Speaker
Description
We report on our computation of the eta transition form factor $\mathcal{F}_{\eta \rightarrow \gamma^* \gamma^*}$ from
twisted mass lattice QCD at physical quark masses and at a single lattice spacing.
On the lattice, we have access to a broad range of (space-like) photon momenta and
can therefore produce data complementary to the experimentally accessible singly
virtual case. We use the form factor to determine the eta pole contribution to the
hadronic light-by-light scattering in the muon $g-2$, leading to a first lattice QCD estimate. Our estimate of $a_\mu^{\eta-pole}$ obtained at a single lattice spacing achieves an
accuracy of below 40%. Since so far there are no determinations of this contribution
from first principles, even such a crude determination is interesting from a
phenomenological point of view.
