Cornering New Physics with Generic Precision Calculations

• Applicant: Dr. Johannes Braathen
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 520070247

Understanding the fundamental laws of Nature promises profound implications for science and society. While the Standard Model of Particle Physics (SM) has so far been very successful in describing Physics across a wide range of energies, it is clear, from both theoretical considerations and experimental results, that it cannot be the ultimate theory of Nature. One of the most pressing challenges of High-Energy Physics is therefore to access the nature of Physics beyond the SM (BSM). Direct collider searches have not yet found any concrete evidence of what BSM Physics might be. However, vast amounts of data will soon be available from various other sources – Higgs precision measurements, low-energy observables, cosmological observations, etc. – offering unique complementary opportunities to investigate BSM Physics. To properly assess discovery sensitivies, and to make reliable use of experimental data to determine viable regions of BSM parameter space, theorists must provide highly accurate predictions for relevant observables, which are compared to experimental measurements and limits. Moreover, this must be done in the plethora of BSM models devised to address deficiencies of the SM. This formidable task can be achieved efficiently with automation: i.e. calculating the observable of interest for a general renormalisable theory, and then applying this result to specific models. This proposal aims to broaden the applicability and increase the accuracy of automated calculations, thereby significantly strengthening our ability to probe electroweak (EW) symmetry breaking and CP violation, and in turn to constrain BSM theories. First, we will include new higher-order corrections to Higgs couplings and decays and improve the interpretation of experimental limits in terms of constraints on BSM parameter space. These developments will enable strong constraints on models with extended scalar sectors, with reaches to much higher energy scales than direct searches. Next, we will provide accurate assessments of the strength of the EW phase transition (EWPT) in general theories, and derive generic predictions for spectra of gravitational waves or densities of primordial black holes produced during first-order phase transitions (EWPT or other). This will open an entirely new direction to investigate BSM theories in general using cosmological observations. Finally, we will compute electric dipole moments for composite states in generic models, to considerably enhance limits on possible BSM sources of CP violation, by complementing existing results for elementary particles. This project will open the way to comprehensive searches of New Physics exploiting the full wealth of experimental data awaited in the near future, eventually helping to shed light on what lies beyond the SM.

• DFG Programme: Independent Junior Research Groups