2,782 research outputs found
Abelian Hall Fluids and Edge States: a Conformal Field Theory Approach
We show that a Coulomb gas Vertex Operator representation of 2D Conformal
Field Theory gives a complete description of abelian Hall fluids: as an
euclidean theory in two space dimensions leads to the construction of the
ground state wave function for planar and toroidal geometry and characterizes
the spectrum of low energy excitations; as a Minkowski theory gives the
corresponding dynamics of the edge states. The difference between a generic
Hall fluid and states of the Jain's sequences is emphasized and the presence,
in the latter case, of of an extended algebra
and the consequent propagation on the edges of a single charged mode and
neutral modes is discussed.Comment: Latex, 22 page
Knizhnik-Zamolodchikov equation and extended symmetry for stable Hall states
We describe a component abelian Hall fluid as a system of {\it composite
bosons} moving in an average null field given by the external magnetic field
and by the statistical flux tubes located at the position of the particles. The
collective vacuum state, in which the bosons condense, is characterized by a
Knizhnik-Zamolodchikov differential equation relative to a
Wess-Zumino model. In the case of states belonging to Jain's sequences the
Knizhnik-Zamolodchikov equation naturally leads to the presence of an
\hat{U}(1)\ot \hat{SU}(n) extended algebra. Only the mode is
charged while the modes are neutral, in agreement with recent
results obtained in the study of the edge states.Comment: 11 pages, Late
2+1 Einstein Gravity as a Deformed Chern-Simons Theory
The usual description of 2+1 dimensional Einstein gravity as a Chern-Simons
(CS) theory is extended to a one parameter family of descriptions of 2+1
Einstein gravity. This is done by replacing the Poincare' gauge group symmetry
by a q-deformed Poincare' gauge group symmetry, with the former recovered when
q-> 1. As a result, we obtain a one parameter family of Hamiltonian
formulations for 2+1 gravity. Although formulated in terms of noncommuting
dreibeins and spin-connection fields, our expression for the action and our
field equations, appropriately ordered, are identical in form to the ordinary
ones. Moreover, starting with a properly defined metric tensor, the usual
metric theory can be built; the Christoffel symbols and space-time curvature
having the usual expressions in terms of the metric tensor, and being
represented by c-numbers. In this article, we also couple the theory to
particle sources, and find that these sources carry exotic angular momentum.
Finally, problems related to the introduction of a cosmological constant are
discussed.Comment: Latex file, 26 pages, no figure
Comments on the Non-Commutative Description of Classical Gravity
We find a one-parameter family of Lagrangian descriptions for classical
general relativity in terms of tetrads which are not c-numbers. Rather, they
obey exotic commutation relations. These noncommutative properties drop out in
the metric sector of the theory, where the Christoffel symbols and the Riemann
tensor are ordinary commuting objects and they are given by the usual
expression in terms of the metric tensor. Although the metric tensor is not a
c-number, we argue that all measurements one can make in this theory are
associated with c-numbers, and thus that the common invariant sector of our
one--parameter family of deformed gauge theories (for the case of zero torsion)
is physically equivalent to Einstein's general relativity.Comment: Latex file, 13 pages, no figure
Comment on "Quantitative wave-particle duality in multibeam interferometers"
In a recent paper [Phys. Rev. {\bf A64}, 042113 (2001)] S. D\"urr proposed an
interesting multibeam generalization of the quantitative formulation of
interferometric wave-particle duality, discovered by Englert for two-beam
interferometers. The proposed generalization is an inequality that relates a
generalized measure of the fringe visibility, to certain measures of the
maximum amount of which-way knowledge that can be stored in a which-way
detector. We construct an explicit example where, with three beams in a pure
state, the scheme proposed by D\"{u}rr leads to the possibility of an ideal
which-way detector, that can achieve a better path-discrimination, at the same
time as a better fringe visibility. In our opinion, this seems to be in
contrast with the intuitive idea of complementarity, as it is implemented in
the two-beams case, where an increase in path discrimination always implies a
decrease of fringe visibility, if the beams and the detector are in pure
states.Comment: 4 pages, 1 encapsulated figure. In press on Phys. Rev.
Adaptive Multi-Paddock Grazing of Cover Crops in Integrated Crop-Livestock Systems in Mediterranean Regions: a Review
Small-grain farming systems in Mediterranean climatic regions are characterized by poor quality soils, high climate variability, and resulting heavy agrochemical reliance. The integration of continuously grazed monocrop pasture phases has improved soil fertility, crop productivity, and mitigated financial risk. However, emerging sustainability issues such as herbicide resistance, inputs costs rising disproportionately to product prices, and increasing climate variability and predictability, drive the need for ongoing innovation in crop-livestock integration. The option of growing multi-species cover crops as a dual-forage and service crop is evaluated within Mediterranean climate contexts. Furthermore, the option of subjecting the cover crops to adaptive multi-paddock (AMP) grazing management as an alternative to the standard set stocking approach is discusse
On Interferometric Duality in Multibeam Experiments
We critically analyze the problem of formulating duality between fringe
visibility and which-way information, in multibeam interference experiments. We
show that the traditional notion of visibility is incompatible with any
intuitive idea of complementarity, but for the two-beam case. We derive a
number of new inequalities, not present in the two-beam case, one of them
coinciding with a recently proposed multibeam generalization of the inequality
found by Greenberger and YaSin. We show, by an explicit procedure of
optimization in a three-beam case, that suggested generalizations of Englert's
inequality, do not convey, differently from the two-beam case, the idea of
complementarity, according to which an increase of visibility is at the cost of
a loss in path information, and viceversa.Comment: 26 pages, 1 figure, substantial changes in the text, new material has
been added in Section 3. Version to appear in J.Phys.
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