50 research outputs found
Eccentric inflation and WMAP
For uniform arrangements of magnetic fields, strings, or domain walls
(together with the cosmological constant and non-relativistic matter), exact
solutions to the Einstein equations are shown to lead to a universe with
ellipsoidal expansion. We argue the results can be used to explain some
features in the WMAP data. The magnetic field case is the easiest to motivate
and has the highest possibility of yielding reliable constraints on
observational cosmology.Comment: 5 pages, 1 figur
Construction of multi-instantons in eight dimensions
We consider an eight-dimensional local octonionic theory with the
seven-sphere playing the role of the gauge group. Duality conditions for two-
and four-forms in eight dimensions are related. Dual fields--octonionic
instantons--solve an 8D generalization of the Yang-Mills equation. Modifying
the ADHM construction of 4D instantons, we find general -instanton 8D
solutions which depends on effective parameters
Decomposition of geometric perturbations
For an infinitesimal deformation of a Riemannian manifold, we prove that the
scalar, vector, and tensor modes in decompositions of perturbations of the
metric tensor, the scalar curvature, the Ricci tensor, and the Einstein tensor
decouple if and only if the manifold is Einstein. Four-dimensional space-time
satisfying the condition of the theorem is homogeneous and isotropic.
Cosmological applications are discussed.Comment: 7 page
A practical approach to cosmological perturbations in modified gravity
The next generation of large scale surveys will not only measure cosmological
parameters within the framework of General Relativity, but will also allow for
precision tests of the framework itself. At the order of linear perturbations,
departures from the growth in the LCDM model can be quantified in terms of two
functions of time and Fourier number k. We argue that in local theories of
gravity, in the quasi-static approximation, these functions must be ratios of
polynomials in k, with the numerator of one function being equal to the
denominator of the other. Moreover, the polynomials are even and of second
degree in practically all viable models considered today. This means that,
without significant loss of generality, one can use data to constraint only
five functions of a single variable, instead of two functions of two variables.
Furthermore, since the five functions are expected to be slowly varying, one
can fit them to data in a non-parametric way with the aid of an explicit
smoothness prior. We discuss practical application of this parametrization to
forecasts and fits.Comment: 9 pages, v2: matching the published versio
The Transverse Quark Distribution and Proton Electromagnetic Form Factors in Skew Distribution Formalism
Skew density matrices can be diagonalized to yield probability
interpretation. The power-counting prediction of perturbative QCD is found
consistent with recent CEBAF data on Comment: 4 pages, Presented May 23, 2000 by John Ralston. Published in the
Proceedings of the 7th International Conference on Intersections of Particle
and Nuclear Physics, (May 22-28, 2000 Quebec City), Edited by Z. Parseh and
W. Marciano, (AIP Conference Proceedings Number 549.
Electromagnetic Form Factors and the Localization of Quark Orbital Angular Momentum in the Proton
A new picture is given of generalized parton distributions probed in
experiments in which the probe scale and the momentum transfer
\DD^{2} are well separated. Application of this picture to the
dependence of the form factors shows that gauge invariant quark
orbital angular momentum can be measured and indeed {\it localized} in the
transverse profile of the proton. A previous prediction that
is generalized to GPD
language. This prediction appears to have been confirmed by recent CEBAF data.Comment: 6 pages, 1 figure. To appear in DIS 2001, 9th International Workshop
on Deep Inelastic Scattering, Bologna, 27 April - 1 May, 200