The particle theory group investigates the most fundamental constituents of matter and their interactions. Excluding gravity, the primary theoretical framework for such an investigation is quantum field theory. One of the aims of the group is the development of a fundamental theory of particle interactions, consistent with the principles of quantum mechanics and relativity, which could lead to the explanation of phenomena as diverse as (1) chemistry, (2) radioactive decays, (3) nuclear structure, and (4) planetary motion and the behavior of black holes. Each of these first four types of process is governed by a different interaction : electromagnetism, weak interactions, strong interactions and gravitation.

Important progress has been made in recent decades towards the fulfillment of the above goals. All experiments which do not include gravity can be explained by a quantum field theory known as the Standard Model. Explaining the scale of the weak interactions requires some extension of the Standard Model; supersymmetry is a promising candidate for the principle underlying that extension. The inclusion of quantum gravity requires us to go beyond the Standard Model. The leading candidate for a quantum theory of gravity is string theory. A central focus for the group is exploring the many facets of string theory including, for example, the physics of black holes, holography, the structure of string vacua and implications of symmetry.

Any list of research topics is necessarily incomplete and very likely dated. For example, some questions of current interest to group members include the use of quantum simulation and quantum computing in particle theory, and the exploration of novel structures that lie somewhere between local quantum field theory and full string theory.

## YOICHIRO NAMBU

Yoichiro Nambu (1921-2015) was a giant of 20th century theoretical physics and a recipient of the 2008 Nobel Prize in Physics. His seminal work on spontaneous symmetry breaking, color gauge theory, and string theory provided conceptual foundations for our current understanding of the nature of elementary particles, their interactions, and unification with gravity.