an:00892578
Zbl 0854.14009
Crew, Richard
The differential Galois theory of regular singular \(p\)-adic differential equations
EN
Math. Ann. 305, No. 1, 45-64 (1996).
00033926
1996
j
14F30 12H25 32S40 18E30
transfer theorem for regular singular \(p\)-adic different equations; overconvergent isocrystals; Tannakian categories
Let \(k\) be a perfect field of characteristic \(p>0\), \(X\) a smooth curve over \(k\) and suppose that there is a lifting \(X_K\) of \(X\) to an algebraic curve over a field \(K\) of characteristic zero. Let \(M\) be a locally free sheaf with connection on \(X_K\) satisfying some convergence condition (namely it is ``soluble'' in generic disks). Then, by restriction to strict neighborhoods of a formally smooth lifting of \(X\), \(M\) defines an ``overconvergent isocrystal'' \(M^\dagger\) on \(X\). If \(X_K\) has a \(K\)-rational point \(x\), the category of overconvergent isocrystals and the category of locally free sheaves on \(X_K\) with connection are neutral Tannakian categories. In both situations, the fiber functor associated to \(x\) restricted to the smallest tensor subcategory containing \(M\) (resp. \(M^\dagger\)) enables to define the ``monodromy group'' \(\text{DGal} (M)\) (resp. \(\text{DGal} (M^\dagger)\)). The main result of the paper is that if \(M^\dagger\) is regular, with \(p\)-adic integers exponents two of which do not differ by a \(p\)-adic Liouville number, then \(\text{DGal} (M)\) and \(\text{DGAL} (M^\dagger)\) are isomorphic.
As applications, first the unicity, up to homothety, of the Frobenius structure for irreducible \(F\)-isocrystals is shown, secondly a comparison result between monodromy groups of some isocrystals arising from geometry (Gauss-Manin connections) and corresponding \(\ell\)-adic monodromy groups is established. Proofs are based on the so-called ``transfer theorem for regular singular \(p\)-adic differential equations''. The author gives two conditions for a locally free sheaf to be overconvergent. Let us point out that, at least over a curve, the second one is implied by the first one.
G.Christol (Paris)