This award funds research activities of Professor Ken D. Olum in the Tufts Institute of Cosmology at Tufts University.
Cosmic strings are microscopically thin or even fundamental objects of cosmological length, which may or may not exist in our universe. 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. In addition to the bursts of gravitational waves that have recently been discovered by the LIGO and VIRGO observatories, there is likely to be a "background" of gravitational waves that is always present. Loops of cosmic strings are one of the sources that may contribute to this background, and observation of the background is an important way in which cosmic strings might be discovered. Professor Olum will study how the shape and motion of cosmic string loops changes during their lives and how this affects their emission of gravitational waves that become part of this background. If and when the gravitational wave background is discovered, this research will help us to distinguish whether it comes from cosmic strings or some other source, and to determine the properties of the cosmic string network if it is the source of the background. As such, research in this direction advances the national interest by further the development of basic sciences in the United States. Professor Olum will also involve graduate students in his work and thereby train future generations of research physicists. This work will also connect studies of the universe with studies of the fundamental laws of nature.
More technically, Professor Olum will analyze gravitational back-reaction on cosmic string loops, to see how features such as cusps and kinks are modified by back-reaction. He will simulate realistic populations of cosmic string loops to see how their shapes evolve under back-reaction and compute the resulting gravitational emission spectrum for comparison with observations. He will also study the velocities acquired by loops in reaction to anisotropic gravitational wave emission, the so-called "rocket effect".
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.