22,196 research outputs found
D0-brane tension in string field theory
We compute the D0-brane tension in string field theory by representing it as
a tachyon lump of the D1-brane compactified on a circle of radius . To this
aim, we calculate the lump solution in level truncation up to level L=8. The
normalized D0-brane tension is independent on . The compactification radius
is therefore chosen in order to cancel the subleading correction . We
show that an optimal radius indeed exists and that at the
theoretical prediction for the tension is reproduced at the level of .
As a byproduct of our calculation we also discuss the determination of the
marginal tachyon field at .Comment: 13 pages, 3 Eps figure
New Evidence on the Convergence of International Income from a Group of 29 Countries
This paper updates and extends the time-series evidence on the convergence of international incomes using a set of 29 countries over the period 1900-2001. Time-series tests for stochastic convergence are supplemented with tests which provide evidence on the notion of "Beta-convergence" predicted by the Solow model. The evidence indicates that the relative income series of 21 countries are consistent with stochastic convergence, and that Beta-convergence has occurred in at least 17 countries at some point over the 1900-2001 period. Further examination of the properties of the Beta- convergence test provides anecdotal evidence of conditional convergence during the post-war period in seven countries for which the convergence hypothesis was initially rejected. Analysis of the cross-country dispersion of incomes over time also suggests that convergence has occurred over the 1900-2001 period, with structural breaks associated with World War II in many countries causing a break in the convergence process.
Geometry versus Entanglement in Resonating Valence Bond Liquids
We investigate the behavior of bipartite as well as genuine multipartite
entanglement of a resonating valence bond state on a ladder. We show that the
system possesses significant amounts of bipartite entanglement in the steps of
the ladder while no substantial bipartite entanglement is present in the rails.
Genuine multipartite entanglement present in the system is negligible. The
results are in stark contrast with the entanglement properties of the same
state on isotropic lattices in two and higher dimensions, indicating that the
geometry of the lattice can have important implications on the quality of
quantum information and other tasks that can be performed by using multiparty
states on that lattice.Comment: 6 pages, 8 figures, RevTeX
Free-field Representations and Geometry of some Gepner models
The geometry of Gepner model, where is investigated by
free-field representation known as "bc\bet\gm"-system. Using this
representation it is shown directly that internal sector of the model is given
by Landau-Ginzburg -orbifold. Then we consider
the deformation of the orbifold by marginal anti-chiral-chiral operator.
Analyzing the holomorphic sector of the deformed space of states we show that
it has chiral de Rham complex structure of some toric manifold, where toric
dates are given by certain fermionic screening currents. It allows to relate
the Gepner model deformed by the marginal operator to the -model on CY
manifold realized as double cover of with ramification along
certain submanifold.Comment: LaTex, 14 pages, some acknowledgments adde
Energy Momentum Tensor and Marginal Deformations in Open String Field Theory
Marginal boundary deformations in a two dimensional conformal field theory
correspond to a family of classical solutions of the equations of motion of
open string field theory. In this paper we develop a systematic method for
relating the parameter labelling the marginal boundary deformation in the
conformal field theory to the parameter labelling the classical solution in
open string field theory. This is done by first constructing the
energy-momentum tensor associated with the classical solution in open string
field theory using Noether method, and then comparing this to the answer
obtained in the conformal field theory by analysing the boundary state. We also
use this method to demonstrate that in open string field theory the tachyon
lump solution on a circle of radius larger than one has vanishing pressure
along the circle direction, as is expected for a codimension one D-brane.Comment: LaTeX file, 25 pages; v2: minor addition
Example of a first-order N\'eel to Valence-Bond-Solid transition in two-dimensions
We consider the Heisenberg model with nearest-neighbor interaction
and an additional multi-spin interaction on the square lattice. The
term consists of three bond-singlet projectors and is chosen to favor the
formation of a valence-bond solid (VBS) where the valence bonds (singlet pairs)
form a staggered pattern. The model exhibits a quantum phase transition from
the N\'eel state to the VBS as a function of . We study the model using
quantum Monte Carlo (stochastic series expansion) simulations. The N\'eel-VBS
transition in this case is strongly first-order in nature, in contrast to
similar previously studied models with continuous transitions into columnar VBS
states. The qualitatively different transitions illustrate the important role
of an emerging U(1) symmetry in the latter case, which is not possible in the
present model due to the staggered VBS pattern (which does not allow local
fluctuations necessary to rotate the local VBS order parameter).Comment: 8 pages, 7 figure
Dual quantum-correlation paradigms exhibit opposite statistical-mechanical properties
We report opposite statistical mechanical behaviors of the two major
paradigms in which quantum correlation measures are defined, viz., the
entanglement-separability paradigm and the information-theoretic one. We show
this by considering the ergodic properties of such quantum correlation measures
in transverse quantum XY spin-1/2 systems in low dimensions. While entanglement
measures are ergodic in such models, the quantum correlation measures defined
from an information-theoretic perspective can be nonergodic.Comment: 8 pages, 5 figures, REVTeX 4.1; v2: published version, 9 page
Channel Capacities versus Entanglement Measures in Multiparty Quantum States
For quantum states of two subsystems, entanglement measures are related to
capacities of communication tasks -- highly entangled states give higher
capacity of transmitting classical as well as quantum information. However, we
show that this is no more the case in general: quantum capacities of
multi-access channels, motivated by communication in quantum networks, do not
have any relation with genuine multiparty entanglement measures. Along with
revealing the structural richness of multi-access channel capacities, this
gives us a tool to classify multiparty quantum states from the perspective of
its usefulness in quantum networks, which cannot be visualized by known
multiparty entanglement measures.Comment: 6 pages, 2 figures, RevTeX4; v2: minor changes, some implications
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