title: Problems with the definition of renormalized Hamiltonians for momentum-space renormalization transformations.
abstract: For classical lattice systems with finite (Ising) spins, we show that the implementation of momentum-space renormalization at the level of Hamiltonians runs into the same type of difficulties as found for real-space transformations: Renormalized Hamiltonians are ill-defined in certain regions of the phase diagram.
authors.affiliation: Institute for Theoretical Physics, Rijksuniversiteit Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands. AENTER@PHYS.RUG.NL
authors.forename: A C
authors.initials: AC
authors.lastname: van Enter
authors.forename: R
authors.initials: R
authors.lastname: Fernández