Correlation effects in spin models in the presence of a spin bath

Abstract: We analyze the effect of a bath of spins interacting with a spin system in terms of the equation of motion technique. We show that this formalism can be used with general spin systems and baths, and discuss the concrete case of a Quantum Ising model longitudinally coupled to the bath. We show how the uncorrelated solutions change when spin-spin correlations are included, the properties of the quasiparticle excitations and the effect of internal dynamics in the spin bath.