Precision Calculations in the Higgs Sector - Paving the Way to the New Physics Landscape

• Applicant: Professorin Dr. Milada Margarete Mühlleitner
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
• Term: from 2016 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 318580798

• Final Report Year: 2020

Final Report Abstract

Questions that cannot be answered within the Standard Model (SM) require new physics (NP) extensions beyond the SM (BSM). The SM-like behavior of the discovered Higgs boson together with the fact that no direct sign of NP has been discovered so far calls for high-precision predictions of the Higgs boson observables in order to be able to search indirectly for new physics effects in the Higgs sector by looking for departures of the Higgs boson properties from the SM expectations. The proposed project contributed to this effort through the computation of the higher-order corrections of the Higgs boson decays in some archetypical BSM Higgs sector extensions. We computed the higher-order electroweak (EW) corrections to the Higgs boson decays of the CP-conserving 2-Higgs-Doublet Model (2HDM) and its singlet extension, the Next-to-2HDM (N2HDM), as well as the (SUSY-)EW and SUSY-QCD corrections to the neutral Higgs boson decays of the CP-violating next-to-minimal supersymmetric extension (NMSSM). For the 2HDM and N2HDM, we were the first ones to derive renormalisation schemes of the mixing angles that are gauge-parameter independent, do not encounter unnaturally large corrections and are also process independent. The corrections have been implemented in the computer codes 2HDECAY, ewN2HDECAY and NMSSMCALCEW, respectively, including the possibility to choose among different renormalisation schemes. We performed phenomenological investigations and studied and compared the impact of the higher-order corrections and the remaining theoretical error due to missing higher-order corrections. The corrections turned out to be significant and therefore have to be taken into account to make meaningful predictions. The theoretical error has been reduced through the inclusion of the higher-order corrections. For the NMSSM we also computed the EW corrections to the charged NMSSM Higgs decay in a typical experimental signature for the search of charged Higgs bosons. We showed that the mixture of different higher-order corrections encountered by the necessity to match the experimentally measured Higgs mass value, induces a significant gauge parameter dependence. For the CP-violating 2HDM, we developed the code C2HDM HDECAY and analysed its phenomenology taking into account the most relevant theoretical and up-to-date experimental constraints including the latest ones on the electric dipole moments (EDMs). The minimal supersymmetric extension of the SM (MSSM) can be matched on a 2HDM as its low-energy limit. In this context, the hMSSM approach allows to describe the complicated supersymmetric parameter space with solely a few parameters by making use of the phenomenologically measured Higgs boson mass. While this leads to a reliable prediction of the Higgs decays into SM particles it fails to describe Higgs-to-Higgs decays. We carefully re-investigated the problem and were able to suggest an improved Higgs self-coupling definition thus improving the predictions for the important SM-like Higgs pair production process through resonant heavy Higgs decays. Due to the early departure of the involved postdoctoral researcher (he got an offer for a permanent university lecturer position) we did not finish the EW corrections to the SM extension by a complex singlet field (CxSM). Hiring not long after another postdoc, we still laid the grounds for this project and are presently computing these corrections. In continuation of our works within this proposal, we extended the computation of the higher-order corrections to the charged Higgs boson decays in the remaining decay channels. Additionally, we started a broad analysis of the Higgs pair production processes of the 2HDM, C2HDM, N2HDM, and NMSSM with the aim to propose benchmark points for these processes that are one of the main focuses of the high-luminosity LHC. The computer codes implementing the results of this project are broadly used by the highenergy particle physics community. With this project we have significantly contributed to the advancement of high-precision predictions and analyses of the new physics landscape allowing for a meaningful interpretation of the experimental results and advancing our understanding of Nature.

Publications

• Gauge-independent Renormalization of the N2HDM, JHEP 12 (2017) 077
  M. Krause, D. Lopez-Val, M. Mühlleitner, R. Santos
  
• The C2HDM revisited, JHEP 02 (2018) 073
  D. Fontes, M. Mühlleitner, J.C. Romão R. Santos, J.P. Silva, J. Wittbrodt
  
• The hMSSM approach for Higgs selfcouplings revisited, Eur. Phys. J. C 79 (2019) 1
  S. Liebler, M. M¨hlleitner, M. Spira, M. Stadelmaier
  
• 2HDECAY - A program for the calculation of the electroweak one-loop corrections to Higgs decays in the Two-Higgs-Doublet Model including the state-of-the-art QCD corrections, Comput. Phys. Commun. 246 (2020) 106852
  M. Krause, M. Mühlleitner, M. Spira
  
• ewN2HDECAY - A program for the Calculation of Electroweak One-Loop Corrections to Higgs Decays in the Next-to-Minimal Two-Higgs-Doublet Model Including State-of-the-Art QCD Corrections, Comput. Phys. Commun. 247 (2020) 106924
  M. Krause, M. Mühlleitner
  
• Gauge dependences of higherorder corrections to NMSSM Higgs boson masses and the charged Higgs Decay H ± → W ± hi , Eur. Phys. J. C 80 (2020) 3, 292
  Thi Nhung Dao, L. Fritz, M. Krause, M. Mühlleitner, S. Patel
  
• Impact of Electroweak Corrections on Neutral Higgs Boson Decays in Extended Higgs Sectors, JHEP 04 (2020) 083
  M. Krause, M. Mühlleitner
  
• One-Loop Corrections to the Two-Body Decays of the Neutral Higgs Bosons in the Complex NMSSM, Eur. Phys. J. C 80 (2020) 10, 960
  J. Baglio, Thi Nhung Dao, M. Mühlleitner