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Séminaire de Théorie des Nombres

Modular Symbols associated to Eisenstein Series

Vinayak Vatsal

( UBC Vancouver )

Salle de Conférences

le 26 avril 2013 à 14:00

Let EE and ff be an Eisenstein series and a cusp form, respectively, of the same weight k2k\geq 2 and of the same level NN, both eigenfunctions of the Hecke operators, and both normalized so that a1=1a_1 = 1. The main result we prove is that when EE and ff are congruent mod a prime p\mathfrak{p} (which we take to be a prime of Q\overline{Q} lying over a rational prime p>2p >2), the algebraic parts of the special values L(E,χ,j)L(E,\chi ,j) and L(f,χ,j)L(f,\chi ,j) satisfy congruences mod the same prime. More explicitly, we prove that, under certain conditions, \[ \frac{\tau (\bar{\chi })L(f,\chi ,j)}{(2 \pi i)^{j-1}\Omega _f^{\text{sgn}(E)}} \equiv \frac{\tau (\bar{\chi })L(E,\chi ,j)}{(2 \pi i)^{j}\Omega _E} \pmod{\mathfrak{p}} \] where the sign of EE is ±1\pm 1 depending on EE, and Ωfsgn(E)\Omega _f^{\text{sgn}(E)} is the corresponding canonical period for ff. Also, χ\chi is a primitive Dirichlet character of conductor mm, τ(χˉ)\tau (\bar{\chi }) is a Gauss sum, and jj is an integer with 0<j<k0< j< k such that (1)j1χ(1)=sgn(E)(-1)^{j-1}\cdot \chi(-1) = \text{sgn}(E). Finally, ΩE\Omega _E is a p\mathfrak{p}-adic unit which is independent of χ\chi and jj. This is a generalization of earlier results of Stevens and Vatsal for weight k=2k=2. The main point is the construction of a modular symbol associated to an Eisenstein series.