Infrared and threshold effects in QCD

• Applicants: Professor Dr. Johannes Henn; Professor Dr. Matthias Steinhauser
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
• Term: from 2015 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 281686883

• Final Report Year: 2018

Final Report Abstract

The results obtained within this project allowed to answer important questions about the universal structure of infrared divergences in gauge theories. One particular highlight are the results obtained for the cusp anomalous dimension at four loops, both for massless and massive particles. The cusp anomalous dimension is an ubiquitous quantity in gauge theories. It is of great interest both for conceptual and practical reasons, and is being studied by several research groups. Within this project, we obtained novel results for this quantity, some of which were later confirmed by other groups. In the massless case, we obtained the full result in the planar limit, as well as first results for general color, in the large nf expansion. In the massless case, we were able to determine the quartic Casimir contribution at small angle. This is the first analytic result for a quartic Casimir contribution to the cusp anomalous dimension, showing that Casimir scaling is violated.

Publications

• “Fourloop photon quark form factor and cusp anomalous dimension in the large-Nc limit of QCD,” JHEP 1703 (2017) 139
  Henn, Johannes; Lee, Roman N.; Smirnov, Alexander V.; Smirnov, Vladimir A. & Steinhauser, Matthias
  
• “High energy behaviour of form factors,” JHEP 1706 (2017) 125
  Ahmed, Taushif; Henn, Johannes M. & Steinhauser, Matthias
  
• “Massive threeloop form factor in the planar limit,” JHEP 1701 (2017) 074
  Henn, Johannes; Smirnov, Alexander V.; Smirnov, Vladimir A. & Steinhauser, Matthias
  
• “On the Casimir scaling violation in the cusp anomalous dimension at small angle,” JHEP 1710, 052 (2017)
  Grozin, Andrey; Henn, Johannes & Stahlhofen, Maximilian
  
• “The n2f contributions to fermionic four-loop form factors,” Phys. Rev. D 96 (2017) no.1, 014008
  Lee, Roman N.; Smirnov, Alexander V.; Smirnov, Vladimir A. & Steinhauser, Matthias
  
• “Three-loop massive form factors: complete light-fermion and large-Nc corrections for vector, axial-vector, scalar and pseudo-scalar currents,” JHEP 1805 (2018) 187
  Lee, Roman N.; Smirnov, Alexander V.; Smirnov, Vladimir A. & Steinhauser, Matthias
  
• “Three-loop massive form factors: complete light-fermion corrections for the vector current,” JHEP 1803 (2018) 136
  Lee, Roman N.; Smirnov, Alexander V.; Smirnov, Vladimir A. & Steinhauser, Matthias
  
• “Three-Loop Quark Jet Function,” Phys. Rev. Lett. 121, no. 7, 072003 (2018)
  Brüser, Robin; Liu, Ze Long & Stahlhofen, Maximilian