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Local-global principle for certain biquadratic normic bundles

Yang Cao, Yongqi Liang (2014)

Acta Arithmetica

Let X be a proper smooth variety having an affine open subset defined by the normic equation N k ( a , b ) / k ( x ) = Q ( t , . . . , t ) ² over a number field k. We prove that: (1) the failure of the local-global principle for zero-cycles is controlled by the Brauer group of X; (2) the analogue for rational points is also valid assuming Schinzel’s hypothesis.

Minimal resolution and stable reduction of X 0 ( N )

Bas Edixhoven (1990)

Annales de l'institut Fourier

Let N 1 be an integer. Let X 0 ( N ) be the modular curve over Z , as constructed by Katz and Mazur. The minimal resolution of X 0 ( N ) over Z [ 1 / 6 ] is computed. Let p 5 be a prime, such that N = p 2 M , with M prime to p . Let n = ( p 2 - 1 ) / 2 . It is shown that X 0 ( N ) has stable reduction at p over Q [ p n ] , and the fibre at p of the stable model is computed.

Models of group schemes of roots of unity

A. Mézard, M. Romagny, D. Tossici (2013)

Annales de l’institut Fourier

Let 𝒪 K be a discrete valuation ring of mixed characteristics ( 0 , p ) , with residue field k . Using work of Sekiguchi and Suwa, we construct some finite flat 𝒪 K -models of the group scheme μ p n , K of p n -th roots of unity, which we call Kummer group schemes. We carefully set out the general framework and algebraic properties of this construction. When k is perfect and 𝒪 K is a complete totally ramified extension of the ring of Witt vectors W ( k ) , we provide a parallel study of the Breuil-Kisin modules of finite flat models...

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