Cohomological flatness over discrete valuation rings: numerical and logarithmic criteria

We give sufficient conditions for cohomological flatness (in dimension 0) over discrete valuation rings, generalising a classical result of Raynaud in two different ways. The first is an extension of Raynaud's numerical criterion to higher dimensions. The second is a logarithmic criterion: we show that a proper, fs log smooth morphism to a log regular discrete valuation ring is cohomologically flat in dimension 0. We apply this latter result to curves and torsors under abelian varieties with good reduction, providing necessary and sufficient conditions for the log smoothness of their regular models over arbitrary discrete valuation rings.