The Standard Model instability and the scale of new physics

We apply a general formalism for the improved effective potential with seve ral mass scales to compute the scale M of new physics which is needed to st abilize the Standard Model potential in the presence of a light Higgs. We f ind, by imposing perturbativity of the new physics, that M can be as large as one order of magnitude higher than the instability scale of the Standard Model. This implies that, with the present lower bounds on the Higgs mass, the new physics could easily (but not necessarily) escape detection in the present and future accelerators. (C) 2000 Elsevier Science B.V. All rights reserved.