NSF Award
2412818
This award funds some of the research activities of Professor Ken D. Olum in the Tufts Institute of Cosmology at Tufts University.<br/><br/>Cosmic strings are microscopically thin or possibly even fundamental objects of cosmological length which may or may not exist in our universe. If they exist, they may play a role in the generation of dark matter. Detection of cosmic strings would provide a window into fundamental physics at energies beyond the reach of any accelerator. Observation of a cosmic superstring network could provide a confirmation of the correctness of string theory. The best hope for discovering a cosmic string network is through observation of gravitational waves. The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) and other pulsar timing arrays have found strong evidence for a gravitational wave background formed by many sources throughout the universe. These sources could be pairs of giant black holes, but they could also be cosmic string loops. Professor Olum will study the gravitational waves that would be emitted by cosmic strings and compare them with current and forthcoming NANOGrav observations. His work will advance the national interest by promoting the progress of science in the recent and rapidly growing field of gravitational waves and their possible sources, and in learning about fundamental physics at very high energies. Professor Olum will involve graduate students and postdoctoral researchers in the work and thus train future generations of research physicists. The work will further connect studies of the universe with studies of the fundamental laws of nature.<br/><br/>More technically, Professor Olum will use the gravitational wave spectra that he and his group have derived from a realistic population of cosmic string loops evolving under gravitational self-interaction to compare with pulsar timing observations from the NANOGrav collaboration (of which he is a full member) and the international pulsar timing array. He will develop a new technique for simulation of axion strings using the Kalb-Ramond formalism, and so improve the calibration of axion dark matter densities. He will study the velocities acquired by loops in reaction to anisotropic gravitational wave emission, called "the rocket effect", to determine how much cosmic string loops cluster in galaxies, which is important for other possible observational mechanisms.<br/><br/>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.
