Speaker
Dr
Diego Lonardoni
(Facility for Rare Isotope Beams (FRIB) and Los Alamos National Laboratory (LANL))
Description
The appearance of strange baryons in the inner regions of a neutron star (NS), where the density can exceed several times the nuclear saturation density, is likely to happen due to energetic considerations. The onset of strange degrees of freedom is considered as an effective mechanism to soften the equation of state (EoS). This softening affects the entire structure of the star, reducing the pressure and, therefore, the maximum mass that the star can stably support.
The observation of very massive NSs, however, seems to rule out soft EoS, apparently excluding the possibility of hyperon formation in the core of the star. This inconsistency, usually referred to as the "hyperon puzzle", is based on what we currently know about the interaction between strange particles and nucleons. The combination of a poor knowledge of hypernuclear interactions and the difficulty of obtaining clear astrophysical evidence of the presence of hyperons in NSs makes the solution of the hyperon puzzle an intriguing challenge.
We give our contribution to the discussion by studying the general problem of the hyperon-nucleon interaction. We attack the issue by studying properties of hypernuclei using an accurate quantum Monte Carlo (QMC) technique. We show that many-body hypernuclear forces are fundamental to properly reproduce the ground-state physics of light and medium-mass $\Lambda$ hypernuclei [1,2]. However, the poor abundance of experimental data on strange nuclei leaves room for a good deal of indetermination in the construction of hypernuclear potentials.
This lack of accuracy leads to uncertainties in the prediction of NS properties. We apply the same QMC algorithm and the same hypernuclear interactions to study an infinite system of neutrons and $\Lambda$ particles, deriving NS observables [3]. We show that the appearance of hyperons in the inner core of NSs is strongly dependent on the details of the underlying many-body hypernuclear interactions. A detailed analysis of the $\Lambda$ separation energy in medium-mass hypernuclei [4] indicates the possibility to investigate features of the hyperon-nucleon-nucleon force in the medium-mass region of the hypernuclear chart, where new spectroscopy experiments are currently planned at Jefferson Laboratory. These studies could potentially provide new hints to the solution of the hyperon puzzle.
This work is supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, under the FRIB Theory Alliance Grant Contract No. DE-SC0013617 titled "FRIB Theory Center - A path for the science at FRIB", and by the NUCLEI SciDAC program. Computational resources have been provided by the National Energy Research Scientific Computing Center (NERSC), which is supported by the U.S. Department of Energy, Office of Science, under contract DE-AC02-05CH11231.
[1] D. Lonardoni, S. Gandolfi, and F. Pederiva, Phys. Rev. C 87, 041303(R) (2013)
[2] D. Lonardoni, F. Pederiva, and S. Gandolfi, Phys. Rev. C 89, 014314 (2014)
[3] D. Lonardoni, A. Lovato, S. Gandolfi, and F. Pederiva, Phys. Rev. Lett. 114, 092301 (2015)
[4] D. Lonardoni and F. Pederiva, arXiv:1711.07521 (2017)
Primary author
Dr
Diego Lonardoni
(Facility for Rare Isotope Beams (FRIB) and Los Alamos National Laboratory (LANL))
