112,875 research outputs found
Exclusive glueball production in high energy nucleus-nucleus collisions
The cross sections for the glueball candidates production in quasi-real
photon-photon collisions and on central diffraction processes, i.e. double
Pomeron exchange, in heavy ion interactions at RHIC and LHC are computed. The
rates for these distinct production channels are compared and they may be a
fruitful approach to the investigation of glueballs.Comment: 6 pages, 2 tables. Final version to be published in Physical Review
Impurity susceptibility and the fate of spin-flop transitions in lightly-doped La(2)CuO(4)
We investigate the occurrence of a two-step spin-flop transition and spin
reorientation when a longitudinal magnetic field is applied to lightly
hole-doped La(2)CuO(4). We find that for large and strongly frustrating
impurities, such as Sr in La(2-x)Sr(x)CuO(4), the huge enhancement of the
longitudinal susceptibility suppresses the intermediate flop and the
reorientation of spins is smooth and continuous. Contrary, for small and weakly
frustrating impurities, such as O in La(2)CuO(4+y), a discontinuous spin
reorientation (two-step spin-flop transition) takes place. Furthermore, we show
that for La(2-x)Sr(x)CuO(4) the field dependence of the magnon gaps differs
qualitatively from the La(2)CuO(4) case, a prediction to be verified with Raman
spectroscopy or neutron scattering.Comment: 4 pages, 3 figures, For the connection between spin-flops and
magnetoresistance, see cond-mat/061081
Field dependence of the magnetic spectrum in anisotropic and Dzyaloshinskii-Moriya antiferromagnets: I. Theory
We consider theoretically the effects of an applied uniform magnetic field on
the magnetic spectrum of anisotropic two-dimensional and Dzyaloshinskii-Moriya
layered quantum Heisenberg antiferromagnets. The first case is relevant for
systems such as the two-dimensional square lattice antiferromagnet
Sr(2)CuO(2)Cl(2), while the later is known to be relevant to the physics of the
layered orthorhombic antiferromagnet La(2)CuO(4). We first establish the
correspondence betwenn the low-energy spectrum obtained within the anisotropic
non-linear sigma model and by means of the spin-wave approximation for a
standard easy-axis antiferromagent. Then, we focus on the field-theory approach
to calculate the magnetic field dependence of the magnon gaps and spectral
intensities for magnetic fields applied along the three possible
crystallographic directions. We discuss the various possible ground states and
their evolution with temperature for the different field orientations, and the
occurrence of spin-flop transitions for fields perpendicular to the layers
(transverse fields) as well as for fields along the easy axis (longitudinal
fields). Measurements of the one-magnon Raman spectrum in Sr(2)CuO(2)Cl(2) and
La(2)CuO(4) and a comparison between the experimental results and the
predictions of the present theory will be reported in part II of this research
work [L. Benfatto et al., cond-mat/0602664].Comment: 21 pages, 11 figures, final version. Part II of the present work is
presented in cond-mat/060266
Meson decay in the Fock-Tani Formalism
The Fock-Tani formalism is a first principle method to obtain effective
interactions from microscopic Hamiltonians. Usually this formalism was applied
to scattering, here we introduced it to calculate partial decay widths for
mesons.Comment: Presented at HADRON05 XI. "International Conference on Hadron
Spectroscopy" Rio de Janeiro, Brazil, August 21 to 26, 200
Meson decay in a corrected model
Extensively applied to both light and heavy meson decay and standing as one
of the most successful strong decay models is the model, in which
pair production is the dominant mechanism. The pair production can
be obtained from the non-relativistic limit of a microscopic interaction
Hamiltonian involving Dirac quark fields. The evaluation of the decay amplitude
can be performed by a diagrammatic technique for drawing quark lines. In this
paper we use an alternative approach which consists in a mapping technique, the
Fock-Tani formalism, in order to obtain an effective Hamiltonian starting from
same microscopic interaction. An additional effect is manifest in this
formalism associated to the extended nature of mesons: bound-state corrections.
A corrected is obtained and applied, as an example, to
and decays.Comment: 3 figures. To appear in Physical Review
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