33,809 research outputs found
Froissart Bound on Total Cross-section without Unknown Constants
We determine the scale of the logarithm in the Froissart bound on total
cross-sections using absolute bounds on the D-wave below threshold for
scattering. E.g. for scattering we show that for c.m. energy
, where .Comment: 6 page
Froissart Bound on Inelastic Cross Section Without Unknown Constants
Assuming that axiomatic local field theory results hold for hadron
scattering, Andr\'e Martin and S. M. Roy recently obtained absolute bounds on
the D-wave below threshold for pion-pion scattering and thereby determined the
scale of the logarithm in the Froissart bound on total cross sections in terms
of pion mass only. Previously, Martin proved a rigorous upper bound on the
inelastic cross-section which is one-fourth of the
corresponding upper bound on , and Wu, Martin,Roy and Singh
improved the bound by adding the constraint of a given . Here we
use unitarity and analyticity to determine, without any high energy
approximation, upper bounds on energy averaged inelastic cross sections in
terms of low energy data in the crossed channel. These are Froissart-type
bounds without any unknown coefficient or unknown scale factors and can be
tested experimentally. Alternatively, their asymptotic forms,together with the
Martin-Roy absolute bounds on pion-pion D-waves below threshold, yield absolute
bounds on energy-averaged inelastic cross sections. E.g. for
scattering, defining ,we show that for c.m. energy ,
where . This bound is
asymptotically one-fourth of the corresponding Martin-Roy bound on the total
cross section, and the scale factor is one-fourth of the scale factor in
the total cross section bound. The average over the interval (s,2s) of the
inelastic cross section has a bound of the same form with
replaced by .Comment: 9 pages. Submitted to Physical Review
Results of a botanical expedition to Mount Roraima, Guyana : 2., Lichens
Lichen exploration of the Upper Mazaruni District, Guyana yielded 273 species, of which 179 were found for the first time in the Guianas and 13 were as yet undescribed. A list of all taxa encountered is presented, with indications of habitat and distribution in the investigated area as well as first descriptions for the following 7 species: Buellia aptrootii, Byssoloma farkasii, Myriotrema guianense, M. neofrondosum, M. subdactyliferum, Ocellularia astrolucens, and Thelotrema albomaculatum. Mazosia bambusae is recorded for the first time from the Neotropics. The richest areas for lichens appear to be the rocky tablelands with scrub vegetation on top of the lower mountains. The slopes of Mount Roraima are of special interest because they support some montane species which are unlikely to be found elsewhere in the Guianas; otherwise they are less rich in lichens, probably because of the high humidity, which favours bryophyte growth
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