N ov 2 00 8 Linear dimension - free estimates for the Hermite - Riesz transforms ∗ Oliver Dragičević and Alexander Volberg

We utilize the Bellman function technique to prove a bilinear dimension-free inequality for the Hermite operator. The Bellman technique is applied here to a non-local operator, which at first did not seem to be feasible. As a consequence of our bilinear inequality one proves dimension-free boundedness for the Riesz-Hermite transforms on L with linear growth in terms of p. A feature of the proof is a theorem establishing L(R) estimates for a class of spectral multipliers with bounds independent of n and p. Connections with known results on the Heisenberg group as well as with results for Hilbert transform along the parabola are also explored. We believe our approach is quite universal in the sense that one could apply it to a whole range of Riesz transforms arising from various differential operators. As a first step towards this goal we prove our dimension-free bilinear embedding theorem for quite a general family of Schrödinger semigroups.