20,536 research outputs found
Novel Symmetries in Christ-Lee Model
We demonstrate that the gauge-fixed Lagrangian of the Christ-Lee model
respects four fermionic symmetries, namely; (anti-)BRST symmetries,
(anti-)co-BRST symmetries within the framework of BRST formalism. The
appropriate anticommutators amongst the fermionic symmetries lead to a unique
bosonic symmetry. It turns out that the algebra obeyed by the symmetry
transformations (and their corresponding conserved charges) is reminiscent of
the algebra satisfied by the de Rham cohomological operators of differential
geometry. We also provide the physical realizations of the cohomological
operators in terms of the symmetry properties. Thus, the present model provides
a simple model for the Hodge theory.Comment: LaTeX File, 12 Pages, Text Modified, Typos Fixed, Refences Added, No
Figure
Spinodal decomposition: An alternate mechanism of phase conversion
The scenario of homogeneous nucleation is investigated for a first order
quark-hadron phase transition in a rapidly expanding background of quark gluon
plasma. It is found that significant supercooling is possible before
hadronization begins. This study also suggests that spinodal decomposition
competes with nucleation and may provide an alternative mechanism for phase
conversion.Comment: LaTeX, 4 pages with 3 Postscript figures. Talk given at International
Conference on Physics and Astrophysics of Quark Gluon Plasma (ICPAQGP 2001),
Nov. 26-30, 2001, Jaipur, Indi
Nonlinear wave-wave interactions in quantum plasmas
Wave-wave interaction in plasmas is a topic of important research since the
16th century. The formation of Langmuir solitons through the coupling of
high-frequency (hf) Langmuir and low-frequency (lf) ion-acoustic waves, is one
of the most interesting features in the context of turbulence in modern plasma
physics. Moreover, quantum plasmas, which are ubiquitous in ultrasmall
electronic devices, micromechanical systems as well as in dense astrophysical
environments are a topic of current research. In the light of notable interests
in such quantum plasmas, we present here a theoretical investigation on the
nonlinear interaction of quantum Langmuir waves (QLWs) and quantum ion-acoustic
waves (QIAWs), which are governed by the one-dimensional quantum Zakharov
equations (QZEs). It is shown that a transition to spatiotemporal chaos (STC)
occurs when the length scale of excitation of linear modes is larger than that
of the most unstable ones. Such length scale is, however, to be larger
(compared to the classical one) in presence of the quantum tunneling effect.
The latter induces strong QIAW emission leading to the occurrence of collision
and fusion among the patterns at an earlier time than the classical case.
Moreover, numerical simulation of the QZEs reveals that many solitary patterns
can be excited and saturated through the modulational instability (MI) of
unstable harmonic modes. In a longer time, these solitons are seen to appear in
the state of STC due to strong QIAW emission as well as by the collision and
fusion in stochastic motion. The energy in the system is thus strongly
redistributed, which may switch on the onset of Langmuir turbulence in quantum
plasmas.Comment: 6 pages, 6 figures (To appear in AIP Conf. Proceedings 2010
Theory of nonlinear optical properties of phenyl-substituted polyacetylenes
In this paper we present a theoretical study of the third-order nonlinear
optical properties of poly(diphenyl)polyacetylene (PDPA) pertaining to the
third-harmonic-generation (THG) process. We study the aforesaid process in
PDPA's using both the independent electron Hueckel model, as well as
correlated-electron Pariser-Parr-Pople (P-P-P) model. The P-P-P model based
calculations were performed using various configuration interaction (CI)
methods such as the the multi-reference-singles-doubles CI (MRSDCI), and the
quadruples-CI (QCI) methods, and the both longitudinal and the transverse
components of third-order susceptibilities were computed. The Hueckel model
calculations were performed on oligo-PDPA's containing up to fifty repeat
units, while correlated calculations were performed for oligomers containing up
to ten unit cells. At all levels of theory, the material exhibits highly
anisotropic nonlinear optical response, in keeping with its structural
anisotropy. We argue that the aforesaid anisotropy can be divided over two
natural energy scales: (a) the low-energy response is predominantly
longitudinal and is qualitatively similar to that of polyenes, while (b) the
high-energy response is mainly transverse, and is qualitatively similar to that
of trans-stilbene.Comment: 13 pages, 7 figures (included), to appear in Physical Review B (April
15, 2004
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