699 research outputs found
New Phenomenon of Nonlinear Regge Trajectory and Quantum Dual String Theory
The relation between the spin and the mass of an infinite number of particles
in a -deformed dual string theory is studied. For the deformation parameter
a root of unity, in addition to the relation of such values of with the
rational conformal field theory, the Fock space of each oscillator mode in the
Fubini-Veneziano operator formulation becomes truncated. Thus, based on general
physical grounds, the resulting spin-(mass) relation is expected to be
below the usual linear trajectory. For such specific values of , we find
that the linear Regge trajectory turns into a square-root trajectory as the
mass increases.Comment: 12 pages, Latex, HU-SEFT R 1994-0
The Hagedorn temperature Revisited
The Hagedorn temperature, T_H is determined from the number of hadronic
resonances including all mesons and baryons. This leads to a stable result T_H
= 174 MeV consistent with the critical and the chemical freeze-out temperatures
at zero chemical potential. We use this result to calculate the speed of sound
and other thermodynamic quantities in the resonance hadron gas model for a wide
range of baryon chemical potentials following the chemical freeze-out curve. We
compare some of our results to those obtained previously in other papers.Comment: 13 pages, 4 figure
Affine Lie Algebras in Massive Field Theory and Form-Factors from Vertex Operators
We present a new application of affine Lie algebras to massive quantum field
theory in 2 dimensions, by investigating the limit of the q-deformed
affine symmetry of the sine-Gordon theory, this limit occurring
at the free fermion point. Working in radial quantization leads to a
quasi-chiral factorization of the space of fields. The conserved charges which
generate the affine Lie algebra split into two independent affine algebras on
this factorized space, each with level 1 in the anti-periodic sector, and level
in the periodic sector. The space of fields in the anti-periodic sector can
be organized using level- highest weight representations, if one supplements
the \slh algebra with the usual local integrals of motion. Introducing a
particle-field duality leads to a new way of computing form-factors in radial
quantization. Using the integrals of motion, a momentum space bosonization
involving vertex operators is formulated. Form-factors are computed as vacuum
expectation values in momentum space. (Based on talks given at the Berkeley
Strings 93 conference, May 1993, and the III International Conference on
Mathematical Physics, String Theory, and Quantum Gravity, Alushta, Ukraine,
June 1993.)Comment: 13 pages, CLNS 93/125
Two-spin entanglement distribution near factorized states
We study the two-spin entanglement distribution along the infinite
chain described by the XY model in a transverse field; closed analytical
expressions are derived for the one-tangle and the concurrences ,
being the distance between the two possibly entangled spins, for values of the
Hamiltonian parameters close to those corresponding to factorized ground
states. The total amount of entanglement, the fraction of such entanglement
which is stored in pairwise entanglement, and the way such fraction distributes
along the chain is discussed, with attention focused on the dependence on the
anisotropy of the exchange interaction. Near factorization a characteristic
length-scale naturally emerges in the system, which is specifically related
with entanglement properties and diverges at the critical point of the fully
isotropic model. In general, we find that anisotropy rule a complex behavior of
the entanglement properties, which results in the fact that more isotropic
models, despite being characterized by a larger amount of total entanglement,
present a smaller fraction of pairwise entanglement: the latter, in turn, is
more evenly distributed along the chain, to the extent that, in the fully
isotropic model at the critical field, the concurrences do not depend on .Comment: 14 pages, 6 figures. Final versio
Power counting with one-pion exchange
Techniques developed for handing inverse-power-law potentials in atomic
physics are applied to the tensor one-pion exchange potential to determine the
regions in which it can be treated perturbatively. In S-, P- and D-waves the
critical values of the relative momentum are less than or of the order of 400
MeV. The RG is then used to determine the power counting for short-range
interaction in the presence of this potential. In the P-and D-waves, where
there are no low-energy bound or virtual states, these interactions have
half-integer RG eigenvalues and are substantially promoted relative to naive
expectations. These results are independent of whether the tensor force is
attractive or repulsive. In the 3S1 channel the leading term is relevant, but
it is demoted by half an order compared to the counting for the effective-range
expansion with only a short-range potential. The tensor force can be treated
perturbatively in those F-waves and above that do not couple to P- or D-waves.
The corresponding power counting is the usual one given by naive dimensional
analysis.Comment: 18 pages, RevTeX (further details, explanation added
Effective boost and "point-form" approach
Triangle Feynman diagrams can be considered as describing form factors of
states bound by a zero-range interaction. These form factors are calculated for
scalar particles and compared to point-form and non-relativistic results. By
examining the expressions of the complete calculation in different frames, we
obtain an effective boost transformation which can be compared to the
relativistic kinematical one underlying the present point-form calculations, as
well as to the Galilean boost. The analytic expressions obtained in this simple
model allow a qualitative check of certain results obtained in similar studies.
In particular, a mismatch is pointed out between recent practical applications
of the point-form approach and the one originally proposed by Dirac.Comment: revised version as accepted for publicatio
On the SO(2,1) symmetry in General Relativity
The role of the SO(2,1) symmetry in General Relativity is analyzed.
Cosmological solutions of Einstein field equations invariant with respect to a
space-like Lie algebra G_r, with r between 3 and 6 and containing so(2,1) as a
subalgebra, are also classified.Comment: 10 pages, latex, no figure
Infinite Symmetry in the Quantum Hall Effect
Free planar electrons in a uniform magnetic field are shown to possess the
symmetry of area-preserving diffeomorphisms (-infinity algebra).
Intuitively, this is a consequence of gauge invariance, which forces dynamics
to depend only on the flux. The infinity of generators of this symmetry act
within each Landau level, which is infinite-dimensional in the thermodynamical
limit. The incompressible ground states corresponding to completely filled
Landau levels (integer quantum Hall effect) are shown to be infinitely
symmetric, since they are annihilated by an infinite subset of generators. This
geometrical characterization of incompressibility also holds for fractional
fillings of the lowest level (simplest fractional Hall effect) in the presence
of Haldane's effective two-body interactions. Although these modify the
symmetry algebra, the corresponding incompressible ground states proposed by
Laughlin are again symmetric with respect to the modified infinite algebra.Comment: 28 page
Information geometry of Gaussian channels
We define a local Riemannian metric tensor in the manifold of Gaussian
channels and the distance that it induces. We adopt an information-geometric
approach and define a metric derived from the Bures-Fisher metric for quantum
states. The resulting metric inherits several desirable properties from the
Bures-Fisher metric and is operationally motivated from distinguishability
considerations: It serves as an upper bound to the attainable quantum Fisher
information for the channel parameters using Gaussian states, under generic
constraints on the physically available resources. Our approach naturally
includes the use of entangled Gaussian probe states. We prove that the metric
enjoys some desirable properties like stability and covariance. As a byproduct,
we also obtain some general results in Gaussian channel estimation that are the
continuous-variable analogs of previously known results in finite dimensions.
We prove that optimal probe states are always pure and bounded in the number of
ancillary modes, even in the presence of constraints on the reduced state input
in the channel. This has experimental and computational implications: It limits
the complexity of optimal experimental setups for channel estimation and
reduces the computational requirements for the evaluation of the metric:
Indeed, we construct a converging algorithm for its computation. We provide
explicit formulae for computing the multiparametric quantum Fisher information
for dissipative channels probed with arbitrary Gaussian states, and provide the
optimal observables for the estimation of the channel parameters (e.g. bath
couplings, squeezing, and temperature).Comment: 19 pages, 4 figure
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