Graptemys pseudogeographica

Number of Pages: 6Integrative BiologyGeological Science

Graptemys oculifera

Number of Pages: 2Integrative BiologyGeological Science

Pseudemys alabamensis

Number of Pages: 2Integrative BiologyGeological Science

Shadowing and Absorption Effects on J/psi Production in dA Collisions

We study medium modifications of J/psi production in cold nuclear media in deuterium-nucleus collisions. We discuss several parameterizations of the modifications of the parton densities in the nucleus, known as shadowing, an initial-state effect. We also include absorption of the produced J/psi by nucleons, a final-state effect. Both spatially homogeneous and inhomogeneous shadowing and absorption are considered. We use the number of binary nucleon-nucleon collisions as a centrality measure. Results are presented for d+Au collisions at sqrt{S_{NN}} = 200 GeV and for d+Pb collisions at sqrt{S_{NN}} = 6.2 TeV. To contrast the centrality dependence in pA and dA collisions, we also present pPb results at sqrt{S_{NN}} = 8.8 TeV.Comment: 22 pages, 11 figures, uses revte

The annihilation of virtual photons into pseudoscalar mesons

We investigate the possibility to constrain the pion distribution amplitude from the gamma* gamma* -> pi transition. For a surprisingly large range in the two photon virtualities we find that the transition form factor is essentially independent of the distribution amplitude. This in turn entails a parameter-free prediction of QCD. The gamma* gamma* -> eta, eta' form factors are also briefly discussed. We estimate that experimental studies might be feasible at the existing e+ e- experiments BaBar, Belle, and CLEO.Comment: 22 pages latex, 9 figure

Two-Photon Annihilation into Baryon-Antibaryon Pairs

We study the handbag contribution to two-photon annihilation into baryon-antibaryon pairs at large energy and momentum transfer. We derive factorization of the process amplitude into a hard gamma gamma -> q qbar subprocess and form factors describing the soft q qbar -> B Bbar transition, assuming that the process is dominated by configurations where the (anti)quark approximately carries the full momentum of the (anti)baryon. The form factors represent moments of time-like generalized parton distributions, so-called B Bbar distribution amplitudes. A characteristic feature of the handbag mechanism is the absence of isospin-two components in the final state, which in combination with flavor symmetry provides relations among the form factors for the members of the lowest-lying baryon octet. Assuming dominance of the handbag contribution, we can describe current experimental data with form factors of plausible size, and predict the cross sections of presently unmeasured B Bbar channels.Comment: 20 pages latex, 4 figures. v2: minor clarifications, references update

Magnetic Field Seeding by Galactic Winds

The origin of intergalactic magnetic fields is still a mystery and several scenarios have been proposed so far: among them, primordial phase transitions, structure formation shocks and galactic outflows. In this work we investigate how efficiently galactic winds can provide an intense and widespread "seed" magnetisation. This may be used to explain the magnetic fields observed today in clusters of galaxies and in the intergalactic medium (IGM). We use semi-analytic simulations of magnetised galactic winds coupled to high resolution N-body simulations of structure formation to estimate lower and upper limits for the fraction of the IGM which can be magnetised up to a specified level. We find that galactic winds are able to seed a substantial fraction of the cosmic volume with magnetic fields. Most regions affected by winds have magnetic fields in the range -12 < Log B < -8 G, while higher seed fields can be obtained only rarely and in close proximity to wind-blowing galaxies. These seed fields are sufficiently intense for a moderately efficient turbulent dynamo to amplify them to the observed values. The volume filling factor of the magnetised regions strongly depends on the efficiency of winds to load mass from the ambient medium. However, winds never completely fill the whole Universe and pristine gas can be found in cosmic voids and regions unaffected by feedback even at z=0. This means that, in principle, there might be the possibility to probe the existence of primordial magnetic fields in such regions.Comment: 14 pages, 5 figures. Accepted for publications by MNRAS. A high resolution version of the paper is available at http://astronomy.sussex.ac.uk/~sb207/Papers/bb.ps.g