## Tag Archives: spectral radius

### Katok’s entropy conjecture

In dynamics there are several conjectures related to entropy. The first is the famous Shub Entropy Conjecture:

Let $f:M\to M$ be a differentiable map (or a diffeomorphism), $s(f_*)$ be the spectral radius of the linear map $f_{*}:\oplus H_k(M,\mathbb{R})\to \oplus H_k(M,\mathbb{R})$. Then
$h_{\mathrm{top}}(f)\ge s(f_*)$.
Moveover find characteristics of maps satisfying $h_{\mathrm{top}}(f)= s(f_*)$ in each homotopy class.

I am not sure whether the following special problem is still open (it is proved if $E^u$ is orientable):

If $f:M\to M$ is an Anosov diffeomorphism, then $h_{\mathrm{top}}(f)= s(f_*)$.

There is another entropy conjecture due to Katok. In fact Katok proved that the topological entropy and the Liouville entropy of a geodesic flow on a negatively curved surface agree only if the curvature is constant, that is, the metric is locally symmetric. He conjectured that the same holds in any dimension. One of the best result in this direction is

Besson, Courtois and Gallot, the topological entropy of geodesic flow is minimized only for locally symmetric metrics.