# Theoretical Particle Physics Overview

The Standard Model (SM) of strong, electromagnetic and weak interactions is the crowning achievement of twentieth century physics. However, despite its many spectacular successes, the SM is theoretically inconsistent at high energies and should be superseded by a new, more fundamental theory at the teraelectron-volt (TeV) energy scale. In addition, the SM cannot incorporate dark matter, whose existence has been confirmed by numerous astrophysical observations.

Many theoretical ideas about the physics at the TeV scale and the nature of dark matter have been proposed; examples include supersymmetry, extra dimensions of space, and new strong interactions. Members of

Cornell theory group are active in investigating these ideas and their experimental and observational consequences. Currently, the Large Hadron Collider (LHC) at the CERN laboratory in Switzerland is exploring the TeV scale experimentally for the first time in history. Theoretical interpretation of the LHC data is expected to be a major focus of research in the next few years. In this work, Cornell theorists benefit from traditionally close connections with the

LEPP experimental group, which participates in the CMS experiment at the LHC.

Another research area actively pursued at Cornell is string theory, which combines quantum field theory and gravity in a consistent framework. A key goal is to understand the properties of the four-dimensional effective theories derived from compactifications of string theory. Cornell theorists create new analytical techniques for the study of flux compactifications, use these tools to find novel solutions of supergravity, and then characterize the resulting effective actions. A primary application of these methods is in the study of the very early universe: questions about inflation can often be mapped into questions about the geometry of the internal space or about the potential governing deformations of this space. Theorists at Cornell have led the exploration of the interface between string theory and inflationary cosmology, which holds the prospect of bringing string theory into contact with cosmological observations.

Particle theory students at Cornell have the opportunity to explore a wide range of research areas, ranging from experiment-driven theory to highly mathematical analyses of supersymmetric field theories or quantum theories of gravity. There is also work at the interface between condensed matter physics and particle physics, where mathematical and numerical techniques from relativistic quantum field theory are adapted for use on condensed matter systems, and ideas from condensed matter physics are applied to quantum field theories. Work can be analytical, or it can be computational, as in numerical simulations of quantum chromodynamics and other quantum field theories—a research area invented at Cornell. The particle theory program is very flexible: it is easy for theory students to work in more than one area, and it is not unusual for a student to co-author papers with more than one professor during their graduate career. In addition, there is close collaboration with Cornell’s theoretical astrophysics group, focused on problems of common interest to particle physics and astrophysics/cosmology.