Abstract:

I shall present a new, potentially very fruitful extension of the now ten-years-old technique of the exclusive exponentiation within the Monte Carlo event generators. It is also related to the Yennie- Frautschi-Suura works on exponentiation, it goes however in a new direction: the entire formulation of the exponentiation is now done in terms of the spin amplitudes, instead of squared spin-summed amplitudes. The advantages of the new method are numerous: the QED interferences, like for example the initial-final state interferences are handled easily and consistently, the non-IR virtual corrections are generally simpler, the exact and efficient control of the spin polarization effects is now available for all particles, the powerful spinor techniques for calculating exact multiple bremsstrahlung spin amplitudes becomes the inherent part of the exponentiation technique. In the example of the resonant annihilation, thanks to Monte Carlo technique the full scale quantum mechanical coherence effects between the initial and final state photon emission are implemented. We are able, for the final state with photons, to sum up coherently over all partitions of photons among initial and final state. With the Monte Carlo technique the coherent sum is done without any approximations Ð hard photons are included smoothly into the game, contrary to other methods based on coherent states, semi-classical approximation, soft-photon approximations etc. The MC event generators based on the new techniques are of interest for LEP2, CLIC, TESLA, NLC and -colliders. The sample numerical results from new event generator for will be presented.