The discovery of the relation between the quantum energy-momentum tensor (EMT) and General Parton Distributions [1, 2] provides a unique way to study the EMT of the nucleon [3,4].
It was shown that the expectation value of the EMT for an unpolarized proton target in the Breit frame has the same structure as that of an anisotropic perfect fluid density [5,6]. Thus, in this case one can identify terms related to the internal energy and transverse/radial pressure inside a proton. We illustrate these results using current phenomenological knowledge of the EMT form factors.
 X.-D. Ji; Phys.Rev. D55 (1997) 7114-7125.
 X.-D. Ji; Phys.Rev.Lett. 78 (1997) 610-613.
 M.V. Polyakov; Phys.Lett. B555 (2003) 57-62.
 M. Burkardt; Int.J.Mod.Phys. A18 (2003) 173-208.
 M.V. Polyakov, P. Schweitze; Int.J.Mod.Phys. A33 (2018) 1830025
 C. Lorcé, H. Moutarde, A.P. Trawiński; Eur.Phys.J. C79 (2019) 89