51 research outputs found
Majorana neutrinos and other Majorana particles:Theory and experiment
This is a somewhat modified version of Chapter 15 of the book "The Physics of
Ettore Majorana", by Salvatore Esposito with contributions by Evgeny Akhmedov
(Ch. 15) and Frank Wilczek (Ch. 14), Cambridge University Press, 2014.Comment: LaTeX, 53 pages, 4 figure
Relic neutrino detection through angular correlations in inverse -decay
Neutrino capture on beta-decaying nuclei is currently the only known
potentially viable method of detection of cosmic background neutrinos. It is
based on the idea of separation of the spectra of electrons or positrons
produced in captures of relic neutrinos on unstable nuclei from those from the
usual -decay and requires very high energy resolution of the detector,
comparable to the neutrino mass. In this paper we suggest an alternative method
of discrimination between neutrino capture and -decay, based on periodic
variations of angular correlations in inverse beta decay transitions induced by
relic neutrino capture. The time variations are expected to arise due to the
peculiar motion of the Sun with respect to the CB rest frame and the
rotation of the Earth about its axis and can be observed in experiments with
both polarized and unpolarized nuclear targets. The main advantage of the
suggested method is that it does not depend crucially on the energy resolution
of detection of the produced -particles and can be operative even if
this resolution exceeds the largest neutrino mass.Comment: 24 pages, 1 figure. v2: title changed, section 4 modified, Appendix B
added, references added. v3: section 4 slightly expanded; eq. (B.7)
corrected. Final version to be published in JCA
Another look at synchronized neutrino oscillations
In dense neutrino backgrounds present in supernovae and in the early Universe
neutrino oscillations may exhibit complex collective phenomena, such as
synchronized oscillations, bipolar oscillations and spectral splits and swaps.
We consider in detail possible decoherence effects on the simplest of these
phenomena -- synchronized neutrino oscillations that can occur in a uniform and
isotropic neutrino gas. We develop an exact formalism of spectral moments of
the flavour spin vectors describing such a system and then apply it to find
analytical approaches that allow one to study decoherence effects on its
late-time evolution. This turns out to be possible in part due to the existence
of the (previously unknown) exact conservation law satisfied by the quantities
describing the considered neutrino system. Interpretation of the decoherence
effects in terms of neutrino wave packet separation is also given, both in the
adiabatic and non-adiabatic regimes of neutrino flavour evolution.Comment: LaTeX, 32 pages, 3 figures. V2: minor textual changes, references and
an acknowledgement added, results and conclusions unchange
Comment on 'Time-energy uncertainty relations for neutrino oscillations and the Mossbauer neutrino experiment'
We discuss the implications of the time-energy uncertainty relation to
recoillessly emitted and captured neutrinos (Mossbauer neutrinos) and show that
it does not preclude oscillations of these neutrinos, contrary to a recent
claim (J. Phys. G35 (2008) 095003, arXiv:0803.0527).Comment: LaTeX, 6 pages, no figures; v2 has been extended compared to v1 and
matches the published version; title changed in journa
Coherent scattering and macroscopic coherence: Implications for neutrino, dark matter and axion detection
We study the question of whether coherent neutrino scattering can occur on
macroscopic scales, leading to a significant increase of the detection cross
section. We concentrate on radiative neutrino scattering on atomic electrons
(or on free electrons in a conductor). Such processes can be coherent provided
that the net electron recoil momentum, i.e. the momentum transfer from the
neutrino minus the momentum of the emitted photon, is sufficiently small. The
radiative processes is an attractive possibility as the energy of the emitted
photons can be as large as the momentum transfer to the electron system and
therefore the problem of detecting extremely low energy recoils can be avoided.
The requirement of macroscopic coherence severely constrains the phase space
available for the scattered particle and the emitted photon. We show that in
the case of the scattering mediated by the usual weak neutral current and
charged current interactions this leads to a strong suppression of the
elementary cross sections and therefore the requirement of macroscopic
coherence results in a reduction rather than an increase of the total detection
cross section. However, for the scattering mediated by neutrino
magnetic or electric dipole moments coherence effects can actually increase the
detection rates. Effects of macroscopic coherence can also allow detection of
neutrinos in 100 eV -- a few keV energy range, which is currently not
accessible to the experiment. A similar coherent enhancement mechanism can work
for relativistic particles in the dark sector, but not for the conventionally
considered non-relativistic dark matter.Comment: LaTeX, 31 page, 2 figures. v2: a section on coherent axion detection
and an appendix added; title modifie
Improving Electro-Weak Fits with TeV-scale Sterile Neutrinos
We study the impact of TeV-scale sterile neutrinos on electro-weak precision
observables and lepton number and flavour violating decays in the framework of
a type-I see-saw extension of the Standard Model. At tree level sterile
neutrinos manifest themselves via non-unitarity of the PMNS matrix and at
one-loop level they modify the oblique radiative corrections. We derive
explicit formulae for the S,T,U parameters in terms of the neutrino masses and
mixings and perform a numerical fit to the electro-weak observables. We find
regions of parameter space with a sizable active-sterile mixing which provide a
better over-all fit compared to the case where the mixing is negligible.
Specifically we find improvements of the invisible Z-decay width, the
charged-to-neutral-current ratio for neutrino scattering experiments and of the
deviation of the W boson mass from the theoretical expectation.Comment: 16 pages, 17 figures, Journal accepted versio
Reply to "Comment on "Damping of neutrino oscillations, decoherence and the lengths of neutrino wave packets""
In arXiv:2209.00561 our treatment arXiv:2208.03736 of effects of particles
emitted together with neutrinos on neutrino wave packets is criticized on
several grounds. We show here that this criticism is based on misinterpretation
of our results and is invalid. Our conclusions and, in particular, the
conclusion that neutrino wave packet separation effects are unobservable in
reactor and neutrino source experiments, remain unchanged.Comment: 3 pages, 1 figur
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