Arithmetic differential operators over the p-adic integers

148 Pages·2012·0.86 MB·English

by  Claire C Ralph

LONDON MATHEMATICAL SOCIETY LECTURE NOTE SERIES
ManagingEditor:ProfessorM.Reid,MathematicsInstitute,
UniversityofWarwick,CoventryCV47AL,UnitedKingdom
Thetitlesbelowareavailablefrombooksellers,orfromCambridgeUniversityPress
athttp://www.cambridge.org/mathematics
287 TopicsonRiemannsurfacesandFuchsiangroups,E.BUJALANCE,A.F.COSTA&E.MARTÍNEZ(eds)
288 Surveysincombinatorics,2001,J.W.P.HIRSCHFELD(ed)
289 AspectsofSobolev-typeinequalities,L.SALOFF-COSTE
290 QuantumgroupsandLietheory,A.PRESSLEY(ed)
291 Titsbuildingsandthemodeltheoryofgroups,K.TENT(ed)
292 Aquantumgroupsprimer,S.MAJID
293 SecondorderpartialdifferentialequationsinHilbertspaces,G.DAPRATO&J.ZABCZYK
294 Introductiontooperatorspacetheory,G.PISIER
295 Geometryandintegrability,L.MASON&Y.NUTKU(eds)
296 Lecturesoninvarianttheory,I.DOLGACHEV
297 Thehomotopycategoryofsimplyconnected4-manifolds,H.-J.BAUES
298 Higheroperads,highercategories,T.LEINSTER(ed)
299 Kleiniangroupsandhyperbolic3-manifolds,Y.KOMORI,V.MARKOVIC&C.SERIES(eds)
300 IntroductiontoMöbiusdifferentialgeometry,U.HERTRICH-JEROMIN
301 StablemodulesandtheD(2)-problem,F.E.A.JOHNSON
302 DiscreteandcontinuousnonlinearSchrödingersystems,M.J.ABLOWITZ,B.PRINARI&A.D.TRUBATCH
303 Numbertheoryandalgebraicgeometry,M.REID&A.SKOROBOGATOV(eds)
304 GroupsStAndrews2001inOxfordI,C.M.CAMPBELL,E.F.ROBERTSON&G.C.SMITH(eds)
305 GroupsStAndrews2001inOxfordII,C.M.CAMPBELL,E.F.ROBERTSON&G.C.SMITH(eds)
306 Geometricmechanicsandsymmetry,J.MONTALDI&T.RATIU(eds)
307 Surveysincombinatorics2003,C.D.WENSLEY(ed.)
308 Topology,geometryandquantumfieldtheory,U.L.TILLMANN(ed)
309 Coringsandcomodules,T.BRZEZINSKI&R.WISBAUER
310 Topicsindynamicsandergodictheory,S.BEZUGLYI&S.KOLYADA(eds)
311 Groups:topological,combinatorialandarithmeticaspects,T.W.MÜLLER(ed)
312 Foundationsofcomputationalmathematics,Minneapolis2002,F.CUCKERetal(eds)
313 Transcendentalaspectsofalgebraiccycles,S.MÜLLER-STACH&C.PETERS(eds)
314 Spectralgeneralizationsoflinegraphs,D.CVETKOVIC,P.ROWLINSON&S.SIMIC
315 Structuredringspectra,A.BAKER&B.RICHTER(eds)
316 Linearlogicincomputerscience,T.EHRHARD,P.RUET,J.-Y.GIRARD&P.SCOTT(eds)
317 Advancesinellipticcurvecryptography,I.F.BLAKE,G.SEROUSSI&N.P.SMART(eds)
318 Perturbationoftheboundaryinboundary-valueproblemsofpartialdifferentialequations,D.HENRY
319 DoubleaffineHeckealgebras,I.CHEREDNIK
320 L-functionsandGaloisrepresentations,D.BURNS,K.BUZZARD&J.NEKOVÁR(eds)
321 Surveysinmodernmathematics,V.PRASOLOV&Y.ILYASHENKO(eds)
322 Recentperspectivesinrandommatrixtheoryandnumbertheory,F.MEZZADRI&N.C.SNAITH(eds)
