35 research outputs found
Stationary vs. singular points in an accelerating FRW cosmology derived from six-dimensional Einstein-Gauss-Bonnet gravity
Six-dimensional Einstein-Gauss-Bonnet gravity (with a linear Gauss-Bonnet
term) is investigated. This theory is inspired by basic features of results
coming from string and M-theory. Dynamical compactification is carried out and
it is seen that a four-dimensional accelerating FRW universe is recovered, when
the two-dimensional internal space radius shrinks. A non-perturbative structure
of the corresponding theory is identified which has either three or one stable
fixed points, depending on the Gauss-Bonnet coupling being positive or
negative. A much richer structure than in the case of the perturbative regime
of the dynamical compactification recently studied by Andrew, Bolen, and
Middleton is exhibited.Comment: 9 pages, 20 figures, accepted in PL
Measurement of dijet photoproduction for events with a leading neutron at HERA
Differential cross sections for dijet photoproduction and this process in
association with a leading neutron, e+ + p -> e+ + jet + jet + X (+ n), have
been measured with the ZEUS detector at HERA using an integrated luminosity of
40 pb-1. The fraction of dijet events with a leading neutron was studied as a
function of different jet and event variables. Single- and double-differential
cross sections are presented as a function of the longitudinal fraction of the
proton momentum carried by the leading neutron, xL, and of its transverse
momentum squared, pT^2. The dijet data are compared to inclusive DIS and
photoproduction results; they are all consistent with a simple pion-exchange
model. The neutron yield as a function of xL was found to depend only on the
fraction of the proton beam energy going into the forward region, independent
of the hard process. No firm conclusion can be drawn on the presence of
rescattering effects.Comment: 40 pages, 18 figure