The Cauchy problem for 3-evolution equations with data in Gelfand-Shilov spaces

We consider the Cauchy problem for a third order evolution operator P with (t,x)-depending coefficients and complex valued lower order terms. We assume the initial data to be Gevrey regular with an exponential decay at infinity, that is, the data belong to some Gelfand-Shilov space of type $mathscr{S}$. Under suitable assumptions on the decay at infinity of the imaginary parts of the coefficients of P we prove the existence of a solution with the same Gevrey regularity of the data and we describe its behavior for |x| tending to infinity.