631 research outputs found
Rates of asymptotic entanglement transformations for bipartite mixed states: Maximally entangled states are not special
We investigate the asymptotic rates of entanglement transformations for
bipartite mixed states by local operations and classical communication (LOCC).
We analyse the relations between the rates for different transitions and obtain
simple lower and upper bound for these transitions. In a transition from one
mixed state to another and back, the amount of irreversibility can be different
for different target states. Thus in a natural way, we get the concept of
"amount" of irreversibility in asymptotic manipulations of entanglement. We
investigate the behaviour of these transformation rates for different target
states. We show that with respect to asymptotic transition rates under LOCC,
the maximally entangled states do not have a special status. In the process, we
obtain that the entanglement of formation is additive for all maximally
correlated states. This allows us to show irreversibility in asymptotic
entanglement manipulations for maximally correlated states in 2x2. We show that
the possible nonequality of distillable entanglement under LOCC and that under
operations preserving the positivity of partial transposition, is related to
the behaviour of the transitions (under LOCC) to separable target states.Comment: 9 pages, 3 eps figures, REVTeX4; v2: presentation improved, new
considerations added, title changed; v3: minor changes, published versio
The mass gap and vacuum energy of the Gross-Neveu model via the 2PPI expansion
We introduce the 2PPI (2-point-particle-irreducible) expansion, which sums
bubble graphs to all orders. We prove the renormalizibility of this summation.
We use it on the Gross-Neveu model to calculate the mass gap and vacuum energy.
After an optimization of the expansion, the final results are qualitatively
good.Comment: 14 pages,19 eps figures, revtex
On the evolution of cosmic-superstring networks
We model the behaviour of a network of interacting (p,q) strings from IIB
string theory by considering a field theory containing multiple species of
string, allowing us to study the effect of non-intercommuting events due to two
different species crossing each other. This then has the potential for a string
dominated Universe with the network becoming so tangled that it freezes. We
give numerical evidence, explained by a one-scale model, that such freezing
does not take place, with the network reaching a scaling limit where its
density relative to the background increases with N, the number of string
types.Comment: Extra references added showing constraints on cosmic superstrings, 7
pages, 7 figure
Continuity of the von Neumann entropy
A general method for proving continuity of the von Neumann entropy on subsets
of positive trace-class operators is considered. This makes it possible to
re-derive the known conditions for continuity of the entropy in more general
forms and to obtain several new conditions. The method is based on a particular
approximation of the von Neumann entropy by an increasing sequence of concave
continuous unitary invariant functions defined using decompositions into finite
rank operators. The existence of this approximation is a corollary of a general
property of the set of quantum states as a convex topological space called the
strong stability property. This is considered in the first part of the paper.Comment: 42 pages, the minor changes have been made, the new applications of
the continuity condition have been added. To appear in Commun. Math. Phy
An accelerated closed universe
We study a model in which a closed universe with dust and quintessence matter
components may look like an accelerated flat Friedmann-Robertson-Walker (FRW)
universe at low redshifts. Several quantities relevant to the model are
expressed in terms of observed density parameters, and
, and of the associated density parameter related
to the quintessence scalar field .Comment: 11 pages. For a festschrift honoring Alberto Garcia. To appear in
Gen. Rel. Gra
Ab-initio calculation of Kerr spectra for semi-infinite systems including multiple reflections and optical interferences
Based on Luttinger's formulation the complex optical conductivity tensor is
calculated within the framework of the spin-polarized relativistic screened
Korringa-Kohn-Rostoker method for layered systems by means of a contour
integration technique. For polar geometry and normal incidence ab-initio Kerr
spectra of multilayer systems are then obtained by including via a 2x2 matrix
technique all multiple reflections between layers and optical interferences in
the layers. Applications to Co|Pt5 and Pt3|Co|Pt5 on the top of a semi-infinite
fcc-Pt(111) bulk substrate show good qualitative agreement with the
experimental spectra, but differ from those obtained by applying the commonly
used two-media approach.Comment: 32 pages (LaTeX), 5 figures (Encapsulated PostScript), submitted to
Phys. Rev.
Looking Beyond Inflationary Cosmology
In spite of the phenomenological successes of the inflationary universe
scenario, the current realizations of inflation making use of scalar fields
lead to serious conceptual problems which are reviewed in this lecture. String
theory may provide an avenue towards addressing these problems. One particular
approach to combining string theory and cosmology is String Gas Cosmology. The
basic principles of this approach are summarized.Comment: invited talk at "Theory Canada 1" (Univ. of British Columbia,
Vancouver, Canada, June 2 - 4, 2005) (references updated
Thermodynamics of Modified Chaplygin Gas and Tachyonic Field
Here we generalize the results of the work of ref. [10] in modified Chaplygin
gas model and tachyonic field model. Here we have studied the thermodynamical
behaviour and the equation of state in terms of volume and temperature for both
models. We have used the solution and the corresponding equation of state of
our previous work [12] for tachyonic field model. We have also studied the
thermodynamical stability using thermal equation of state for the tachyonic
field model and have shown that there is no critical points during
thermodynamical expansion. The determination of due to expansion for
the tachyonic field have been discussed by assuming some initial conditions.
Here, the thermal quantities have been investigated using some reduced
parameters.Comment: 10 page
- âŠ