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Added by
J. Schaffner-Bielich
Publication date
2008
fields
Physics
and research's language is
English
Authors
Jurgen Schaffner-Bielich
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The role of hypernuclear physics for the physics of neutron stars is delineated. Hypernuclear potentials in dense matter control the hyperon composition of dense neutron star matter. The three-body interactions of nucleons and hyperons determine the stiffness of the neutron star equation of state and thereby the maximum neutron star mass. Two-body hyperon-nucleon and hyperon-hyperon interactions give rise to hyperon pairing which exponentially suppresses cooling of neutron stars via the direct hyperon URCA processes. Non-mesonic weak reactions with hyperons in dense neutron star matter govern the gravitational wave emissions due to the r-mode instability of rotating neutron stars.
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Hypernuclear research will be one of the main topics addressed by the PANDA experiment at the planned Facility for Anti-proton and Ion Research FAIR at Darmstadt, Germany. A copious production of Xi-hyperons at a dedicated internal target in the stored anti-proton beam is expected, which will enable the high-precision gamma-spectroscopy of double strange systems for the first time. In addition to the general purpose PANDA setup, the hypernuclear experiments require an active secondary target of silicon layers and absorber material as well as high purity germanium (HPGe) crystals as gamma-detectors. The design of the setup and the development of these detectors is progressing: a first HPGe crystal with a new electromechanical cooling system was prepared and the properties of a silicon strip detector as a prototype to be used in the secondary target were studied. Simultaneously to the hardware projects, detailed Monte Carlo simulations were performed to predict the yield of particle stable hypernuclei. With the help of the Monte Carlo a procedure for Lambda-Lambda-hypernuclei identification by the detection and correlation of the weak decay pions was developed.
Neutron stars are some of the densest manifestations of massive objects in the universe. They are ideal astrophysical laboratories for testing theories of dense matter physics and provide connections among nuclear physics, particle physics and astrophysics. Neutron stars may exhibit conditions and phenomena not observed elsewhere, such as hyperon-dominated matter, deconfined quark matter, superfluidity and superconductivity with critical temperatures near ${10^{10}}$ kelvin, opaqueness to neutrinos, and magnetic fields in excess of $10^{13}$ Gauss. Here, we describe the formation, structure, internal composition and evolution of neutron stars. Observations that include studies of binary pulsars, thermal emission from isolated neutron stars, glitches from pulsars and quasi-periodic oscillations from accreting neutron stars provide information about neutron star masses, radii, temperatures, ages and internal compositions.
In the new millennium hypernuclear physics is undergoing a renewed interest, both theoretically and experimentally.
Observations of massive ($M approx 2.0~M_odot$) neutron stars (NSs), PSRs J1614-2230 and J0348+0432, rule out most of the models of nucleon-hyperon matter employed in NS simulations. Here we construct three possible models of nucleon-hyperon matter consistent with the existence of $2~M_odot$ pulsars as well as with semi-empirical nuclear matter parameters at saturation, and semi-empirical hypernuclear data. Our aim is to calculate for these models all the parameters necessary for modelling dynamics of hyperon stars (such as equation of state, adiabatic indices, thermodynamic derivatives, relativistic entrainment matrix, etc.), making them available for a potential user. To this aim a general non-linear hadronic Lagrangian involving $sigmaomegarhophisigma^ast$ meson fields, as well as quartic terms in vector-meson fields, is considered. A universal scheme for calculation of the $ell=0,1$ Landau Fermi-liquid parameters and relativistic entrainment matrix is formulated in the mean-field approximation. Use of this scheme allow us to obtain numerical tables with the equation of state, Landau quasiparticle effective masses, adiabatic indices, the $ell=0,1$ Landau Fermi-liquid parameters, and the relativistic entrainment matrix for the selected models of nucleon-hyperon matter. These data are available on-line and suitable for numerical implementation in computer codes modelling various dynamical processes in NSs, in particular, oscillations of superfluid NSs and their cooling.
A recent solution of the hyperon puzzle by a first order phase transition to color superconducting quark matter is revisited in order to replace the Maxwell construction by an interpolation method which describes a mixed phase. To do this, we apply for the first time the finite-range polynomial interpolation method for constructing a transition between hadronic and quark matter phases to the situation that is characterized in the literature as the reconfinement problem. For the description of the hadronic phase the lowest order constrained variational method is used while for the quark phase the nonlocal Nambu-Jona-Lasinio model with constant (model nlNJLA) and with density-dependent (model nlNJLB) parameters is employed. Applying the replacement interpolation method to both quark matter models results in a hybrid equation of state that allows a coexistence of nuclear matter, hypernuclear matter and quark matter in a mixed phase between the pure hadronic and quark phases which can also be realized in the structure of the corresponding hybrid star sequences. The predicted hybrid stars fulfill the constraints on the mass-radius relation for neutron stars obtained from recent observations.
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