arXiv:0910.3812 Geometric criteria for tame ramification from arXiv Front: math.AG by Johannes Nicaise We prove an A’Campo type formula for the tame monodromy zeta function of a smooth and proper variety over a discretely valued field . As a first application, we relate the orders of the tame monodromy eigenvalues on the -adic cohomology of a -curve to the geometry of a relatively minimal -model, and we show that the semi-stable reduction theorem and Saito’s criterion for cohomological tameness are immediate consequences of this result. As a second application, we compute the error term in the trace formula for smooth and proper -varieties. We see that the validity of the trace formula would imply a partial generalization of Saito’s criterion to arbitrary dimension.
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