– University of Copenhagen

Effective field theory

The Standard Model of particle physics must be extended due to its deficiencies in explaining Dark Matter, Baryogenesis, Inflation and Neutrino masses.

The Standard Model is also sensitive to quantum corrections coupling higher mass scales into the observed Higgs boson mass. Extensive experimental efforts have not yet uncovered direct evidence of the new model to construct to address these issues. This is surprising! As a result, attempting to guess what model will supplant the Standard Model, a paradigm that has held sway for decades, is giving way to a new systematic approach -- the Standard Model Effective Field Theory (SMEFT).

Fig. 1

Fig. 2

The particle phenomenology group is primarily focused on developing the SMEFT and using this formalism to study physics at the Large Hadron Collider and related experimental facilities. The idea is to cast as wide a net as possible for the effects of physics beyond the Standard Model and to narrow down on possible deviations, if they appear in the future LHC physics program. Such deviations would hold precious clues as to the nature of new physics that addresses the deficiencies of the Standard Model. To this end we have recently been systematically reformulating SM calculations into the SMEFT to develop the global constraint picture. This is required in RunII that is gearing up at LHC, as alternative formalisms - such as the famous “kappa” approach (illustrated in Fig 1,2) that is currently used used to characterize the properties of the Higgs boson will no longer be a consistent theoretical description as measurements get more precise on the properties of the Higgs. This means that it is required to calculate one loop corrections to the SMEFT to consistently incorporate the higher precision data expected out of LHC.

A sample of recent diagrams calculated in the group is given in Fig 3. Neglecting such corrections reduces the strength of the conclusions that can be drawn from the data. The group has a very active research program in determining the global constraint picture in the SMEFT as illustrated by Fig 4. The particle pheno group also has strong interests in Neutrino physics, Cosmology and Flavour physics and jumps on the ball of anomalies that appear from time to time. 

The unifying theme of the research programs is the use of Effective Field Theory techniques.

Fig. 3

Fig. 4