2,937 research outputs found
Dressed-quarks and the Roper resonance
A Dyson-Schwinger equation calculation of the light hadron spectrum, which
correlates the masses of meson and baryon ground- and excited-states within a
single framework, produces a description of the Roper resonance that
corresponds closely with conclusions drawn recently by EBAC. Namely, the Roper
is a particular type of radial excitation of the nucleon's dressed-quark core
augmented by a material meson cloud component. There are, in addition, some
surprises.Comment: 4 pages, 3 figures. Contribution to the Proceedings of "NSTAR2011 -
The 8th International Workshop on the Physics of Excited Nucleons," Thomas
Jefferson National Accelerator Facility, Newport News, Virginia USA, 17-20
May 201
Mass segregation trends in SDSS galaxy groups
It has been shown that galaxy properties depend strongly on their host
environment. In order to understand the relevant physical processes driving
galaxy evolution it is important to study the observed properties of galaxies
in different environments. Mass segregation in bound galaxy structures is an
important indicator of evolutionary history and dynamical friction timescales.
Using group catalogues derived from the Sloan Digital Sky Survey Data Release 7
(SDSS DR7) we investigate mass segregation trends in galaxy groups at low
redshift. We investigate average galaxy stellar mass as a function of
group-centric radius and find evidence for weak mass segregation in SDSS
groups. The magnitude of the mass segregation depends on both galaxy stellar
mass limits and group halo mass. We show that the inclusion of low mass
galaxies tends to strengthen mass segregation trends, and that the strength of
mass segregation tends to decrease with increasing group halo mass. We find the
same trends if we use the fraction of massive galaxies as a function of
group-centric radius as an alternative probe of mass segregation. The magnitude
of mass segregation that we measure, particularly in high-mass haloes,
indicates that dynamical friction is not acting efficiently.Comment: 6 pages, 2 figures, accepted for publication in MNRAS Letter
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