Prof. Dr. Johannes Henn
Main research interests:
Scattering amplitudes in gauge and gravity theories
Infrared properties of gauge theories
Conformal symmetry and supersymmetry
Maximally supersymmetric Yang-Mills theory
Exploring the structure of scattering processes beyond the planar limit
B. Mistlberger and J.M. Henn,
``Four-Gluon Scattering at Three Loops, Infrared Structure, and the Regge Limit``
Phys. Rev. Lett. 117
(2016) 17, 171601
This paper represents a new milestone in theoretically describing scattering processes of elementary particles,
by computing a full four particle scattering amplitude at the three-loop order in quantum field theory. Our ability
to compute scattering amplitudes at high perturbative order is a crucial ingredient for fully exploiting the wealth of
experimental information collected from particle collisions at experiments such as the Large Hadron Collider. At the
theoretical level, analytic results are an important catalyst for developments. They help to understand better the
underlying structure of quantum field theory, to search for hidden simplicity and symmetries, and they provide a
testing ground for novel techniques. While previously results at the three-loop order had only been available in
the planar approximation, we now provide for the first time a full, non-planar result. Our result can be used to
glean insights into the universal structure of scattering processes, such as high-energy scattering, and important
effects due to the emission of soft radiation. In the former case, we provide new data that can be used to test and
further develop Regge theory. In the latter case, a recent effective field theory calculation showed that at the
three-loop order, non-trivial correlations between four particles exist, violating a previous dipole conjecture.
Our calculation provides a first independent confirmation of this important result.
A prototypical non-planar Feynman diagram contributing to three-loop four-gluon scattering
in Yang-Mills theory. Progress in theoretical methods allowed for the first time the analytic evaluation of the
corresponding scattering amplitude. The result provides valuable insights into the structure of scattering amplitudes.
Hidden symmetry: from classical mechanics to quantum field theory
S. Caron-Huot and J.M. Henn,
``Solvable Relativistic Hydrogenlike System in Supersymmetric Yang-Mills Theory``
Phys. Rev. Lett. 113
(2014) 16, 161601
Editor's suggestion in Phys. Rev. Lett.
This paper shows how a well-known hidden symmetry in classical and quantum mechanics can be realized in quantum field theory, helping to analyze bound-state energy levels of two-particle systems. In the development of physics, symmetry has been an important guiding principle for identifying and understanding the laws of nature. An example is the equivalence principle, which postulates that observers in different reference frames experience the same physical laws. These symmetries, which are not always obvious, can be used to understand important physical models. In classical mechanics, for example, the Kepler problem has a hidden symmetry that explains the stability of planetary orbits; in quantum mechanics, this hidden symmetry allows one to find the energy spectrum of the hydrogen atom. In this paper, we identify the same hidden symmetry within a supersymmetric quantum field theory, which describes systems at even higher energies (or equivalently, at shorter distances), like the particle interactions being explored by the Large Hadron Collider. Identifying this symmetry and applying it to the calculation of the energy levels of hydrogen-like bound states signifies an important step toward the first analytic solution of a bound-state problem in a four-dimensional quantum field theory.
``From the Motion of Planets to Quantum Field Theory``
The Institute Letter Summer 2015
Groundbreaking new method for Feynman integral computations
``Multiloop integrals in dimensional regularization made simple``
Phys. Rev. Lett. 110
(2013) 25, 251601
In this paper, I proposed a groundbreaking new method allowing for a systematic analytic computation of many previously unknown loop integrals for NNLO virtual corrections. Applications include processes involving top quarks, vector boson production, Bhabha scattering, heavy-quark effective theory (HQET). The results obtained with this method are also conceptionally beautiful and simple: for each problem, defined by the kinematics of the physical scattering process, an alphabet of differential forms is identified. Iterated integrals of the latter are then sufficient to fully describe the solution for the loop integrals, to all orders in the epsilon expansion near integer dimensions. The rules for how to form 'words', i.e. how to write down the explicit solution, is simply encoded in a set of constant N x N matrices, where N is the number of (master) integrals. Using this method, the analytic solution, to any order in epsilon, can be written down by algebraic means.
This paper has had a profound impact on the field, and the method proposed has become standard in state-of-the-art computations.