Abstract
The Galois representations associated to weight 1 eigenforms over \(\bar{\mathbb {F}}_{p}\) are remarkable in that they are unramified at \(p\), but the effective computation of these modular forms presents challenges. One complication in this setting is that a weight 1 cusp form over \(\bar{\mathbb {F}}_{p}\) need not arise from reducing a weight 1 cusp form over \(\bar{\mathbb {Q}}\). In this article we propose a unified Hecke stability method for computing spaces of weight 1 modular forms of a given level in all characteristics simultaneously. Our main theorems outline conditions under which a finite-dimensional Hecke module of ratios of modular forms must consist of genuine modular forms. We conclude with some applications of the Hecke stability method that are motivated by the refined inverse Galois problem.
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References
Bergeron, N., Venkatesh, A.: The asymptotic growth of torsion homology for arithmetic groups. J. Inst. Math. Jussieu 12, 391–447 (2012)
Bröker, R., Lauter, K., Sutherland, A.V.: Modular polynomials via isogeny volcanoes. Math. Comp. 81, 1201–1231 (2012)
Buhler, J.P.: Icosahedral Galois Representations. Springer, Berlin (1978)
Buzzard, K.: Computing weight one modular forms over \(\mathbb{C}\) and \(\bar{\mathbb{F}}_{p}\). In: Böckle, G., Wiese, G. (eds.) Proceedings of the Summer School and Conference, “Computations with Modular Forms,” pp. 129–146. Springer, Heidelberg (2012)
Bruin, P.J.: Modular Curves, Arakelov Theory, Algorithmic Applications. Ph.D. Thesis, University of Leiden (2010)
Calegari, F., Geraghty, D.: Modularity Lifting Beyond the Taylor-Wiles Method. arXiv:1207.4224 and arXiv:1209.6293. Preprint (2012)
Calegari, F., Venkatesh, A.: Towards a Torsion Jacquet-Langlands Correspondence. arXiv:1212.3847. Preprint (2012)
Coleman, R., Voloch, J.-F.: Companion forms and Kodaira-Spencer theory. Invent. Math. 110, 263–328 (1992)
Dembélé, L.: A non-solvable Galois extension of ramified at \(2\) only. Comptes Rendus Math. 347, 111–116 (2008)
Dembélé, L., Greenberg, M., Voight, J.: Nonsolvable number fields ramified only at \(3\) and \(5\). Comp. Math. 147, 716–734 (2011)
Deligne, P.: Formes modulaires et représentations \(\ell \)-adiques. Sem. Bourbaki 355, 136–172 (1968)
Deligne, P., Serre, J.-P.: Formes modulaires de poids 1. Annales scientifiques de l’É.N.S., 4e série 7, 507–530 (1974)
Diamond, F., Shurman, J.M.: A First Course in Modular Forms. Springer, Heidelberg (2005)
Dicskon, L.E.: Linear Groups, with an Exposition of the Galois Field Theory. Teubner, Leipzig (1901)
Dieulefait, L.V.: A non-solvable extension of \(\mathbb{Q}\) unramified outside \(7\). Compos. Math. 148, 669–674 (2012)
Edixhoven, B.: “Serre’s Conjectures” in Modular Forms and Fermat’s Last Theorem. Springer, Heidelberg (1997)
Edixhoven, B.: Comparison on integral structures of modular forms of weight two, and computation of spaces of forms mod \(2\) of weight one. With appendices by Jean-François Mestre and Gabor Wiese. J. Inst. Math. Jussieu 5, 1–34 (2006)
Edixhoven, B., Couveignes, J.-M. (eds.): Computational Aspects of Modular Forms and Galois Representations. Princeton University Press, Princeton (2011)
Goren, E.Z.: Lectures on Hilbert Modular Varieties and Modular Forms. Centre de Recherches Mathématiques, Montreal (2002)
Frey, G. (ed.): On Artin’s Conjecture for Odd \(2\)-dimensional Representations. Springer, Berlin (1994)
Goren, E.Z., Lauter, K.E.: Class invariants for quartic CM fields. Annales de l’Institut Fourier 57, 457–480 (2007)
