In this paper, we consider the natural complex Hamiltonian systems with homogeneous potential $V\left(q\right)$, $q\in {ℂ}^n$, of degree $k\in {\mathbb{Z}}^{☆}$. The known results of Morales and Ramis give necessary conditions for the complete integrability of such systems. These conditions are expressed in terms of the eigenvalues of the Hessian matrix $V^{\prime \prime }\left(c\right)$ calculated at a non-zero point $c\in {ℂ}^n$, such that $V^{\prime }\left(c\right)=c$. The main aim of this paper is to show that there are other obstructions for the integrability which appear if the matrix $V^{\prime \prime }\left(c\right)$ is not diagonalizable....

For a class of quadratic polynomial endomorphisms $f:{ℂ}^2\to {ℂ}^2$ close to the standard torus map $(x,y)\to (x^2,y^2)$, we show that the Julia set J(f) is homeomorphic to the torus. We identify J(f) as the closure ℛ of the set of repelling periodic points and as the Shilov boundary of the set K(f) of points with bounded forward orbit. Moreover, it turns out that (J(f),f) is a mixing repeller and supports a measure of maximal entropy for f which is uniquely determined as the harmonic measure for K(f).

We study the jumps of topological entropy for $C^r$ interval or circle maps. We prove in particular that the topological entropy is continuous at any $f\in C^r\left([0,1]\right)$ with $h_{top}\left(f\right)>\left(log⁺\right||f^{\text{'}}{\left|\right|}_{\infty })/r$. To this end we study the continuity of the entropy of the Buzzi-Hofbauer diagrams associated to $C^r$ interval maps.