460 research outputs found
Plasma induced neutrino radiative decay instead of neutrino spin light
The conversion nu_L -> nu_R gamma^* of a neutrino with a magnetic moment is
considered, caused by the additional Wolfenstein energy acquired by a
left-handed neutrino in medium, with an accurate taking account of the photon
\gamma^* dispersion in medium. It is shown that the threshold arises in the
process, caused by the photon (plasmon) effective mass. This threshold leaves
no room for the so-called "neutrino spin light" in the most of astrophysical
situations.Comment: 7 pages, LaTeX, 1 EPS figure, submitted to Modern Physics Letters
Probing non-standard decoherence effects with solar and KamLAND neutrinos
It has been speculated that quantum gravity might induce a "foamy" space-time
structure at small scales, randomly perturbing the propagation phases of
free-streaming particles (such as kaons, neutrons, or neutrinos). Particle
interferometry might then reveal non-standard decoherence effects, in addition
to standard ones (due to, e.g., finite source size and detector resolution.) In
this work we discuss the phenomenology of such non-standard effects in the
propagation of electron neutrinos in the Sun and in the long-baseline reactor
experiment KamLAND, which jointly provide us with the best available probes of
decoherence at neutrino energies E ~ few MeV. In the solar neutrino case, by
means of a perturbative approach, decoherence is shown to modify the standard
(adiabatic) propagation in matter through a calculable damping factor. By
assuming a power-law dependence of decoherence effects in the energy domain
(E^n with n = 0,+/-1,+/-2), theoretical predictions for two-family neutrino
mixing are compared with the data and discussed. We find that neither solar nor
KamLAND data show evidence in favor of non-standard decoherence effects, whose
characteristic parameter gamma_0 can thus be significantly constrained. In the
"Lorentz-invariant" case n=-1, we obtain the upper limit gamma_0<0.78 x 10^-26
GeV at 95% C.L. In the specific case n=-2, the constraints can also be
interpreted as bounds on possible matter density fluctuations in the Sun, which
we improve by a factor of ~ 2 with respect to previous analyses.Comment: Minor changes. Version accepted for publication in Phys. Rev.
Methods of approaching decoherence in the flavour sector due to space-time foam
In the first part of this work we discuss possible effects of stochastic
space-time foam configurations of quantum gravity on the propagation of
``flavoured'' (Klein-Gordon and Dirac) neutral particles, such as neutral
mesons and neutrinos. The formalism is not the usually assumed Lindblad one,
but it is based on random averages of quantum fluctuations of space time
metrics over which the propagation of the matter particles is considered. We
arrive at expressions for the respective oscillation probabilities between
flavours which are quite distinct from the ones pertaining to Lindblad-type
decoherence, including in addition to the (expected) Gaussian decay with time,
a modification to oscillation behaviour, as well as a power-law cutoff of the
time-profile of the respective probability. In the second part we consider
space-time foam configurations of quantum-fluctuating charged black holes as a
way of generating (parts of) neutrino mass differences, mimicking appropriately
the celebrated MSW effects of neutrinos in stochastically fluctuating random
media. We pay particular attention to disentangling genuine quantum-gravity
effects from ordinary effects due to the propagation of a neutrino through
ordinary matter. Our results are of interest to precision tests of quantum
gravity models using neutrinos as probes.Comment: 35 pages revtex, no figures, typos corrected in section II
Impact of right-handed interactions on the propagation of Dirac and Majorana neutrinos in matter
Dirac and Majorana neutrinos can be distinguished in relativistic neutrino
oscillations if new right-handed interactions exist, due to their different
propagation in matter. We review how these new interactions affect neutrino
oscillation experiments and discuss the size of this eventually observable
effect for different oscillation channels, baselines and neutrino energies.Comment: 26 pages, 5 figure
Fixing the Solar Neutrino Parameters with Sterile Neutrinos
Neutrino mixing matrix appears to be close to bimaximal mixing, but for the
solar mixing angle which is definitively smaller than forty five degrees.
