18,966 research outputs found
Graded Differential Geometry of Graded Matrix Algebras
We study the graded derivation-based noncommutative differential geometry of
the -graded algebra of complex -matrices
with the ``usual block matrix grading'' (for ). Beside the
(infinite-dimensional) algebra of graded forms the graded Cartan calculus,
graded symplectic structure, graded vector bundles, graded connections and
curvature are introduced and investigated. In particular we prove the
universality of the graded derivation-based first-order differential calculus
and show, that is a ``noncommutative graded manifold'' in a
stricter sense: There is a natural body map and the cohomologies of and its body coincide (as in the case of ordinary graded manifolds).Comment: 21 pages, LATE
K-->pipi amplitudes from lattice QCD with a light charm quark
We compute the leading-order low-energy constants of the DeltaS=1 effective
weak Hamiltonian in the quenched approximation of QCD with up, down, strange,
and charm quarks degenerate and light. They are extracted by comparing the
predictions of finite volume chiral perturbation theory with lattice QCD
computations of suitable correlation functions carried out with quark masses
ranging from a few MeV up to half of the physical strange mass. We observe a
large DeltaI=1/2 enhancement in this corner of the parameter space of the
theory. Although matching with the experimental result is not observed for the
DeltaI=1/2 amplitude, our computation suggests large QCD contributions to the
physical DeltaI=1/2 rule in the GIM limit, and represents the first step to
quantify the role of the charm quark-mass in K-->pipi amplitudes.Comment: 4 pages, 1 figure. Minor modifications. Final version to appear on
PR
Approximate gravitational field of a rotating deformed mass
A new approximate solution of vacuum and stationary Einstein field equations
is obtained. This solution is constructed by means of a power series expansion
of the Ernst potential in terms of two independent and dimensionless parameters
representing the quadrupole and the angular momentum respectively. The main
feature of the solution is a suitable description of small deviations from
spherical symmetry through perturbations of the static configuration and the
massive multipole structure by using those parameters. This quality of the
solution might eventually provide relevant differences with respect to the
description provided by the Kerr solution.Comment: 16 pages. Latex. To appear in General Relativity and Gravitatio
Correlation functions at small quark masses with overlap fermions
We report on recent work on the determination of low-energy constants
describing Delta{S}=1 weak transitions, in order to investigate the origins of
the Delta{I}=1/2 rule. We focus on numerical techniques designed to enhance the
statistical signal in three-point correlation functions computed with overlap
fermions near the chiral limit.Comment: Talk presented at Lattice2004(weak), Fermilab, 21-26 June 2004, 3
pages, 2 figure
Winding number instability in the phase-turbulence regime of the Complex Ginzburg-Landau Equation
We give a statistical characterization of states with nonzero winding number
in the Phase Turbulence (PT) regime of the one-dimensional Complex
Ginzburg-Landau equation. We find that states with winding number larger than a
critical one are unstable, in the sense that they decay to states with smaller
winding number. The transition from Phase to Defect Turbulence is interpreted
as an ergodicity breaking transition which occurs when the range of stable
winding numbers vanishes. Asymptotically stable states which are not
spatio-temporally chaotic are described within the PT regime of nonzero winding
number.Comment: 4 pages,REVTeX, including 4 Figures. Latex (or postscript) version
with figures available at http://formentor.uib.es/~montagne/textos/nupt
Characteristics of solar meridional flows during solar cycle 23
We have analyzed available full-disc data from the Michelson Doppler Imager
(MDI) on board SoHO using the "ring diagram" technique to determine the
behavior of solar meridional flows over solar cycle 23 in the outer 2% of the
solar radius. We find that the dominant component of meridional flows during
solar maximum was much lower than that during the minima at the beginning of
cycles 23 and 24. There were differences in the flow velocities even between
the two minima. The meridional flows show a migrating pattern with
higher-velocity flows migrating towards the equator as activity increases.
Additionally, we find that the migrating pattern of the meridional flow matches
those of sunspot butterfly diagram and the zonal flows in the shallow layers. A
high latitude band in meridional flow appears around 2004, well before the
current activity minimum. A Legendre polynomial decomposition of the meridional
flows shows that the latitudinal pattern of the flow was also different during
the maximum as compared to that during the two minima. The different components
of the flow have different time-dependences, and the dependence is different at
different depths.Comment: To appear in Ap
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