1,535 research outputs found
Topological Andr\'e-Quillen homology for cellular commutative -algebras
Topological Andr\'e-Quillen homology for commutative -algebras was
introduced by Basterra following work of Kriz, and has been intensively studied
by several authors. In this paper we discuss it as a homology theory on CW
-algebras and apply it to obtain results on minimal atomic -local
-algebras which generalise those of Baker and May for -local spectra and
simply connected spaces. We exhibit some new examples of minimal atomic
-algebras.Comment: Final revision, a version will appear in Abhandlungen aus dem
Mathematischen Seminar der Universitaet Hambur
Bethe--Salpeter equation in QCD
We extend to regular QCD the derivation of a confining
Bethe--Salpeter equation previously given for the simplest model of scalar QCD
in which quarks are treated as spinless particles. We start from the same
assumptions on the Wilson loop integral already adopted in the derivation of a
semirelativistic heavy quark potential. We show that, by standard
approximations, an effective meson squared mass operator can be obtained from
our BS kernel and that, from this, by expansion the
corresponding Wilson loop potential can be reobtained, spin--dependent and
velocity--dependent terms included. We also show that, on the contrary,
neglecting spin--dependent terms, relativistic flux tube model is reproduced.Comment: 23 pages, revte
A New Deformation of W-Infinity and Applications to the Two-loop WZNW and Conformal Affine Toda Models
We construct a centerless W-infinity type of algebra in terms of a generator
of a centerless Virasoro algebra and an abelian spin-1 current. This algebra
conventionally emerges in the study of pseudo-differential operators on a
circle or alternatively within KP hierarchy with Watanabe's bracket.
Construction used here is based on a special deformation of the algebra
of area preserving diffeomorphisms of a 2-manifold. We show that
this deformation technique applies to the two-loop WZNW and conformal affine
Toda models, establishing henceforth invariance of these models.Comment: 8 page
On Two-Current Realization of KP Hierarchy
A simple description of the KP hierarchy and its multi-hamiltonian structure
is given in terms of two Bose currents. A deformation scheme connecting various
W-infinity algebras and relation between two fundamental nonlinear structures
are discussed. Properties of Fa\'a di Bruno polynomials are extensively
explored in this construction. Applications of our method are given for the
Conformal Affine Toda model, WZNW models and discrete KP approach to Toda
lattice chain.Comment: 28 pages, IFT-P/020/92-SAO-PAULO, Late
Long-distance contribution to the forward-backward asymmetry in decays K+ --> pi+ l+ l-
The long-distance contribution via the two-photon intermediate state to the
forward-backward asymmetries in decays K+ --> pi+ l+ l- (l=e and mu) has been
studied within the standard model. In order to evaluate the dispersive part of
the K+ --> pi+ gamma* gamma* --> pi+ l+ l- amplitude, we employ a
phenomenological form factor to soften the ultraviolet behavior of the
transition. It is found that, this long-distance transition, although subject
to some theoretical uncertainties, can lead to significant contributions to the
forward-backward asymmetries, which could be tested in the future high-precise
experiments.Comment: 13 pages, 5 figure
Thomae type formulae for singular Z_N curves
We give an elementary and rigorous proof of the Thomae type formula for
singular curves. To derive the Thomae formula we use the traditional
variational method which goes back to Riemann, Thomae and Fuchs.Comment: 22 page
A mechanism for morphogen-controlled domain growth
Many developmental systems are organised via the action of graded distributions of morphogens. In the Drosophila wing disc, for example, recent experimental evidence has shown that graded expression of the morphogen Dpp controls cell proliferation and hence disc growth. Our goal is to explore a simple model for regulation of wing growth via the Dpp gradient: we use a system of reaction-diffusion equations to model the dynamics of Dpp and its receptor Tkv, with advection arising as a result of the flow generated by cell proliferation. We analyse the model both numerically and analytically, showing that uniform domain growth across the disc produces an exponentially growing wing disc
Backward pion-nucleon scattering
A global analysis of the world data on differential cross sections and
polarization asymmetries of backward pion-nucleon scattering for invariant
collision energies above 3 GeV is performed in a Regge model. Including the
, , and trajectories, we
reproduce both angular distributions and polarization data for small values of
the Mandelstam variable , in contrast to previous analyses. The model
amplitude is used to obtain evidence for baryon resonances with mass below 3
GeV. Our analysis suggests a resonance with a mass of 2.83 GeV as
member of the trajectory from the corresponding Chew-Frautschi
plot.Comment: 12 pages, 16 figure
Virus shapes and buckling transitions in spherical shells
We show that the icosahedral packings of protein capsomeres proposed by
Caspar and Klug for spherical viruses become unstable to faceting for
sufficiently large virus size, in analogy with the buckling instability of
disclinations in two-dimensional crystals. Our model, based on the nonlinear
physics of thin elastic shells, produces excellent one parameter fits in real
space to the full three-dimensional shape of large spherical viruses. The
faceted shape depends only on the dimensionless Foppl-von Karman number
\gamma=YR^2/\kappa, where Y is the two-dimensional Young's modulus of the
protein shell, \kappa is its bending rigidity and R is the mean virus radius.
The shape can be parameterized more quantitatively in terms of a spherical
harmonic expansion. We also investigate elastic shell theory for extremely
large \gamma, 10^3 < \gamma < 10^8, and find results applicable to icosahedral
shapes of large vesicles studied with freeze fracture and electron microscopy.Comment: 11 pages, 12 figure
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