HEP
In the literature: open
Do the SM gauge forces unify into a single group?
In plain words
The strengths of the three forces change with energy and nearly meet near $1e16\, \mathrm{GeV}$. Whether they truly become one force is unknown.
Precise statement
Determine whether SU(3) x SU(2) x U(1) embeds in a simple group ($\mathrm{SU}(5), \mathrm{SO}(10), \mathrm{E6}$) broken near $M_{\mathrm{GUT}} \sim 1e15\ \text{to}\ 1e16\,\mathrm{GeV}$. In the SM the three couplings do not meet at a point; in the MSSM they meet at $\sim 2e16\,\mathrm{GeV}$. An answer is an observation of a unification-specific effect such as proton decay with a branching pattern fixed by the group.
What would settle it
Detection of proton decay in one or more channels with branching ratios matching a specific GUT.
Related problems
- More general than Does the proton decay to an antineutrino and a kaon?
- More general than Is the proton lifetime to $e+ \pi0$ below $1e35\,\mathrm{years}$?