I am well aware of how quantum tunnelling works and how it is responsible (among other things) for the alpha decay.

Inside a nucleon, there are two quarks with the same charge, so they will repel each other. There's also the strong force binding them together (via exchange of gluons).

So isn't this attractive+repulsive potential similar in shape to the one that allows alpha decay? Can there be quantum tunnelling of quarks from a nucleon?

  • $\begingroup$ I think the problem you may be running into is that quark dynamics can not be described properly by an effective single particle potential. That there is an OK effective field theory for nucleons is a lucky break for nuclear physics that nature does not seem to want to repeat for the vacuum in general. $\endgroup$
    – CuriousOne
    Dec 13, 2014 at 1:43

2 Answers 2


The holy grail of theoretical physics is the unification of all forces, once gravitation is quantized consistently with the other three.

The behavior of the coupling constants as the energies probed increases gives an indication that indeed weak strong and electromagnetic may be of the same strength at some high energy as the measurements indicate :

coupling running

The slope at low energies is an experimental fact, and the hope of Grand Unified theories is that they will coincide at one value at the very high energies of 10^16 GeV or so.

The difference between the electroweak sector functional form of the force lies in the self interactions that the strong force exhibits.

The strong force acts between quarks. Unlike all other forces (electromagnetic, weak, and gravitational), the strong force does not diminish in strength with increasing distance. After a limiting distance (about the size of a hadron) has been reached, it remains at a strength of about 10,000 newtons, no matter how much farther the distance between the quarks. In QCD this phenomenon is called colour confinement; it implies that only hadrons, not individual free quarks, can be observed. The explanation is that the amount of work done against a force of 10,000 newtons (about the weight of a one-metric ton mass on the surface of the Earth) is enough to create particle-antiparticle pairs within a very short distance of an interaction. In simple terms, the very energy applied to pull two quarks apart will create a pair of new quarks that will pair up with the original ones. The failure of all experiments that have searched for free quarks is considered to be evidence for this phenomenon.

Tunneling is a phenomenon which can be calculated and a probability given for it to occur. The above paragraph indicates that the probability of a free quark is practically zero, which agrees with observations, and this will include also tunneling, because similar numbers will enter in the calculation.

There do exist papers in QCD calculations where tunneling is considered, but is within the confines of the overall confinement,


No, it is not possible, the reason being the phenomenon of "Color confinement", often simply called confinement, which is the phenomenon that color charged particles (such as quarks) cannot be isolated singularly, and therefore cannot be directly observed. Quarks, by default, clump together to form groups, or hadrons. The two types of hadrons are the mesons (one quark, one antiquark) and the baryons (three quarks). The constituent quarks in a group cannot be separated from their parent hadron, and this is why quarks currently cannot be studied or observed in any more direct way than at a hadron level.

For more information read here, and the links therein.


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