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Noncommutative Bloch analysis of Bochner Laplacians with nonvanishing gauge fields

Given an invariant gauge potential and a periodic scalar potential \tilde{V} on a Riemannian manifold \tilde{M} with a discrete symmetry group Γ, consider a Γ-periodic quantum Hamiltonian \tilde{H}=-\tildeΔ_{B}+\tilde{V} where \tildeΔ_{B} is the Bochner Laplacian. Both the gauge group and the symmetry group Γcan be noncommutative, and the gauge field need not vanish. On the other hand, Γis supposed to be of type I. To any unitary representation Λof Γone relates a Hamiltonian H^Λ=-Δ_{B}^Λ+V on M=\tilde{M}/Γwhere V is the projection of \tilde{V} to M. We describe a construction of the Bloch decomposition of \tilde{H} into a direct integral whose components are H^Λ, with Λrunning over the dual space \hatΓ. The evolution operator and the resolvent decompose correspondingly. Conversely, given Λ\in\hatΓ, one can express the propagator \mathcal{K}_{t}^Λ(y_{1},y_{2}) (the kernel of \exp(-itH^Λ)) in terms of the propagator \tilde{\mathcal{K}}_{t}(y_{1},y_{2}) (the kernel of \exp(-it\tilde{H})) as a weighted sum over Γ. Such a formula is known in theoretical physics for the case when the gauge field vanishes and \tilde{M} is a universal covering of a multiply connected space M. We show that these constructions are mutually inverse. Analogous formulas exist for resolvents and their kernels (Green functions) as well.