Heim, B., Murase, A.: Borcherds lifts on \({\rm Sp}_2(\mathbb{Z})\). In: Yoshinori, H., Ichikawa, T., Murase, A., Sugano, T. (eds.) Geometry and Analysis of Automorphic forms, pp. 56–76. World Scientific Publishing Co., Singapore (2009)
Jones, J.W., Roberts, D.P.: Galois number fields with small root discriminant. J. Number Theory 122, 379–409 (2007)
Jones, J.W., Roberts, D.P.: A database of number fields. LMS J. Comput. Math. 17, 595–618 (2014)
Jones, J.W., Wallington, R.Q.: Number fields with solvable Galois groups and small Galois root discriminants. Math. Comput. 81, 555–567 (2012)
Katz, N.M.: \(p\)-Adic Properties of Modular Schemes and Modular Forms. International Summer School on Modular Forms, Antwerp (1972)
Khare, C.: Serre’s modularity conjecture: the level one case. Duke Math. J. 134, 557–589 (2006)
Khare, C.: Modularity of Galois representations and motives with good reduction properties. J. Ramanujan Math. Soc. 22, 1–26 (2007)
Khare, C., Wintenberger, J.-P.: Serre’s modularity conjecture. Inv. Math. 178, 485–586 (2009)
Marshall, S., Müller, W.: On the torsion in the cohomology of arithmetic hyperbolic \(3\)-manifolds. Duke Math. J. 162, 863–888 (2013)
Mestre, J.-F.: La méthode des graphes, exemples et applications. Notes (2004)
Page, A.: Méthodes explicites pour les groupes arithmétiques. Ph.D. Thesis, Univesité de Bordeaux (2012)
Raimbault, J.: Asymptotics of analytic torsion for hyperbolic \(3\)-manifolds. arXiv:1212.3161 (2013)
Roberts, D.P.: Chebyshev covers and exceptional number fields. (2008)
Roberts, D.P.: Personal communication (November, 2013)
Schaeffer, G.J.: The Hecke stability method and ethereal forms. Ph.D. Thesis, University of California, Berkeley (2012)
Şengün, M.H.: On the integral cohomology of Bianchi groups. Exp. Math. 20, 487–505 (2011)
Serre, J.-P.: Propriétés galoisiennes des points d’ordre fini des courbes elliptiques. Invent. Math. 15, 259–331 (1972)
Serre, J.-P.: Quelques applications du théorème de densité de Chebotarev. Publ. Math. I.H.E.S 54, 123–201 (1981)
Serre, J.-P.: Minoration de discriminants. Note of October 1975. Œuvres. Volume III, pp. 1972–1984. Springer, Heidelberg (2003)
Shimura, G.: Introduction to the arithmetic theory of automorphic functions. Publication of Mathematical Society of Japan, vol. 11. Princeton University Press, Princeton (1971)
Stein, W.: Modular forms: a computational approach. Graduate studies in mathematics, vol 79. American Mathematical Society (2007)
Stein, W.: Computing with Modular Forms, Course Notes. Harvard University, Harvard (2004)
Wallington, R.Q.: Number fields with solvable Galois groups and small Galois root discriminants. Ph.D. Thesis, Arizona State University (2009)
Wiese, G.: Dihedral Galois representations and Katz modular forms. Doc. Math. 9, 123–133 (2004)
Wiese, G.: On Galois representations of weight one. Doc. Math. 19, 689–707 (2014)
Acknowledgments
The author would like to thank Akshay Venkatesh, John Voight, Kevin Buzzard, Frank Calegari, Dave Roberts, Chandrashekhar Khare, and Haruzo Hida for their input and support. The author would also like to thank the anonymous referee for their helpful comments and suggestions.
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The author was partially supported by the NSF under Grants DMS-0838697 and DMS-0854949.
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Schaeffer, G.J. Hecke stability and weight \(1\) modular forms. Math. Z. 281, 159–191 (2015). https://doi.org/10.1007/s00209-015-1477-9
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DOI: https://doi.org/10.1007/s00209-015-1477-9