4,265 research outputs found
Results on the nucleon spin structure
SMC performed an investigation of the spin structure of the nucleon by
measuring deep inelastic scattering of polarised muons off polarised protons
and deuterons. A summary of the results for spin structure functions and sum
rules is given.Comment: 8 pages, LaTeX, Talk given at the Workshop on "Symmetry and Spin -
PRAHA98", Prag, September 1998. Proceedings to be published by Czech. Journ.
Phy
Effects of site dilution on the magnetic properties of geometrically frustrated antiferromagnets
The effect of site dilution by non magnetic impurities on the susceptibility
of geometrically frustrated antiferromagnets (kagome and pyrochlore lattices)
is discussed in the framework of the Generalized Constant Coupling model, for
both classical and quantum Heisenberg spins. For the classical diluted
pyrochlore lattice, excellent agreement is found when compared with Monte Carlo
data. Results for the quantum case are also presented and discussed.Comment: 5 pages, 3 figure
A new approach to calculate the gluon polarization
We derive the Leading-Order master equation to extract the polarized gluon
distribution G(x;Q^2) = x \deltag(x;Q^2) from polarized proton structure
function, g1p(x;Q^2). By using a Laplace-transform technique, we solve the
master equation and derive the polarized gluon distribution inside the proton.
The test of accuracy which are based on our calculations with two different
methods confirms that we achieve to the correct solution for the polarized
gluon distribution. We show that accurate experimental knowledge of g1p(x;Q^2)
in a region of Bjorken x and Q^2, is all that is needed to determine the
polarized gluon distribution in that region. Therefore, to determine the gluon
polarization \deltag /g,we only need to have accurate experimental data on
un-polarized and polarized structure functions (F2p (x;Q^2) and g1p(x;Q^2)).Comment: 12 pages, 5 figure
Spin dependent structure function at small and small
Theoretical expectations concerning the low and low behaviour of
are summarized and compared with the recent SMC data.Comment: 4 pages, plain LATEX, 1 eps figure; contribution to 3rd UK
Phenomenology Workshop on HERA Physics, St. John's College, Durham, UK,
September 199
Critical behavior of 2 and 3 dimensional ferro- and antiferromagnetic spin ice systems in the framework of the Effective Field Renormalization Group technique
In this work we generalize and subsequently apply the Effective Field
Renormalization Group technique to the problem of ferro- and
antiferromagnetically coupled Ising spins with local anisotropy axes in
geometrically frustrated geometries (kagome and pyrochlore lattices). In this
framework, we calculate the various ground states of these systems and the
corresponding critical points. Excellent agreement is found with exact and
Monte Carlo results. The effects of frustration are discussed. As pointed out
by other authors, it turns out that the spin ice model can be exactly mapped to
the standard Ising model but with effective interactions of the opposite sign
to those in the original Hamiltonian. Therefore, the ferromagnetic spin ice is
frustrated, and does not order. Antiferromagnetic spin ice (in both 2 and 3
dimensions), is found to undergo a transition to a long range ordered state.
The thermal and magnetic critical exponents for this transition are calculated.
It is found that the thermal exponent is that of the Ising universality class,
whereas the magnetic critical exponent is different, as expected from the fact
that the Zeeman term has a different symmetry in these systems. In addition,
the recently introduced Generalized Constant Coupling method is also applied to
the calculation of the critical points and ground state configurations. Again,
a very good agreement is found with both exact, Monte Carlo, and
renormalization group calculations for the critical points. Incidentally, we
show that the generalized constant coupling approach can be regarded as the
lowest order limit of the EFRG technique, in which correlations outside a
frustrated unit are neglected, and scaling is substituted by strict equality of
the thermodynamic quantities.Comment: 28 pages, 9 figures, RevTeX 4 Some minor changes in the conclussions.
One reference adde
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