We show how to solve Merton optimal investment stochastic control problem for Hawkesbased models in finance and insurance (Propositions 1 and 2), i.e., for a wealth portfolio X(t) consisting of a bond and a stock price described by general compound Hawkes process (GCHP), and for a capital R(t)...

We introduce and study a new stochastic SARS model (based on stochastic SIR model with semi-Markov regime-switchings) and investigate its behavior in averaging, merging and diffusion approximation schemes. The main method is based on general theory of random differential equations in semi-Markov...