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arXiv 1504.07618math.NT
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计算附在椭圆曲线上的伽罗瓦表示的图像

Computing images of Galois representations attached to elliptic curves

Andrew V. Sutherland

摘要:

设E是数域K上不含复乘(CM)的椭圆曲线,G_E(ell)是K的绝对伽罗瓦群在E的ell-挠子群上的作用所诱导的伽罗瓦表示的象.本文提出了两种通过Frobenius元素的采样图像同时确定所有素数e11直到局部共轭的G_E(e11)的概率算法:一种是Las Vegas型算法,另一种是Monte Carlo算法。它们确定了G_E(ell)至多为GL_2(Z/ell Z)的两个具有相同半化简的子群的同构共轭类之一,每一个同构共轭类都出现在与E同构的椭圆曲线上.在GRH下,它们的运行时间在积分Weierstrass方程E的位大小n中是多项式的,并且对于我们的Monte Carlo算法,在n中是准线性的。我们将我们的算法应用于Cremona表和Stein-Watkins数据库中的非CM椭圆曲线,约1.4亿条导体曲线,最多可达10^10,从而获得了E/Q无CM时产生的63个例外Galois像G_E(ell)的完全列表。在这个猜想下,我们确定了二次域上非CM椭圆曲线的160个具有有理j-不变量的例外Galois象G_E(ell)的完整列表.我们还给出了例外伽罗瓦图像的例子,出现非CM椭圆曲线在二次域只有当j-不变量是不合理的。

英文摘要:

Let E be an elliptic curve without complex multiplication (CM) over a number field K, and let G_E(ell) be the image of the Galois representation induced by the action of the absolute Galois group of K on the ell-torsion subgroup of E. We present two probabilistic algorithms to simultaneously determine G_E(ell) up to local conjugacy for all primes ell by sampling images of Frobenius elements; one is of Las Vegas type and the other is a Monte Carlo algorithm. They determine G_E(ell) up to one of at most two isomorphic conjugacy classes of subgroups of GL_2(Z/ell Z) that have the same semisimplification, each of which occurs for an elliptic curve isogenous to E. Under the GRH, their running times are polynomial in the bit-size n of an integral Weierstrass equation for E, and for our Monte Carlo algorithm, quasi-linear in n. We have applied our algorithms to the non-CM elliptic curves in Cremona's tables and the Stein--Watkins database, some 140 million curves of conductor up to 10^10, thereby obtaining a conjecturally complete list of 63 exceptional Galois images G_E(ell) that arise for E/Q without CM. Under this conjecture we determine a complete list of 160 exceptional Galois images G_E(ell) the arise for non-CM elliptic curves over quadratic fields with rational j-invariants. We also give examples of exceptional Galois images that arise for non-CM elliptic curves over quadratic fields only when the j-invariant is irrational.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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