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Register a new userPairing in pure neutron matter
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We review the long standing problem of superfluid pairing in pure neutron matter. For the $s$-wave pairing, we summarize the state of the art of many-body approaches including different $nn$ interactions, medium polarization, short-range correlations and BCS-BEC crossover effects, and compare them with quantum Monte Carlo results at low-densities. We also address pairing in the $p$-wave, which appears at higher densities and hence has large uncertainties due to the poorly constrained interactions, medium effects and many-body forces.
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We present an inference of the nuclear symmetry energy magnitude $J$, the slope $L$ and the curvature $K_{rm sym}$ by combining neutron skin data on Ca, Pb and Sn isotopes and our best theoretical information about pure neutron matter (PNM). A Bayesian framework is used to consistently incorporate prior knowledge of the PNM equation of state from chiral effective field theory calculations. Neutron skins are modeled in a Hartree-Fock approach using an extended Skyrme energy-density functional which allows for independent variation of $J$, $L$ and $K_{rm sym}$ without affecting the symmetric nuclear matter equation of state. We discuss the choice of neutron skin data sets, and combining errors in quadrature we obtain 95% credible values of $J=31.3substack{+4.2 -5.9}$ MeV, $L=40substack{+34 -26}$ MeV and $K_{tau} = L - 6K_{rm sym}= -444substack{+100 -84}$ MeV using uninformative priors in $J$, $L$ and $K_{rm sym}$, and $J=31.9substack{+1.3 -1.3}$ MeV, $L=37substack{+9 -8}$ MeV and $K_{tau} = -480substack{+25 -26}$ MeV using PNM priors. The correlations between symmetry energy parameters induced by neutron skin data is discussed and compared with the droplet model. Neutron skin data alone is shown to place limits on the symmetry energy parameters as stringent as those obtained from chiral effective field theory alone, and when combined the 95% credible intervals are reduced by a factor of 4-5. Ahead of new measurements of lead and calcium neutron skins from parity-violating electron scattering experiments at Jefferson Lab and Mainz Superconducting Accelerator, we make predictions based on existing data on neutron skins of tin for the neutron skins of calcium and lead of 0.166$pm$0.008 fm and $0.169 pm 0.014$ fm respectively, using uninformative priors, and 0.167$pm$0.008 fm and $0.172 pm 0.015$ fm respectively, using PNM priors.
We investigate the dynamics of a quantized vortex and a nuclear impurity immersed in a neutron superfluid within a fully microscopic time-dependent three-dimensional approach. The magnitude and even the sign of the force between the quantized vortex and the nuclear impurity have been a matter of debate for over four decades. We determine that the vortex and the impurity repel at neutron densities, 0.014 fm$^{-3}$ and 0.031 fm$^{-3}$, which are relevant to the neutron star crust and the origin of glitches, while previous calculations have concluded that the force changes its sign between these two densities and predicted contradictory signs. The magnitude of the force increases with the density of neutron superfluid, while the magnitude of the pairing gap decreases in this density range.
The self-energy effect on the neutron-proton (np) pairing gap is investigated up to the third order within the framework of the extend Bruecker-Hartree-Fock (BHF) approach combined with the BCS theory. The self-energy up to the second-order contribution turns out to reduce strongly the effective energy gap, while the emph{renormalization} term enhances it significantly. In addition, the effect of the three-body force on the np pairing gap is shown to be negligible. To connect the present results with the np pairing in finite nuclei, an effective density-dependent zero-range pairing force is established with the parameters calibrated to the microscopically calculated energy gap.
The phase diagram of isospin-asymmetrical nuclear matter may feature a number of unconventional phases, which include the translationally and rotationally symmetric, but isospin-asymmetrical BCS condensate, the current-carrying Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) phase, and the heterogeneous phase-separated phase. Because the Cooper pairs of the condensate carry a single unit of charge, these phases are charged superconductors and respond to electromagnetic gauge fields by either forming domains (type-I superconductivity) or quantum vortices (type-II superconductivity). We evaluate the Ginzburg-Landau (GL) parameter across the phase diagram and find that the unconventional phases of isospin-asymmetrical nuclear matter are good type-II superconductors and should form Abrikosov vortices with twice the quantum of magnetic flux. We also find that the LOFF phase at the boundary of the transition to the type-I state, with the GL parameter being close to the critical value $1/sqrt{2}$.
The Bose-Einstein condensation of $alpha$ partciles in the multicomponent environment of dilute, warm nuclear matter is studied. We consider the cases of matter composed of light clusters with mass numbers $Aleq 4$ and matter that in addition these clusters contains $isotope[56]{Fe}$ nuclei. We apply the quasiparticle gas model which treats clusters as bound states with infinite life-time and binding energies independent of temperature and density. We show that the $alpha$ particles can form a condensate at low temperature $Tle 2$ MeV in such matter in the first case. When the $isotope[56]{Fe}$ nucleus is added to the composition the cluster abundances are strongly modified at low temperatures, with an important implication that the $alpha$ condensation at these temperatures is suppressed.
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