What is varpi in Zhang's notation?

Question

In his video from this summer at the IHES on bounded gaps between primes, T.Tao uses the $\varpi$ notation as shown here :

When asked what his notation means in this context, he answers that he follows Zhang's notation. Another person from the audience tells the others that they would call it $\epsilon$ (epsilon), which I guess is some kind of French equivalent (it's at the IHES after all) of $\varpi$.

Upon searching on google, all I found was riemann's varpi function, which does not seem to be what is used here.

What is, in this context, $\varpi$ ?

Answer 1

I don't know the subject at all, but in Zhang's paper "Bounded gaps between primes" (which can be googled) I find this excerpt:

Let $\varpi>0$ be a small constant. If $$ D=x^{1/4+\varpi} \tag{2.5} $$ and $k_0$ is sufficiently large in terms of $\varpi$, then ...

This fits the audience member's assertion that it would usually be called $\varepsilon$.