218 research outputs found
Constraints on transmission, dispersion, and density of states in dielectric multilayers and stepwise potential barriers with arbitrary layer arrangement
Normal-incidence transmission and dispersion properties of optical
multilayers and one-dimensional stepwise potential barriers in the
non-tunneling regime are analytically investigated. The optical paths of every
constituent layer in a multilayer structure, as well as the parameters of every
step of the stepwise potential barrier, are constrained by a generalized
quarter-wave condition. No other restrictions on the structure geometry is
imposed, i.e., the layers are arranged arbitrarily. We show that the density of
states (DOS) spectra of the multilayer or barrier in question are subject to
integral conservation rules similar to the Barnett-Loudon sum rule but ocurring
within a finite frequency or energy interval. In the optical case, these
frequency intervals are regular. For the potential barriers, only non-periodic
energy intervals can be present in the spectrum of any given structure, and
only if the parameters of constituent potential steps are properly chosen.
Abstract The integral conservation relations derived analytically have also
been verified numerically. The relations can be used in dispersion-engineered
multilayer-based devices, e.g., ultrashort pulse compressors or ultracompact
optical delay lines, as well as to design multiple-quantum-well electronic
heterostructures with engineered DOS.Comment: 10 pages, 5 figures, to be submitted to PR
Gravitational catalysis of chiral and color symmetry breaking of quark matter in hyperbolic space
We study the dynamical breaking of chiral and color symmetries of dense quark
matter in the ultrastatic hyperbolic spacetime in the framework
of an extended Nambu--Jona-Lasinio model. On the basis of analytical
expressions for chiral and color condensates as functions of curvature and
temperature, the phenomenon of dimensional reduction and gravitational
catalysis of symmetry breaking in strong gravitational field is demonstrated in
the regime of weak coupling constants. In the case of strong couplings it is
shown that curvature leads to small corrections to the flat-space values of
condensate and thus enhances the symmetry breaking effects. Finally, using
numerical calculations phase transitions under the influence of chemical
potential and negative curvature are considered and the phase portrait of the
system is constructed.Comment: 14 pages, 5 figure
Chiral dynamics in QED and QCD in a magnetic background and nonlocal noncommutative field theories
We study the connection of the chiral dynamics in QED and QCD in a strong
magnetic field with noncommutative field theories (NCFT). It is shown that
these dynamics determine complicated nonlocal NCFT. In particular, although the
interaction vertices for electrically neutral composites in these gauge models
can be represented in the space with noncommutative spatial coordinates, there
is no field transformation that could put the vertices in the conventional form
considered in the literature. It is unlike the Nambu-Jona-Lasinio (NJL) model
in a magnetic field where such a field transformation can be found, with a cost
of introducing an exponentially damping form factor in field propagators. The
crucial distinction between these two types of models is in the characters of
their interactions, being short-range in the NJL-like models and long-range in
gauge theories. The relevance of the NCFT connected with the gauge models for
the description of the quantum Hall effect in condensed matter systems with
long-range interactions is briefly discussed.Comment: 19 pages, REVTeX4, v2: clarifications added, v3: to match PRD versio
Inhomogeneous charged pion condensation phenomenon in the NJL model with quark number and isospin chemical potentials
The properties of two-flavored massive Nambu--Jona-Lasinio model in
(1+1)-dimensional spacetime are investigated in the presence of isospin and
quark number chemical potentials. The consideration is performed in the
large- limit, where is the number of colored quarks. It is shown in
the framework of this model that charged pion condensation phenomenon of dense
quark/hadron isotopically asymmetric matter is rather a spatially inhomogeneous
than a homogeneous one.Comment: 11 pages, 8 figures; version accepted for publication in PRD. arXiv
admin note: text overlap with arXiv:1106.2928, arXiv:1102.407
ВИКОРИСТАННЯ ПРОГРАМИ «ВИХОВАННЯ ХАРАКТЕРУ» В СУЧАСНІЙ АМЕРИКАНСЬКІЙ ШКОЛІ. (Using the Program "Character Educations" in modern American schools.)
У статті проаналізовано поняття, мету, зміст, методи та засоби реалізації програми «Виховання характеру» в сучасній американській школі. Розкрито актуальність її використання та географію поширення в школах США.
(In this article the concept, purpose, contents, methods and means of the program «Character education» in modern American schools are analyzed. The importance and geography of its use in the schools of the USA is revealed.
Color superconductivity in the static Einstein Universe
We study the behavior of quark and diquark condensates in dense quark matter
under the influence of a gravitational field adopting as a simple model the
static dimensional Einstein Universe. Calculations are performed in the
framework of the extended Nambu--Jona-Lasinio model at finite temperature and
quark density on the basis of the thermodynamic potential and the gap
equations. Quark and diquark condensates as functions of the chemical potential
and temperature at different values of the curvature have been studied. Phase
portraits of the system have been constructed
Chiral phase transitions in strong chromomagnetic fields at finite temperature and dimensional reduction
Dynamical fermion mass generation in external chromomagnetic fields is
considered at non--zero temperature. The general features of dynamical chiral
symmetry breaking () are investigated for several field
configurations in relation to their symmetry properties and the form of the
quark spectrum. According to the fields, there arises dimensional reduction by
one or two units. In all cases there exists even at weak quark
attraction, confirming the idea about the dimensional insensitivity of this
mechanism in a chromomagnetic field.Comment: LATEX file, 12 pages, no figure
Switchable lasing in coupled multimode microcavities
We propose the new concept of a switchable multimode microlaser. As a
generic, realistic model of a multimode microresonator a system of two coupled
defects in a two-dimensional photonic crystal is considered. We demonstrate
theoretically that lasing of the cavity into one selected resonator mode can be
caused by injecting an appropriate optical pulse at the onset of laser action
(injection seeding). Temporal mode-to-mode switching by re-seeding the cavity
after a short cool-down period is demonstrated by direct numerical solution. A
qualitative analytical explanation of the mode switching in terms of the laser
bistability is presented.Comment: Accepted for publication in Physical Review Letters. Published,
somewhat shortened versio
Chiral density waves in the NJL model with quark number and isospin chemical potentials
We investigate the phase portrait of the (1+1)-dimensional massless
two-flavored NJL model containing a quark number chemical potential
and an isospin chemical potential in the limit of a large number of
colors . Particular attention is paid to the question to what
extent the inclusion of an isospin asymmetry affects chiral condensates to have
a spatial inhomogeneity in the form of the so-called chiral density waves (CDW)
(chiral spirals). It is shown that at zero temperature and comparatively small
values of , i.e. at ( is the dynamical
quark mass in the vacuum) only the homogeneous charged pion condensation phase
is realized for arbitrary nonzero values of . Contrary to this, for
large values of , two CDW phases appear in the -phase
diagram of the model. In the first phase, CDWs are clockwise twisted chiral
spirals and in the second phase they are counterclockwise. The influence of
nonzero temperature on the formation of the CDW phases is also investigated.Comment: 14 pages, 9 figures; typos corrected; one reference adde
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