Supersymmetry with light higgsinos

The main part of this Report is divided into two chapters, with Chapter 2 treating topics of more theoretical interest, while Chapter 3 is focussed on phenomenology. In Section 2.1 we will begin with a brief review of the particle content and the parameters characterizing the MSSM, since this is the low-scale model we will be mostly concerned with. We will subsequently review the MSSM Higgs sector and the chargino-neutralino sector, to the extent that is needed for the subsequent discussion, exhibiting in particular some characteristics of higgsino-like neutralinos and charginos. This is followed by a discussion of the μ problem in Section 2.2, i.e. the problem of generating a supersymmetric higgsino mass of the order of (or below) the scale MS which characterizes supersymmetry breaking within the MSSM supermultiplets. We will review several aspects of this problem in global and local supersymmetry, and also briefly discuss it in the context of gauge-mediated models and of the MSSM. Section 2.3 follows Refs. [1,3] in discussing a solution to the μ problem motivated by higher-dimensional grand unified theories, where the structure of the MSSM Higgs sector at the grand-unified scale is dictated by a shift symmetry. In Section 2.4 we will discuss the generation of a μ parameter in gravity-mediated models with approximate R-symmetries, following Ref. [2]. Section 2.5 deals with the possibility to generate a μ parameter independently of supersymmetry breaking as originally proposed in Ref. [9], while the subject of Section 2.6 is the generation of the μ parameter in the hybrid gauge-gravity mediated models of Refs. [4,6,7]. Finally in Section 2.7 we discuss light higgsinos in the context of an extremely split scenario where almost all superpartners have masses close to the Planck scale [10]. We begin chapter 3 by reviewing the production (in Section 3.1) and decays (in Section 3.2) of higgsino-like neutralinos and charginos at colliders. Present-day collider constraints are collected in Section 3.3. We subsequently discuss the discovery potential for light higgsinos in Section 3.4, both at the LHC (drawing upon Ref. [5] among others) and at a future linear collider, recapitulating the ILC analysis of Ref. [8]. Section 3.5 contains a brief discussion of higgsino dark matter. Finally, conclusions and some possible future directions are given in Chapter 4. (author)