Radiative Enhancement of Stop Mixing
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Radiative Enhancement of Stop Mixing Kwang Sik Jeong∗ Department of Physics, Pusan National University, Busan 46241, Korea (Received 18 September 2020; accepted 25 September 2020) A supersymmetric extension of the Standard Model should rely on the mixing in the stop sector in order to accommodate the 125 GeV Higgs boson if the stops are around or below the multi-TeV, as would be required to avoid severe fine-tuning in the electroweak symmetry breaking and to achieve the gauge coupling unification. Using approximate analytic solutions to the renormalization group equations for the stop sector couplings, we examine how to enhance the stop mixing at low energy scales through radiative corrections. Sizable stop mixing can be obtained in the mediation scheme of supersymmetry breaking where the sum of the mass squareds for the scalar fields associated with the top quark Yukawa coupling is negative at the messenger scale. In addition, the gauginos can induce a considerable enhancement if they have non-universal masses at the unification scale, which is the case in the mixed mediation scheme where the relative strength of anomaly mediation is comparable to those of other flavor and CP conserving mediations, such as gauge and moduli mediation. Keywords: Supersymmetry, Models beyond the standard model, Higgs boson DOI: 10.3938/jkps.77.960
I. INTRODUCTION
As sensitive to unknown ultraviolet physics via quantum corrections, the Higgs sector is considered to be a window to uncover physics beyond the Standard Model (SM) of particle physics. A natural way to reduce the sensitivity to ultraviolet physics is to invoke supersymmetry (SUSY). Though the experimental evidence is absent yet, SUSY remains as a well-motivated scenario for physics beyond the SM not only because it can explain the origin of electroweak symmetry breaking but also because it helps to solve problems of the SM, such as dark matter, unification, and cosmic inflation. The SM-like Higgs boson observed at the Large Hadron Collider (LHC) constrains the minimal supersymmetric SM (MSSM) to have a sizable mixing in the stop sector if tan β is low or if the stops are around or below the multi-TeV [1,2]. Here tan β is the ratio of the vacuum expectation values of the Higgs doublets. It is thus important to explore how to enhance the stop mixing at low energy scales within the MSSM with SUSY breaking mediated via flavor and CP conserving interactions, as is required unless the sfermions are very heavy, above 100 TeV. In this paper we point out that the size of stop mixing at low energy scales is limited by the ratio between the scalar trilinear coupling and the sum of soft scalar mass squareds for the fields associated with the top quark ∗ E-mail:
Yukawa coupling, i.e. by At /Ct at a given energy scale, where Ct2 ≡ m2Hu + m2t˜L + m2R˜ . The approximate analytic solutions to the renormalization group equations for those parameters show that the stop mixing can be considerably enhanced by radiative corrections if Ct2 is negative at the messenger scale Λmess , or if the gauginos hav
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