Abstract
We investigate constraints from the observed branching ratio for b→sγ and fine-tuning in the framework of natural supersymmetry. The natural supersymmetry requires the large trilinear coupling of the stop sector, light higgsinos (a small μ parameter) and light stops, in order to reduce the fine-tuning in the Higgs sector while avoiding the LEP constraint. It is found that in such a scenario 5% (10%) level of fine-tuning is inevitable due to the b→sγ constraint even if the messenger scale is as low as 105 GeV(104 GeV), provided that the gaugino masses satisfy the GUT relation.
Highlights
The Standard Model (SM) of particle physics has achieved a remarkable success in describing physical phenomena accessible so far
As listed in Refs. [4, 5], naturalness argument calls for several conditions in addition to light stops; an adequate value of tan β in the Higgs sector, the large stop trilinear coupling At, the small Higgsino mass parameter μ in the superpotential and the small messenger scale. (Definition of those parameters are given in the sction.) The first two conditions are related to the Higgs mass bound [6, 7, 8], while the others are to improve naturalness, which is discussed in the subsequent section
In this letter we have studied the level of fine-tuning in the Higgs sector, considering the constraints from the observation of the branching ratio for b → sγ in the Minimal Supersymmetric Standard Model (MSSM)
Summary
The Standard Model (SM) of particle physics has achieved a remarkable success in describing physical phenomena accessible so far. Naturalness in the supersymmetric models, on the other hand, requires the third generation squarks, especially stops, to have their masses around the electroweak scale It is worth studying the case where only the third generation squarks are relatively light and the other superparticles are beyond the reach of the current collider experiments. (Definition of those parameters are given in the sction.) The first two conditions are related to the Higgs mass bound [6, 7, 8], while the others are to improve naturalness, which is discussed in the subsequent section Such a light stop scenario is favored in terms of the naturalness argument, contributions of superparticles to the inclusive decay rate B → Xsγ are enhanced [9], and it should be carefully taken care of. While the constraints given there would be relaxed by R-parity violation or in compressed superparticle mass spectra scenario, our result is robust even for such cases
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