Constraining hypernuclear density functional with Λ-hypernuclei and compact stars

Abstract

We present a simultaneous calculation of heavy single-Λ hypernuclei and compact stars containing hypernuclear core within a relativistic density functional theory based on a Lagrangian which includes the hyperon octet and lightest isoscalar-isovector mesons which couple to baryons with density-dependent couplings. The corresponding density functional allows for SU(6) symmetry breaking and mixing in the isoscalar sector, whereby the departures in the σ -Λ and σ -Σ couplings away from their values implied by the SU(3) symmetric model are used to adjust the theory to the laboratory and astronomical data. We fix σ -Λ coupling using the data on the single-Λ hypernuclei and derive an upper bound on the σ -Σ from the requirement that the lower bound on the maximum mass of a compact star is 2M .

Equations of state for supernovae and compact stars

“…Seminal results are the variational calculations by Friedman and Pandharipande (1981) and Akmal, Pandharipande, and Ravenhall (1998) using the Urbana and Argonne nuclear two-and three-body forces. BHF calculations have been reported for instance by Baldo, Bombaci, and Burgio (1997) and Zhou et al (2004), and DBHF results by van Dalen, Fuchs, and Faessler (2004), Krastev and Sammarruca (2006) Schwenk (2006b, 2006c) applied the virial expansion to dilute neutron matter at nonzero temperature. An early application of the virial expansion was the description of a neutron gas in supernovae by Buchler and Coon (1977) using the soft-core Reid potential.…”

Many-body Forces in Magnetic Neutron Stars

“…On the other hand, the EoS softening due to the appearance of exotica might turn some nuclear models incompatible with observational data, in particular with the recently measured massive neutron stars. One possible way to overcome this puzzle is the introduction of an extra repulsion in the YY interaction Schaffner & Mishustin (1996), Bombaci (2016), allowing models with hyperons to be able to reproduce massive stars (Dexheimer & Schramm 2008;Bednarek et al 2012;Weissenborn et al 2012;Banik et al 2014;Bhowmick et al 2014;Gusakov et al 2014;Lopes & Menezes 2014;van Dalen et al 2014;Yamamoto et al 2014;Gomes et al 2015). Another possible solution is the introduction of a deconfinement phase transition at high densities Bombaci (2016), with a stiff EoS for quark matter, usually associated with quark vector interactions (see Klähn et al 2013 and references therein).…”

Hypernuclei and the hyperon problem in neutron stars

“…Simple calculations assuming a weak interaction between neutrons and Λs show that the softening of the equation of state makes it very difficult for an equation of state with Λ degrees of freedom to support a star with a mass around two solar masses as recently observed [3,4]. This apparent contradiction is sometimes referred to as "the hyperon problem" [5][6][7][8][9][10][11][12][13][14]. A few ways to solve this paradox immediately come to mind.…”