Topological defects at the boundary of neutron ${}^3{P}_2$ superfluids in neutron stars

Abstract

We study surface effects of neutron ${}^3{P}_2$ superfluids in neutron stars. ${}^3{P}_2$ superfluids are in uniaxial nematic (UN), D${}_2$ biaxial nematic (BN), or D${}_4$ BN phase, depending on the strength of magnetic fields from small to large. We suppose a neutron ${}^3{P}_2$ superfluid in a ball with a spherical boundary. Adopting a suitable boundary condition for ${}^3{P}_2$ condensates, we solve the Ginzburg-Landau equation to find several surface properties for the neutron ${}^3{P}_2$ superfluid. First, the phase on the surface can be different from that of the bulk, and symmetry restoration or breaking occurs in general on the surface. Second, the distribution of the surface energy density has an anisotropy depending on the polar angle in the sphere, which may lead to the deformation of the geometrical shape of the surface. Third, the order parameter manifold induced on the surface, which is described by two-dimensional vector fields induced on the surface from the condensates, allows topological defects (vortices) on the surface, and there must exist such defects even in the ground state thanks to the Poincaré-Hopf theorem: although the numbers of the vortices and antivortices depend on the bulk phases, the difference between them is topologically invariant (the Euler number $\chi =2$) irrespective of the bulk phases. These vortices, which are not extended to the bulk, are called boojums in the context of liquid crystals and helium-3 superfluids. The surface properties of the neutron ${}^3{P}_2$ superfluid found in this paper may provide us useful information to study neutron stars.

30 pages, 11 figures

References in corpus (23)

• GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral
• Shapiro delay measurement of a two solar mass neutron star
• A Massive Pulsar in a Compact Relativistic Binary
• Rapid Cooling of the Neutron Star in Cassiopeia A Triggered by Neutron Superfluidity in Dense Matter
• Discrete symmetries and 1/3-quantum vortices in condensates of F=2 cold atoms
• Superfluidity and Superconductivity in Neutron Stars
• Spin Polarized Asymmetric Nuclear Matter and Neutron Star Matter Within the Lowest Order Constrained Variational Method
• Quasi-Nambu-Goldstone Modes in Bose-Einstein Condensates
• Anyonic particle-vortex statistics and the nature of dense quark matter
• Nuclear pairing from microscopic forces: singlet channels and higher-partial waves
• Superfluid phases of triplet pairing and rapid cooling of the neutron star in Cassiopeia A
• Colorful boojums at the interface of a color superconductor
• Collective modes of the order parameter in a triplet superfluid neutron liquid
• Topology and symmetry of surface Majorana arcs in cyclic superconductors
• Reexamining Ginzburg-Landau theory for neutron ${}^3{P}_2$ superfluidity in neutron stars
• Zero sound in triplet-correlated superfluid neutron matter
• Neutrino emissivity of anisotropic neutron superfluids
• Phase structure of neutron ${}^3{P}_2$ superfluids in strong magnetic fields in neutron stars
• Possible Ferromagnetism in the Large N(c) and N(f) limit of quark matter
• Microscopic description of axisymmetric vortices in ${}^3{P}_2$ superfluids
• Critical endpoint and universality class of neutron ${}^3{P}_2$ superfluids in neutron stars
• New eigen-mode of spin oscillations in the triplet superfluid condensate in neutron stars
• Possibility of ferromagnetic neutron matter

Cited by in corpus (10)

• Non-Abelian Half-Quantum Vortices in ${}^3{P}_2$ Topological Superfluids
• 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
• Strong-coupling effects of pairing fluctuations, and Anderson-Bogoliubov mode in neutron ${}^1$S${}_0$ superfluids in neutron stars
• Strongly interacting matter in extreme magnetic fields
• 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
• Topological Shell Structures in Neutron Stars: Effects on Equilibrium, Oscillations, and Gravitational-Wave Signatures