7,705 research outputs found
The nonperturbative closed string tachyon vacuum to high level
We compute the action of closed bosonic string field theory at quartic order
with fields up to level ten. After level four, the value of the potential at
the minimum starts oscillating around a nonzero negative value, in contrast
with the proposition made in [5]. We try a different truncation scheme in which
the value of the potential converges faster with the level. By extrapolating
these values, we are able to give a rather precise value for the depth of the
potential.Comment: 24 pages. v2: typos corrected, clarified extrapolation in scheme B,
and added extrapolated tachyon and dilaton vev's at the end of Section
Testing Closed String Field Theory with Marginal Fields
We study the feasibility of level expansion and test the quartic vertex of
closed string field theory by checking the flatness of the potential in
marginal directions. The tests, which work out correctly, require the
cancellation of two contributions: one from an infinite-level computation with
the cubic vertex and the other from a finite-level computation with the quartic
vertex. The numerical results suggest that the quartic vertex contributions are
comparable or smaller than those of level four fields.Comment: 14 pages, LaTeX. v2: New references to work of Beccaria and Rampino,
and Taylor. Improved numerical analysis at the end of section
Quantum Open-Closed Homotopy Algebra and String Field Theory
We reformulate the algebraic structure of Zwiebach's quantum open-closed
string field theory in terms of homotopy algebras. We call it the quantum
open-closed homotopy algebra (QOCHA) which is the generalization of the
open-closed homotopy algebra (OCHA) of Kajiura and Stasheff. The homotopy
formulation reveals new insights about deformations of open string field theory
by closed string backgrounds. In particular, deformations by Maurer Cartan
elements of the quantum closed homotopy algebra define consistent quantum open
string field theories.Comment: 36 pages, fixed typos and small clarifications adde
Hypercapnia-induced and stimulus-induced changes in cerebral blood volume (CBV) in human at 7T
Association of Pathogen Load in Pigs with Retail Pork Contamination.
Salmonella and Campylobacter are estimated to cause 3.9 million illnesses annually in the United States, and most of these illnesses are food-related. Pigs can be sub-clinically infected with these pathogens and fecal contamination of meat during processing is a food safety risk. Quantitative measures of foodborne safety risk are rarely reported and are a critical data gap for development of quantitative risk assessments. The goal of this study was to determine the association between the concentration of Salmonella and Campylobacter in porcine feces and hide with concentrations in meat
Time Dependent Solution in Cubic String Field Theory
We study time dependent solutions in cubic open string field theory which are
expected to describe the configuration of the rolling tachyon. We consider the
truncated system consisting of component fields of level zero and two, which
are expanded in terms of cosh n x^0 modes. For studying the large time behavior
of the solution we need to know the coefficients of all and, in particular,
large n modes. We examine numerically the coefficients of the n-th mode, and
find that it has the leading n-dependence of the form (-\beta)^n \lambda^{-n^2}
multiplied by a peculiar subleading part with peaks at
n=2^m=4,8,16,32,64,128,.... This behavior is also reproduced analytically by
solving simplified equations of motion of the tachyon system.Comment: 22 pages, 12 figures, LaTeX2e, v3:minor correction
Proof of vanishing cohomology at the tachyon vacuum
We prove Sen's third conjecture that there are no on-shell perturbative
excitations of the tachyon vacuum in open bosonic string field theory. The
proof relies on the existence of a special state A, which, when acted on by the
BRST operator at the tachyon vacuum, gives the identity. While this state was
found numerically in Feynman-Siegel gauge, here we give a simple analytic
expression.Comment: 19 pages, 4 figures; v2: references adde
Exact noncommutative solitons in p-adic strings and BSFT
The tachyon field of p-adic string theory is made noncommutative by replacing
ordinary products with noncommutative products in its exact effective action.
The same is done for the boundary string field theory, treated as the p -> 1
limit of the p-adic string. Solitonic lumps corresponding to D-branes are
obtained for all values of the noncommutative parameter theta. This is in
contrast to usual scalar field theories in which the noncommutative solitons do
not persist below a critical value of theta. As theta varies from zero to
infinity, the solution interpolates smoothly between the soliton of the p-adic
theory (respectively BSFT) to the noncommutative soliton.Comment: 1+14 pages (harvmac b), 1 eps figure, v2: references added, typos
correcte
Symmetric Anderson impurity model with a narrow band
The single channel Anderson impurity model is a standard model for the
description of magnetic impurities in metallic systems. Usually, the bandwidth
represents the largest energy scale of the problem. In this paper, we analyze
the limit of a narrow band, which is relevant for the Mott-Hubbard transition
in infinite dimensions. For the symmetric model we discuss two different
effects: i) The impurity contribution to the density of states at the Fermi
surface always turns out to be negative in such systems. This leads to a new
crossover in the thermodynamic quantities that we investigate using the
numerical renormalization group. ii) Using the Lanczos method, we calculate the
impurity spectral function and demonstrate the breakdown of the skeleton
expansion on an intermediate energy scale. Luttinger's theorem, as an example
of the local Fermi liquid property of the model, is shown to still be valid.Comment: 4 pages RevTeX, 2 eps figures included, final versio
News discourses on distant suffering: A critical discourse analysis of the 2003 SARS outbreak
News carries a unique signifying power, a power to represent events in particular ways (Fairclough, 1995). Applying Critical Discourse Analysis and Chouliaraki's theory on the mediation of suffering (2006), this article explores the news representation of the 2003 global SARS outbreak. Following a case-based methodology, we investigate how two Belgian television stations have covered the international outbreak of SARS. By looking into the mediation of four selected discursive moments, underlying discourses of power, hierarchy and compassion were unraveled. The analysis further identified the key role of proximity in international news reporting and supports the claim that Western news media mainly reproduce a Euro-American centered world order. This article argues that news coverage of international crises such as SARS constructs and maintains the socio-cultural difference between 'us' and 'them' as well as articulating global power hierarchies and a division of the world in zones of poverty and prosperity, danger and safety
- …