Eikonalized mini-jet cross-sections in γγ\gamma \gamma collisions

In this note we assess the validity and uncertainties in the predictions of the eikonalised mini-jet model for $\sigma^{inel}_{\gamma \gamma}$. We are able to find a choice of parameters where the predictions are compatible with the current data. Even for this restricted range of parameters the predictions at the high c.m. energies, which can be reached at the TeV energy $e^+e^-$ colliders, differ by about $\pm 25\%$. LEP 2 data can help pinpoint these parameters and hence reduce the uncertainties in the predictions.Comment: 5 pages, latex, requires epsfig.sty, a4wide.sty, full ps file available at http://hpteor.lnf.infn.it/pancheri/lc2000.p

Total Cross-sections

We examine the energy dependence of total cross-sections for photon processes and discuss the QCD contribution to the rising behaviourComment: 5 pages, LaTeX, 2 figures, talk presented by G. Pancheri at Photon - 2001, The International Conference on Structure and Interactions of Photons, Ascona, Sept. 2-7,2001. To appear in the proceeding

Total Photonic and Hadronic Cross-sections

We discuss total cross-sections within the context of the QCD calculable mini-jet model, highlighting its successes and failures. In particular we show its description of $\gamma \gamma \to hadrons$ and compare it with OPAL and L3 data. We extrapolate this result to $\gamma p$ total cross-sections and propose a phenomenological ans\"atz for virtual photon cross-sections. We point out that the good agreement with data obtained with the Eikonal Minijet Model should not hide the many uncertainties buried in the impact parameter distribution. A model obtained from Soft Gluon Summation is briefly discussed and its application to hadronic cross-sections is shown.Comment: 10 pages, 5 figures, LaTeX, uses aipproc.sty. To appear in the proceedings of Photon 2000, Ambelside, U.K., Aug 2000. The title, the number of pages and the number of figures in the announcement were corrected to correspond to the submitted pape

Invisible Decays of the Supersymmetric Higgs and Dark Matter

We discuss effects of the light sparticles on decays of the lightest Higgs in a supersymmetric model with nonuniversal gaugino masses at the high scale, focusing on the `invisible' decays into neutralinos. These can impact significanlty the discovery possibilities of the lightest Higgs at the LHC. We show that due to these decays, there exist regions of the $M_2-\mu$ space where the B.R. $(h \to \gamma \gamma)$ becomes dangerously low even after imposing the LEP constraints on the sparticle masses, implying a possible preclusion of its discovery in the $\gamma \gamma$ channel. We find that there exist regions in the parameter space with acceptable relic density and where the ratio ${B.R. (h \to \gamma \gamma)_{SUSY} \over B.R. (h \to \gamma \gamma)_{SM}}$ falls below 0.6, implying loss of signal in the $\gamma \gamma$ channel. These regions correspond to $\tilde \chi_1^+, \tilde \chi_2^0$ masses which should be accessible already at the Tevatron. Further we find that considerations of relic density put lower limit on the U(1) gaugino mass parameter $M_1$ independently of $\mu, \tan \beta$ and $m_0$.Comment: 17 pages, 11 figures, Talk presented at Appi2002, Accelerator and Particle Physics Institute, Appi, Iwate, Japan, February 13--16 200

QCD and Total Cross-sections

We discuss models for total cross-sections, show their predictions for photon-photon collisions and compare them with the recent LEP measurements. We show that the extrapolations to high center of mass energies within various models differ by large factors at high energies and discuss the precision required from future measurements at the proposed Linear Collider which would allow to distinguish between them.Comment: 7 pages, 4 figures, laTeX, requires sprocl.sty, added at the end. To appear in the Proceedings of XXIX International Symposium on Mutliparticle Dynamics, Brwon University, U.S.A., June 9

Photon-Photon total inelastic cross-section

We discuss predictions for the total inelastic gamma-gamma cross-section and their model dependence on the input parameters. We compare results from a simple extension of the Regge Pomeron exchange model as well as predictions from the eikonalized mini-jet model with recent LEP data.Comment: 7 pages, LateX, 2 eps figures. Talk presented at Photon'97, Egmond aan Zee, May 199

Total Cross-sections and Bloch-Nordsieck Gluon Resummation

The physics underlying the fall and eventual rise in various total cross-sections at high energies has been investigated over a decade using a model based on the Bloch-Nordsieck resummation in QCD. Here a brief review of our latest results is presented and comparison made with experimental data on $pp$, $\gamma proton$ and $\gamma \gamma$ total cross-sections.Comment: Presented by G. Pancheri at ISMD04, Sonoma State University. Under publication in Acta Physica Polonica. LaTeX format, 10 *.eps files, 7 page

Total Cross Sections

A unified approach to total cross-sections, based on the QCD contribution to the rise with energy, is presented for the processes $pp$, $p{\bar p}$, $\gamma p, \gamma \gamma, e^+e^- \to hadrons$. For proton processes, a discussion of the role played by soft gluon summation in taming the fast rise due to mini-jets is presented. For photon-photon processes, a comparison with other models indicates the need for precision measurements in both the low and high energy region, likely only with measurements at future Linear Colliders.Comment: 15 pages, 9 figures, LaTeX, uses hsproc.sty and art10.sty. Talk given by G. Pancheri at 'International Hadron Structure-2000', October 1-6, Staralesn