Cosmological and Astrophysical Signatures of Axions

This award funds the research activities of Professor Andrew Long at Rice University.

Over 40-years ago a hypothetical elementary particle known as the axion was proposed to explain a perplexing property of the neutron. For the following decades experimental campaigns have been underway to try to detect axions and axion-like particles in the laboratory. Through his work Professor Long aims to make robust predictions for several cosmological and astrophysical signatures of axions.

These theoretical predictions will motivate future observations and facilitate the interpretation of data, with the goal of making possible the discovery of the axion. These efforts advance the national interest by promoting the progress of fundamental science, since the discovery of an axion would have deep and far-reaching implications for our understanding of the laws of nature and the composition of the Universe.

In addition to its central science objectives, this project will have substantial broader impacts. At least one graduate student researcher will assist Professor Long’s research, thereby providing an opportunity for essential training of early-career physicists. In addition, Professor Long will deliver lectures at local high schools and invite students to visit the campus of his university in order to encourage the next generation of scientists.

More technically, this research program is divided into three objectives. First, Professor Long's research group will study how axion strings may leave a subtle imprint on the polarization of the cosmic microwave background radiation. They will calculate the appropriate two-point correlation function using a combination of analytical and numerical methods, and by comparing these predictions with the existing data and the projected sensitivities of next-generation surveys, they will evaluate the efficacy of these cosmological measurements to probe axion strings.

Second, they will study the electromagnetic radiation produced when an axion star transits the strong magnetic field environment of a neutron star. They will model this system with a numerical lattice simulation, calculate the resultant radiation spectrum, both directly from the simulation as well as using a dipole approximation, and assess the prospects for detecting this radiation with radio observations.

As the third and final objective, the PI’s group will study the emission of axion particles from stars including our own Sun. By focusing on a previously-unstudied interaction between the axion particles and ordinary matter, the group will calculate the flux of axions produced by these stars, evaluate the effect that this radiation has on the temperature of the star, and assess the implications for recent anomalies related to stellar axion emission.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.