Speaker
Description
Strange quark matter (SQM) has long been proposed as a possible true ground state of QCD at high baryon density, motivating extensive research on exotic compact objects and unusual cosmic-ray signatures. Recent observations strengthen this interest: the remnant HESS J1731-347 hosts an exceptionally low-mass neutron star, $M = 0.77^{+0.20}_{-0.17}\,M_\odot$ and $R = 10.4^{+0.86}_{-0.78}\,\mathrm{km}$, making it a compelling candidate for a strange quark star. Additional environments such as GW170817 and GRB 250702B provide conditions conducive to the formation of strangelets, stable clusters of SQM that may emerge during the transition between the 2SC and CFL color-superconducting phases. These strangelets could produce monochromatic very-high-energy $\gamma$-ray lines through self-annihilation, offering a distinctive observational signature.
This work investigates strangelet stability, production cross-sections, and mass-to-charge ratios using QCD-motivated models. Data from H.E.S.S., Fermi-LAT, MAGIC-II, and CTA are used to constrain narrow spectral features and possible fluxes associated with strangelet annihilation. The results indicate that detecting such lines will require improved sensitivity from next-generation instruments. By integrating multimessenger observations with dense-matter QCD simulations, this study examines the equations of state for compact stars and explores the broader cosmological implications of SQM.
A complementary question concerns whether some of these exotic SQM composites could survive propagation to Earth and be observed directly. While microscopic strangelets and solitonic dark-matter candidates produced in mergers or color-superconducting phase transitions are unlikely to remain stable over interstellar distances, macro-scale objects such as nuclearites and Q-balls possess extremely large mass-to-charge ratios and correspondingly high ionization densities, enabling them to traverse the interstellar medium and penetrate the terrestrial atmosphere. Such objects would generate continuous, bright, high-ionization tracks, thermal shock fronts, or slow luminous transits in large-area detectors. Existing searches from SLIM, MACRO, ANTARES, and IceCube already constrain parts of this parameter space, and upcoming facilities, including the Chinese high-energy observatories LHAASO (KM2A, WCDA, WFCTA), provide additional sensitivity to both atmospheric penetration signatures and sub-relativistic luminous events. Incorporating these possibilities broadens the observational landscape: in addition to monochromatic very-high-energy $\gamma$-ray lines from strangelet annihilation, direct searches for macro-SQM and solitonic dark-matter candidates offer an independent pathway to probe the stability, astrophysical production, and cosmological role of strange quark matter.