323 Poissongeometry,deformationquantisationandgrouprepresentations,S.GUTTetal(eds)
324 Singularitiesandcomputeralgebra,C.LOSSEN&G.PFISTER(eds)
325 LecturesontheRicciflow,P.TOPPING
326 ModularrepresentationsoffinitegroupsofLietype,J.E.HUMPHREYS
327 Surveysincombinatorics2005,B.S.WEBB(ed)
328 Fundamentalsofhyperbolicmanifolds,R.CANARY,D.EPSTEIN&A.MARDEN(eds)
329 SpacesofKleiniangroups,Y.MINSKY,M.SAKUMA&C.SERIES(eds)
330 Noncommutativelocalizationinalgebraandtopology,A.RANICKI(ed)
331 Foundationsofcomputationalmathematics,Santander2005,L.MPARDO,A.PINKUS,E.SÜLI&M.J.TODD(eds)
332 Handbookoftiltingtheory,L.ANGELERIHÜGEL,D.HAPPEL&H.KRAUSE(eds)
333 Syntheticdifferentialgeometry(2ndEdition),A.KOCK
334 TheNavier–Stokesequations,N.RILEY&P.DRAZIN
335 Lecturesonthecombinatoricsoffreeprobability,A.NICA&R.SPEICHER
336 Integralclosureofideals,rings,andmodules,I.SWANSON&C.HUNEKE
337 MethodsinBanachspacetheory,J.M.F.CASTILLO&W.B.JOHNSON(eds)
338 Surveysingeometryandnumbertheory,N.YOUNG(ed)
339 GroupsStAndrews2005I,C.M.CAMPBELL,M.R.QUICK,E.F.ROBERTSON&G.C.SMITH(eds)
340 GroupsStAndrews2005II,C.M.CAMPBELL,M.R.QUICK,E.F.ROBERTSON&G.C.SMITH(eds)
341 Ranksofellipticcurvesandrandommatrixtheory,J.B.CONREY,D.W.FARMER,F.MEZZADRI&
N.C.SNAITH(eds)
342 Ellipticcohomology,H.R.MILLER&D.C.RAVENEL(eds)
343 AlgebraiccyclesandmotivesI,J.NAGEL&C.PETERS(eds)
344 AlgebraiccyclesandmotivesII,J.NAGEL&C.PETERS(eds)
345 Algebraicandanalyticgeometry,A.NEEMAN
346 Surveysincombinatorics2007,A.HILTON&J.TALBOT(eds)
347 Surveysincontemporarymathematics,N.YOUNG&Y.CHOI(eds)
348 Transcendentaldynamicsandcomplexanalysis,P.J.RIPPON&G.M.STALLARD(eds)
349 ModeltheorywithapplicationstoalgebraandanalysisI,Z.CHATZIDAKIS,D.MACPHERSON,A.PILLAY&
A.WILKIE(eds)
350 ModeltheorywithapplicationstoalgebraandanalysisII,Z.CHATZIDAKIS,D.MACPHERSON,A.PILLAY&
A.WILKIE(eds)
351 FinitevonNeumannalgebrasandmasas,A.M.SINCLAIR&R.R.SMITH
352 Numbertheoryandpolynomials,J.MCKEE&C.SMYTH(eds)
353 Trendsinstochasticanalysis,J.BLATH,P.MÖRTERS&M.SCHEUTZOW(eds)
354 Groupsandanalysis,K.TENT(ed)
355 Non-equilibriumstatisticalmechanicsandturbulence,J.CARDY,G.FALKOVICH&K.GAWEDZKI
356 EllipticcurvesandbigGaloisrepresentations,D.DELBOURGO
357 Algebraictheoryofdifferentialequations,M.A.H.MACCALLUM&A.V.MIKHAILOV(eds)
358 Geometricandcohomologicalmethodsingrouptheory,M.R.BRIDSON,P.H.KROPHOLLER&I.J.LEARY(eds)
359 Modulispacesandvectorbundles,L.BRAMBILA-PAZ,S.B.BRADLOW,O.GARCÍA-PRADA&
S.RAMANAN(eds)
360 Zariskigeometries,B.ZILBER
361 Words:Notesonverbalwidthingroups,D.SEGAL
362 Differentialtensoralgebrasandtheirmodulecategories,R.BAUTISTA,L.SALMERÓN&R.ZUAZUA
363 Foundationsofcomputationalmathematics,HongKong2008,F.CUCKER,A.PINKUS&M.J.TODD(eds)
