Critical endpoint and universality class of neutron ${}^3{P}_2$ superfluids in neutron stars

Abstract

We study the thermodynamics and critical behavior of neutron ${}^3{P}_2$ superfluids in the inner cores of neutron stars. ${}^3{P}_2$ superfluids offer a rich phase diagram including uniaxial/biaxial nematic phases, the ferromagnetic phase, and the cyclic phase. Using the Bogoliubov-de Gennes (BdG) equation as superfluid Fermi liquid theory, we show that a strong (weak) magnetic field drives the first (second) order transition from the dihedral-two biaxial nematic phase to dihedral-four biaxial nematic phase in low (high) temperatures, and their phase boundaries are divided by the critical endpoint (CEP). We demonstrate that the set of critical exponents at the CEP satisfies the Rushbrooke, Griffiths, and Widom equalities, indicating a new universality class. At the CEP, the ${}^3{P}_2$ superfluid exhibits critical behavior with nontrivial critical exponents, indicating a new universality class. Furthermore, we find that the Ginzburg-Landau (GL) equation up to the 8th-order expansion satisfies three equalities and properly captures the physics of the CEP. This implies that the GL theory can provide a tractable way for understanding critical phenomena which may be realized in the dense core of realistic magnetars.

15 pages, 5 figures

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• Topological confinement of vortices in two-flavor dense QCD
• Non-Abelian Half-Quantum Vortices in ${}^3{P}_2$ Topological Superfluids
• Non-Abelian Anyons and Non-Abelian Vortices in Topological Superconductors
• Coexistence phase of ${}^1{S}_0$ and ${}^3{P}_2$ superfluids in neutron stars
• Spin-polarized phases of ${}^3{P}_2$ superfluids in neutron stars
• Core structures of vortices in Ginzburg-Landau theory for neutron ${}^3{P}_2$ superfluids
• Proximity effects of vortices in neutron ${}^3{P}_2$ superfluids in neutron stars: Vortex core transitions and covalent bonding of vortex molecules
• Alice meets Boojums in neutron stars: vortices penetrating two-flavor quark-hadron continuity
• Strongly interacting matter in extreme magnetic fields
• Strong-coupling effects of pairing fluctuations, and Anderson-Bogoliubov mode in neutron ${}^1$S${}_0$ superfluids in neutron stars
• Symmetry classification of uniform states in spin-2 Bose-Einstein condensates and neutron ${}^3{P}_2$ superfluids
• Emergent chirality and superfluidity of parity-doubled baryons in neutron stars
• Critical behaviour near critical end points and tricritical points in disordered spin-1 ferromagnets