# Paper: Persistent Gravitational-Wave Observables: General Framework

This post summarizes a paper about three new procedures by which one can measure generalized notions of gravitational-wave memory. The paper was an Editors’ Suggestion in Phys. Rev. D, and it had a synopsis published about it in Physics.

## Paper Highlighted

- E. E. Flanagan, A. M. Grant, A. I. Harte,
**D. A. Nichols**. “Persistent gravitational-wave observables: General framework.” Phys. Rev. D 99, 084004 (2019), arXiv:1901.00021.

## Summary of the Paper

The gravitational-wave memory effect is often characterized by the lasting displacement it would cause between freely falling observers after a burst of gravitational waves pass by their locations. Subsequently, it was realized that there other types of memory effects that freely falling observers could measure, including lasting relative velocities, changes in proper time elapsed, and relative rotation of inertial gyroscopes. We were interested in determining procedures that observers could, in principle implement, by which observers could meaure all these memory effects (and potentially other new effects). We in fact found three such types of procedures, which encompass the known memory effects, and potentially other new ones. The first procedure involved measuring a type of deviation vector between two neary accelerating observers. The second involves transporting a certain kind of linear and angular momentum around a closed curve in spacetime. The third is based on measuring the location, linear momentum, and intrinsic angular momentum of a nearby spinning point particle. We called the outcome of these measurement procedures “persistent gravitational-wave observables,” and we are currently investigating their properties in specific gravitational-wave spacetimes.