Allard-type boundary regularity for C1,α boundaries.

In this paper, we show boundary monotonicity formulae for rectifiable varifolds having a C1,α “boundary”. In particular, we show that the area ratios of balls centered at this “boundary” satisfy a nice monotonicity formula, similar to that for interior balls proved by Allard in [Ann. of Math. (2) 95 (1972), 417–491]. This extends the boundary monotonicity formulae of Allard [Ann. of Math. (2) 101 (1975), 418–446], which require that the boundary is C1,1. As a corollary, the regularity results of [Ann. of Math. (2) 101 (1975), 418–446] extend to this case and provide a regularity result for rectifiable varifolds with a C1,α “boundary”. [ABSTRACT FROM AUTHOR]