364 Partialdifferentialequationsandfluidmechanics,J.C.ROBINSON&J.L.RODRIGO(eds)
365 Surveysincombinatorics2009,S.HUCZYNSKA,J.D.MITCHELL&C.M.RONEY-DOUGAL(eds)
366 Highlyoscillatoryproblems,B.ENGQUIST,A.FOKAS,E.HAIRER&A.ISERLES(eds)
367 Randommatrices:Highdimensionalphenomena,G.BLOWER
368 GeometryofRiemannsurfaces,F.P.GARDINER,G.GONZÁLEZ-DIEZ&C.KOUROUNIOTIS(eds)
369 Epidemicsandrumoursincomplexnetworks,M.DRAIEF&L.MASSOULIÉ
370 Theoryofp-adicdistributions,S.ALBEVERIO,A.YU.KHRENNIKOV&V.M.SHELKOVICH
371 Conformalfractals,F.PRZYTYCKI&M.URBANSKI
372 Moonshine:Thefirstquartercenturyandbeyond,J.LEPOWSKY,J.MCKAY&M.P.TUITE(eds)
373 Smoothness,regularityandcompleteintersection,J.MAJADAS&A.G.RODICIO
374 Geometricanalysisofhyperbolicdifferentialequations:Anintroduction,S.ALINHAC
375 Triangulatedcategories,T.HOLM,P.JØRGENSEN&R.ROUQUIER(eds)
376 Permutationpatterns,S.LINTON,N.RUŠKUC&V.VATTER(eds)
377 AnintroductiontoGaloiscohomologyanditsapplications,G.BERHUY
378 Probabilityandmathematicalgenetics,N.H.BINGHAM&C.M.GOLDIE(eds)
379 Finiteandalgorithmicmodeltheory,J.ESPARZA,C.MICHAUX&C.STEINHORN(eds)
380 Realandcomplexsingularities,M.MANOEL,M.C.ROMEROFUSTER&C.T.C.WALL(eds)
381 Symmetriesandintegrabilityofdifferenceequations,D.LEVI,P.OLVER,Z.THOMOVA&P.WINTERNITZ(eds)
382 Forcingwithrandomvariablesandproofcomplexity,J.KRAJÍCEK
383 Motivicintegrationanditsinteractionswithmodeltheoryandnon-ArchimedeangeometryI,R.CLUCKERS,
J.NICAISE&J.SEBAG(eds)
384 Motivicintegrationanditsinteractionswithmodeltheoryandnon-ArchimedeangeometryII,R.CLUCKERS,
J.NICAISE&J.SEBAG(eds)
385 EntropyofhiddenMarkovprocessesandconnectionstodynamicalsystems,B.MARCUS,K.PETERSEN&
T.WEISSMAN(eds)
386 Independence-friendlylogic,A.L.MANN,G.SANDU&M.SEVENSTER
387 GroupsStAndrews2009inBathI,C.M.CAMPBELLetal(eds)
388 GroupsStAndrews2009inBathII,C.M.CAMPBELLetal(eds)
389 Randomfieldsonthesphere,D.MARINUCCI&G.PECCATI
390 Localizationinperiodicpotentials,D.E.PELINOVSKY
391 FusionsystemsinalgebraandtopologyM.ASCHBACHER,R.KESSAR&B.OLIVER
392 Surveysincombinatorics2011,R.CHAPMAN(ed)
393 Non-abelianfundamentalgroupsandIwasawatheory,J.COATESetal(eds)
394 VariationalProblemsinDifferentialGeometry,R.BIELAWSKI,K.HOUSTON&M.SPEIGHT(eds)
395 Howgroupsgrow,A.MANN
396 ArithmeticDifferentialOperatorsoverthep-adicIntegers,C.C.RALPH&S.R.SIMANCA
397 HyperbolicgeometryandapplicationsinquantumChaosandcosmology,J.BOLTE&F.STEINER(eds)
LONDON MATHEMATICAL SOCIETY LECTURE
NOTE SERIES: 396
Arithmetic Differential Operators
over the p-adic Integers
CLAIRE C. RALPH
CornellUniversity,USA
SANTIAGO R. SIMANCA
UniversitédeNantes,France
cambridge university press
