Abstract

Consider the Drinfeld modular curve \(X_{0}(\mathfrak {p})\) for Open image in new window a prime ideal of \(\mathbb {F}_{q}[T]\). It was previously known that if j is the j-invariant of a Weierstrass point of \(X_{0}(\mathfrak {p})\), then the reduction of j modulo Open image in new window is a supersingular j-invariant. In this paper, we show the converse: Every supersingular j-invariant is the reduction modulo Open image in new window of the j-invariant of a Weierstrass point of \(X_{0}(\mathfrak {p})\).

Highlights

  • Introduction and statement of resultsGiven a smooth irreducible projective curve of genus g ≥ 2 defined over an algebraically closed field of characteristic 0, we say that a point P on X is a Weierstrass point if there is a nonzero rational function F on X with a pole of order less than or equal to g at P and regular everywhere else

  • In Section ‘Hyperderivatives and quasimodular forms’, we introduce Drinfeld quasimodular forms and some differentials operators that are needed in the definition of the Drinfeld modular form W (z)

  • We prove some elementary results concerning the action of these operators on Drinfeld modular forms

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Summary

Drinfeld modular curves

We turn our attention to Drinfeld modular curves and to the family X0(p). The map f → f (z)dz identifies the space of double cusp forms of weight 2 and type 1 for to the space of regular differential forms on X. From this theorem, it follows that the dimension of the space of double cusp forms of weight 2 and type 1 for is g , where g is the genus of the curve X. It follows by a standard argument that all spaces of Drinfeld modular forms of a fixed weight and type for a congruence group are finite dimensional. The space of Drinfeld double cusp forms of weight 2 and type 1 for 0(p) has a basis of forms with integral coefficients.

Expansions at the cusps
Drinfeld quasimodular forms
Higher derivatives
Because of the correspondence between the space
We compute
We first investigate the number
Recall from
And so
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