[Abstract of Mahboubeh Shahrbaf Motlagh]
Strange particles are abundantly produced and studied in dedicated hadron and hypernuclear physics experiments at J-PARC, as well as in high-energy heavy-ion collision experiments such as HADES at GSI, ALICE at CERN, STAR at RHIC, and NA61/SHINE at CERN. These experiments provide valuable constraints on the properties of dense baryonic matter and hyperon interactions. Under the extreme densities reached in neutron star (NS) interiors, strange degrees of freedom are also expected to appear; however, their actual presence remains one of the most fundamental open questions in dense matter physics. Understanding their role is essential for constraining the equation of state (EoS) of strongly interacting matter and for connecting terrestrial measurements with astrophysical observations.
In the first part of this talk, I will briefly review my microscopic study of hyperonic matter within the lowest-order constrained variational (LOCV) framework. Using realistic spin- and parity-dependent ΛN and ΛΛ interactions constrained by hypernuclear data, I will discuss the resulting EoS and the macroscopic properties of NSs. The inclusion of Λ hyperons leads to a moderate softening of the EoS and reduces the maximum mass of NS, giving rise to the so-called hyperon puzzle. Possible mechanisms to resolve this puzzle will be discussed in light of current observational constraints from NICER and gravitational-wave measurements.
In the second part, I will consider a relativistic mean-field framework, specifically the DD2Y-T model, and explore how the inclusion of a deeply bound H-dibaryon-like particle, the so-called sexaquark with quark content uuddss, can modify the hyperonic EoS. This combined treatment of hyperons and sexaquarks highlights how these two strangeness-bearing components may jointly influence the internal composition and observable properties of NSs. Our results suggest that, for a favorable sexaquark mass range, the onset of sexaquark degrees of freedom in NS matter may facilitate an early transition to deconfined quark matter within a smooth crossover construction.

[Abstract of Dr. Davood Rafiei]
Dark matter makes up more than 85% of the matter in the Universe, yet its microscopic nature remains unknown. Neutron stars, because of their extreme density and strong gravity, provide unique natural laboratories to probe dark matter and other exotic degrees of freedom through multimessenger observations.
In this talk, I will discuss two approaches to probing dark-matter-admixed neutron stars. First, I will present a two-fluid framework in which normal neutron-star matter and sub-GeV self-interacting bosonic dark matter are treated as two separate fluids that interact only
through gravity. Depending on the dark matter mass, coupling strength, and fraction, the
dark component may form either a compact core or an extended halo, affecting the mass-radius relation, tidal deformability, and pulse-profile modeling. I will show how current multimessenger constraints can restrict the corresponding dark matter parameter space.
Second, I will discuss a single-fluid framework in which exotic or dark components are produced inside dense neutron-star matter and directly modify the effective equation of state. I will focus on f-mode oscillation frequencies, damping times, and quasi-universal relations, with applications to gravitational-wave asteroseismology. In this context, I
will consider hyperons, sexaquarks or deeply bound H-dibaryons, and deconfined quark matter. These studies show that exotic and dark components can leave observable signatures in future gravitational-wave detections.