Cambridge,NewYork,Melbourne,Madrid,CapeTown,
Singapore,SãoPaulo,Delhi,Tokyo,MexicoCity
CambridgeUniversityPress
TheEdinburghBuilding,CambridgeCB28RU,UK
PublishedintheUnitedStatesofAmericabyCambridgeUniversityPress,NewYork
www.cambridge.org
Informationonthistitle:www.cambridge.org/9781107674141
©C.RalphandS.Simanca,2012
Thispublicationisincopyright.Subjecttostatutoryexception
andtotheprovisionsofrelevantcollectivelicensingagreements,
noreproductionofanypartmaytakeplacewithoutthewritten
permissionofCambridgeUniversityPress.
Firstpublished2012
PrintedintheUnitedKingdomattheUniversityPress,Cambridge
AcataloguerecordforthispublicationisavailablefromtheBritishLibrary
ISBN978-1-107-67414-1Paperback
CambridgeUniversityPresshasnoresponsibilityforthepersistenceor
accuracyofURLsforexternalorthird-partyinternetwebsitesreferredtoin
thispublication,anddoesnotguaranteethatanycontentonsuchwebsitesis,
orwillremain,accurateorappropriate.
Contents
1 Introduction page 1
2 The p-adic numbers Qp 8
2.1 A pragmatic realization of Qp 11
2.2 The p-adic integers Zp and their field of fractions 13
2.3 The topology of Qp 15
2.4 Analytic and algebraic properties of Qp 17
2.5 (p−1)-roots of unity in Qp 20
3 Some classical analysis on Qp 23
3.1 The Artin–Hasse exponential function 30
3.2 The completion of the algebraic closure of Qp 33
3.3 Zeta functions 38
4 Analytic functions on Zp 48
4.1 Strassmann’s theorem 53
5 Arithmetic differential operators on Zp 55
5.1 Multiple primes I 61
6 A general view of arithmetic differential operators 65
6.1 Basic algebraic concepts 67
6.2 General δp-functions: arithmetic jet spaces 73
6.3 The analogue of a δp-linear operators for group
schemes 82
6.4 Multiple primes II 86
7 Analyticity of arithmetic differential operators 103
8 Characteristic functions of discs in Zp: p-adic
coordinates 107
8.1 Characteristic functions of discs of radii 1/p 107
8.2 Characteristic functions of discs of radii 1/pn 116
v
vi Contents
9 Characteristic functions of discs in Zp: harmonic co-
ordinates 119
9.1 A matrix associated to pm 120
9.2 Analytic functions and arithmetic differential
operators 122
10 Some differences between δ-operators over Zp and
Z(cid:2)ur 127
p
References 135
Index 138
1
Introduction
Our purpose in this monograph is to provide a concise and complete
introduction to the study of arithmetic differential operators over the
p-adic integers Zp. These are the analogues of the usual differential op-
erators over say, the ring C[x], but where the role of the variable x is
replaced by a prime p, and the roles of a function f(x) and its deriva-
tive df/dx are now played by an integer a ∈ Z and its Fermat quotient
δpa=(a−ap)/p.
