Selftuning and its footprints

We reconsider the selftuning idea in brane world models of finite volume. We notice that in a large class of selftuning models, the four-dimensional physics is sensitive to the vacuum energy on the brane. In particular the compactification volume changes each time the tension of the brane is modified: consequently, observable constants, as the effective Planck mass or masses of matter fields, change as well. We notice that the selftuning mechanism and the stabilization mechanism of the size of the extra dimensions are generically in apparent conflict. We focus on a selftuning model in six spacetime dimensions to analyze how the above considerations are explicitly realized. (C) 2003 Elsevier B.V. All rights reserved.