STABILITY OF GROUND STATES IN SECTORS AND ITS APPLICATION TO THE WIGNER–WEISSKOPF MODEL
2001 ◽
Vol 13
(04)
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pp. 513-528
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Keyword(s):
A Value
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We consider two kinds of stability (under a perturbation) of the ground state of a self-adjoint operator: the one is concerned with the sector to which the ground state belongs and the other is about the uniqueness of the ground state. As an application to the Wigner–Weisskopf model which describes one mode fermion coupled to a quantum scalar field, we prove in the massive case the following: (a) For a value of the coupling constant, the Wigner–Weisskopf model has degenerate ground states; (b) for a value of the coupling constant, the Wigner–Weisskopf model has a first excited state with energy level below the bottom of the essential spectrum. These phenomena are nonperturbative.