1,095 research outputs found
Smooth Bosonization as a Quantum Canonical Transformation
We consider a 1+1 dimensional field theory which contains both a complex
fermion field and a real scalar field. We then construct a unitary operator
that, by a similarity transformation, gives a continuum of equivalent theories
which smoothly interpolate between the massive Thirring model and the
sine-Gordon model. This provides an implementation of smooth bosonization
proposed by Damgaard et al. as well as an example of a quantum canonical
transformation for a quantum field theory.Comment: 20 pages, revte
Unstable Modes in Three-Dimensional SU(2) Gauge Theory
We investigate SU(2) gauge theory in a constant chromomagnetic field in three
dimensions both in the continuum and on the lattice. Using a variational method
to stabilize the unstable modes, we evaluate the vacuum energy density in the
one-loop approximation. We compare our theoretical results with the outcomes of
the numerical simulations.Comment: 24 pages, REVTEX 3.0, 3 Postscript figures included. (the whole
postscript file (text+figures) is available on request from
[email protected]
Improved bounds in entropic uncertainty relations
Entropic uncertainty relations place nontrivial lower bounds to the sum of
Shannon information entropies for noncommuting observables. Here we obtain a
novel lower bound on the entropy sum for general pairs of observables in
finite-dimensional Hilbert space, which improves on the best bound known to
date [Maassen and Uffink, Phys. Rev. Lett. 60, 1103 (1988)] for a wide class of
observables. This result follows from another formulation of the uncertainty
principle, the Landau-Pollak inequality, whose relationship to the
Maassen-Uffink entropic uncertainty relation is discussed.Comment: 11 pages, 1 Postscript figur
Duality symmetry, strong coupling expansion and universal critical amplitudes in two-dimensional \Phi^{4} field models
We show that the exact beta-function \beta(g) in the continuous 2D g\Phi^{4}
model possesses the Kramers-Wannier duality symmetry. The duality symmetry
transformation \tilde{g}=d(g) such that \beta(d(g))=d'(g)\beta(g) is
constructed and the approximate values of g^{*} computed from the duality
equation d(g^{*})=g^{*} are shown to agree with the available numerical
results. The calculation of the beta-function \beta(g) for the 2D scalar
g\Phi^{4} field theory based on the strong coupling expansion is developed and
the expansion of \beta(g) in powers of g^{-1} is obtained up to order g^{-8}.
The numerical values calculated for the renormalized coupling constant
g_{+}^{*} are in reasonable good agreement with the best modern estimates
recently obtained from the high-temperature series expansion and with those
known from the perturbative four-loop renormalization-group calculations. The
application of Cardy's theorem for calculating the renormalized isothermal
coupling constant g_{c} of the 2D Ising model and the related universal
critical amplitudes is also discussed.Comment: 16 pages, REVTeX, to be published in J.Phys.A:Math.Ge
Pathologies of Quenched Lattice QCD at non--zero Density and its Effective Potential
We simulate lattice QCD at non--zero baryon density and zero temperature in
the quenched approximation, both in the scaling region and in the infinite
coupling limit. We investigate the nature of the forbidden region -- the range
of chemical potential where the simulations grow prohibitively expensive, and
the results, when available, are puzzling if not unphysical. At weak coupling
we have explored the sensitivity of these pathologies to the lattice size, and
found that using a large lattice () does not remove them. The
effective potential sheds considerable light on the problems in the
simulations, and gives a clear interpretation of the forbidden region. The
strong coupling simulations were particularly illuminating on this point.Comment: 49 pages, uu-encoded expanding to postscript;also available at
ftp://hlrz36.hlrz.kfa-juelich.de/pub/mpl/hlrz72_95.p
Practical private database queries based on a quantum key distribution protocol
Private queries allow a user Alice to learn an element of a database held by
a provider Bob without revealing which element she was interested in, while
limiting her information about the other elements. We propose to implement
private queries based on a quantum key distribution protocol, with changes only
in the classical post-processing of the key. This approach makes our scheme
both easy to implement and loss-tolerant. While unconditionally secure private
queries are known to be impossible, we argue that an interesting degree of
security can be achieved, relying on fundamental physical principles instead of
unverifiable security assumptions in order to protect both user and database.
We think that there is scope for such practical private queries to become
another remarkable application of quantum information in the footsteps of
quantum key distribution.Comment: 7 pages, 2 figures, new and improved version, clarified claims,
expanded security discussio
Phase Transitions in SO(3) Lattice Gauge Theory
The phase diagram of SO(3) lattice gauge theory is investigated by Monte
Carlo techniques on both symmetric and asymmetric lattices with a view (i) to
understanding the relationship between the bulk transition and the
deconfinement transition, and (ii) to resolving the current ambiguity about the
nature of the high temperature phase. A number of tests, including an
introduction of a magnetic field and measurement of different correlation
functions in the phases with positive and negative values for the adjoint
Polyakov line, lead to the conclusion that the two phases correspond to the
same physical state. Studies on lattices of different sizes reveal only one
phase transition for this theory on all of them and it appears to have a
deconfining nature.Comment: Latex 19 pages, 9 figures. Minor changes in introduction and summary
sections. The version that appeared in journa
Stochastic Quantization of Scalar Fields in Einstein and Rindler Spacetime
We consider the stochastic quantization method for scalar fields defined in a
curved manifold and also in a flat space-time with event horizon. The two-point
function associated to a massive self-interacting scalar field is evaluated, up
to the first order level in the coupling constant, for the case of an Einstein
and also a Rindler Euclidean metric, respectively. Its value for the asymptotic
limit of the Markov parameter is exhibited. The divergences therein are taken
care of by employing a covariant stochastic regularization
Impediments to mixing classical and quantum dynamics
The dynamics of systems composed of a classical sector plus a quantum sector
is studied. We show that, even in the simplest cases, (i) the existence of a
consistent canonical description for such mixed systems is incompatible with
very basic requirements related to the time evolution of the two sectors when
they are decoupled. (ii) The classical sector cannot inherit quantum
fluctuations from the quantum sector. And, (iii) a coupling among the two
sectors is incompatible with the requirement of physical positivity of the
theory, i.e., there would be positive observables with a non positive
expectation value.Comment: RevTex, 21 pages. Title slightly modified and summary section adde
Enhanced Decay, Inclusive Production, and the Gluon Anomaly
The experimental hint of large is linked to the
penguins via the gluon anomaly. Using running in the
-- coupling, the standard penguin alone seems
insufficient, calling for the need of dipole at 10% level from new
physics, which could also resolve the and charm counting
problems. The intereference of standard and new physics contributions may
result in direct CP asymmetries at 10% level, which could be observed soon at B
Factories.Comment: 12 pages, revtex, 3 figs. (version to appear in Phys. Rev. Lett.
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