The two-phase Alt-Phillips problem for quasilinear operators

We establish interior regularity and optimal growth estimates for sign-changing minimizers of the $p-$singular or $p-$degenerate quasilinear Alt–Phillips functional throughout the full range of $1<p<\mathrm{\infty }$ and of the nonlinearity power $0<\gamma <p$. In addition, we obtain local finite perimeter and density estimates, from which we deduce the local $(N-1)$-rectifiability of the reduced and two-phase free boundaries and the local finiteness of their $(N-1)$-dimensional Hausdorff measure for a restricted range of $\gamma$.