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 $\ln s$ and $\ln^2s$ behavior of $pp$ and $\bar pp$ cross sections. By exploiting high quality low energy data, analyticity resolves this ambiguity in favor of cross sections that grow asymptotically as $\ln^2s$. 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, $\gamma p$ and $\gamma\gamma$ 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 $\rho$-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