String theory is an important cornerstone of the theoretical research program at the PRISMA+ Cluster of Excellence - and is represented by Professor Hans Jockers, a proven expert in the field. Since May 2021, the 44-year-old physicist has held a W3 professorship in Mathematical Physics.
It is the interplay between physics and mathematics that has fascinated Hans Jockers since his school days: "String theory represents this wonderful connection in an ideal way." It runs like a thread through his research career, as he already dedicated his master's thesis in 2002 at the University of Texas in Austin, Texas to this theoretical model for describing fundamental forces and particles.
Unlike quantum field theory, on which the Standard Model of particle physics is based, string theory describes the fundamental building blocks of matter not as point-like particles but as spatially extended objects. At the beginning, these were often visualized as strings and gave the theory its name. More than that, string theory envisions the existence of higher-dimensional spacetime, i.e., more than four spacetime dimensions. Many modern developments in theoretical high-energy physics, which is also a focus of fundamental particle physics research in Mainz, are often related to string theory.
In order to establish the relation between the quantum field theoretical description of particle physics in the known four spacetime dimensions and string theory, physicists have to consider so-called compactifications: Here, the extra dimensions of string theory are combined into a compact entity whose spatial extent is so small that it cannot be directly observed with the experimentally available (lower) energies. However, the compact extra dimensions define the phenomenological properties of the particles in the effective four-dimensional theory. "During my various research stations, I have focused partly on this phenomenologically driven approach, to again return to the purely mathematical description of string theory," explains Hans Jockers, adding, "Because I find it very exciting to derive physical predictions from a mathematical description on the one hand, and to transfer physical phenomena to the level of mathematics on the other."
In his eyes, the importance of string theory has increasingly changed in recent years: Originally developed with the goal of deriving a new world formula by determining the geometric properties of the extra dimensions and thus replacing the incomplete Standard Model, string theory today "provides a very good framework for describing gravity and particle physics in a unified, i.e., quantum mechanical, way." Thus, string theory can now make statements as to whether certain extensions of the Standard Model are compatible with the gravitational interaction and thus represent consistent models of particle physics even at very high energy scales.
This is because while three of the four observed fundamental forces can be described in a consistent way by means of quantum field theory for a long time, string theory also includes the gravitational interaction, i.e., the fourth force. "In this sense, modern string theory today has all the ingredients to describe very many phenomena in nature," formulates Hans Jockers.
What he particularly appreciates about Mainz as a research location is that it is very well and broadly positioned in physics, both theoretically and experimentally, under the umbrella of the PRISMA+ cluster, and that it offers exciting topics and focal points in mathematics. Above all, he finds here anew the ideal interface of mathematics and physics, which has accompanied him since his studies and has not let go. "This makes Mainz one of the most exciting places nationwide for me to advance my research."