This award funds the research activities of Professor James Halverson at Northeastern University.String theory attempts to describe physical laws, such as those governing electromagnetism, nuclear physics, and gravity, in a common unified framework.  One central aspect of string theory is that it predicts the existence of extra dimensions of space, and the properties of these extra dimensions play a large role in determining how particles interact in the theory.  However, it turns out that there are many self-consistent possibilities for these extra dimensions in string theory.   The central goal of Professor Halverson's research is to determine a set of very common possibilities and to analyze their corresponding predictions for potential additional laws of particle physics.  Research in this area serves the national interest by promoting the progress of science at its most fundamental level, in this case by providing motivation for new physical laws from unified theories such as string theory.   This project will also have substantial broader impacts. Professor Halverson will involve a postdoc and students in his research, and thereby provide critical training for junior physicists as they begin their research careers.  He will also communicate his research results and related developments in the field to Boston-area high-school students through the NSF-funded Physics TheoryNet program, and also to his undergraduate students at Northeastern.More technically, Professor Halverson will study the string landscape, using regions away from weak coupling and also string consistency conditions to motivate extended particle sectors (EPS) that are novel from the point of view of quantum field theory.  One major aspect of this project will be the formal study of non-Higgsable clusters in F-theory, including their physical origin in four dimensions and associated implications for visible and dark EPS.  He will develop new mathematics to understand the connection between matter and knots in the context of F-theory geometries, and will also study singular limits in G2 compactifications of M-theory and how string consistency conditions may require the existence of exotic matter.  One potential contribution of this work is to develop a notion of typicality of certain EPS in the landscape, thereby providing motivation for models that are either novel or ad hoc in other physical frameworks.