2,113 research outputs found
Towards Spectral Geometry for Causal Sets
We show that the Feynman propagator (or the d'Alembertian) of a causal set
contains the complete information about the causal set. Intuitively, this is
because the Feynman propagator, being a correlator that decays with distance,
provides a measure for the invariant distance between pairs of events. Further,
we show that even the spectra alone (of the self-adjoint and anti-self-adjoint
parts) of the propagator(s) and d'Alembertian already carry large amounts of
geometric information about their causal set. This geometric information is
basis independent and also gauge invariant in the sense that it is relabeling
invariant (which is analogue to diffeomorphism invariance). We provide
numerical evidence that the associated spectral distance between causal sets
can serve as a measure for the geometric similarity between causal sets.Comment: 15 pages, 8 figures. v2: Minor edits and additions, references added,
discussion added on distinguishing manifoldlike causal sets from
non-manifoldlike causal sets, comments added on the extension of results to
4D and on spectral dimensio
Plasma Lens Backgrounds at a Future Linear Collider
A 'plasma lens' might be used to enhance the luminosity of future linear
colliders. However, its utility for this purpose depends largely on the
potential backgrounds that may be induced by the insertion of such a device in
the interaction region of the detector. In this note we identify different
sources of such backgrounds, calculate their event rates from the elementary
interaction processes, and evaluate their effects on the major parts of a
hypothetical Next Linear Collider (NLC) detector. For plasma lens parameters
which give a factor of seven enhancement of the luminosity, and using the NLC
design for beam parameters as a reference, we find that the background yields
are fairly high, and require further study and improvements in detector
technology to avoid their impact.Comment: 14 pages incl. 3 figures; contributed to the 4th International
Workshop, Electron-Electron Interactions at TeV Energies, Santa Cruz,
California, Dec. 7 - 9, 2001. To be published in Int.Journ. Mod. Phys.
Majorana Fermions in Strongly Interacting Helical Liquids
Majorana fermions were proposed to occur at edges and interfaces of gapped
one-dimensional systems where phases with different topological character meet
due to an interplay of spin-orbit coupling, proximity-induced superconductivity
and external magnetic fields. Here we investigate the effect of strong particle
interactions, and show that the helical liquid offers a mechanism that protects
the very existence of Majorana edge states: whereas moderate interactions close
the proximity gap which supports the edge states, in helical liquids the gap
re-opens due to two-particle processes. However, gapless fermionic excitations
occur at spatial proximity to the Majorana states at interfaces and may
jeopardize their long term Majorana coherence.Comment: 7 pages, 4 figure
L-amino acid oxidases with specificity for basic L-amino acids in cyanobacteria
The two closely related fresh water cyanobacteria Synechococcus elongatus PCC 6301 and Synechococcus elongatus PCC 7942 have previously been shown to constitutively express a FAD-containing L-amino acid oxidase with high specificity for basic L-amino acids (L-arginine being the best substrate). In this paper we show that such an enzyme is also present in the fresh water cyanobacterium Synechococcus cedrorum PCC 6908. In addition, an improved evaluation of the nucleotide/amino acid sequence of the L-amino acid oxidase of Synechococcus elongatus PCC 6301 (encoded by the aoxA gene) with respect to the FAD-binding site and a translocation pathway signal sequence will be given. Moreover, the genome sequences of 24 cyanobacteria will be evaluated for the occurrence of an aoxA-similar gene. In the evaluated cyanobacteria 15 genes encoding an L-amino acid oxidase-similar protein will be found
Dissipative Hydrodynamics and Heavy Ion Collisions
Recent discussions of RHIC data emphasized the exciting possibility that the
matter produced in nucleus-nucleus collisions shows properties of a
near-perfect fluid. Here, we aim at delineating the applicability of fluid
dynamics, which is needed to quantify the size of corresponding dissipative
effects. We start from the equations for dissipative fluid dynamics, which we
derive from kinetic theory up to second order (Israel-Stewart theory) in a
systematic gradient expansion. In model studies, we then establish that for too
early initialization of the hydrodynamic evolution (\tau_0 \lsim 1 fm/c) or
for too high transverse momentum (p_T \gsim 1 GeV) in the final state, the
expected dissipative corrections are too large for a fluid description to be
reliable. Moreover, viscosity-induced modifications of hadronic transverse
momentum spectra can be accommodated to a significant degree in an ideal fluid
description by modifications of the decoupling stage. We argue that these
conclusions, drawn from model studies, can also be expected to arise in
significantly more complex, realistic fluid dynamics simulations of heavy ion
collisions.Comment: 18 pages, 5 figures, uses revtex4; v2: references added, typos
correcte
Identification of novel components of Trypanosoma brucei editosomes
The editosome is a multiprotein complex that catalyzes the insertion and deletion of uridylates that occurs during RNA editing in trypanosomatids. We report the identification of nine novel editosome proteins in Trypanosoma brucei. They were identified by mass spectrometric analysis of functional editosomes that were purified by serial ion exchange/gel permeation chromatography, immunoaffinity chromatography specific to the TbMP63 editosome protein, or tandem affinity purification based on a tagged RNA editing ligase. The newly identified proteins have ribonuclease and/or RNA binding motifs suggesting nuclease function for at least some of these. Five of the proteins are interrelated, as are two others, and one is related to four previously identified editosome proteins. The implications of these findings are discussed
Anti–de Sitter/Conformal-Field-Theory Calculation of Screening in a Hot Wind
One of the challenges in relating experimental measurements of the suppression in the number of J/ψ mesons produced in heavy ion collisions to lattice QCD calculations is that whereas the lattice calculations treat J/ψ mesons at rest, in a heavy ion collision a cc̅ pair can have a significant velocity with respect to the hot fluid produced in the collision. The putative J/ψ finds itself in a hot wind. We present the first rigorous nonperturbative calculation of the consequences of a wind velocity v on the screening length Ls for a heavy quark-antiquark pair in hot N=4 supersymmetric QCD. We find Ls(v,T)=f(v)[1-v2]1/4/πT with f(v) only mildly dependent on v and the wind direction. This Ls(v,T)∼Ls(0,T)/sqrt[γ] velocity scaling, if realized in QCD, provides a significant additional source of J/ψ suppression at transverse momenta which are high but within experimental reach
Generalization of Quantum Error Correction via the Heisenberg Picture
We show that the theory of operator quantum error correction can be naturally
generalized by allowing constraints not only on states but also on observables.
The resulting theory describes the correction of algebras of observables (and
may therefore suitably be called ``operator algebra quantum error
correction''). In particular, the approach provides a framework for the
correction of hybrid quantum-classical information and it does not require the
state to be entirely in one of the corresponding subspaces or subsystems. We
discuss applications to quantum teleportation and to the study of information
flows in quantum interactions.Comment: 5 pages, preprint versio
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