TITLE: EFFECTIVE SOMMERFELD PARAMETERS IN DOUBLE PHOTOIONIZATION AUTHORS: M. A. Kornberg (1) and V. D. Rodriguez (2) AFFILIATIONS: (1) Max-Planck-Institut fuer Quantenoptik, Hans-Kopfermann-strasse 1, D-85748 Garching, Germany (2) Departamento de Fisica, Universidad de Buenos Aires, FCEyN, 1428 Buenos Aires, Argentina SUMMARY: We present calculations of the fivefold differential cross section (FDCS) for double photoionization of helium. Our results are obtained using for the final double-continuum state a product of three Coulomb wave functions, with the Sommerfeld parameters modified to describe the strength of interaction of any two particles affected by the third particle. Calculations are compared with recent measurements.