Up-down quark matter may be more stable than strange quark matter

The claim is deliberately modal: it asserts that up-down quark matter (udQM) may be more stable than strange quark matter (SQM), not that it is. The verdict therefore turns on whether credible calculations support the possibility and whether anything excludes it.

The principal support is now verified: quark-meson model calculations find bulk udQM has lower energy per baryon than SQM↗︎ is a faithful report of Holdom, Ren, and Zhang, Phys. Rev. Lett. 120, 222001 (2018), arxiv.org/abs/1707.06610, and some NJL-model calculations find two-flavor quark matter more stable than three-flavor↗︎ corroborates the flavor ordering in an independent framework (e.g. arxiv.org/abs/1908.01325). The counter-consideration, the bag-model result favoring strangeness↗︎, is real and historically dominant, but it weighs against the non-modal ordering rather than against the stated possibility: it shows the question is model-dependent, not that udQM cannot be the more stable form. Given first-principles QCD cannot settle the stability question↗︎, neither side can close the case, and the modal claim stands.

Two limits on the verdict. First, several NJL-type studies find that bulk ud quark matter, while favored over strange matter in flavor ordering, is not absolutely stable relative to nuclei for reasonable parameters (see the discussion in arxiv.org/abs/2312.17102); this constrains the stronger reading of the hypothesis (udQM as the true ground state above baryon number 300) but not the relative ordering the claim states. Second, consistency of the A>300 stability threshold with ordinary nuclear stability↗︎ is required for the hypothesis to be viable at all; it is unassessed here but uncontroversial in the literature, resting on standard surface-effect arguments.

No source instances are yet recorded on either side. The status would move toward contested if a credible line emerged arguing the possibility itself is excluded (for instance, a robust first-principles or observational result fixing the flavor ordering), and toward verified-as-open only trivially; a non-modal resolution would instead be reflected in the sibling claim that strange quark matter is the true ground state. Credence 0.9 reflects that the possibility is genuinely open on current evidence, with residual weight on the chance that the quark-meson result reflects a model artifact and the true ordering robustly favors strangeness.