LEAPS-MPS: Exploring New Physics with More Accurate Signals from Cosmic Strings

The recent evidence for a gravitational wave background is one of the most significant discoveries for cosmology since LIGO first saw gravitational waves from merging black holes. The gravitational-wave background is a ‘hum’ filling space, much like background conversation in a crowded room. And just like a crowded room, it can be hard to pick out a single voice—but easier if it’s the voice of someone you know. The gravitational-wave background is full of many “voices” from different astrophysical and cosmological sources, and to be able to understand the whole, we need to be able to recognize each voice. Only then can we determine which sources are present, and thereby learn more about the physics of our Universe. The particular voice/source this proposal focuses on is cosmic strings: long, thin, oscillating objects predicted to have formed in the very early universe. This proposal comprises two projects, both making use of the most recent advances in modeling the “voices” of cosmic strings. The first aims to integrate current constraints on the cosmic string background with projected sensitivities for next-generation gravitational-wave detectors. Current constraints will come from the NANOGrav collaboration, serving as an indirect test of a variety of models of new physics. The likelihoods of different theories will then feed into updated constraints on the ability of the Laser Interferometer Space Antenna (LISA) to detect cosmic strings; this multidetector analysis provides more robust predictions than using either detector alone, and aims to inspire the next refinement in model-building for new physics models. The second project will find new predictions for the strength and rate of bursts of gravitational waves from cosmic strings, as seen by LISA. This will provide a complementary method of searching for strings, and thus for new physics. Both projects will have significant student involvement. Students will develop transferable skills in data analysis, computational techniques, visualization, and communication while broadening their professional networks by interacting with scientists from international collaborations.

The recent evidence for a gravitational wave background is one of the most significant discoveries for cosmology since LIGO first saw gravitational waves from merging black holes. The full gravitational-wave background is a sum of many different sources, including those from new-physics theories. Careful modeling of all sources is important for disentangling the full background into these constituent parts. Cosmic strings are important signs of new physics, being generic predictions in many beyond-the-standard-model theories. Recent progress in simulations of gravitational self-interactions of cosmic strings has found how the shapes and gravitational-wave emissions of the strings evolves over their lifetimes. This project will use the data which provided the evidence for a background as well as these self-interaction results to make improved predictions for the detectability of cosmic strings. Recent results show that the background’s amplitude decreases at all frequencies, weakening current constraints from PTA experiments like NANOGrav as well as forecasts in experiments like LISA. These forecasts will be integrated into upcoming NANOGrav data releases. Improved predictions for the shape, emission patterns, and evolution of a typical string loop will determine more precisely the likelihood and rate of a LISA detection of gravitational-waves bursts from strings. Because these bursts happen at high frequencies but low amplitudes, below the LIGO sensitivity, LISA is the next experiment with a chance of detecting bursts, making precise predictions essential. This project will highlight how beyond-the-standard-model theories are constrained by their results, providing guidance for the next round of model-building and experimental searches for new physics. It will also build on a framework for generic multi-detector comparisons and burst event rate calculations, making them applicable to other current and future experiments, such as LIGO or Cosmic Explorer. Students working on the project will gain skills in data analysis, programming, and. scientific communication, and will make connections in international collaborations. In addition, as part of the project, a scientific computing mini course for Boston Public School system high school students will be conducted and activities will be carried out with music students and faculty at local universities for a sonification project of cosmic string signals.

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.

Award Number: 2532438
Principal Investigator: Jeremy Wachter
Funds Obligated: $196,670
State: MA