Abstract. The aim of this paper is to derive explicitly a connection between the Zagier elliptic trilogarithm and Mahler measures of certain families of three-variable polynomials defining K3 surfaces. In addition, we prove some linear relations satisfied by the elliptic trilogarithm evaluated at torsion points on elliptic curves. The latter result can be viewed as a higher dimensional analogue of exotic relations of the elliptic dilogarithm.
IntroductionFor m ∈ N, the classical m th polylogarithm function is defined byOne can obtain a multivalued function on C−{0, 1} from Li m (z) by extending it analytically. There are many versions of higher polylogarithms in the literature, including the followingwhereand B k is the k th Bernoulli number (B 0 = 1, B 1 = −1/2, B 2 = 1/6, B 3 = 0, . . .). It can be extended to a continuous function on P 1 (C) by the functional equationThe dilogarithm function and the function D(z) have been studied extensively and are known to satisfy several interesting properties. They are also found to have fruitful applications in algebraic K-theory and other related areas (see, for example, [23] where |z| ≤ 1. Now let us consider an "averaged" version of the function D(z), which will be described below. Let E be an elliptic curve defined over C. Then there exist τ ∈ H := {τ ∈ C | Im(τ ) > 0} and isomorphismswhere Λ = Z + Zτ , and ℘ Λ denotes the Weierstrass ℘-function. Using the transformations above, Bloch [4] defined the elliptic dilogarithmwhere q = e 2πiτ and x = e 2πiu is the image of P in C × /q Z . ( . It can be shown that Re(R E ) = D E , and that − Im(R E ) is the real-valued function given by3 log 2 |q|B 3 log |x| log |q| , where J(x) = log |x| log |1 − x|, and B n (X) denotes the n th Bernoulli polynomial. Similar to D E , the function J E is well-defined and invariant under x → qx. We can also extend R E , D E , and J E by linearity to the group of divisors on E(C).Recall that for any nonzero Laurent polynomial P ∈ C[X ±1 1 , . . . , X ±1 n ], the Mahler measure of P is defined byLet us denote m 2 (t) := 2m(x + x −1 + y + y −1 + t 1/2 ), m 3 (t) := 3m(x 3 + y 3 + 1 − t 1/3 xy).
THE ELLIPTIC TRILOGARITHM AND MAHLER MEASURES OF K3 SURFACES 3Boyd [6] and Rodriguez Villegas [16] verified numerically that for many values of t ∈ Z, m 2 (t) and m 3 (t) appear to be of the formwhere E is the elliptic curve over Q defined by the zero locus of x + x −1 + y + y −1 + t 1/2 or x 3 + y 3 + 1 − t 1/3 xy, depending on j, and A ∼ Q B means B = cA for some c ∈ Q. (Note that by the functional equation of L(E, s), one has |L ′ (E, 0)| = (2π) −2 N E L(E, 2), where N E is the conductor of E.) However, most of these conjectured formulas have remained unproved. Rodriguez Villegas [16] proved some of these formulas when the corresponding elliptic curves have complex multiplication by showing first that m 2 (t) and m 3 (t) can be expressed in terms of Eisenstein-Kronecker series. Afterward, Lalín and Rogers [10] verified that for every t ∈ C, if E is the elliptic curve defined by x + x −1 + y + y −1 + ...