We discuss possible definitions of discrete Dirac operators,
and discuss their continuum limits. It is well-known in the lattice
field theory that the straightforward discretization of the Dirac
operator introduces unwanted particles (spectral subspaces), and this
phenomenon is known as the fermion doubling. In order to overcome this
difficulty, two methods were proposed.
(1) Introduce a new term, called the Wilson term;
(2) The KS-fermion model or the staggered fermion model.
We discuss mathematical formulations of these, and study their
continuum limits. The preprint is available at
https://arxiv.org/abs/2306.14180.