It is proposed that the neutral, B=2, flavor singlet sexaquark (S) composed of uuddss quarks, has mass m_S <~ 2 GeV. If m_S < 2 (m_p + m_e), it is absolutely stable, while for m_S < m_p+m_e + m_Lambda, its lifetime can be greater than the age of the Universe. Lattice gauge theory cannot yet predict m_S, but indirect evidence supports the hypothesis of stability. A stable S is consistent with QCD theory and would have eluded detection in accelerator and non-accelerator experiments. If it exists, the S is a good Dark Matter candidate. Analyses of existing Upsilon decay and LHC data can be used to discover it and measure its mass.Glennys R. Farrar, "Stable Sexaquark" (August 29, 2017).
While the premise that a sexaquark that was lighter than two time the mass of a proton would be absolutely stable is sound, I have no confidence whatsoever that Farrar's heuristic argument that the not yet calculated mass of a sexaquark is less than twice the proton mass has any validity whatsoever. indeed, the fact of its non-detection at colliders so far strongly militates against this hypothesis.
It would be a convenient dark matter candidate that would explain the lack of fundamental dark matter particles, but the cross-section of interaction would be too high and the gravitational dynamics would probably be wrong as well.