Physical running of couplings in quadratic gravity

We argue that the well-known beta functions of quadratic gravity do not correspond to the physical dependence of scattering amplitudes on external momenta, and derive the correct physical beta functions. Asymptotic freedom turns out to be compatible with the absence of tachyons.
Comment: 8 pages, 2 figures, 2 tables; v2: Some modifications throughout the text. Revised version as accepted by PRL