3,631 research outputs found
Scheme Dependence at Small x
We discuss the evolution of F_2^p at small x, emphasizing the uncertainties
related to expansion, fitting, renormalization and factorization scheme
dependence. We find that perturbative extrapolation from the measured region
down to smaller x and lower Q^2 may become strongly scheme dependent.Comment: 8 pages, LaTeX with epsfig, 2 uuencoded figure
BFKL at NNLO
We present a recent determination of an approximate expression for the
O(alpha_s^3) contribution chi_2 to the kernel of the BFKL equation. This
includes all collinear and anticollinear singular contributions and is derived
using duality relations between the GLAP and BFKL kernels.Comment: 8 pages. Talk presented at 12th International Conference on Elastic
and Diffractive Scattering: Forward Physics and QCD, Hamburg, DESY, Germany,
21-25 May 200
Mapping the galaxy NGC 4486 (M87) through its Globular Cluster System
As shown in previous works, globular clusters can be used to trace the
overall structure of the diffuse stellar populations in early type galaxies if
the number of clusters per unit stellar mass depends on metallicity. In this
paper we further test this assumption in the galaxy NGC 4486 (M 87), by
combining several data sources. The results show that globular clusters allow
the mapping of the galaxy in terms of the surface brightness profile,
integrated colour gradient, chemical abundance, and mass to luminosity ratios
up to 1000 arcsec (or 80.4 kpc) from its centre (i.e. some 10 effective radii).
The analysis indicates the presence of a dominant high metallicity bulge
associated with the red globulars, whose ellipticity increases outwards, and of
a more flattened low metallicity halo connected with the blue globulars. The
chemical abundance gradient of the composite stellar population is remarkably
similar to that inferred from X ray observations of hot gas. The
mass-metallicity spectrum of the stellar population can, in principle, be
understood in terms of inhomogeneous enrichment models. In turn, the
distribution of the bluest GCs, and lowest metallicity halo stars, has an
intriguing similarity with that of dark matter, a feature shared with NGC 1399.
Also, in these two galaxies, the number of blue GCs per dark mass unit is
identical within the errors, \approx 1.0(\pm0.3) \times 10^{-9} . The total
stellar mass derived for NGC 4486 is 6.8(\pm1.1) \times 10^{11} M\odot with a
baryonic mass fraction fb = 0.08(\pm 0.01).Comment: 18 pages, 23 figure
The complex star cluster system of NGC 1316 (Fornax A)
This paper presents Gemini- high quality photometry for cluster
candidates in the field of NGC 1316 (Fornax A) as part of a study that also
includes GMOS spectroscopy. A preliminary discussion of the photometric data
indicates the presence of four stellar cluster populations with distinctive
features in terms of age, chemical abundance and spatial distribution. Two of
them seem to be the usually old (metal poor and metal rich) populations
typically found in elliptical galaxies. In turn, an intermediate-age (5 Gyr)
globular cluster population is the dominant component of the sample (as
reported by previous papers). We also find a younger cluster population with a
tentative age of 1 Gyr
Re-evaluation of the Gottfried sum using neural networks
We provide a determination of the Gottfried sum from all available data,
based on a neural network parametrization of the nonsinglet structure function
F_2. We find S_G=0.244 +- 0.045, closer to the quark model expectation S_G=1/3
than previous results. We show that the uncertainty from the small x region is
somewhat underestimated in previous determinations.Comment: 4 pages, 3 figures, latex with revte
- …