86,928 research outputs found
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
Glueball-glueball scattering in a constituent gluon model
In this work we use a mapping technique to derive in the context of a
constituent gluon model an effective Hamiltonian that involves explicit gluon
degrees of freedom. We study glueballs with two gluons using the Fock-Tani
formalism. In the present work we consider two possibilities for : (i)
as a pure and calculate, in the context of a quark interchange
picture, the cross-section; (ii) as a glueball where a new calculation for this
cross-section is made, in the context of the constituent gluon model, with
gluon interchange.Comment: Proceedings of the International Workshop IX Hadron Physics and VII
Relativistic Aspects of Nuclear Physics (HADRON-RANP 2004
Competing impurities and reentrant magnetism in La(2-x)Sr(x)Cu(1-z)Zn(z)O(4) revisited. The role of the Dzyaloshinskii-Moriya and XY anisotropies
We study the order-from-disorder transition and reentrant magnetism in
La(2-x)Sr(x)Cu(1-z)Zn(z)O(4) within the framework of a long-wavelength
nonlinear sigma model that properly incorporates the Dzyaloshinskii-Moriya and
XY anisotropies. Doping with nonmagnetic impurities, such as Zn, is considered
according to classical percolation theory, whereas the effect of Sr, which
introduces charge carriers into the CuO(2) planes, is described as a dipolar
frustration of the antiferromagnetic order. We calculate several magnetic,
thermodynamic, and spectral properties of the system, such as the
antiferromagnetic order parameter, the Neel temperature, the spin-stiffness,
and the anisotropy gaps, as well as their evolution with both Zn and Sr doping.
We explain the nonmonotonic and reentrant behavior experimentally observed for
T_N by Hucker et al. in Phys. Rev. B 59, R725 (1999), as resulting from the
reduction, due to the nonmagnetic impurities, of the dipolar frustration
induced by the charge carriers (order-from-disorder). Furthermore, we find a
similar nonmonotonic and reentrant behavior for all the other observables
studied. Most remarkably, our results show that while for x=2% and z=0 the
Dzyaloshinskii-Moriya gap \Delta_{DM}=0, for z=15% it is approximately
\Delta_{DM} = 7.5 cm^(-1). The later is larger than the lowest low-frequency
cutoff for Raman spectroscopy (~ 5 cm^(-1)), and could thus be observed in
one-magnon Raman scattering.Comment: 13 pages, 10 figure
Domain wall description of superconductivity
In the present work we shall address the issue of electrical conductivity in
superconductors in the perspective of superconducting domain wall solutions in
the realm of field theory. We take our set up made out of a dynamical complex
scalar field coupled to gauge field to be responsible for superconductivity and
an extra scalar real field that plays the role of superconducting domain walls.
The temperature of the system is interpreted through the fact that the soliton
following accelerating orbits is a Rindler observer experiencing a thermal
bath.Comment: 9 pages, 5 figures, Latex. Version to appear in PL
A laser technique for characterizing the geometry of plant canopies
The interception of solar power by the canopy is investigated as a function of solar zenith angle (time), component of the canopy, and depth into the canopy. The projected foliage area, cumulative leaf area, and view factors within the canopy are examined as a function of the same parameters. Two systems are proposed that are capable of describing the geometrical aspects of a vegetative canopy and of operation in an automatic mode. Either system would provide sufficient data to yield a numerical map of the foliage area in the canopy. Both systems would involve the collection of large data sets in a short time period using minimal manpower
Testing Asteroseismic Radii of Dwarfs and Subgiants with Kepler and Gaia
We test asteroseismic radii of Kepler main-sequence and subgiant stars by
deriving their parallaxes which are compared with those of the first Gaia data
release. We compute radii based on the asteroseismic scaling relations as well
as by fitting observed oscillation frequencies to stellar models for a subset
of the sample, and test the impact of using effective temperatures from either
spectroscopy or the infrared flux method. An offset of 3%, showing no
dependency on any stellar parameters, is found between seismic parallaxes
derived from frequency modelling and those from Gaia. For parallaxes based on
radii from the scaling relations, a smaller offset is found on average;
however, the offset becomes temperature dependent which we interpret as
problems with the scaling relations at high stellar temperatures. Using the
hotter infrared flux method temperature scale, there is no indication that
radii from the scaling relations are inaccurate by more than about 5%. Taking
the radii and masses from the modelling of individual frequencies as reference
values, we seek to correct the scaling relations for the observed temperature
trend. This analysis indicates that the scaling relations systematically
overestimate radii and masses at high temperatures, and that they are accurate
to within 5% in radius and 13% in mass for main-sequence stars with
temperatures below 6400 K. However, further analysis is required to test the
validity of the corrections on a star-by-star basis and for more evolved stars.Comment: 12 pages, 9 figures. Accepted for publication in MNRA
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