Constructive use of holographic projections Dedicated to Klaus Fredenhagen on the occasion of his 60th birthday

Revisiting the old problem of existence of interacting models of QFT with new conceptual ideas and mathematical tools, one arrives at a novel view about the nature of QFT. The recent success of algebraic methods in establishing the existence of factorizing models suggests new directions for a more intrinsic constructive approach beyond Lagrangian quantization. Holographic projection simplifies certain properties of the bulk theory and hence is a promising new tool for these new attempts. To appear in: ”Quantum field theory –Competitive Methods” Birkhhäuser Basel, 2008, Eds. B. Fauser, J. Tolksdorf and E. Zeidler 1 Historical background and present motivations