Static chaos and scaling behavior in the spin-glass phase

We discuss the problem of static chaos in spin glasses. In the case of magnetic-field perturbations, we propose a scaling theory for the spin-glass phase. Using the mean-field approach we argue that some pure states are suppressed by the magnetic field and their free-energy cost is determined by the finite-temperature fixed-point exponents. In this framework, numerical results suggest that mean-field chaos exponents are probably exact in finite dimensions. If we use the droplet approach, numerical results suggest that the zero-temperature fixed-point exponent {θ} is very close to (d-3)/2. In both approaches d=3 is the lower critical dimension in agreement with recent numerical simulations.