5,633 research outputs found
Majorana Neutrinos and Same-Sign Dilepton Production at LHC and in Rare Meson Decays
We discuss same-sign dilepton production mediated by Majorana neutrinos in
high-energy proton-proton collisions pp\ra \ell^+ \ell^{\prime +}X for
at the LHC energy TeV, and
in the rare decays of , , , and mesons of the type M^{+}\ra
M^{\prime -}\ell ^{+}\ell ^{\prime+}. For the reaction, assuming one
heavy Majorana neutrino of mass , we present discovery limits in the
plane where are the mixing
parameters. Taking into account the present limits from low energy experiments,
we show that at LHC for the nominal luminosity L=100 fb there is no room
for observable same-sign dilepton signals. However, increasing the integrated
luminosity by a factor 30, one will have sensitivity to heavy Majorana
neutrinos up to a mass TeV only in the dilepton channels
and , but other dilepton states will not be detectable due to the
already existing strong constraints. We work out a large number of rare meson
decays, both for the light and heavy Majorana neutrino scenarios, and argue
that the present experimental bounds on the branching ratios are too weak to
set reasonable limits on the effective Majorana masses.Comment: 18 pages, 4 figures (requires graphicx), a coefficient in Eq. (4)
corrected leading to drastic reduction in the Majorana-induced same-sign
dilepton cross-section at LHC; revised Figs. 2 and 3; references adde
Neutrino dispersion in external magnetic fields
We calculate the neutrino self-energy operator Sigma (p) in the presence of a
magnetic field B. In particular, we consider the weak-field limit e B <<
m_\ell^2, where m_\ell is the charged-lepton mass corresponding to the neutrino
flavor \nu_\ell, and we consider a "moderate field" m_\ell^2 << e B << m_W^2.
Our results differ substantially from the previous literature. For a moderate
field, we show that it is crucial to include the contributions from all Landau
levels of the intermediate charged lepton, not just the ground-state. For the
conditions of the early universe where the background medium consists of a
charge-symmetric plasma, the pure B-field contribution to the neutrino
dispersion relation is proportional to (e B)^2 and thus comparable to the
contribution of the magnetized plasma.Comment: 9 pages, 1 figure, revtex. Version to appear in Phys. Rev. D
(presentation improved, reference list revised, numerical error in Eq.(41)
corrected, conclusions unchanged
Propagation of axions in a strongly magnetized medium
The polarization operator of an axion in a degenerate gas of electrons
occupying the ground-state Landau level in a superstrong magnetic field G is investigated in a model with a
tree-level axion-electron coupling. It is shown that a dynamic axion mass,
which can fall within the allowed range of values , is generated under the conditions of strongly
magnetized neutron stars. As a result, the dispersion relation for axions is
appreciably different from that in a vacuum.Comment: RevTex, no figures, 13 pages, Revised version of the paper published
in J. Exp. Theor. Phys. {\bf 88}, 1 (1999
New type of stable particle like states in chiral magnets (Chiral bobbers)
We present a new type of a thermodynamically stable magnetic state at
interfaces and surfaces of chiral magnets. The state is a soliton solution of
micromagnetic equations localized in all three dimensions near a boundary and
contains a singularity, but nevertheless has a finite energy. Both features
combine to a quasi-particle state for which we expect unusual transport and
dynamical properties. It exhibits high thermal stability and thereby can be
considered as promising object for fundamental research and practical
applications in spintronic devices. We provide arguments that such a state can
be found in different B20-type alloys e.g. MnFeGe,
MnFeSi, FeCoSi.Comment: accepted in PR
Lepton pair production by high-energy neutrino in an external electromagnetic field
The process of the lepton pair production by a neutrino propagating in an
external electromagnetic field is investigated in the framework of the Standard
Model. Relatively simple exact expression for the probability as the single
integral is obtained, which is suitable for a quantitative analysis.Comment: 9 pages, LATEX, 2 PS figures, submitted to Modern Physics Letters
Quality estimation of structurally ordered assembly for threaded connection welding
Structurally ordered assembly for threaded connection welding allowing supporting high accuracy of relative position of a product connectable components has been considere
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