15 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interesting and previouusly unpublished results are included here.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
Integrable Open Spin Chains and the Doubling Trick in N = 2 SYM with Fundamental Matter
We demonstrate that the one-loop anomalous dimension matrix in N = 2 SYM with
a single chiral hypermultiplet of fundamental matter, which is dual to AdS_5 X
S^5 with a D7-brane filling AdS_5 and wrapped around an $^3 in the S^5, is an
integrable open spin chain Hamiltonian. We also use the doubling trick to
relate these open spin chains to closed spin chains in pure N = 4 SYM. By using
the AdS/CFT correspondence, we find a relation between the corresponding open
and closed strings that differs from a simple doubling trick by terms that
vanish in the semiclassical limit. We also demonstrate that in some cases the
closed string is simpler and easier to study than the corresponding open
string, and we speculate on the nature of corrections due to the presence of
D-branes that this implies.Comment: 30 pages, 14 figure
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The troposphere-to-stratosphere transition in kinetic energy spectra and nonlinear spectral fluxes as seen in ECMWF analyses
Global horizontal wavenumber kinetic energy spectra and spectral fluxes of rotational kinetic energy and enstrophy are computed for a range of vertical levels using a T799 ECMWF operational analysis. Above 250 hPa, the kinetic energy spectra exhibit a distinct break between steep and shallow spectral ranges, reminiscent of dual power-law spectra seen in aircraft data and high-resolution general circulation models. The break separates a large-scale ‘‘balanced’’ regime in which rotational flow strongly dominates divergent flow and a mesoscale ‘‘unbalanced’’ regime where divergent energy is comparable to or larger than rotational energy. Between 230 and 100 hPa, the spectral break shifts to larger scales (from n 5 60 to n 5 20, where n is spherical harmonic index) as the balanced component of the flow preferentially decays. The location of the break remains fairly stable throughout the stratosphere. The spectral break in the analysis occurs at somewhat larger scales than the break seen in aircraft data. Nonlinear spectral fluxes defined for the rotational component of the flow maximize between about 300 and 200 hPa. Large-scale turbulence thus centers on the extratropical tropopause region, within which there are two distinct mechanisms of upscale energy transfer: eddy–eddy interactions sourcing the transient energy peak in synoptic scales, and zonal mean–eddy interactions forcing the zonal flow. A well-defined downscale enstrophy flux is clearly evident at these altitudes. In the stratosphere, the transient energy peak moves to planetary scales and zonal mean–eddy interactions become dominant
Finishing the euchromatic sequence of the human genome
The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead