We give proofs of de Rham comparison isomorphisms for rigid-analytic varieties, with coefficients and in families. This relies on the theory of perfectoid spaces. Another new ingredient is the pro-étale site, which makes all constructions completely functorial.
Mathematics Subject Classification: 14G22, 14C30 (primary); 14G20, 32J27 (secondary)
OverviewThis paper studies p-adic comparison theorems in the general setting of rigid-analytic varieties: that is, the p-adic analogue of complex-analytic varieties. Up to now, such comparison isomorphisms were studied for algebraic varieties over p-adic fields, but we show here that large parts of the theory extend to rigid-analytic varieties over p-adic fields. This was already suggested by Tate in his pioneering work on p-adic Hodge(-Tate) decompositions for p-divisible groups, and is of course in analogy with classical Hodge theory, which works for general (Kähler) complex-analytic spaces.One key problem in the p-adic case, as compared to the complex case, is that rigid-analytic varieties are not locally contractible. However, we show that locally they are K(π, 1)'s (for p-adic coefficients): that is, the higher homotopy groups vanish. However, the π 1 is very big, and contains lots of interesting arithmetic information.Then we proceed to discuss several analogues of known results about complex-analytic spaces. The first is finiteness of p-adicétale cohomology, corresponding to finiteness of singular cohomology in the complex case. For this, we give a proof that is inspired by the Cartan-Serre proof of finiteness of coherent cohomology in the complex case. Next, we establish an analogue of the Riemann-Hilbert correspondence between local systems and modules with an integrable connection. In the p-adic setup, (p-adic) local systems have a much richer arithmetic structure; therefore, in this case, one has to consider modules with an integrable connection together with a Finally, we compare the cohomology of a p-adic local system with the cohomology of the associated filtered module with integrable connection. Moreover, we give a Hodge-Tate decomposition (analogous to the Hodge decomposition over the complex numbers), and we prove degeneration of the Hodge-to-de Rham spectral sequence. Interestingly, the latter two results work in complete generality in the p-adic case, with no analogue of a Kähler condition being necessary. Relative situations are also considered, and can be handled with the same methods.These results generalize many previous results. For algebraic varieties, the results for constant coefficients were known by Faltings (with different proofs given by Tsuji, Niziol and Beilinson). Also, it was known by Brinon how to pass from de Rham local systems to filtered modules with integrable connection, although we improve on his results. However, for example the results comparing cohomology with nontrivial coefficients and the relative results are new even in the algebraic case.Technically, our results rest on our theory of perfectoid spaces, which give...