Whereas it seems quite easy to understand bimaximal mixing with the use of new
global symmetries, as in models using , understanding the
about to eleven degrees of deviation in the observed solar angle seems less
simple. We suggest that such a deviation could be due to a light sterile
neutrino that mixes with the active sector. The mass scale needed to produce
the effect has to be smaller than atmospheric scale, and it would introduce a
new mass squared difference which should be smaller than the solar scale. We
present a toy model that exemplifies these features.Comment: 19 pages, two figures. Discussion extended. References adde
Field-induced interaction of a pseudoscalar particle with photon in a magnetized plasma
The effective interaction of a pseudoscalar particle with photon in plasma
with the presence of a constant uniform magnetic field is investigated. It is
shown that under some physical conditions the effective coupling between
pseudoscalar particle and photon does not depend on medium parameters and
particles momentum. The probability of the familon decay into photon pair in a
strongly magnetized degenerate ultrarelativistic plasma is calculated.Comment: 10 pages, 2 figures. To be published in Modern Physics Letters
Neutrino magnetic moment in a magnetized plasma
The contribution of a magnetized plasma to the neutrino magnetic moment is
calculated. It is shown that only part of the additional neutrino energy in
magnetized plasma connecting with its spin and magnetic field strength defines
the neutrino magnetic moment. It is found that the presence of magnetized
plasma does not lead to the considerable increase of the neutrino magnetic
moment in contrast to the results presented in literature previously.Comment: 7 page, 1 figures, based on the talk presented by E.N.Narynskaya at
the XVI International Seminar Quarks'2010, Kolomna, Moscow Region, June 6-12,
2010, to appear in the Proceeding
Plasma induced fermion spin-flip conversion
The fermion spin-flip conversion is considered, caused
by the difference of the additional energies of the electroweak origin,
acquired by left- and right-handed fermions (neutrino, electron) in medium. An
accurate taking account of the fermion and photon dispersion in medium is shown
to be important.Comment: 5 pages, LaTeX, 1 PS figure, based on the talk presented by A.V.
Kuznetsov at the XV International Seminar Quarks'2008, Sergiev Posad, Moscow
Region, May 23-29, 2008, to appear in the Proceeding
On the Evolution of the Neutrino State inside the Sun
We reexamine the conventional physical description of the neutrino evolution
inside the Sun. We point out that the traditional resonance condition has
physical meaning only in the limit of small values of the neutrino mixing
angle, theta<<1. For large values of theta, the resonance condition specifies
neither the point of the maximal violation of adiabaticity in the nonadiabatic
case, nor the point where the flavor conversion occurs at the maximal rate in
the adiabatic case. The corresponding correct conditions, valid for all values
of theta including theta>pi/4, are presented. An adiabaticity condition valid
for all values of theta is also described. The results of accurate numerical
computations of the level jumping probability in the Sun are presented. These
calculations cover a wide range of Delta m^2, from the vacuum oscillation
region to the region where the standard exponential approximation is good. A
convenient empirical parametrization of these results in terms of elementary
functions is given. The matter effects in the so-called "quasi-vacuum
oscillation regime" are discussed. Finally, it is shown how the known
analytical results for the exponential, 1/x, and linear matter distributions
can be simply obtained from the formula for the hyperbolic tangent profile. An
explicit formula for the jumping probability for the distribution N_e ~
(coth(x/l) +- 1) is obtained.Comment: 34 pages, 8 figure
Dirac neutrino magnetic moment and the shock wave revival in a supernova explosion
The process of the two-step conversion of the neutrino helicity, , is analysed in the supernova conditions, where the first
stage is realized due to the interaction of the neutrino magnetic moment with
the plasma electrons and protons in the supernova core. The second stage is
caused by the neutrino resonant spin-flip in a magnetic field of the supernova
envelope. Given the neutrino magnetic moment within the interval , and with the existence of the
magnetic field at the scale G between the neutrinosphere and the
shock-wave stagnation region, it is shown that an additional energy of the
order of erg can be injected into this region during the typical time
of the shock-wave stagnation. This energy could be sufficient for stumulation
of the damped shock wave.Comment: 6 pages, LaTeX, 2 PS figures, based on the talk presented by N.V.
Mikheev at the XV International Seminar Quarks'2008, Sergiev Posad, Moscow
Region, May 23-29, 2008, to appear in the Proceeding
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