64 research outputs found
Non-perturbative Corrections to Particle Production from Coherent Oscillation
We investigate particle production from coherent oscillation by using the
method based on the Bogolyubov transformation. Especially, we study the case
when the amplitude of the oscillation and also the coupling constants with the
oscillating field are small in order to avoid the non-perturbative corrections
from the broad parametric resonance. We derive the expressions for the
distribution functions and the number densities of produced particles at the
leading order of coupling constant. It is, however, found that these results
fail to describe the exact particle production eventually due to the
non-perturbative effects even if the coupling constants are small. We then
introduce a simple method to handle with such corrections, i.e., the time
averaging method. It is shown that this method successfully provides the
evolution of the occupation numbers of the growing mode. Further, we point out
that the approximate results by this method satisfy the exact scaling
properties coming from the periodicity of the coherent oscillation.Comment: 24 pages, 8 figure
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
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