Electroweak phase transitions with BSM fermions

Martin Gabelmann,Jonas Müller,M Margarete Mühlleitner

doi:10.1007/jhep01(2022)012

Martin Gabelmann, Jonas Müller + Show 1 more

Open Access

https://doi.org/10.1007/jhep01(2022)012

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Abstract

We study the impact of additional beyond-the-Standard Model (BSM) fermions, charged under the Standard Model (SM) SU(2)L ⊗ U(1)Y gauge group, on the electroweak phase transition (EWPT) in a 2-Higgs-Doublet-Model (2HDM) of type II. We find that the strength of the EWPT can be enhanced by about 40% compared to the default 2HDM. Therefore, additional light fermions are a useful tool to weaken the tension between increasing mass constraints on BSM scalars and the requirement of additional light scalar degrees of freedom to accommodate a strong first order EWPT. The findings are of particular interest for a variety of (non-minimal) split supersymmetry scenarios which necessarily introduce additional light fermion degrees of freedom.

Highlights

JHEP01(2022)012 searches for colored scalars are pushing the soft-SUSY-breaking scale of top superpartners above the TeV-scale [10, 11]
We study the impact of additional beyond-the-Standard Model (BSM) fermions, charged under the Standard Model (SM) SU(2)L ⊗ U(1)Y gauge group, on the electroweak phase transition (EWPT) in a 2-Higgs-Doublet-Model (2HDM) of type II
Additional light fermions are a useful tool to weaken the tension between increasing mass constraints on BSM scalars and the requirement of additional light scalar degrees of freedom to accommodate a strong first order EWPT

Summary

A 2HDM with electroweakinos

We work in the softly-broken Z2 symmetric version of the 2HDM [32, 33]. It is useful to define a basis with two Higgs doublets Hu and Hd with different isospin, Hu = Φ2, Hd = −iσ2Φ∗1 ,. Such that Hu, Hd and tan β = Hu / Hd coincide with the corresponding tree-level quantities of the MSSM. We extend the default particle content of the real CP-conserving 2HDM by additional non-SM like fermions. The BSM fermion sector should resemble the additional non-SM fermion part of the MSSM. For g1u = g1d = g1MSSM and g2u = g2d = g2MSSM, eq (2.3) coincides with the corresponding part of the tree-level Lagrangian of the MSSM. The abbreviation ‘sym.’ indicates that the matrix is symmetric with the corresponding entries to be filled in

Finite temperature corrections

Phenomenology of the EWPT

Prospects for split-SUSY

Findings

Conclusions