We analyse the fine-tuning in the Constrained Minimal Supersymmetric Standard Model (CMSSM) in the light of the present and expected ATLAS and CMS SUSY searches. Even with 10 fb −1 of data and no discovery of SUSY valid regions might remain with finetuning less than 20. Moreover we investigate the fine-tuning price of GUT scale Yukawa coupling relations. Considering a 2σ constraint for (g − 2) µ and fine-tuning less than 30 yields an allowed range of y τ /y b = [1.31, 1.70], which points towards the alternative GUT prediction y τ /y b = 3/2. Relaxing the (g − 2) µ constraint to 5σ extends the possible region to [1.02,1.70], allowing for approximate b − τ Yukawa coupling unification.
We analyse the naturalness of the Minimal Supersymmetric Standard Model (MSSM) in the light of recent LHC results from the ATLAS and CMS experiments. We study nonuniversal boundary conditions for the scalar and the gaugino sector, with fixed relations between some of the soft breaking parameters, and find a significant reduction of finetuning for non-universal gaugino masses. For a Higgs mass of about 125 GeV, as observed recently, we find parameter regions with a fine-tuning of O (10), taking into account experimental and theoretical uncertainties. These regions also survive after comparison with simplified model searches in ATLAS and CMS. For a fine-tuning less than 20 the lightest neutralino is expected to be lighter than about 400 GeV and the lighter stop can be as heavy as 3.5 TeV. On the other hand, the gluino mass is required to be above 1.5 TeV. For non-universal gaugino masses, we discuss which fixed GUT scale ratios can lead to a reduced fine-tuning and find that the recent Higgs results have a strong impact on which ratio is favoured. We also discuss the naturalness of GUT scale Yukawa relations, comparing the non-universal MSSM with the CMSSM.
Abstract:We study the collider phenomenology of the minimal unified version of the supersymmetry breaking scheme called Tree-level Gauge Mediation. We identify a peculiar source of gaugino mass non-universality related to the necessary SU(5)-breaking in the light fermion mass ratios and a gaugino mass sum rule at the GUT scale, 3M 2 + 2M 3 = 5M 1 , which represents a smoking gun of this scenario, together with the known treelevel sfermion mass ratiom d c ,l = √ 2m q,u c ,e c . The boundary conditions of the soft SUSY breaking terms can be parameterised in terms of six relevant parameters only (plus the sign of the µ-parameter). We analyze the parameter space and define three benchmark points, corresponding to the three possible NLSPs, a bino-or wino-like neutralino or the stau. The LSP is the gravitino as in gauge mediation. For these benchmark points we show possible signatures at the LHC focusing on the Razor variable. We also comment on the Higgs mass.
Tree-level gauge mediation (TGM) is a scenario of SUSY breaking in which the tree-level exchange of heavy (possibly GUT) vector fields generates flavor-universal sfermion masses. In this work we extend this framework to the case of E 6 that is the natural extension of the minimal case studied so far. Despite the number of possible E 6 subgroups containing G SM is large (we list all rank 6 subgroups), there are only three different cases corresponding to the number of vector messengers. As a robust prediction we find that sfermion masses are SU(5) invariant at the GUT scale, even if the gauge group does not contain SU(5). If SUSY breaking is mediated purely by the U(1) generator that commutes with SO(10) we obtain universal sfermion masses and thus can derive the CMSSM boundary conditions in a novel scenario.
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