  In this work, we investigate the dynamical stability of pre-formed Neptune
Trojans under the gravitational influence of the four giant planets in compact
planetary architectures, over 10 Myr. In our modelling, the initial orbital
locations of Uranus and Neptune (aN) were varied to produce systems in which
those planets moved on non-resonant orbits, or in which they lay in their
mutual 1:2, 2:3 and 3:4 mean-motion resonances (MMRs). In total, 420
simulations were carried out, examining 42 different architectures, with a
total of 840000 particles across all runs. In the non-resonant cases, the
Trojans suffered only moderate levels of dynamical erosion, with the most
compact systems (those with aN less than or equal 18 AU) losing around 50% of
their Trojans by the end of the integrations. In the 2:3 and 3:4 MMR scenarios,
however, dynamical erosion was much higher with depletion rates typically
greater than 66% and total depletion in the most compact systems. The 1:2
resonant scenarios featured disruption on levels intermediate between the
non-resonant cases and other resonant scenarios, with depletion rates of the
order of tens of percent. Overall, the great majority of plausible
pre-migration planetary architectures resulted in severe levels of depletion of
the Neptunian Trojan clouds. In particular, if Uranus and Neptune formed near
their mutual 2:3 or 3:4 MMR and at heliocentric distances within 18 AU (as
favoured by recent studies), we found that the great majority of pre-formed
Trojans would have been lost prior to Neptune's migration. This strengthens the
case for the great bulk of the current Neptunian Trojan population having been
captured during that migration.
