Physics at \ggam and \egam colliders

I discuss, what really new could give Photon Colliders ($\gamma\gamma$ and $e\gamma$) after LHC and \epe Linear Collider operations.Comment: 7pages,LaTEX, To be published in proceedings "PHOTON99". The forgotten title, author and abstract are added in the tex

Laser cooling of electron beams at linear colliders

A method of electron beam cooling is considered which can be used for linear colliders. The electron beam is cooled during collision with focused powerful laser pulse. The ultimate transverse emittances are much below those achievable by other methods. This method is especially useful for high energy gamma-gamma colliders. In this paper we review and analyse limitations in this method, also discuss a new method of obtaining very high laser powers required for the laser cooling, radiation conditions and finaly present a possible scheme for the laser cooling of electron beams.Comment: 17 pages, Latex, 3 figures (.eps), Invited talk at the International Symposium on New Visions in Laser-Beam Interactions, October 11-15, 1999, Tokyo, Metropolitan University Tokyo, Japan. To be published in Nucl. Instr. and Meth.

How to measure the Pomeron phase in diffractive dipion photoproduction

The study of charge asymmetry of pions in the high-energy process gamma p -> pi+ pi- p (e p -> e pi+ pi- p) at very small dipion momenta offers a method to measure the phase of the forward hadronic (quasi)elastic amplitude gamma p -> rho p. We estimate potential of such measurements at HERA.Comment: 12 pages, 2 figures; v4: more elaborate parametrizations of dipion spectra implemented, discussion extende

CP violation in photon-photon collisions

The effective lagrangian parametrization is used to determine the CP violating effects in $\gamma \gamma$ collisions. for the processes studied the effects are found to be very small, the one exception being scalar production.Comment: 11 pages,. Requires epsf.tex, four figures in separate files f1.ps -- f4.ps attached at then en

Two-Higgs-doublet model from the group-theoretic perspective

In the two-Higgs-doublet model, different Higgs doublets can be viewed as components of a generic "hyperspinor". We decompose the Higgs potential of this model into irreducible representations of the SU(2) group of transformations of this hyperspinor. We discuss invariant combinations of the Higgs potential parameters lambda_i that arise in this decomposition and provide simple and concise sets of conditions for the hidden Z_2-symmetry, Peccei-Quinn symmetry, and explicit CP-conservation in 2HDM. We show that some results obtained previously by brute-force calculations are reduced to simple linear algebraic statements in our approach.Comment: 10 pages; v3: expanded section on consequences, added subsections on CP-conservation, PQ symmetry, RG evolution; v4: misprints corrected; to appear in Physics Letters

Magnetic flux dynamics in critical state of one-dimensional discrete superconductor

We give a theoretical description of avalanche-like dynamics of magnetic flux in the critical state of "hard" type-II superconductors using a model of a one-dimensional multijunction SQUID that well reproduces the main magnetic properties of these objects. We show that the system under consideration demonstrates the self-organized criticality. The avalanches of vortices manifest themselves as jumps of the total magnetic flux in the sample. The sizes of these jumps have a power-law distribution. Our results are in qualitative agreement with experiments.Comment: 7 pages, 5 figure

The global nilpotent variety is Lagrangian

The purpose of this note is to present a short elementary proof of a theorem due to Faltings and Laumon, saying that the global nilpotent cone is a Lagrangian substack in the cotangent bundle of the moduli space of G-bundles on a complex compact curve. This result plays a crucial role in the Geometric Langlands program, due to Beilinson-Drinfeld, since it insures that the D-modules on the moduli space of G-bundles whose characteristic variety is contained in the global nilpotent cone are automatically holonomic, hence, e.g. have finite length.Comment: LaTeX, 9pp. Final version, to appear in Duke Math.