Inmakingourpresentationofthesetypeofoperators,wefindnobet-
ter way than discussing the p-adic numbers in detail also, and some of
the classical differential analysis on the field of p-adic numbers, empha-
sizing the aspects that give rise to the philosophy behind the arithmetic
differentialoperators.Thereaderisurgedtocontrasttheseideasatwill,
while keeping in mind that our study is neither exhaustive nor intended
to be so, and most of the time we shall content ourselves by explain-
ing the differential aspect of an arithmetic operator by way of analogy,
rather than appealing to the language of jet spaces. But even then, the
importance of these operators will be justified by their significant ap-
pearanceinnumbertheoreticconsiderations.Oneofourgoalswillbeto
illustrate how different these operators are when the ground field where
they are defined is rather coarse, as are the p-adic integers Zp that we
use.
In order to put our work in proper perspective, it is convenient to
introduce some basic facts first, and recall a bit of history. Given a
prime p, we may define the p-adic norm (cid:3) (cid:3)p over the field of rational
numbersQ.Thecompletionoftherationalsinthemetricthatthisnorm
induces is the field Qp of p-adic numbers, and this field carries a non-
Archimedeanp-adicnormextendingtheoriginalp-adicnormonQ.This
isthedescriptionofQpasgivenbyK.Henselcirca1897(see,forinstance,
1
2 Introduction
[28]). Two decades later, A. Ostrovski [39] proved that any nontrivial
normonQisequivalenttoeithertheEuclideannormortoap-adicnorm
forsomeprimep.Inthisway,therearosethephilosophicalprinciplethat
treats the real numbers and all of the p-adic numbers on equal footing.
In the twentieth century, the p-adic numbers had a rich history. We
briefly mention some major results.
The idea that studying a question about the field Q can be answered
by putting together the answers to the same question over the fields R
and Qp for all ps was born with the Hasse–Minkowski’s theorem. This
states that a quadratic form over Q has a nontrivial zero in Qn if, and
only if, it has a nontrivial zero in Rn and a nontrivial zero in Qn for
p
each prime p. This theorem was proven by Hasse in his thesis around
1921 [27], the problem having been proposed to him by Hensel who had
proventhen=2caseafewyearsearlier.Suchaprinciplefailsforcubics.
Thedevelopmentabovecameafterseveralinterestingresultsthatpre-
cededtheintroductionofthep-adicnumbers.Thelocal-to-globalprinci-
ple embodied in the Hasse–Minkowski theorem had a precedent in Rie-
mannian geometric, since as recently as 1855, Bonnet had proved that
if the curvature of a compact surface was bounded below by a positive
constant,thenitsdiameterwasboundedabovebyaquantitydepending
only on the said constant. Strictly on the arithmetic side of things, in
the seventeenth century J. Bernoulli defined the(cid:3)Bernoulli numbers Bk,
the coefficients in the expansion et/(et −1) = k(cid:3)Bktk/k!, used them
to compute closed-form expressions for the sums m jn, and devel-
j=0
oped several identities that these numbers satisfy. A century later, the
Bernoulli numbers were used by Euler to show heuristically that if ζ is
(cid:3)
theRiemmanzetafunction,thenζ(1−k)= ∞n=11/n1−k =−Bk/k for
any integer k ≥2. In the mid nineteenth century, Riemman proved that
(cid:3)
ζ(s) = ∞ 1/ns is a meromorphic function on the complex plane C,
n=1
giving Euler’s argument complete sense. Further, he used the Gamma
(cid:4) (cid:5)
functiontodefineΛ(s)=π−s2Γ 2s ζ(s)andprovedthefunctionalequa-
tion Λ(s) = Λ(1−s). The intimate relationship between the Bernoulli
numbers and the values of ζ(s) at negative integers led to the idea that
these numbers have profound arithmetical properties, a fact discovered
by Kummer in his work on Fermat’s last theorem circa 1847. The ideal
class group of Q(ζN), ζN a primitive N-th root of unity, is the quotient
of the fractional ideals of Q(ζN) by the set of principal ideals, and it
turnsouttobeagroupoffiniteorderhN withrespecttoidealmultipli-
cation. A prime p is said to be regular if p(cid:2)hp, and irregular otherwise.
Kummer proved that p is regular if, and only if, p does not divide the