Essential self-adjointness of n-dimensional Dirac operators with a variable mass term

We give some results about the essential self-adjointness of the Dirac operator H = (n)Sigma(j=1) alpha(j) p(j) + m(x) alpha(n+1) + V(x) I-N (N = 2[n+1/2]) on [C-0(infinity) (R-n \ 0)](N), where the alpha(j) (j = 1, 2,. . ., n) are Dirac matrices and m(x) and V(x) are real-valued functions. We are mainly interested in a singularity of V(x) and m (x) near the origin which preserves the essential self-adjointness of H. As a result, if m = m(r) is spherically symmetric or m(x) equivalent to V(x), then we can permit a singularity of m and V which is stronger than that of the Coulomb potential.