  By means of functional integrations spectral properties of semi-relativistic
Pauli-Fierz Hamiltonians in quantum electrodynamics is considered. Two
self-adjoint extensions of a semi-relativistic Pauli-Fierz Hamiltonian are
defined. An essential self-adjointness, a spatial decay of bound states, a
Gaussian domination of the ground state and the existence of a measure
associated with the ground state are shown.
