A zig-zag conjecture and local constancy for Galois representations

Abstract

We make a zig-zag conjecture describing the reductions of irreducible crystalline two-dimensional representations of $G_{{\mathbb{Q}}_p}$ of half-integral slopes and exceptional weights. Such weights are two more than twice the slope mod $(p-1)$. We show that zig-zag holds for half-integral slopes at most $\frac{3}{2}$. We then explore the connection between zig-zag and local constancy results in the weight. First we show that known cases of zig-zag force local constancy to fail for small weights. Conversely, we explain how local constancy forces zig-zag to fail for some small weights and half-integral slopes at least $2$. However, we expect zig-zag to be qualitatively true in general. We end with some compatibility results between zig-zag and other results.

arXiv admin note: text overlap with arXiv:1901.01728

References in corpus (1)

• Reduction modulo p of two-dimensional crystalline representations of G_{Q_p} of slope less than three