16,492 research outputs found
Chiral Symmetry Breaking and Pion Wave Function
We consider here chiral symmetry breaking through nontrivial vacuum structure
with quark antiquark condensates. We then relate the condensate function to the
wave function of pion as a Goldstone mode. This simultaneously yields the pion
also as a quark antiquark bound state as a localised zero mode in vacuum. We
illustrate the above with Nambu Jona-Lasinio model to calculate different
pionic properties in terms of the vacuum structure for breaking of exact or
approximate chiral symmetry, as well as the condensate fluctuations giving rise
to mesons.Comment: latex, revtex, 16 page
Constraints on nuclear matter parameters of an Effective Chiral Model
Within an effective non-linear chiral model, we evaluate nuclear matter
parameters exploiting the uncertainties in the nuclear saturation properties.
The model is sternly constrained with minimal free parameters, which display
the interlink between nuclear incompressibility (), the nucleon effective
mass (), the pion decay constant () and the meson
mass (). The best fit among the various parameter set is then
extracted and employed to study the resulting Equation of state (EOS). Further,
we also discuss the consequences of imposing constraints on nuclear EOS from
Heavy-Ion collision and other phenomenological model predictions.Comment: 10 pages, 8 figure
Canted Ferromagnetism in Double Exchange Model with on-site Coulomb Repulsion
The double exchange model with on-site Coulomb repulsion is considered.
Schwinger-bosons representation of the localized spins is used and two
spin-singlet Fermion operators are introduced. In terms of the new Fermi fields
the on-site Hund's interaction is in a diagonal form and the true magnons of
the system are identified. The singlet fermions can be understood as electrons
dressed by a cloud of repeatedly emitted and reabsorbed magnons. Rewritten in
terms of Schwinger-bosons and spin-singlet fermions the theory is U(1) gauge
invariant. We show that spontaneous breakdown of the gauge symmetry leads to
\emph{\textbf{canted ferromagnetism with on-site spins of localized and
delocalized electrons misaligned}}. On-site canted phase emerges in double
exchange model when Coulomb repulsion is large enough. The quantum phase
transition between ferromagnetism and canted phase is studied varying the
Coulomb repulsion for different values of parameters in the theory such as
Hund's coupling and chemical potential.Comment: 8 pages, 6 figure
Mechanisms and Representations of Language-Mediated Visual Attention
The experimental investigation of language-mediated visual attention is a promising way to study the interaction of the cognitive systems involved in language, vision, attention, and memory. Here we highlight four challenges for a mechanistic account of this oculomotor behavior: the levels of representation at which language-derived and vision-derived representations are integrated; attentional mechanisms; types of memory; and the degree of individual and group differences. Central points in our discussion are (a) the possibility that local microcircuitries involving feedforward and feedback loops instantiate a common representational substrate of linguistic and non-linguistic information and attention; and (b) that an explicit working memory may be central to explaining interactions between language and visual attention. We conclude that a synthesis of further experimental evidence from a variety of fields of inquiry and the testing of distinct, non-student, participant populations will prove to be critical
Learning from the early adopters: developing the digital practitioner
This paper explores how Sharpe and Beethamâs Digital Literacies Framework which was derived to model studentsâ digital literacies, can be applied to lecturersâ digital literacy practices. Data from a small-scale phenomenological study of higher education lecturers who used Web 2.0 in their teaching and learning practices are used to examine if this pyramid model represents their motivations for adopting technology-enhanced learning in their pedagogic practices. The paper argues that whilst Sharpe and Beethamâs model has utility in many regards, these lecturers were mainly motivated by the desire to achieve their pedagogic goals rather than by a desire to become a digital practitioner
Gluon Condensates, Chiral Symmetry Breaking and Pion Wave Function
We consider here chiral symmetry breaking in quantum chromodynamics arising
from gluon condensates in vacuum. Through coherent states of gluons simulating
a mean field type of approximation, we show that the off-shell gluon
condensates of vacuum generate a mass-like contribution for the quarks, giving
rise to chiral symmetry breaking. We next note that spontaneous breaking of
global chiral symmetry links the four component quark field operator to the
pion wave function. This in turn yields many hadronic properties in the light
quark sector in agreement with experiments, leading to the conclusion that low
energy hadron properties are primarily driven by the vacuum structure of
quantum chromodynamics.Comment: 25 pages, IP/BBSR/92-76, revte
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