https://doi.org/10.1140/epjc/s10052-017-4734-8
Regular Article - Theoretical Physics
Two-loop corrections to the 
parameter in Two-Higgs-Doublet models
Max-Planck-Institut für Physik (Werner-Heisenberg-Institut), Föhringer Ring 6, 80805, Munich, Germany
* e-mail: shessen@mpp.mpg.de
Received:
20
December
2016
Accepted:
3
March
2017
Published online:
21
March
2017
Models with two scalar doublets are among the simplest extensions of the Standard Model which fulfill the relation 
at lowest order for the parameter as favored by experimental data for electroweak observables allowing only small deviations from unity. Such small deviations 
originate exclusively from quantum effects with special sensitivity to mass splittings between different isospin components of fermions and scalars. In this paper the dominant two-loop electroweak corrections to are calculated in the CP-conserving THDM, resulting from the top-Yukawa coupling and the self-couplings of the Higgs bosons in the gauge-less limit. The on-shell renormalization scheme is applied. With the assumption that one of the CP-even neutral scalars represents the scalar boson observed by the LHC experiments, with standard properties, the two-loop non-standard contributions in can be separated from the standard ones. These contributions are of particular interest since they increase with mass splittings between non-standard Higgs bosons and can be additionally enhanced by 
and 
, an additional free coefficient of the Higgs potential, and can thus modify the one-loop result substantially. Numerical results are given for the dependence on the various non-standard parameters, and the influence on the calculation of electroweak precision observables is discussed.
© The Author(s), 2017
