Triplet pairing in neutron matter in a comprehensive diagrammatic approach

TL;DR

The paper addresses triplet pairing in dense neutron matter and develops a large-scale diagrammatic approach that includes parquet diagrams and beyond-parquet contributions to derive an in-medium effective interaction from realistic v8 forces. It shows that many-body correlations substantially reduce the in-medium spin-orbit interaction, leading to a suppressed $^3P_2-^3F_2$ gap and an enhanced $^3P_0$ gap, highlighting the importance of beyond-parquet processes. The approach provides a more complete, BC S-like description of triplet pairing in neutron matter and has implications for neutron-star cooling and dense-matter phenomenology. Future work could incorporate three-body forces to assess residual uncertainties.

Abstract

We apply a large-scale summation of Feynman diagrams, including the class of parquet diagrams plus important contributions outside the parquet class, for calculating effective pairing interactions and subsequently the superfluid gap in P-wave pairing in neutron matter. We use realistic nucleon-nucleon interactions of the $v_8$ type and perform calculations up to a Fermi momentum of 1.8 fm$^{-1}$. We find that many-body correlations lead to a strong reduction of the spin-orbit interaction, and, therefore, to a radical suppression of the $^3P_2-^3F_2$ gap and an enhancement of the $^3P_0$ gap.

Figures (3)

• Figure 1: Examples of diagrams discussed in the text: (a) Parquet and (b) beyond-parquet diagram; (c) exchange diagrams.
• Figure 2: The in-medium spin-orbit effective interaction for the Reid $v_8$ interaction at different values of Fermi momentum (solid lines) compared with the bare interaction (dashed line).
• Figure 3: (a) The $^3P_2- ^3\!F_2$ gap and (b) the $^3P_0$ gap calculated in this work with the indicated interactions.