Antisymmetric galaxy cross-correlations as a cosmological probe
  The auto-correlation between two members of a galaxy population is symmetric
under the interchange of the two galaxies being correlated. The
cross-correlation between two different types of galaxies, separated by a
vector $\bf{r}$, is not necessarily the same as that for a pair separated by
$-\bf{r}$. Local anisotropies in the two-point cross-correlation function may
thus indicate a specific direction which when mapped as a function of position
trace out a vector field. This vector field can then be decomposed into
longitudinal and transverse components, and those transverse components written
as positive- and negative-helicity components. A locally asymmetric
cross-correlation of the longitudinal type arises naturally in halo clustering,
even with Gaussian initial conditions, and could be enhanced with local-type
non-Gaussianity. Early-Universe scenarios that introduce a vector field may
also give rise to such effects. These antisymmetric cross-correlations also
provide a new possibility to seek a preferred cosmic direction correlated with
the hemispherical power asymmetry in the cosmic microwave background and to
seek a preferred location associated with the CMB cold spot. New ways to seek
cosmic parity breaking are also possible.
