Postdoctoral Fellowship: MPS-Ascend: Looking for dark radiation: Utilizing Data and Theory

About This Grant

Current astrophysical observations indicate that visible matter constitutes only about 5% of the universe. The remaining 95% is attributed to the enigmatic dark sector, comprising dark energy and dark matter—components that remain largely unexplained. This project aims to address one of the most profound open questions in physics: understanding the fundamental properties of dark matter particles, including their interactions and masses. A particular focus will be on the hypothetical particle known as the axion, a well-motivated dark matter candidate. To pursue this ambitious goal, Dr. Bagherian will integrate numerical calculations, computer simulations, and theoretical model building. The development and application of these tools are not only crucial for advancing our understanding of dark matter but also hold potential benefits across various areas of physics and related sciences. Moreover, as significant investments are being made in experimental efforts to find axions—such as haloscopes (e.g., ADMX), helioscopes (e.g., CAST, IAXO), light-shining-through-a-wall experiments, and spin-precession setups (e.g., CASPEr)—it is imperative to conduct thorough theoretical investigations of the axion particle. These studies will guide and interpret experimental searches, ensuring that national resources are effectively utilized in the quest to uncover the nature of dark matter. By advancing theoretical frameworks and computational techniques, this project contributes to the progress of science and has the potential to impact welfare through a deeper understanding of the universe. Dr. Bagherian also plans a series of presentations and a website that explain the way graduate school works, in terms of the application, financial considerations, career path, and other pertinent information. Dark matter's invisibility makes its models difficult to constrain. This project leverages existing cosmological tensions to gain insights into the dark sector. Specifically, it examines the phenomenology of a dark radiation (DR) component within the dark sector, focusing on data analysis, simulations, and the development of theoretical models extending up to quantum gravity scales. The presence of DR in the early universe could alleviate several cosmological tensions. Notably, the Hubble tension—a discrepancy exceeding 5σ between local measurements of the universe’s expansion rate and those inferred from cosmic microwave background (CMB) data—and large-scale structure tensions, which show a 3σ difference between direct clustering measurements and CMB-inferred values. Additionally, there is a controversial tension in the Lyman-α 1D flux power spectrum data, linking the hydrogen content in the intergalactic medium to matter clustering, with inconsistencies up to 3σ across different measurements. A key focus of this project is on axion dark matter models, where axions—a prominent dark matter candidate—decay into dark photons, contributing to DR. Exploring this direction can provide insights into axions as viable dark matter candidates. Given the rich phenomenology of axions, developing these models can also address related questions, such as their potential role as dark energy candidates and the production of dark matter axions from axion strings. By the end of this project, significant progress will be made in data analysis techniques, including N-body and Monte Carlo simulations of large-scale cosmic data, and in addressing key open questions in physics beyond the Standard Model. The tools and methods developed will offer substantial intellectual merit, and broader impacts, contributing to the broader scientific community’s understanding of the universe. In addition, Dr. Bagherian will conduct outreach activities to the broader physics community as part of STEM workforce development. 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.