# Pure quasifree states of the Dirac field from the fermionic projector

August 07, 2014

We consider the quantised free Dirac field on oriented and globally
hyperbolic ultrastatic slab spacetimes with compact spatial section and
demonstrate how a gauge invariant, pure and quasifree state on the
C*-completion of the self-dual CAR-algebra can be extracted from the fermionic
projector construction of Finster and Reintjes. This state is analogous to the
"SJ-state" of the free scalar field recently discussed in the literature. We
prove that this state generically fails to be Hadamard. However, we also show
how a modified version of the construction, inspired by work of Brum and
Fredenhagen, yields states which are Hadamard. We also relate the Hadamard
condition to the finiteness of fluctuations of Wick polynomials.

Keywords:

Dirac fields, Hadamard states, quantum fields in curved spacetimes