412 research outputs found
Ultra-short solitons and kinetic effects in nonlinear metamaterials
We present a stability analysis of a modified nonlinear Schroedinger equation
describing the propagation of ultra-short pulses in negative refractive index
media. Moreover, using methods of quantum statistics, we derive a kinetic
equation for the pulses, making it possible to analyze and describe partial
coherence in metamaterials. It is shown that a novel short pulse soliton, which
is found analytically, can propagate in the medium.Comment: 6 pages, 2 figures, to appear in Phys. Rev.
The casuality and/or energy-momentum conservation constraints on QCD amplitudes in small x regime
The causality and/or the energy-momentum constraints on the amplitudes of
high energy processes are generalized to QCD. The constraints imply that the
energetic parton may experience at most one inelastic collision only and that
the number of the constituents in the light cone wave function of the
projectile is increasing with the collision energy and the atomic number.Comment: 24 pages,8 figures. The paper is streamlined, some references are
changed and misprints are eliminate
Vertex Operators in 2K Dimensions
A formula is proposed which expresses free fermion fields in 2K dimensions in
terms of the Cartan currents of the free fermion current algebra. This leads,
in an obvious manner, to a vertex operator construction of nonabelian free
fermion current algebras in arbitrary even dimension. It is conjectured that
these ideas may generalize to a wide class of conformal field theories.Comment: Minor change in notation. Change in references
Quantum-limited metrology and Bose-Einstein condensates
We discuss a quantum-metrology protocol designed to estimate a physical
parameter in a Bose-Einstein condensate of N atoms, and we show that the
measurement uncertainty can decrease faster than 1/N. The 1/N scaling is
usually thought to be the best possible in any measurement scheme. From the
perspective of quantum information theory, we outline the main idea that leads
to a measurement uncertainty that scales better than 1/N. We examine in detail
some potential problems and challenges that arise in implementing such a
measurement protocol using a Bose-Einstein condensate. We discuss how some of
these issues can be dealt with by using lower-dimensional condensates trapped
in nonharmonic potentials.Comment: 32 pages, 1 figure, updated reference
Geometric derivation of the quantum speed limit
The Mandelstam-Tamm and Margolus-Levitin inequalities play an important role
in the study of quantum mechanical processes in Nature, since they provide
general limits on the speed of dynamical evolution. However, to date there has
been only one derivation of the Margolus-Levitin inequality. In this paper,
alternative geometric derivations for both inequalities are obtained from the
statistical distance between quantum states. The inequalities are shown to hold
for unitary evolution of pure and mixed states, and a counterexample to the
inequalities is given for evolution described by completely positive
trace-preserving maps. The counterexample shows that there is no quantum speed
limit for non-unitary evolution.Comment: 8 pages, 1 figure
Explicitly symmetrical treatment of three-body phase space
We derive expressions for three-body phase space that are explicitly
symmetrical in the masses of the three particles. We study geometrical
properties of the variables involved in elliptic integrals and demonstrate that
it is convenient to use the Jacobian zeta function to express the results in
four and six dimensions.Comment: 20 pages, latex, 2 postscript figure
Black Hole Complementarity vs. Locality
The evaporation of a large mass black hole can be described throughout most
of its lifetime by a low-energy effective theory defined on a suitably chosen
set of smooth spacelike hypersurfaces. The conventional argument for
information loss rests on the assumption that the effective theory is a local
quantum field theory. We present evidence that this assumption fails in the
context of string theory. The commutator of operators in light-front string
theory, corresponding to certain low-energy observers on opposite sides of the
event horizon, remains large even when these observers are spacelike separated
by a macroscopic distance. This suggests that degrees of freedom inside a black
hole should not be viewed as independent from those outside the event horizon.
These nonlocal effects are only significant under extreme kinematic
circumstances, such as in the high-redshift geometry of a black hole.
Commutators of space-like separated operators corresponding to ordinary
low-energy observers in Minkowski space are strongly suppressed in string
theory.Comment: 32 pages, harvmac, 3 figure
On the Infrared Behavior of the Pressure in Thermal Field Theories
We study non-perturbatively, via the Schwinger-Dyson equations, the leading
infrared behavior of the pressure in the ladder approximation. This problem is
discussed firstly in the context of a thermal scalar field theory, and the
analysis is then extended to the Yang-Mills theory at high temperatures. Using
the Feynman gauge, we find a system of two coupled integral equations for the
gluon and ghost self-energies, which is solved analytically. The solutions of
these equations show that the contributions to the pressure, when calculated in
the ladder approximation, are finite in the infrared domain.Comment: 20 pages plus 4 figures available by request, IFUSP/P-100
Abelian Dyons in the Maximal Abelian Projection of SU(2) Gluodynamics
Correlations of the topological charge Q, the electric current J^e and the
magnetic current J^m in SU(2) lattice gauge theory in the Maximal Abelian
projection are investigated. It occurs that the correlator > is
nonzero for a wide range of values of the bare charge. It is shown that: (i)
the abelian monopoles in the Maximal Abelian projection are dyons which carry
fluctuating electric charge; (ii) the sign of the electric charge e(x)
coincides with that of the product of the monopole charge m(x) and the
topological charge density Q(x).Comment: 6 pages, 2 EPS figures, LaTeX, uses epsf.sty; revision: minor
corrections, references adde
A (1,2) Heterotic String with Gauge Symmetry
We construct a (1,2) heterotic string with gauge symmetry and determine its
particle spectrum. This theory has a local N=1 worldsheet supersymmetry for
left movers and a local N=2 worldsheet supersymmetry for right movers and
describes particles in either two or three space-time dimensions. We show that
fermionizing the bosons of the compactified N=1 space leads to a particle
spectrum which has nonabelian gauge symmetry. The fermionic formulation of the
theory corresponds to a dimensional reduction of self dual Yang Mills. We also
give a worldsheet action for the theory and calculate the one-loop path
integral.Comment: 17 pages, added reference
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