7,683 research outputs found
A fresh look at midpoint singularities in the algebra of string fields
In this paper we study the midpoint structure of the algebra of open strings
from the standpoint of the operator/Moyal formalism. We construct a split
string description for the continuous Moyal product of hep-th/0202087, study
the breakdown of associativity in the star algebra, and identify in infinite
sequence of new (anti)commutative coordinates for the star product in in the
complex plane. We also explain how poles in the open string
non(anti)commutativity parameter correspond to certain ``null'' operators which
annihilate the vertex, implying that states proportional to such operators tend
to have vanishing star product with other string fields. The existence of such
poles, we argue, presents an obstruction to realizing a well-defined
formulation of the theory in terms of a Moyal product. We also comment on the
interesting, but singular, representation which has appeared prominently
in the recent studies of Bars {\it et al}.Comment: 40 pages, 5 figures. Version to be submitted to JHEP. Some
interesting and previouusly unpublished results are included here. These
include both an interpretation of poles in the open string noncommutativity
parameter as corresponding to null operators in the algebra, and an
identification of an infinite sequence of new commutative and null
coordinates in the complex plan
Level Truncation and Rolling the Tachyon in the Lightcone Basis for Open String Field Theory
A recent paper by Gross and Erler (hep-th/0406199) showed that by making a
certain well-defined, unitary transformation on the mode basis for the open
bosonic string--one that identifies the lightcone component of position with
the string midpoint--it is possible to render the action for cubic string field
theory local in lightcone time. In this basis, then, cubic string field theory
possesses a well-defined initial value formulation and a conserved Hamiltonian.
With this new understanding it seems natural to study time dependent solutions
representing the the decay of an unstable D-branes. In this paper we study such
solutions using level truncation of mode oscillators in the lightcone basis,
finding both homogenous solutions by perturbatively expanding the string field
in modes , and inhomogenous solutions by integrating the equations of
motion on a lattice. Truncating the theory to level in
oscillators, we find time dependent solutions whose behavior seems
to converge to that of earlier solutions constructed in the center of mass
basis, where the cubic action contains an infinite number of time derivatives.
We further construct time-dependent inhomogeneous solutions including all
fields up to level . These solutions at the outset
display rather erratic behavior due to an unphysical instability introduced by
truncating the theory at the linear level. However upon truncating away the
field responsible for the instability, we find more reasonable solutions which
may possibly represent an approximation to tachyon matter. We conclude with
some discussion of future directions.Comment: 29 pages, 21 figure
Introduction to Library Trends 44 (2) Fall 1995: The Library and Undergraduate Education
published or submitted for publicatio
The impact of exogenous shocks on the dynamics and persistence of inflation: a macroeconomic model-based approach for Greece
The paper analyses the dynamic response of inflation to various economic shocks and investigates the sources of inflation persistence through a set of counter factual simulations. Analysis shows that inflation seems to be more persistent in Greece than, on average, in Euro Area. Inflation persistence tends to be higher in response to fiscal shocks than others shocks. Only an indirect tax shock could be classified as “non-persistent” for Greece. Inflation persistence is crucially affected by the degree of competition in product market and it is mainly of intrinsic nature while nominal rigidities and frictions in the labor market do not seem important in explaining the relatively higher persistence of Greek inflation.Inflation persistence,macroeconomic models,impulse response function
The High Chromospheres of the Late A Stars
We report the detection of N V 1239 A transition region emission in HST/GHRS
spectra of the A7 V stars, Alpha Aql and Alpha Cep. Our observations provide
the first direct evidence of 1-3 x 10^5 K material in the atmospheres of normal
A-type stars. For both stars, and for the mid-A--type star Tau3 Eri, we also
report the detection of chromospheric emission in the Si III 1206 A line. At a
B-V color of 0.16 and an effective temperature of 8200 K, Tau3 Eri becomes the
hottest main sequence star known to have a chromosphere and thus an outer
convection zone. We see no firm evidence that the Si III line surface fluxes of
the A stars are any lower than those of moderately active, solar-type, G and K
stars. This contrasts sharply with their coronal X-ray emission, which is >100
times weaker than that of the later-type stars. Given the strength of the N V
emission observed here, it now appears unlikely that the X-ray faintness of the
A stars is due to their forming very cool, <= 1 MK coronae. An alternative
explanation in terms of mass loss in coronal winds remains a possibility,
though we conclude from moderate resolution spectra of the Si III lines that
such winds, if they exist, do not penetrate into the chromospheric Si
III--forming layers of the star, since the profiles of these lines are *not*
blueshifted, and may well be redshifted with respect to the star.Comment: LaTex, 12 pages, 3 Postscript figures, uses aaspp4, accepted by Ap
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