1,061 research outputs found
Spinwave damping in the two-dimensional ferromagnetic XY model
The effect of damping of spinwaves in a two-dimensional classical
ferromagnetic XY model is considered. The damping rate is
calculated using the leading diagrams due to the quartic-order deviations from
the harmonic spin Hamiltonian. The resulting four-dimensional integrals are
evaluated by extending the techniques developed by Gilat and others for
spectral density types of integrals. is included into the memory
function formalism due to Reiter and Solander, and Menezes, to determine the
dynamic structure function . For the infinite sized system, the
memory function approach is found to give non-divergent spinwave peaks, and a
smooth nonzero background intensity (``plateau'' or distributed intensity) for
the whole range of frequencies below the spinwave peak. The background
amplitude relative to the spinwave peak rises with temperature, and eventually
becomes higher than the spinwave peak, where it appears as a central peak. For
finite-sized systems, there are multiple sequences of weak peaks on both sides
of the spinwave peaks whose number and positions depend on the system size and
wavevector in integer units of . These dynamical finite size effects
are explained in the memory function analysis as due to either spinwave
difference processes below the spinwave peak or sum processes above the
spinwave peak. These features are also found in classical Monte Carlo --
Spin-Dynamics simulations.Comment: 20 two-column page
Bi-large neutrino mixing and the Cabibbo angle
Recent measurements of the neutrino mixing angles cast doubt on the validity
of the so-far popular tri-bimaximal mixing ansatz. We propose a parametrization
for the neutrino mixing matrix where the reactor angle seeds the large solar
and atmospheric mixing angles, equal to each other in first approximation. We
suggest such bi-large mixing pattern as a model building standard, realized
when the leading order value of the reactor angle equals the Cabibbo angle.Comment: 4 pages, 2 figs. v2: matches version appearing in Phys.Rev.D, rapid
communication
Biologia e exigências térmicas do ácaro vermelho Tetranychus gigas Pritchard e Baker em soja.
bitstream/item/71549/1/ID-30974.pd
Parameters' domain in three flavour neutrino oscillations
We consider analytically the domain of the three mixing angles
and the CP phase for three flavour neutrino oscillations both in
vacuum and matter. Similarly to the quark sector, it is necessary and
sufficient to let all the mixing angles
and be in the range and ,
respectively. To exploit the full range of will be important in future
when more precise fits are possible, even without CP violation measurements.
With the above assumption on the angles we can restrict ourselves to the
natural order of masses . Considerations of the mass schemes with
some negative 's, though for some reasons useful, are not necessary
from the point of view of neutrino oscillation parametrization and cause double
counting only. These conclusions are independent of matter effects.Comment: references added, to appear in PL
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