Monday, 27 November 2006

nt.number theory - Mod l local Galois representations (l different from p)

My question is referred to the statement and proof of Prop. 2.4 of Diamond's
article "An extension of Wiles' Results", in Modular Forms and Fermat Last
Theorem, page 479.



More precisely: fix l and p two distinct primes, with l odd. Let sigma be an
irreducible, continuous, degree 2 representation of the absolute Galois group
Gp of Qp, with coefficients in k, an algebraic closure of the finite
field with l elements.
Proposition 2.4 states that if the restriction of sigma to the inertia
subgroup of Gp is irreducible and p is odd, then sigma is isomorphic to the
representation induced from a character of the Galois group of a quadratic
ramified extension M of Qp.
The proof given works if the restriction of sigma to the wild inertia of Gp is
reducible (I think there's a typo in the first line of the proof). What if
sigma is irreducible on wild inertia (and p is always odd)? It seems to me that this case is not covered in the proof of the Proposition, but maybe I'm not seeing something obvious.. If such a representation exists, it cannot be induced from a quadratic extension M as above, so how does it fit in the description given by the Proposition? Can one say something about such a representation (for example something about its projective image?).



Thanks

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