1,845 research outputs found
A method of deforming G-structures
We consider deformations of G-structures via the right action on the frame
bundle in a base-point-dependent manner. We investigate which of these
deformations again lead to G-structures and in which cases the original and the
deformed G-structures define the same instantons. Further, we construct a
bijection from connections compatible with the original G-structure to those
compatible with the deformed G-structure and investigate the change of
intrinsic torsion under the aforementioned deformations. Finally, we consider
several examples.Comment: 14 pages; v3: references added, published in Journal of Geometry and
Physic
Fractional Inversion in Krylov Space
The fractional inverse (real ) of a matrix is
expanded in a series of Gegenbauer polynomials. If the spectrum of is
confined to an ellipse not including the origin, convergence is exponential,
with the same rate as for Chebyshev inversion. The approximants can be improved
recursively and lead to an iterative solver for in Krylov
space. In case of , the expansion is in terms of Legendre
polynomials, and rigorous bounds for the truncation error are derived.Comment: Contribution to LAT97 proceedings, 3 page
Transgression of D-branes
Closed strings can be seen either as one-dimensional objects in a target
space or as points in the free loop space. Correspondingly, a B-field can be
seen either as a connection on a gerbe over the target space, or as a
connection on a line bundle over the loop space. Transgression establishes an
equivalence between these two perspectives. Open strings require D-branes:
submanifolds equipped with vector bundles twisted by the gerbe. In this paper
we develop a loop space perspective on D-branes. It involves bundles of simple
Frobenius algebras over the branes, together with bundles of bimodules over
spaces of paths connecting two branes. We prove that the classical and our new
perspectives on D-branes are equivalent. Further, we compare our loop space
perspective to Moore-Segal/Lauda-Pfeiffer data for open-closed 2-dimensional
topological quantum field theories, and exhibit it as a smooth family of
reflection-positive, colored knowledgable Frobenius algebras
Two-flavour Schwinger model with dynamical fermions in the L\"uscher formalism
We report preliminary results for 2D massive QED with two flavours of Wilson
fermions, using the Hermitean variant of L\"uscher's bosonization technique.
The chiral condensate and meson masses are obtained. The simplicity of the
model allows for high statistics simulations close to the chiral and continuum
limit, both in the quenched approximation and with dynamical fermions.Comment: Talk presented at LATTICE96(algorithms), 3 pages, 3 Postscript
figures, uses twoside, fleqn, espcrc2, epsf, revised version (details of
approx. polynomial
Study of a new simulation algorithm for dynamical quarks on the APE-100 parallel computer
First results on the autocorrelation behaviour of a recently proposed fermion
algorithm by M. L\"uscher are presented and discussed. The occurence of
unexpected large autocorrelation times is explained. Possible improvements are
discussed.Comment: 3 pages, compressed ps-file (uufiles), Contribution to Lattice 9
A Perturbative RS I Cosmological Phase Transition
We identify a class of Randall-Sundrum type models with a successful first
order cosmological phase transition during which a 5D dual of approximate
conformal symmetry is spontaneously broken. Our focus is on soft-wall models
that naturally realize a light radion/dilaton and suppressed dynamical
contribution to the cosmological constant. We discuss phenomenology of the
phase transition after developing a theoretical and numerical analysis of these
models both at zero and finite temperature. We demonstrate a model with a
TeV-Planck hierarchy and with a successful cosmological phase transition where
the UV value of the curvature corresponds, via AdS/CFT, to an of ,
where 5D gravity is expected to be firmly in the perturbative regime.Comment: 34pp, 12 figure
Gauge theories on a five-dimensional orbifold
We present a construction of non-Abelian gauge theories on the R^4 x S^1/Z_2
orbifold. We show that no divergent boundary mass term for the Higgs field,
identified with some of the fifth dimensional components of the gauge field, is
generated. The formulation of the theories on the lattice requires only
Dirichlet boundary conditions that specify the breaking of the gauge group. The
first simulations in order to resolve the issue whether these theories can be
used at low energy as weakly interacting effective theories have been
performed. In case of a positive answer, these theories could provide us with a
new framework for studying electroweak symmetry breaking.Comment: 6 pages, 2 figures, talk presented at Lattice 2005 (theoretical
developments
Computing the lowest eigenvalues of the Fermion matrix by subspace iterations
Subspace iterations are used to minimise a generalised Ritz functional of a
large, sparse Hermitean matrix. In this way, the lowest eigenvalues are
determined. Tests with demonstrate that the computational
cost (no. of matrix multiplies) does not increase substantially with . This
implies that, as compared to the case of a , the additional eigenvalues
are obtained for free.Comment: Talk presented at LATTICE96(algorithms), 3 pages, 2 Postscript
figures, uses epsf.sty, espcrc2.st
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