# Dr. Junwu Huang's lunch talk 20/12/2018

by **Lijing Shao**

## Junwu Huang (Perimeter Institute, Canada)

#### Probing axions with neutron star inspirals observed by Advanced LIGO

In certain models of a QCD axion, finite density corrections to the axion potential can result in the axion being sourced by large dense objects. There are a variety of ways to test this phenomenon, but perhaps the most surprising effect is that the axion can mediate forces between neutron stars that can be as strong as gravity. In this talk, I will discuss how axion forces and radiations can be detected by Advanced LIGO observations of neutron star inspirals. The axion mediated forces can be both attractive or repulsive. By a numerical coincidence, axion forces between neutron stars with gravitational strength naturally have an associated length scale of tens of kilometers or longer, similar to that of a neutron star. A significant axion field profile can only be sourced by large dense objects, and therefore evades various fifth force constraints. Observations of neutron star mergers in Advanced LIGO can probe many orders of magnitude of unconstrained axion parameter space. In the talk, I will also discuss using an effective field theory (EFT) approach to calculate the first post-Newtonian corrections to the orbital dynamics, radiated power, and gravitational waveform for binary neutron star mergers in the presence of an axion. These results can be used to perform a detailed forecast of the potential for Advanced LIGO to constrain the free parameters of the EFT, and map these to the mass and decay constant of the axion. [link]

**Place**: 1st floor meeting room, KIAA

**Time**: Thu, 2018-12-20 12:00 to 13:00