13,780 research outputs found
Patterns in Open String Field Theory Solutions
In open string field theory the kinetic operator mixes matter and ghost
sectors, and thus the ghost structure of classical solutions is not universal.
Nevertheless, we have found from numerical analysis that certain ratios of
expectation values for states involving pure ghost excitations appear to be
universal. We give an analytic expression for these ratios and find good
evidence that they are common to all known solutions of open string field
theory, including the tachyon vacuum solution, lump solutions and string fields
representing marginal deformations. We also draw attention to a close
correspondence between the expectation values for the pure matter components in
the tachyon vacuum solution and those in the solution of a simpler equation for
a ghost number zero string field. Finally we observe that the action of L_0 on
the tachyon condensate gives a state that is approximately factorized into a
matter and a ghost part.Comment: 21 pages, LaTe
Clinical Utility of Intra-Operative 6 Hydroxyethyl Starch (130 / 0.4) Supplementation in Hypoxemic Femur Injury Patients: A Preliminary Report of Twenty Cases
Abstract: Posttraumatic intravasation of fat and debris can lead to a cascade of events. Hydroxyethyl starches (HES) markedly suppress neutrophil influx by decreasing pulmonary capillary permeability and facilitating tissue oxygenation by improving microcirculation. It was hypothesized that in hypoxemic femur injury patients undergoing operative stabilization, HES administration will prevent the deterioration of respiratory variables and facilitates recovery. This prospective, double-blind, randomized preliminary study, enrolled twenty posttraumatic hypoxemic patients (room air PaO2 5) scheduled for femur fracture stabilization under general anesthesia. Patients were allocated to receive either; 6% HES 130/0.42, 15 mL/kg or 0.9% normal saline (NS) to maintain their central venous pressure (CVP) 12 + 2 mm Hg. Blood was transfused according to the maximum allowable blood loss and by serial hematocrit estimations. Perioperative Glasgow Coma Scale (GCS), physiological variables, arterial oxygen saturation (SpO2), arterial blood gas (ABG), SS and P/F ratios were recorded until recovery. The partial pressure of oxygen in arterial blood / fraction of inspired oxygen ratio (PaO2/FiO2) improved from a preoperative value of 273.33 ± 13.05 to 435.70 in the 6% Hydroxyethyl starch group (HES) and from 275.24 ± 15.34 to 302.25 ± 70.35 in the NS group over a period of six days (P values =0.970, 0.791, 0.345, 0.226, 0.855, 0.083, 0.221). Time taken to achieve a P/F ratio > 300 and for persistent reduction of Murray’s lung injury score (LIS) were comparable (P = 0.755 and 0.348, respectively). The number of ventilator, intensive care unit (ICU) and hospital stay days, did not differ (P value = 0.234, 1.00, 0. 301, respectively). There were no adverse sequelae or mortalities. A trend showing relatively fast improvement in the P/F ratio and an early reduction in LIS values was observed in hypoxemic, femur injury patients receiving intraoperative colloid supplementation
Exact ground state and kink-like excitations of a two dimensional Heisenberg antiferromagnet
A rare example of a two dimensional Heisenberg model with an exact dimerized
ground state is presented. This model, which can be regarded as a variation on
the kagome lattice, has several features of interest: it has a highly (but not
macroscopically) degenerate ground state; it is closely related to spin chains
studied by earlier authors; in particular, it is probably the first genuinely
two-dimensional quantum system to exhibit domain-wall-like ``kink'' excitations
normally found only in one-dimensional systems. In some limits it decouples
into non-interacting chains, purely dynamically and not because of weakening of
interchain couplings: indeed, paradoxically, this happens in the limit of
strong coupling of the chains.Comment: 4 pages, revtex, 5 figures included via epsfi
Phase Diagram of the Spin-One Heisenberg System with Dimerization and Frustration
We use the density matrix renormalization group method to study the ground
state properties of an antiferromagnetic spin- chain with a next-nearest
neighbor exchange and an alternation of the nearest neighbor
exchanges. We find a line running from a gapless point at upto an almost gapless point at such that
the open chain ground state is -fold degenerate below the line and is unique
above it. A disorder line runs from to about
. To the left of this line, the peak in the structure factor
is at , while to the right of the line, it is at less than .Comment: 11 pages, plain TeX, 3 figures available on reques
One-loop Evolution of a Rolling Tachyon
We study the time evolution of the one-loop diagram in Sen's rolling tachyon
background. We find that at least in the long cylinder case they grow rapidly
at late time, due to the exponential growth of the timelike oscillator terms in
the boundary state. This can also be interpreted as the virtual open string
pair creation in the decaying brane. This behavior indicates a breakdown of
this rolling tachyon solution at some point during the evolution. We also
discuss the closed string emission from this one-loop diagram, and the
evolution of a one-loop diagram connecting a decaying brane to a stable brane,
which is responsible for the physical open string creation on the stable brane.Comment: 21 pages, 2 figures; v2: references added, comments revised in
various places; v3: footnotes 7&8 added, revised version to appear in PR
Mass scales, supersymmetry breaking and open strings
We review physical motivations and possible realizations of string vacua with
large internal volume and/or low string scale and discuss the issue of
supersymmetry breaking. In particular, we describe the key features of
Scherk-Schwarz deformations in type I models and conclude by reviewing the
phenomenon of ``brane supersymmetry breaking'': the tadpole conditions of some
type-I models require that supersymmetry be {\it broken at the string scale} on
a collection of branes, while being exact, to lowest order, in the bulk and on
other branes.Comment: Based on talks presented by the authors at STRINGS '99. Submitted to
Classical and Quantum Gravity. misprints correcte
The Tachyon Potential in the Sliver Frame
We evaluate the tachyon potential in the Schnabl gauge through off-shell
computations in the sliver frame. As an application of the results of our
computations, we provide a strong evidence that Schnabl's analytic solution for
tachyon condensation in open string field theory represents a saddle point
configuration of the full tachyon potential. Additionally we verify that
Schnabl's analytic solution lies on the minimum of the effective tachyon
potential.Comment: v1: 19 pages, 1 figure, 1 table; v2: 20 pages, 1 figure, 2 tables, 1
reference added, comments added; v3: 21 pages, 1 figure, 2 tables, 4
references added, comments adde
A perturbative analysis of tachyon condensation
Tachyon condensation in the open bosonic string is analyzed using a
perturbative expansion of the tachyon potential around the unstable D25-brane
vacuum. Using the leading terms in the tachyon potential, Pad\'e approximants
can apparently give the energy of the stable vacuum to arbitrarily good
accuracy. Level-truncation approximations up to level 10 for the coefficients
in the tachyon potential are extrapolated to higher levels and used to find
approximants for the full potential. At level 14 and above, the resulting
approximants give an energy less than -1 in units of the D25-brane tension, in
agreement with recent level-truncation results by Gaiotto and Rastelli. The
extrapolated energy continues to decrease below -1 until reaching a minimum
near level 26, after which the energy turns around and begins to approach -1
from below. Within the accuracy of this method, these results are completely
consistent with an energy which approaches -1 as the level of truncation is
taken to be arbitrarily large.Comment: 8 pages, 3 eps figures, Latex; v2: typo correcte
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