Speaker
Description
In theoretical and model studies so far the D-term D was always found
negative. The first insights from experiment indicate negative D-terms
for pion and proton. A proof that D < 0 was formulated based on classical
stability arguments. It is therefore interesting to ask whether it is possible
to encounter a positive D-term, if a physical system is unstable. This
question was addressed in the Q-cloud system, an extreme parametric
limit in which a stable soliton dissociates, delocalizes, and spreads out
over all space forming an infinitely dilute gas of free quanta. But even
in this system D < 0 was found. In this work we go a step further:
we show that the previously studied Q-cloud solution was a ground state
which has even more unstable excited states. We study the energy-momentum
tensor and other properties of these Q-cloud excitations, and show that their
D-terms are nevertheless consistently described, and negative --- despite the
extreme instability of this system. We present numerical results that support
our conclusions. We conjecture that stability is a necessary condition for D
to be negative, but not sufficient.
