In quantum field theory, specifically the theory of renormalization, the bare mass of an elementary particle is the limit of its mass as the scale of distance approaches zero or, equivalently, as the energy of a particle collision approaches infinity.
In some versions of QFT, the bare mass of some particles may be plus or minus infinity.
In the theory of the electroweak interaction using the Higgs boson, all particles have a bare mass of zero.
denotes the experimentally observable mass of the particle,
the increase in mass owing to the interaction of the particle with the medium or field.