P-ADIC HEIGHTS of HEEGNER POINTS on SHIMURA CURVES by Daniel Disegni
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p-ADIC HEIGHTS OF HEEGNER POINTS ON SHIMURA CURVES by Daniel Disegni Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Graduate School of Arts and Sciences COLUMBIA UNIVERSITY 2013 c 2013 Daniel Disegni All rights reserved ABSTRACT p-adic Heights of Heegner points on Shimura curves Daniel Disegni Let f be a primitive Hilbert modular form of weight 2 and level N for the totally real field F , and let p - N be an odd rational prime such that f is ordinary at all primes } p. When E is a CM extension of F of relative j discriminant ∆ prime to N p, we give an explicit construction of the p- adic Rankin–Selberg L-function Lp (fE , ) and prove that when the sign of · its functional equation is 1, its central derivative is given by the p-adic − height of a Heegner point on the abelian variety A associated to f . This p-adic Gross–Zagier formula generalises the result obtained by Perrin-Riou when F = Q and N satisfies the so-called Heegner condition. We deduce applications to both the p-adic and the classical Birch and Swinnerton-Dyer conjectures for A. Table of Contents Introduction ............................................ 1 The p-adic Rankin–Selberg L-function .............. 1 Heegner points on Shimura curves and the main theorem ................................................ 4 Applications to the conjecture of Birch and Swinnerton- Dyer .......................................... 6 Plan of the proof .................................. 12 Notation .......................................... 13 Part I. p-adic L-function and measures . 16 1. p-adic modular forms ................................ 16 1.1. Hilbert modular forms ........................ 16 1.2. Fourier expansion .............................. 18 1.3. Operators acting on modular forms ............ 21 1.4. Fourier coefficients of old forms ................ 26 1.5. The functional L .............................. 28 f0 2. Theta measure ........................................ 29 2.1. Weil representation ............................ 30 2.2. Theta series .................................... 31 2.3. Theta measure ................................ 34 2.4. Fourier expansion of the theta measure / I . 36 2.5. Fourier expansion of the theta measure / II . 38 3. Eisenstein measure .................................... 39 3.1. Eisenstein series ................................ 39 3.2. Fourier expansion of the Eisenstein measure . 41 4. The p-adic L-function ................................ 47 4.1. Rankin–Selberg convolution .................... 47 4.2. Convoluted measure and the p-adic L-function . 48 4.3. Toolbox ...................................... 49 4.4. Interpolation property ........................ 51 4.5. Fourier expansion of the measure .............. 53 Part II. Heights ........................................ 57 5. Generalities on p-adic heights and Arakelov theory . 57 5.1. The p-adic height pairing ...................... 57 5.2. p-adic Arakelov theory – local aspects .......... 61 5.3. p-adic Arakelov theory – global aspects . 64 i 6. Heegner points on Shimura curves .................... 67 6.1. Shimura curves ................................ 67 6.2. Heegner points ................................ 69 6.3. Hecke action on Heegner points ................ 72 7. Heights of Heegner points ............................ 75 7.1. Local heights at places not dividing p . 76 7.2. Local heights at p .............................. 79 Part III. Main theorem and consequences . 84 8. Proof of the main theorem ............................ 84 8.1. Basic case ...................................... 84 8.2. Reduction to the basic case .................... 86 9. Periods and the Birch and Swinnerton-Dyer conjecture ................................................ 88 9.1. Real periods .................................. 88 9.2. Quadratic periods .............................. 91 References .............................................. 92 Afterword (for the layman) ............................ 96 ii Acknowledgments I am grateful to my advisor Professor Shou-Wu Zhang for suggesting this area of research and for his support and encouragement; and to Amnon Besser, Luis Garcia Martinez, Yifeng Liu, Jeanine Van Order, Hui Xue and Shou-Wu Zhang for useful conversations or correspondence related to this work. During these years I have learned a lot especially from Professors Do- rian Goldfeld, Aise Johan de Jong, Eric Urban, Shou-Wu Zhang and Wei Zhang, as well as from many discussions with other faculty members and fellow Ph.D. students; while the staff at the Columbia Department of Math- ematics has greatly contributed to the smooth and pleasant running of my doctorate. It is a pleasure to thank them all here. This thesis