Energy momentum tensor, stability and the D-term in soliton models

Manuel Mai
University of Connecticut & University of Heidelberg


The energy momentum tensor carries basic information on the particle
under consideration regarding the energy distribution, angular momentum
and the D-term. The first two tell us the mass and spin of the
particle. The third is an equally fundamental property, but less
familiar. It is related to the distribution of internal forces inside
the particle, which must balance to form a stable particle.

All theoretical studies (lattice QCD, effective theories, models) yield
a negative D-term for various objects (nucleon, pion, nuclei), and in
soliton models it was conjectured, that this negative sign is related
to the stability of the object.

In this talk, the energy momentum tensor of Q-balls is studied, which
are particular non-topological solitons, and an ideal ground to shed
further light on the connection between the D-term and the stability
of the object. For the ground state of Q-ball, the proof is
formulated, that D-term < 0, if the Q-ball is stable.

The results are of interest, as recently it became clear how, among
other properties, the D-term of the nucleon can be accessed in
experiment. At Jefferson Lab and other facilities dedicated efforts
are being done.