Diproton

Diproton refers to a hypothetical nucleus consisting of two protons bound together without neutrons. In free space there is no stable di-proton bound state. The Coulomb repulsion between the two positively charged protons is not overcome by the attractive component of the strong nuclear force at the relevant range, so two protons do not form a bound system. The proton–proton interaction in the spin-singlet channel is attractive but not sufficient to yield a bound state; at most there could be a very short-lived resonance or a virtual state near threshold, but such a state would be unbound and broad.

In nuclear physics, the concept sometimes appears in discussions of two-proton emission and correlations between protons emitted from very proton-rich nuclei. These phenomena reflect reaction or decay dynamics rather than a bound di-proton state; there is no established evidence for a stable diproton.

In astrophysics, the initial step of the proton–proton chain in stars involves two free protons fusing to form deuterium via the weak interaction: p + p -> d + e+ + νe. A bound diproton would alter this pathway, but within the standard model no stable di-proton state exists, so the two-proton system remains transient on the timescale of stellar fusion.

Overall, diproton is a concept of historical and theoretical interest, but there is no experimental or widely accepted evidence for a stable bound di-proton state.