is the natural offspring, or, to use a more mathematical meta- phor, the fibre product, of the works of Perrin-Riou [30] and Zhang [45–47] – the ‘base’ being, of course, the pioneering work of Gross–Zagier [13]. My debt to their ideas cannot be underestimated and will be obvious to the reader. Last but not least, I would like to warmly thank all my family and friends, near and far, for all their friendship and support. This work is dedicated to them. iii p-ADIC HEIGHTS OF HEEGNER POINTS ON SHIMURA CURVES 1 Introduction In this work we generalise Perrin-Riou’s p-adic analogue of the Gross– Zagier formula [30] to totally real fields, in a generality similar to the work of Zhang [45–47]. We describe here the main result and its applications. The p-adic Rankin–Selberg L-function. — Let f be a primitive Hilbert modular form of parallel weight 2, level N and trivial character for the to- tally real field F of degree g and discriminant DF . Let p be a rational prime coprime to 2N. Fix embeddings ι and ιp of the algebraic closure Q of F 1 into C and Qp respectively. We assume that f is ordinary at p, that is, that th for each prime } of F dividing p, the coefficient a(f ,}) of the } Hecke O polynomial of f 2 P ,f (X ) = X a(f ,})X + N} } − is a p-adic unit for the chosen embedding; we let α} = α}(f ) be the unit root of P},f . Let E Q be a CM (that is, quadratic and purely imaginary) extension of ⊂ F of relative discriminant ∆ coprime to N p, let " = "E F : F ×=F × 1 = A ! f± g be the associated Hecke character and N = NE=F be the relative norm. If : E ×=E × Q× W A ! p-ADIC HEIGHTS OF HEEGNER POINTS ON SHIMURA CURVES 2 is a finite order Hecke character(1) of conductor f, the Rankin–Selberg L- function L(fE , , s) is the entire function defined for (s) > 3=2 by W < a f , m r m N∆( ) X ( ) ( ) L fE , , s L W " F ,2s 1 W , ( ) = ( A× ) s W W j − m Nm where N f , r m P a (the sum running over all ∆( ) = ∆ ( ) ( ) = N(a)=m ( ) W W W nonzero ideals of E ) and O N∆( ) X s L W " , s " m m Nm− . ( F ) = ( ) ( ) O W j (m,N∆( ))=1 W W This L-function admits a p-adic analogue (§4). Let E 0 be the maximal 1 abelian extension of E unramified outside p, and E the maximal Zp -extension 1 of E. Then = Gal(E =E) is a direct factor of finite, prime to p index in G 1 0 = Gal(E 0 =E). (It has rank 1 + δ + g over Zp , where δ is the Leopoldt G 1 defect of F .) Theorem A.— There exists a bounded Iwasawa function Lp (fE ) Qp 0 2 JG K satisfying the interpolation property 1=2 τ( )N(∆( )) Vp (f , ) (D) Lp (fE )( ) = W W W W L(fE , ,1), W αN(f)Ωf W for all finite order characters of 0 which are ramified exactly at the places W G (2) 1 w p. Here both sides are algebraic numbers , = − and j W W 2 g Ωf = (8π ) f , f N h i (1)We will throughout use the same notation for a Hecke character, the associated ideal character, and the associated Galois character. (2) 1 1 By a well-known theorem of Shimura [35]. They are compared via ι−p and ι− . 1 p-ADIC HEIGHTS OF HEEGNER POINTS ON SHIMURA CURVES 3 with , N the Petersson inner product (1.1.2); τ( ) is a Gauß sum, Vp (f , ) 〈· ·〉 v WN f W is a product of Euler factors and Q }( ( )). αN(f) = } p α} j g The restriction of Lp (fE ) to satisfies a functional equation with sign ( 1) "(N) G − c relating its values at to its values at − , where c is the nontrivial automor- W W c phism of E=F and (σ) = (cσc). W W This is essentially a special case of results of Panchishkin [28] and Hida [15]; we reprove it entirely here (see §4) because the precise construction of Lp (fE ) will be crucial for us. It is achieved, using a technique of Hida and Perrin-Riou, via the construction of a convolution Φ of Eisenstein and theta measures on 0 valued in p-adic modular forms, giving an analogue of the G kernel of the classical Rankin–Selberg convolution method. The approach we follow is adelic; one novelty introduced here is that the theta measure is constructed via the Weil representation, which seems very natural and would generalise well to higher rank cases. On the other hand, Manin [25] and Dabrowski [11] have constructed a p-adic L-function Lp (f , ) as an analogue of the standard L-function L(f , s). · It is a locally analytic function on the p-adic Lie group of continuous char- acters χ : 0 Cp , where 0 is the Galois group of the maximal abelian GF ! GF extension of F unramified outside p; it satisfies the interpolation property !2 τ(χ ) Y 1 L(f ,χ ,1) L f ,χ 1 p ( ) = + αP } p − α} Ωf j }-P for all finite order characters χ of conductor P which are trivial at infinity. (Here + is a suitable period, cf. §9.1.) Ωf p-ADIC HEIGHTS OF HEEGNER POINTS ON SHIMURA CURVES 4 The corresponding formula for complex L-functions implies a factorisa- tion Ω+Ω+ f f" Lp (fE ,χ N) = Lp (f ,χ )Lp (f ,χ ), ◦ 1=2 " DE− Ωf where f" is the form with coefficients a(f", m) = "(m)a(f , m) and DE = N(∆).