  If in addition to the standard model fields, a new pseudoscalar field that
couples to hypercharge topological number density, the hypercharge axion,
exists, it can be produced in colliders in association with photons or Z
bosons, and detected by looking for its decay into photons or Z's. For a range
of masses below a TeV and coupling above a fraction of 1/TeV, existing data
from LEP II and the Tevatron can already put interesting constraints, and in
future colliders accessible detection range is increased significantly. The
hypercharge axion can help in explaining the matter-antimatter asymmetry in the
universe.
