I was reading this How much of the proton's mass is due to the Higgs field? and finds the discussion says:
As Prof. Strassler explains in the link above, the proton mass is best throught of as arising from the sum of three contributing terms:
- The sum of the rest energies of all of the (many!) quarks and antiquarks
- The kinetic energy of the quarks, antiquarks, and gluons
- The binding energy stored in the gluon fields, which is negative and actually decreases the proton mass relative to what it would be if the quarks did not interact.
I believe that the Higgs mechanism is responsible for the contribution (1), which is much larger than the naive 9.1 MeV from just three quarks, and therefore much more than 1% of the proton mass.
My Question goes as
In the above, we say:
(a) The binding energy stored in the gluon fields, which is negative and actually decreases the proton mass.
But I thought
(b) The SU(3) Yang-Mills gauge theory has mass gap, that has to do with the glue ball and the binding energy stored in the gluon fields --- which should contribute a positive energy and a mass gap --- to the glueball.
Which of (a) and (b) statements are true? How could they, if both (a) and (b), are true?
