Entropy and periodic orbits for equivalent smooth flows
  Given any $K>0$, we construct two equivalent $C^2$ flows, one of which has positive topological entropy larger than $K$ and admits zero as the exponential growth of periodic orbits, in contrast, the other has zero topological entropy and super-exponential growth of periodic orbits. Moreover we establish a $C^{\infty}$ flow on $\mathbb{S}^2$ with super-exponential growth of periodic orbits, which is also equivalent to another flow with zero exponential growth of periodic orbits. On the other hand, any two dimensional flow has only zero topological entropy. 
Gang Liao, Wenxiang Sun
math.DS