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Universal deformation rings need not be complete intersections
Journal article   Peer reviewed

Universal deformation rings need not be complete intersections

Frauke M Bleher and Ted Chinburg
Comptes Rendus Mathematique, Vol.342(4), pp.229-232
2006
DOI: 10.1016/j.crma.2005.12.006
url
https://www.numdam.org/item/10.1016/j.crma.2005.12.006.pdfView
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Abstract

We answer a question of M. Flach by showing that there is a linear representation of a profinite group whose universal deformation ring is not a complete intersection. We show that such examples arise in arithmetic in the following way. There are infinitely many real quadratic fields F for which there is a mod 2 representation of the Galois group of the maximal unramified extension of F whose universal deformation ring is not a complete intersection. To cite this article: F.M. Bleher, T. Chinburg, C. R. Acad. Sci. Paris, Ser. I 342 (2006).

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