  Decay of regular static spherically symmetric solutions in the SU(2)
Yang-Mills-dilaton (YMd) system of equations under the independent excitation
of their unstable eigenmodes has been studied self-consistently in the
nonlinear regime. The considered regular YMd solutions form a discrete family
and can be parametrised by the number $N=1,2,3,4...$ of their unstable
eigenmodes in linear approximation. We have obtained strong numerical evidences
in favour of the following statements: i) all static YMd solutions are distinct
local threshold configurations, separating blowup and scattering solutions; ii)
the main unstable eigenmodes are only those responsible for the
blowup/scattering alternative; iii) excitation of higher unstable eigenmodes
always leads to finite-time blowup; iv) the decay of the lowest N=1 static YMd
solution via excitation of its unique unstable mode is an exceptional case
because the resulting waves propagate as a whole without energy dispersion
revealing features peculiar to solitons. Applications of the obtained results
to Type-I gravitational collapse of massless fields are briefly discussed.
