  A rainbow-ladder truncation of QCD's Dyson-Schwinger equations is used to
calculate rho- and phi-meson valence-quark (twist-two parton) distribution
amplitudes (PDAs) via a light-front projection of their Bethe-Salpeter wave
functions, which possess S- and D-wave components of comparable size in the
meson rest frame. All computed PDAs are broad concave functions, whose dilation
with respect to the asymptotic distribution is an expression of dynamical
chiral symmetry breaking. The PDAs can be used to define an ordering of
valence-quark light-front spatial-extent within mesons: this size is smallest
within the pion and increases through the perp-polarisation to the
parallel-polarisation of the vector mesons; effects associated with the
breaking of SU(3)-flavour symmetry are significantly smaller than those
associated with altering the polarisation of vector mesons. Notably, the
predicted pointwise behaviour of the rho-meson PDAs is in quantitative
agreement with that inferred recently via an analysis of diffractive
vector-meson photoproduction experiments.
