Speaker
Description
The observations of massive neutron stars provide a stringent constraint on the nuclear matter equation of state (EoS). While exotic particles such as hyperons may emerge in high-density neutron-star matter, their appearance generally softens the EoS, making it difficult to sustain neutron stars with masses of $2M_\odot$ or heavier. This apparent inconsistency between hyperonic EoS models and observations is known as the hyperon puzzle. Density-dependent repulsive $\Lambda NN$ and $\Lambda\Lambda N$ three-body interactions may provide a possible mechanism for recovering stiffness, but their effects on neutron-star structure are still unclear.
In this work, we investigate how $\Lambda NN$ and $\Lambda\Lambda N$ three-body interactions affect the neutron-star EoS and mass-radius relation. We construct beta-equilibrated $npe\mu\Lambda$-matter EoSs based on Skyrme-type energy-density functionals, varying the parameters $(A_3,\beta)$ and $(C_3,\gamma)$ associated with $\varepsilon_{\Lambda NN}=A_3 n_\Lambda n_N^{\beta+1}$ and $\varepsilon_{\Lambda\Lambda N}=C_3 n_\Lambda^2 n_N^\gamma$, respectively. The Tolman--Oppenheimer--Volkoff equation is then solved to obtain the corresponding mass--radius relations.
From the numerical calculations, we find that larger coupling constants $A_3$ and $C_3$ and smaller exponents $\beta$ and $\gamma$ tend to increase the maximum mass. The $\Lambda\Lambda N$ interaction mainly stiffens the EoS after $\Lambda$ particles appear, whereas the $\Lambda NN$ interaction can also change the density region where hyperons become important, sometimes producing abrupt softening of the EoS. We analyze the number of extrema of the EoS and, when appropriate, consider the Maxwell construction for a mixed-phase scenario.
In this talk, we will discuss how density-dependent repulsive $\Lambda NN$ and $\Lambda\Lambda N$ three-body interactions modify hyperonic neutron-star EoSs, how these modifications are reflected in the mass-radius relation and the maximum mass, and how extrema of the EoS affect the interpretation of the results.
| Category | Theory |
|---|