Isotopes of helium#Helium-2 .28diproton.29

Di-proton (pp)

A is a hypothetical diproton nucleus of helium, consisting of two protons, but no neutrons. However, it can not stably exist under the conditions prevailing in the universe laws of nature.

It is speculated that if the strength of the strong interaction by only 2 percent would be stronger, all protons would connect to di-protons. This case is sometimes referred to as " Diprotonenkatastrophe ", since in this case the life as it is present in the universe would not be possible. The fusion within the star would be instead caused by the weak by the strong interaction. This process would run 1018 times faster than is the case in our universe, and stars, nuclear fusion would perform so quickly that no life could develop.

The fact that the di-proton is not bound, lets be explained by the Pauli principle, together with a strong spin -spin coupling in the strong interaction. By deuterium, we know that the singlet state, i.e. the state of antiparallel spin of protons and neutrons, is not bound. Only the triplet state with parallel spins is bound. This is due to the strong spin -spin coupling of the two nucleons, which brings an energetic lowering of the triplet and raising the singlet state with themselves. In addition, for the deuteron are no excited states. Since the protons are identical fermions in the hypothetical di-proton, they are subject to the Pauli principle, ie they can not have the same quantum numbers. In analogy to the deuterium this means that the spins of the protons so both in the state with the lowest angular momentum (L = 0) would be located, would be oriented antiparallel. This condition, however, is not limited due to the spin-spin coupling. The same consideration applies to the Dineutron.

• Nuclear physics