be better than that of the
previous experiment PS191, which has placed the most stringent bounds on the
mixing parameters of the heavy neutrinos for 140 MeV< M < 500 MeV.Comment: 26 pages, 17 figure
On neutrinoless double beta decay in the MSM
We consider the neutrinoless double beta () decay in the
so-called MSM, in which three right-handed neutrinos with masses below the
electroweak scale are additionally introduced to the Standard Model. In this
model there appear three heavy neutral leptons , , and
corresponding to right-handed neutrinos. It has been known that the lightest
one with keV mass, which is a candidate for dark matter, gives a
negligible contribution to the decay. By contrast, the
heavier ones and , which are responsible to the seesaw mechanism of
neutrino masses and baryogenesis, give the destructive contribution (compared
with one from active neutrinos). This is because their mass degeneracy at high
precision has been assumed, which is expected by analytical studies of
baryogengesis. In this analysis, we find that the effective mass of the decay becomes larger than one from active neutrinos due to the
and constructive contribution when the mass difference becomes
larger and the mass ordering of active neutrinos is inverted. Such a
possibility will be explored by the current and near future experiments of the
decay.Comment: 10 pages, 6 figures, v2: published version to appear in Physics
Letters
Initial condition for baryogenesis via neutrino oscillation
We consider a baryogenesis scenario via the oscillation of right-handed
neutrinos with Majorana masses of the order of GeV, which are also responsible
for neutrino masses by the seesaw mechanism. We study how the initial condition
alters the prediction of the present baryon asymmetry by this mechanism. It is
usually assumed that the abundance of right-handed neutrinos is zero after the
reheating of the inflationary universe and they are produced in scattering
processes by the renomalizable Yukawa interaction. However, the
higher-dimensional operator with right-handed neutrinos may provide an
additional production which is most effective at the reheating epoch. It is
shown that such an initial abundance of right-handed neutrinos can
significantly modify the prediction when the strong washout of the asymmetry is
absent. This leads to the parameter space of the model for the successful
baryogenesis being enlarged.Comment: 24 pages, 35 figures, v2; correspond to published versio