Anomalously Soft Droplets and Aging in Short-ranged Spin Glasses

We extend the standard droplet scaling theory for isothermal aging in spin glasses assuming that the effective stiffness constant of droplets as large as extended defects is vanishingly small. A novel dynamical order parameter and the associated dynamical susceptibility emerge. Breaking of the fluctuation dissipation theorem takes place at the dynamical order parameter well below the equilibrium Edwards-Anderson order parameter at which the time translational invariance is strongly broken. The scenario is examined numerically in a 4 dimensional EA Ising spin glass model.