660 research outputs found
Spin-Orbit-Like Terms in Semileptonic Weak Hamiltonian
It is shown that new spin-orbit-like terms appear in the effective
nonrelativistic weak Hamiltonian for nucleon provided that nuclear potential is
taken into account. Arguments for their considerable enhancement, in
particular, in relativistic nuclear model of Walecka are advanced.Comment: 3 pages, latex, no figures, submitted to the European Physical
Journal
Electromagnetic modulation of monochromatic neutrino beams
A possibility to produce a modulated monochromatic neutrino beam is
discussed. Monochromatic neutrinos can be obtained in electron capture by
nuclei of atoms or ions, in particular, by nuclei of hydrogen-like ions. It is
shown that monochromatic neutrino beam from such hydrogen-like ions with nuclei
of non-zero spin can be modulated because of different probabilities of
electron capture from hyperfine states. Modulation arises by means of inducing
of electromagnetic transitions between the hyperfine states. Requirements for
the hydrogen-like ions with necessary properties are discussed. A list of the
appropriate nuclei for such ions is presented.Comment: 11 pages, 1 figure, minor corrections to match the final published
versio
Comparison of non-crossing perturbative approach and generalized projection method for strongly coupled spin-fermion systems at low doping
We analyze the two-dimensional spin-fermion model in the strong coupling
regime relevant to underdoped cuprates. We recall the set of general sumrules
that relate moments of spectral density and the imaginary part of fermion
self-energy with static correlation functions. We show that two-pole
approximation of projection method satisfies the sumrules for first four
moments of spectral density and gives an exact upper bound for quasiparticle
energy near the band bottom. We prove that non-crossing approximation that is
often made in perturbative consideration of the model violates the sumrule for
third moment of spectral density. This leads to wrong position of lowest
quasiparticle band. On the other hand, the projection method is inadequate in
weak coupling limit because of approximate treatment of kinetic energy term. We
propose a generalization of projection method that overcomes this default and
give the fermion self-energy that correctly behaves both in weak and strong
coupling limits.Comment: 9 pages, 4 EPS figures, RevTe
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