## Theoretical Particle Physics

### Brent Nelson

Associate Professor and Physics Department Undergraduate Curriculum Chair

PhD University of California, Berkeley, 2001

(617)373-2956

b.nelson@neu.edu

### Research Summary:

My research interests lie in the area of high energy particle physics beyond the Standard Model. In particular, I am interested in theoretical considerations and phenomenology that may be indicative of string theory in low-energy observations. This field of research is still developing and is very likely to grow significantly in importance with the advent of the LHC and other forthcoming experiments. The wide variety of my investigations are all geared towards answering one fundamental question: what observational evidence can be marshalled to bolster the proposition that some particular string theory construction is a strong candidate for an underlying theory of all interactions?

To truly make contact with the observable world a candidate string model must succeed on four fronts: (1) it must produce the Standard Model gauge group, particle content and superpotential couplings; (2) it must allow for moduli stabilization and supersymmetry breaking that produces a realistic phenomenology; (3) it must be capable of explaining any new physics signals found at the LHC and other upcoming experiments; and (4) it must be able to explain early universe physics, at least in those areas where cosmological data is available. My research seeks avenues of attack on each of these challenges.

With the LHC era now here, it has become particularly important to focus on the the issue of how observations made at hadron colliders will shape theoretical model-building for the next decade. There are two (related) problems to consider. First, how well do standard search and measurement techniques fare in situations slightly different from the standard supersymmetric benchmark models of the MSSM? Second, how can multiple observations be brought together to produce a unique and accurate picture of the underlying Lagrangian for the new physics we hope to discover at the LHC? I have devoted much recent thought on these topics, and plan to continue to do so over the next two to three years. Recently, I have begun thinking about the nature of dark matter in string-motivated contexts in which some period of moduli domination exists before Big Bang Nucleosynthesis. The cosmology of such scenarios is an active area of my current research.

From the top down, I have been working on developing large databases of compactification manifolds for phenomenological exploration. I have also been trying to “reverse engineer” the (supersymmetric) Standard Model by seeking a mathematical description of its moduli space in terms of an affine variety in the context of global superspace. These explorations require a large degree of familiarity with advanced concepts in mathematics, and benefit from familiarity with high performance computation, distributed across multiple cores. This is an area of research in which I am actively seeking new students of qualified background.

### Recent Publications:

Gordon Kane, Piyush Kumar, Brent D. Nelson and Bob Zheng, “Dark Matter Production Mechanisms with a Non-Thermal Cosmological History: A Classification”, **arXiv 1502.05406**.

Ross Altman, James Gray, Yang-Hui He, Vishnu Jejjala and Brent D. Nelson, “A Calabi-Yau Database: Threefolds Constructed from the Kreuzer-Skarke List”, **Journal of High Energy Physics** 1502 (2015) 158.

Yang-Hui He, Vishnu Jejjala, Cyril Matti, Brent D. Nelson and Michael Stillman, “The Geometry of Generations” **Communications in Mathematical Physics 339 **(2015) 1.

Yang-Hui He, Vishnu Jejjala, Cyril Matti and Brent D. Nelson, “Veronese Geometry and the Electroweak Vacuum Moduli Space” **Physics Letters B736 **(2014) 20.

Bryan Kaufman and Brent D. Nelson, “Mirage Models Confront the LHC II: Flux-Stabilized Type IIB String Theory,” **Physical Review, D89**, (2014) 085029.

Bryan Kaufman, Brent D. Nelson and Mary K. Gaillard, “Mirage Models Confront the LHC I: Kähler-Stabilized, Heterotic String Theory,” **Physical Review, D88**, (2013) 025003.