Thursday, August 31, 2017

A Stable Sexaquark?

A new preprint proposes that there is a stable (i.e. half-life longer than the age of the universe) hadron that could exist called a sexaquark, a bound state of up, down and strange quarks, which would be a dark matter candidate.
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.


George Williams said...

Here's a link to slides from a talk given at "The 13th international workshop on the "Dark Side of the Universe 2017"

Stable Sexaquark as
Dark Matter

Mitchell said...

There are many papers on uuddss, as "H-dibaryon". It seems that the conservative thing to expect, is that it exists only as a resonance... There is actually a holographic estimate of its mass as 1.7 GeV, which is the lower bound of Farrar's "crucial range of 1.7 to 2 GeV", and that estimate is for the "chiral limit" in which u,d,s are massless, so one might want to add 2 m_strange to that estimate.

andrew said...

Lots of good heuristic reasons to think that this mass estimate is low. Generally speaking, it takes more glue to hold more complex hadrons together than simpler ones.