Let $k$ be a (complete) discretely valued field and $\ell$ a Galois extension of $k$, possibly infinite. The Galois group $\Gamma=\text{Gal}(\ell/k)$ of $\ell$ over $k$ admits a descreasing, $\mathbb R_{\geq0}$-indexed filtration $(\Gamma^r)_{r\geq0}$ called the *ramification filtration* (in upper numbering). Say $r$ is a *jump* in the filtration if $\bigcup_{s>r}\Gamma^s\neq\Gamma^r$.

It is well known that if $\ell/k$ is an abelian extension then the jumps in the filtration are integers. I'm curious about what is known when $\ell$ is a separable closure of $k$.

**Question**: What are the jumps in the ramification filtration on the absolute Galois group of $k$?

Of course, this is only interesting when the residue characteristic of $k$ is positive. There will be jumps at integers and non-integers in general.

**Comment**: I remember coming across a paper once that answered this question. The answer I remember is that there were many jumps: they were dense in the positive reals, something like that. But I have been unable to find this paper again. I would be indebted to anyone who can locate it.