MYSCE, a new Monte Carlo code for star cluster simulations. Axion-like particles and very-high energy astrophysics

This thesis focuses on two different topics: (i) star clusters, as favourite environments for the formation of black holes of very high mass, and (ii) the implications of axionlike particles for very-high energy astrophysics by considering -ray observations from blazars. In the first part of this thesis we develop a new Monte Carlo code MYSCE (Montecarlo Young Star Cluster Evolution) which improves and solves some problems of the original scheme presented by Hénon. We use our code to simulate star clusters and to inquire if an episode of gas infall during the cluster lifetime can lead to the formation of an intermediate mass black hole and/or a super massive black hole seed. In the second part of this thesis we explore axion-like particles in an astrophysical context. We describe their origin and properties within extensions of the Standard Model of elementary particle physics. We show how axion-like particles can in principle solve the cosmic opacity problem for distant blazars and naturally explain the emission of very-high energy photons from at spectrum radio quasars