Classification of radial solutions for semilinear elliptic systems with nonlinear gradient terms

We are concerned with the classification of positive radial solutions for the system Δu=vpΔu=vp, Δv=f(|∇u|)Δv=f(|∇u|), where p>0p>0 and f∈C1[0,∞)f∈C1[0,∞) is a nondecreasing function such that f(t)>0f(t)>0 for all t>0t>0. We show that in the case where the system is posed in the whole space RNRN such solutions exist if and only if ∫1∞(∫0sF(t)dt)−p/(2p+1)ds=∞. This is the counterpart of the Keller–Osserman condition for the case of single semilinear equation. Similar optimal conditions are derived in case where the system is posed in a ball of RNRN. If f(t)=tqf(t)=tq, q>1q>1, using dynamical system techniques we are able to describe the behaviour of solutions at infinity (in case where the system is posed in the whole RNRN) or around the boundary (in case of a ball).