33,998 research outputs found
Ward Identities and chiral anomalies for coupled fermionic chains
Coupled fermionic chains are usually described by an effective model written
in terms of bonding and anti-bonding spinless fields with linear dispersion in
the vicinities of the respective Fermi points. We derive for the first time
exact Ward Identities (WI) for this model, proving the existence of chiral
anomalies which verify the Adler-Bardeen non-renormalization property. Such WI
are expected to play a crucial role in the understanding of the thermodynamic
properties of the system. Our results are non-perturbative and are obtained
analyzing Grassmann functional integrals by means of Constructive Quantum Field
Theory methods.Comment: TeX file, 26 pages, 7 figures. Published version, new section added
to answer referee remarks and derive the Ward Identites, no modifications in
the main resul
Phase diagram of the antiferromagnetic XY model in two dimensions in a magnetic field
The phase diagram of the quasi-two-dimensional easy-plane antiferromagnetic
model, with a magnetic field applied in the easy plane, is studied using the
self-consistent harmonic approximation. We found a linear dependence of the
transition temperature as a function of the field for large values of the
field. Our results are in agreement with experimental data for the spin-1
honeycomb compound BaNi_2V_2O_3Comment: 3 page
Using zeros of the canonical partition function map to detect signatures of a Berezinskii-Kosterlitz-Thouless transition
Using the two dimensional model as a test case, we show that
analysis of the Fisher zeros of the canonical partition function can provide
signatures of a transition in the Berezinskii-Kosterlitz-Thouless ()
universality class. Studying the internal border of zeros in the complex
temperature plane, we found a scenario in complete agreement with theoretical
expectations which allow one to uniquely classify a phase transition as in the
class of universality. We obtain in excellent accordance with
previous results. A careful analysis of the behavior of the zeros for both
regions and in the
thermodynamic limit show that goes to zero in the former
case and is finite in the last one
Magnetic monopole and string excitations in a two-dimensional spin ice
We study the magnetic excitations of a square lattice spin-ice recently
produced in an artificial form, as an array of nanoscale magnets. Our analysis,
based upon the dipolar interaction between the nanomagnetic islands, correctly
reproduces the ground-state observed experimentally. In addition, we find
magnetic monopole-like excitations effectively interacting by means of the
usual Coulombic plus a linear confining potential, the latter being related to
a string-like excitation binding the monopoles pairs, what indicates that the
fractionalization of magnetic dipoles may not be so easy in two dimensions.
These findings contrast this material with the three-dimensional analogue,
where such monopoles experience only the Coulombic interaction. We discuss,
however, two entropic effects that affect the monopole interactions: firstly,
the string configurational entropy may loose the string tension and then, free
magnetic monopoles should also be found in lower dimensional spin ices;
secondly, in contrast to the string configurational entropy, an entropically
driven Coulomb force, which increases with temperature, has the opposite effect
of confining the magnetic defects.Comment: 8 pages. Accepted by Journal of Applied Physics (2009
Efeito de micorrizas arbusculares sobre o crescimento e nutriĆ§Ć£o mineral de Brachiaria brizantha c.v Marandu.
O efeito da inoculaĆ§Ć£o de micorrizas arbusculares (MA) sobre o crescimento ...., foi avaliado sob condiƧƵes de casa-de-vegetaĆ§Ć£o. Foram avaliados oito espĆ©cies de MA: Glomus mossaea, G. fasciculatum, G. etunicatum, G. macrocarpum, Gigaspora margarita, Scutellospora heterogama, Acaulospora laevis e A. muricata.bitstream/item/67179/1/FOL-5289-5879id-.pd
Efeito de micorrizas arbusculares e adubaĆ§Ć£o com fosfato de rocha em Sesbania sesban.
No presente trabalho avaliou-se os efeitos da inoculaĆ§Ć£o de MA e da aplicaĆ§Ć£o de fosfato de rocha sobre o rendimento de forragem e composiĆ§Ć£o quĆmica de Sesbania sesban.bitstream/item/60899/1/COT-194-micorrizasarburscular....pd
InoculaĆ§Ć£o de micorrizas arbusculares em Sesbania sesban.
Este trabalho teve como objetivo avaliar o efeito da inoculaĆ§Ć£o de micorrizas arbusculares sobre a produĆ§Ć£o de biomassa e composiĆ§Ć£o quĆmica de Sesbania sesban
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