Henrik Johansson

Henrik Johansson
Department of Physics and Astronomy
Uppsala university, Box 516
SE-75120 Uppsala
Sweden

phone: +46(0)18 471 3243
e-mail: henrik.johansson@physics.uu.se

RESEARCH

My research interests are in quantum field theory and supergravity, with a focus on formal aspects of scattering amplitudes in these theories. Scattering amplitudes can be used as a powerful tool to understand hidden symmetries and remarkable relations between different classes of theories. My work has led to the realization that a generic gravity theory can be formally understood as a product of two gauge theories.  

KAW project - From Scattering Amplitudes to Gravitational Waves

This project will develop new methods for precise calculations at the forefront of theoretical
physics, ranging from scattering processes in quantum field theory to gravitational wave
emission, by using the Bern-Carrasco-Johansson (BCJ) double-copy framework, that
connects gauge, gravity and string theories. The project will involve cooperation between
the Division of Theoretical Physics at Uppsala University, and the Nordic Institute for Theoretical Physics (Nordita) that is located in Stockholm.

The project consists of five semi-independent parts:

  • Develop new methods for gauge, gravity and string theory scattering amplitudes
  • Simplify perturbative GR: potentials, black-hole mergers and gravitational waves
  • Advance integration techniques for loop amplitudes and classical gravity
  • Understand the origins of color-kinematics duality and the double copy
  • Extend the double copy to curved spaces

Background: In one of my papers from 2008, we introduce the notion of a duality between kinematical quantities (spacetime quantities) and color quantities (internal space quantities). In this framework gauge theories are organized as a specific product of two copies of Lie algebras, one for the color degrees of freedom and one for the kinematical degrees of freedom.  Gravitational theories are analogously organized as a double copy of the kinematical Lie algebras. This is most transparent for S-matrix elements, where this powerful structure has been used for amplitude calculations up to the fifth loop order in certain supersymmetric gauge and gravity theories. 

There is by now a growing list of theories where the duality and double-copy structures have been observed; it includes: pure (super-)Yang-Mills theories, pure (super)gravities, QCD and its supersymmetric extensions, Yang-Mills-Einstein (super)gravities, the nonlinear sigma model (NLSM), Born-Infeld theories and also string theory. Gauge and gravity theories are now more closely linked to each other than ever before, but even effective theories that have no gauge symmetry fit into the new picture. New connections to string theory have also emerged out of this structure: heterotic/closed string theories obeys color-kinematics duality and open string theories are double copies of simpler objects.

When the LIGO experiment in September 2015 discovered the first gravitational waves from binary black holes—which awarded them the 2017 Nobel Prize in Physics—a new window for observations of the universe opened up. In order to fully utilize this new opportunity, both theoretical calculation methods and experiments are expected to undergo significant upgrades in the future. Recent initial studies have convincingly demonstrated that the BCJ double-copy method is able to reproduce low-order binary black-hole dynamics and associated gravitational-wave emissions at significantly reduced computational cost compared to standard methods, and as such it has the potential to revolutionize analytical calculations of gravitational waves.

TEACHING

Recent Publications