10,206 research outputs found
Evidence for the saturation of the Froissart bound
It is well known that fits to high energy data cannot discriminate between
asymptotic ln(s) and ln^2(s) behavior of total cross section. We show that this
is no longer the case when we impose the condition that the amplitudes also
describe, on average, low energy data dominated by resonances. We demonstrate
this by fitting real analytic amplitudes to high energy measurements of the
gamma p total cross section, for sqrt(s) > 4 GeV. We subsequently require that
the asymptotic fit smoothly join the sqrt(s) = 2.01 GeV cross section described
by Dameshek and Gilman as a sum of Breit-Wigner resonances. The results
strongly favor the high energy ln^2(s) fit of the form sigma_{gamma p} = c_0 +
c_1 ln(nu/m) + c_2 ln^2(nu/m) + beta_{P'}/sqrt(nu/m), basically excluding a
ln(s) fit of the form sigma_{\gamma p} = c_0 + c_1 ln(nu/m) +
beta_P'/sqrt(\nu/m), where nu is the laboratory photon energy. This evidence
for saturation of the Froissart bound for gamma p interactions is confirmed by
applying the same analysis to pi p data using vector meson dominance.Comment: 7 pages, Latex2e, 4 postscript figures, uses epsf.st
Discrete component S-band power amplifier
A spacecraft S-band power amplifier for Nimbus satellite is reported that achieves stability by use of moderate Q input and output circuits. The discrete component amplifier uses distributed inductance and small piston capacitors for resonance and impedance matching of the transistor to 50 ohm input and output
Implications from analyticity constraints used in a Landshoff-Donnachie fit
Landshoff and Donnachie[hep-ph/0509240, (2005)] parametrize the energy
behavior of pp and p\bar p scattering cross sections with five parameters,
using: \sigma^+=56.08 s^{-0.4525}+21.70s^{0.0808} for pp, \sigma^-=98.39
s^{-0.4525}+21.70s^{0.0808} for p\bar p. Using the 4 analyticity constraints of
Block and Halzen[M. M. Block and F. Halzen, Phys. Rev. D {\bf 72}, 036006
(2005)], we simultaneously fit the Landshoff-Donnachie form to the same
``sieved'' set of pp and p\bar p cross section and \rho data that Block and
Halzen used for a very good fit to a ln^2 s parametrization. We show that the
satisfaction of the analyticity constraints will require complicated
modifications of the Landshoff-Donnachie parametrization for lower energies,
greatly altering its inherent appeal of simplicity and universality.Comment: 7 pages, 2 figure
Analyticity as a Robust Constraint on the LHC Cross Section
It is well known that high energy data alone do not discriminate between
asymptotic and behavior of and cross sections.
By exploiting high quality low energy data, analyticity resolves this ambiguity
in favor of cross sections that grow asymptotically as . We here show
that two methods for incorporating the low energy data into the high energy
fits give numerically identical results and yield essentially identical tightly
constrained values for the LHC cross section. The agreement can be understood
as a new analyticity constraint derived as an extension of a Finite Energy Sum
Rule.Comment: 8 pages, Latex2e, 2 postscript figures; major changes made; accepted
for publication in Phys Rev
On Factorization, Quark Counting, and Vector Dominance
Using an eikonal structure for the scattering amplitude, Block and Kaidalov
have derived factorization theorems for nucleon-nucleon, and
scattering at high energies, using only some very general
assumptions. We present here an analysis giving experimental confirmation for
factorization of cross sections, nuclear slope parameters B and -values
(ratio of real to imaginary portion of forward scattering amplitudes), showing
that: i) the three factorization theorems hold, ii) the additive quark model
holds to ~1%, and iii) vector dominance holds to better than ~4%.Comment: Latex2e, 11 pages, 6 postscript figures, uses epsfig.sty. Version to
be published in Eur. Phys. Jour.
Gravitational torques in spiral galaxies: gas accretion as a driving mechanism of galactic evolution
The distribution of gravitational torques and bar strengths in the local
Universe is derived from a detailed study of 163 galaxies observed in the
near-infrared. The results are compared with numerical models for spiral galaxy
evolution. It is found that the observed distribution of torques can be
accounted for only with external accretion of gas onto spiral disks. Accretion
is responsible for bar renewal - after the dissolution of primordial bars - as
well as the maintenance of spiral structures. Models of isolated, non-accreting
galaxies are ruled out. Moderate accretion rates do not explain the
observational results: it is shown that galactic disks should double their mass
in less than the Hubble time. The best fit is obtained if spiral galaxies are
open systems, still forming today by continuous gas accretion, doubling their
mass every 10 billion years.Comment: 4 pages, 2 figures, Astronomy and Astrophysics Letters (accepted
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