Resumo
It is shown that the recently introduced positivity and causality preserving
string-local quantum field theory (SLFT) resolves most No-Go situations in
higher spin problems. This includes in particular the Velo-Zwanziger causality
problem which turns out to be related in an interesting way to the solution of
zero mass Weinberg-Witten issue. In contrast to the indefinite metric and
ghosts of gauge theory, SLFT uses only positivity-respecting physical degrees
of freedom. The result is a fully Lorentz-covariant and causal string field
theory in which light- or space-like linear strings transform covariant under
Lorentz transformation.
The cooperation of causality and quantum positivity in the presence of
interacting $s\geq1$ particles leads to remarkable conceptual changes. It
turns out that the presence of $H$-selfinteractions in the Higgs model is not
the result of SSB on a postulated Mexican hat potential, but solely the
consequence of the implementation of positivity and causality. These
principles (and not the imposed gauge symmetry) account also for the
Lie-algebra structure of the leading contributions of selfinteracting vector mesons.
Second order consistency of selfinteracting vector mesons in SLFT requires the
presence of $H$-particles; this, and not SSB, is the raison d'\^{e}tre for
$H.$
The basic conceptual and calculational tool of SLFT is the S-matrix. Its
string-independence is a powerful restriction which determines the form of
interaction densities in terms of the model-defining particle content and
plays a fundamental role in the construction of pl observables and sl
interpolating fields.