  Most recombination-style jet algorithms cluster soft gluons in a complex way.
This leads to correlations in the soft gluon phase space and introduces
logarithmic corrections to jet cross sections. The leading Abelian clustering
logarithms occur at least at next-to leading logarithm (NLL) in the exponent of
the distribution, and we show that new clustering effects contributing at NLL
likely arise at each order. Therefore we find that it is unlikely that
clustering logs can be resummed to NLL. Clustering logarithms make the anti-kT
algorithm theoretically preferred, for which they are power suppressed. They
can arise in Abelian and non-Abelian terms, and we calculate the Abelian
clustering logarithms at two loops for the jet mass distribution using the
Cambridge/Aachen and kT algorithms, including jet radius dependence, which
extends previous results. We find that previously identified logarithms from
clustering effects can be naturally thought of as a class of non-global
logarithms (NGLs), which have traditionally been tied to non-Abelian
correlations in soft gluon emission.
