 96684 Joel Feldman, Manfred Salmhofer, and Eugene Trubowitz
 Perturbation Theory around NonNested Fermi Surfaces
II. Regularity of the Moving Fermi Surface: RPA Contributions
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Dec 21, 96

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Abstract. Regularity of the deformation of the Fermi surface under shortrange
interactions is established for all contributions to the RPA
selfenergy (it is proven in an accompanying paper that
the RPA graphs are the least regular contributions to the selfenergy).
Roughly speaking, the graphs contributing to the RPA
selfenergy are those constructed by contracting two external
legs of a fourlegged graph that consists of a string of bubbles.
This regularity is a necessary ingredient in the proof
that renormalization does not change the model.
It turns out that the selfenergy is more regular when derivatives are
taken tangentially to the Fermi surface than when they are taken
normal to the Fermi surface.
The proofs require a very detailed analysis of the singularities that
occur at those momenta $\p$ where the Fermi surface $S$ is tangent to $S+\p$.
Models in which $S$ is not symmetric under the
reflection $\p \to \p$ are included.
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