653 research outputs found
Field-induced axion decay in KSVZ-model
The axion decay into electron-positron pair is studied in an
external magnetic field in KSVZ-model where axions have only induced coupling
to leptons. The axion lifetime in the field decreases with energy and field
strength to seconds.Comment: 4 pages, latex. Talk given at the International Workshop on Particle
Physics and the Early Universe ``COSMO'97'', Ambleside, Lake District,
England, 15-19 September 199
Universal description of the rotational-vibrational spectrum of three particles with zero-range interactions
A comprehensive universal description of the rotational-vibrational spectrum
for two identical particles of mass and the third particle of the mass
in the zero-range limit of the interaction between different particles is
given for arbitrary values of the mass ratio and the total angular
momentum . If the two-body scattering length is positive, a number of
vibrational states is finite for , zero for
, and infinite for . If the two-body scattering
length is negative, a number of states is either zero for or
infinite for . For a finite number of vibrational states, all the
binding energies are described by the universal function , where ,
,and is the vibrational
quantum number. This scaling dependence is in agreement with the numerical
calculations for and only slightly deviates from those for .
The universal description implies that the critical values and
increase as and ,
respectively, while a number of vibrational states for is
within the range
Influence of spin structures and nesting on Fermi surface and a pseudogap anisotropy in t-t'-U Hubbard model
Influence of two type of spin structures on the form of the Fermi surface
(FS) and a photoemission intensity map is studied for t-t'-U Hubbard model.
Mean field calculations are done for the stripe phase and for the spiral spin
structure. It is shown, that unlike a case of electron doping, the hole-doped
models are unstable with respect to formation of such structures. The pseudogap
anisotropies are different for h- and e- doping. In accordance with ARPES data
for La2SrxCuO4 the stripe phase is characterized by quasi-one-dimensional
segments of FS at k=(\pi,0) and by suppression of spectral weight in diagonal
direction. It is shown that spiral structures display the polarisation
anisotropy: different segments of FS correspond to electros with different spin
polarisations.Comment: 12 pages, 4 figure
Estimation of temperature and thermal pressures in thermalized areas of dense cascades of atomic displacements in the course of ion bombardement
Stepwise quantum decay of self-localized solitons
The two-phonon decay of self-localized soliton in a one-dimensional monatomic
anharmonic lattice caused by cubic anharmonicity is considered. It is shown
that the decay takes place with emission of phonon bursts. The average rate of
emission of phonons is of the order of vibrational quantum per vibrational
period. Characteristic time of the relaxation is determined by the quantum
anharmonicity parameter; this time may vary from a few (quantum lattices, large
anharmonicity) to thousands (ordinary lattices, small anharmonicity) of
vibrational periods.Comment: 6 pages, 3 figure
Itinerant in-plane magnetic fluctuations and many-body correlations in NaCoO
Based on the {\it ab-initio} band structure for NaCoO we derive the
single-electron energies and the effective tight-binding description for the
bands using projection procedure. Due to the presence of the
next-nearest-neighbor hoppings a local minimum in the electronic dispersion
close to the point of the first Brillouin zone forms. Correspondingly,
in addition to a large Fermi surface an electron pocket close to the
point emerges at high doping concentrations. The latter yields the new
scattering channel resulting in a peak structure of the itinerant magnetic
susceptibility at small momenta. This indicates dominant itinerant in-plane
ferromagnetic fluctuations above certain critical concentration , in
agreement with neutron scattering data. Below the magnetic susceptibility
shows a tendency towards the antiferromagnetic fluctuations. We further analyze
the many-body effects on the electronic and magnetic excitations using various
approximations applicable for different ratio.Comment: 10 page
Two-loop renormalization-group theory for the quasi-one-dimensional Hubbard model at half filling
We derive two-loop renormalization-group equations for the half-filled
one-dimensional Hubbard chains coupled by the interchain hopping. Our
renormalization-group scheme for the quasi-one-dimensional electron system is a
natural extension of that for the purely one-dimensional systems in the sense
that transverse-momentum dependences are introduced in the g-ological coupling
constants and we regard the transverse momentum as a patch index. We develop
symmetry arguments for the particle-hole symmetric half-filled Hubbard model
and obtain constraints on the g-ological coupling constants by which resultant
renormalization equations are given in a compact form. By solving the
renormalization-group equations numerically, we estimate the magnitude of
excitation gaps and clarify that the charge gap is suppressed due to the
interchain hopping but is always finite even for the relevant interchain
hopping. To show the validity of the present analysis, we also apply this to
the two-leg ladder system. By utilizing the field-theoretical bosonization and
fermionization method, we derive low-energy effective theory and analyze the
magnitude of all the excitation gaps in detail. It is shown that the low-energy
excitations in the two-leg Hubbard ladder have SO(3) x SO(3) x U(1) symmetry
when the interchain hopping exceeds the magnitude of the charge gap.Comment: 18 pages, 9 figures; Two appendices and one figure adde
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