Abstract
Clozel, Harris and Taylor have recently proved a modularity lifting theorem of the following general form: if \(\rho \) is an \(\ell \)-adic representation of the absolute Galois group of a number field for which the residual representation \(\overline{\rho }\) comes from a modular form then so does \(\rho \). This theorem has numerous hypotheses; a crucial one is that the image of \(\overline{\rho }\) must be “big,” a technical condition on subgroups of \(\mathrm {GL}_n\). In this paper we investigate this condition in compatible systems. Our main result is that in a sufficiently irreducible compatible system the residual images are big at a density one set of primes. This result should make some of the work of Clozel, Harris and Taylor easier to apply in the setting of compatible systems.
A. Snowden was partially supported by NSF fellowship DMS-0902661. A. Wiles was supported by an NSF grant.
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An argument similar to the one given here appeared in [1].
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Acknowledgements
We would like to thank Thomas Barnet-Lamb, Bhargav Bhatt, Brian Conrad, Alireza Salehi Golsefidy and Jiu-Kang Yu for useful discussions. We would also like to thank an anonymous referee for some helpful comments.
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Snowden, A., Wiles, A. (2016). Bigness in Compatible Systems. In: Loeffler, D., Zerbes, S. (eds) Elliptic Curves, Modular Forms and Iwasawa Theory. JHC70 2015. Springer Proceedings in Mathematics & Statistics, vol 188. Springer, Cham. https://doi.org/10.1007/978-3-319-45032-2_13
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DOI: https://doi.org/10.1007/978-3-319-45032-2_13
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