  We show that the Artin representation on concordance classes of string links
induces a well-defined epimorphism modulo order n twisted Whitney tower
concordance, and that the kernel of this map is generated by band sums of
iterated Bing-doubles of any string knot with nonzero Arf invariant. We also
continue J. Levine's work [20, 21, 22] comparing two filtrations of the group
of homology cobordism classes of 3-dimensional homology cylinders, one defined
in terms of an Artin-type representation (the Johnson filtration) and one
defined using clasper surgery (the Goussarov-Habiro filtration). In particular,
the associated graded groups are completely classified up to an unknown
2-torsion summand for the Goussarov-Habiro filtration, for which we obtain an
upper bound, in a precisely analogous fashion to the classification of the
Whitney tower filtration of link concordance.
