Proton mass decomposition: naturalness and interpretations

Understand

I discuss the scope and naturalness of the proton mass decomposition (or sum rule) published in PRL74, 1071 (1995) and answer a few criticisms that appeared recently in the literature, focusing particularly on its interpretation and the quantum anomalous energy contribution.

• I comment on the so-called frame-independent or invariant-mass decomposition from the trace of the energy-momentum tensor.
• I stress the importance of measuring the quantum anomalous energy through experiments.
• Finally, I point out a large discrepancy in the scalar radius of the nucleon extracted from vector-meson productions and lattice QCD calculations.