Abstract
Let p be a prime number. Mazur proved that a geometrically maximal unramified abelian covering of \(X_0(p)\) over \(\mathbb {Q}\) is given by the Shimura covering \(X_2(p) \rightarrow X_0(p)\), that is, a unique subcovering of \(X_1(p) \rightarrow X_0(p)\) of degree \(N_p := (p-1)/\gcd (p-1, 12)\). In this short paper, we show that a geometrically maximal abelian covering \(X_2'(p) \rightarrow X_0(p)\) of \(X_0(p)\) over \(\mathbb {Q}\) unramified outside cusps is cyclic of degree \(2N_p\). The main ingredient for the construction of \(X_2'(p)\) is the generalized Dedekind eta functions.
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References
Katz, N.M., Lang, S.: Finiteness theorems in geometric classfield theory. Enseign. Math. (2) 27(3–4), 285–319 (1981). With an appendix by Kenneth A, Ribet (1982)
Kubert, D.S., Lang, S.: Modular units. Grundlehren der Mathematischen Wissenschaften [Fundamental Principles of Mathematical Science], vol. 244. Springer, New York (1981)
Mazur, B.: Modular curves and the Eisenstein ideal. Inst. Hautes Études Sci. Publ. Math. 47, 33–186 (1978), 1977
Schoeneberg, B.: Elliptic Modular Functions: An Introduction. Springer, New York: Translated from the German by J. R. Smart and E. A, Schwandt, Die Grundlehren der mathematischen Wissenschaften, Band 203 (1974)
Serre, J.-P.: Groupes algébriques et corps de classes. Publications de l’institut de mathématique de l’université de Nancago, VII. Hermann, Paris (1959)
Serre, J.-P.: Local Fields. Graduate Texts in Mathematics, 67. Springer, New York (1979)
Tate, J.: Les conjectures de Stark sur les fonctions \(L\) d’Artin en \(s=0\), Volume 47 of Progress in Mathematics. Birkhäuser Boston, Inc., Boston (1984). Lecture notes edited by Dominique Bernardi and Norbert Schappacher
Yang, Y.: Transformation formulas for generalized Dedekind eta functions. Bull. Lond. Math. Soc. 36(5), 671–682 (2004)
Acknowledgements
The first author would like to thank Masataka Chida and Fu-Tsun Wei for fruitful discussion. He is partially supported by JSPS KAKENHI Grant (18K03232). The second author was partially supported by Grant 106-2115-M-002-009-MY3 of the Ministry of Science and Technology, Republic of China (Taiwan). The authors would like to thank the anonymous referee for the detailed comments.
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Yamazaki, T., Yang, Y. Maximal abelian extension of \(X_0(p)\) unramified outside cusps. manuscripta math. 162, 441–455 (2020). https://doi.org/10.1007/s00229-019-01136-7
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DOI: https://doi.org/10.1007/s00229-019-01136-7