Hamiltonian Hydrodynamics and Irrotational Binary Inspiral

TL;DR

This paper introduces a Hamiltonian framework for modeling irrotational barotropic fluids in binary neutron-star inspirals, enabling more accurate and efficient gravitational waveform simulations by conserving circulation and symplecticity.

Contribution

It develops a novel Hamiltonian and Hamilton-Jacobi formulation for relativistic irrotational fluids, improving numerical relativity simulations of neutron-star binaries.

Findings

Hamiltonian methods conserve circulation and symplecticity.

The approach reduces computational cost for high-precision waveforms.

Applicable to a broad class of relativistic fluid dynamics problems.

Abstract

Gravitational waves from neutron-star and black-hole binaries carry valuable information on their physical properties and probe physics inaccessible to the laboratory. Although development of black-hole gravitational-wave templates in the past decade has been revolutionary, the corresponding work for double neutron-star systems has lagged. Neutron stars can be well-modelled as simple barotropic fluids during the part of binary inspiral most relevant to gravitational wave astronomy, but the crucial geometric and mathematical consequences of this simplification have remained computationally unexploited. In particular, Carter and Lichnerowicz have described barotropic fluid motion via classical variational principles as conformally geodesic. Moreover, Kelvin's circulation theorem implies that initially irrotational flows remain irrotational. Applied to numerical relativity, these concepts lead to novel Hamiltonian or Hamilton-Jacobi schemes for evolving relativistic fluid flows. Hamiltonian methods can conserve not only flux, but also circulation and symplecticity, and moreover do not require addition of an artificial atmosphere typically required by standard conservative methods. These properties can allow production of high-precision gravitational waveforms at low computational cost. This canonical hydrodynamics approach is applicable to a wide class of problems involving theoretical or computational fluid dynamics.