Source: Duke Math. J. Volume 154, Number 2
(2010), 343-418.
We give a criterion under which one can obtain a good decomposition (in the sense of Malgrange) of a formal flat connection on a complex analytic or algebraic variety of arbitrary dimension. The criterion is stated in terms of the spectral behavior of differential operators and generalizes Robba's construction of the Hukuhara-Levelt-Turrittin decomposition in the one-dimensional case. As an application, we prove the existence of good formal structures for flat meromorphic connections on surfaces after suitable blowing up; this verifies a conjecture of Sabbah and extends a result of Mochizuki for algebraic connections. Our proof uses a finiteness argument on the valuative tree associated to a point on a surface in order to verify the numerical criterion.
References
Y. André, Structure des connexions méromorphes formelles de plusieurs variables et semi-continuité de l'irrégularité, Invent. Math. 170 (2007), 147--198.
Y. André and F. Baldassarri, De Rham Cohomology of Differential Modules on Algebraic Varieties, Prog. Math. 189, Birkhäuser, Basel, 2001.
M. Baker, ``An introduction to Berkovich analytic spaces and non-Archimedean potential theory on curves'' in $p$-Adic Geometry, Univ. Lecture Ser. 45, Amer. Math. Soc., Providence, 2008, 123--174.
M. Baker and R. Rumely, Potential Theory and Dynamics on the Berkovich Projective Line, Math. Surveys Monogr. 159, Amer. Math. Soc., Providence, 2010.
F. Baldassarri and L. Di Vizio, Continuity of the radius of convergence of $p$-adic differential equations on Berkovich analytic spaces, preprint.
V. G. Berkovich, Spectral Theory and Analytic Geometry over Non-Archimedean Fields, trans. N. I. Koblitz, Math. Surveys Monogr. 33, Amer. Math. Soc., Providence, 1990.
N. Bourbaki, Commutative Algebra: Chapters 1--7, reprint of the 1989 English translation, Elem. Math. (Berlin), Springer, Berlin, 1998.
—, Algebra II: Chapters 4--7, reprint of the 1990 English ed., Elem. Math. (Berlin), Springer, Berlin, 2003.
E. Corel, On Fuchs' relation for linear differential systems, Compos. Math. 140 (2004), 1367--1398.
P. Deligne, Équations différentielles à points singuliers réguliers, Lecture Notes in Math. 163, Springer, Berlin, 1970.
B. Dwork, G. Gerotto, and F. J. Sullivan, An Introduction to $G$-Functions, Ann. of Math. Stud. 133, Princeton Univ. Press, Princeton, 1994.
C. Favre and M. Jonsson, The Valuative Tree, Lecture Notes in Math. 1853, Springer, Berlin, 2004.
K. S. Kedlaya, Semistable reduction for overconvergent $F$-isocrystals, I: Unipotence and logarithmic extensions, Compos. Math. 143 (2007), 1164--1212.
—, Semistable reduction for overconvergent $F$-isocrystals, II: A valuation-theoretic approach, Compos. Math. 144 (2008), 657--672.
—, Semistable reduction for overconvergent $F$-isocrystals, III: Local semistable reduction at monomial valuations, Compos. Math. 145 (2009), 143--172.
—, Semistable reduction for overconvergent $F$-isocrystals, IV: Local semistable reduction at nonmonomial valuations, preprint.
—, $p$-adic Differential Equations, Cambridge Stud. Adv. Math. 125, Cambridge Univ. Press, Cambridge, 2010.
K. S. Kedlaya and L. Xiao, Differential modules on $p$-adic polyannuli, J. Inst. Math. Jussieu 9 (2010), 155--201.; Erratum, J. Inst. Math. Jussieu 9 (2010), 669--671.
A. H. M. Levelt, Jordan decomposition for a class of singular differential operators, Ark. Mat. 13 (1975), 1--27.
H. Majima, Asymptotic Analysis for Integrable Connecitons with Irregular Singular Points, Lecture Notes in Math. 1075, Springer, Berlin, 1984.
Mathematical Reviews (MathSciNet):
MR757897
B. Malgrange, Sur les points singuliers des équations différentielles, Enseign. Math. (2) 20 (1974), 147--176.
—, ``Connexions méromorphes'' in Singularities (Lille, 1991), London Math. Soc. Lecture Note Ser. 201, Cambridge Univ. Press, Cambridge, 1994.
—, Connexions méromorphes, II: Le réseau canonique, Invent. Math. 124 (1996), 367--387.
H. Matsumura, Commutative Ring Theory, 2nd ed., trans. M. Reid, Cambridge Stud. Adv. Math. 8, Cambridge Univ. Press, Cambridge, 1989.
T. Mochizuki, ``Good formal structure for meromorphic flat connections on smooth projective surfaces'' in Algebraic Analysis and Around, Adv. Stud. Pure Math. 54, Math. Soc. Japan, Tokyo, 2009, 223--253.
—, Wild harmonic bundles and wild pure twistor $D$-modules, preprint.
G. Pólya and G. Szegő, Problems and Theorems in Analysis, I, trans. D. Aeppli, Classics in Math., Springer, Berlin, 1998.
D. Popescu, On a question of Quillen, Bull. Math. Soc. Sci. Math. Roumanie (N.J.) 45(93) (2002), 209--212.
P. Robba, Lemmes de Hensel pour des opérateurs différentiels: Applicatíon à la réduction formelle des équations différentielles, Enseign. Math. (2) 26 (1980), 279--311.
R. T. Rockafellar, Convex Analysis, Princeton Univ. Press, Princeton, 1996.
C. Sabbah, Équations différentielles à points singuliers irréguliers et phénomène de Stokes en dimension 2, Astérisque 263, Soc. Math. France, Montrouge, 2000.
P. Schneider, Nonarchimedean Functional Analysis, Springer Monogr. Math., Springer, Berlin, 2002.
A. Thuillier, Théorie du potentiel sur les courbes en géométrie analytique non archimédienne: Applications à la theorie d'Arakelov, Ph.D. dissertation, Université de Rennes 1, Rennes, France, 2005.
V. S. Varadarajan, Linear meromorphic differential equations: A modern point of view, Bull. Amer. Math. Soc. (N.J.) 33 (1996), 1--42.