This paper introduces a random statistical scan over the high-energy initial parameter space of the minimal SUSY B − L model -denoted as the B − L MSSM. Each initial set of points is renormalization group evolved to the electroweak scale -being subjected, sequentially, to the requirement of radiative B − L and electroweak symmetry breaking, the present experimental lower bounds on the B − L vector boson and sparticle masses, as well as the lightest neutral Higgs mass of ∼125 GeV. The subspace of initial parameters that satisfies all such constraints is presented, shown to be robust and to contain a wide range of different configurations of soft supersymmetry breaking masses. The lowenergy predictions of each such "valid" point -such as the sparticle mass spectrum and, in particular, the LSP -are computed and then statistically analyzed over the full subspace of valid points. Finally, the amount of fine-tuning required is quantified and compared to the MSSM computed using an identical random scan. The B − L MSSM is shown to generically require less fine-tuninng.
We study the minimal gauged U (1)B−L supersymmetric model and show that it provides an attractive theory for spontaneous R-parity violation. Both U (1)B−L and R-parity are broken by the vacuum expectation value of the right-handed sneutrino (proportional to the soft SUSY masses), thereby linking the B − L and soft SUSY scales. In this context we find a consistent mechanism for generating neutrino masses and a realistic mass spectrum, all without extending the Higgs sector of the minimal supersymmetry standard model. We discuss the most relevant collider signals and the connection between the Z ′ gauge boson and R-parity violation.
The structure of the B-L minimal supersymmetric Standard Model (MSSM) theoryspecifically, the relevant mass scales and soft supersymmetric breaking parameters -is discussed. The space of initial soft parameters is explored at the high scale using random statistical sampling subject to a constraint on the range of dimensionful parameters. For every chosen initial point, the complete set of renormalization group equations is solved. The low energy results are then constrained to be consistent with present experimental data. It is shown that a large set of initial conditions satisfy these constraints and lead to acceptable low energy particle physics. Each such initial point has explicit predictions, such as the exact physical sparticle spectrum which is presented for two such points. There are also statistical predictions for the masses of the sparticles and the LSP species which are displayed as histograms. Finally, the fine-tuning of the μ parameter -which is always equivalent to or smaller than in the MSSM -is discussed.An ad hoc Z 2 symmetry -R-parity is invoked in the minimal supersymmetric Standard Model (MSSM) to eliminate certain dimension four operators, which, if present, would induce unobserved rapid proton decay. This leads to the important question: is there a natural explanation for R-parity? Note that R-parity is contained as a finite subgroup of the Abelian group U(1) B-L , and that U(1) B−L can be imposed as a global symmetry of both the MSSM and the right-handed neutrino extended MSSM. One expects, however, that a continuous symmetry of the Lagrangian will appear in its local form; that is, as a gauge symmetry. It has long been known that the MSSM is anomalous under this local symmetry, whereas ‡ Corresponding author 1550085-1 B. A. Ovrut, A. Purves & S. Spinnerthe MSSM extended by three right-handed neutrino chiral multiplets with gauged U(1) B-L -henceforth referred to as the B-L MSSM is anomaly free and renormalizable. Furthermore, it is the minimal such theory. If the gauged U(1) B-L symmetry can be spontaneously broken, then the B-L MSSM gives a natural explanation for the suppression of dimension four proton decay, that is, it is forbidden by gauge invariance rather than by an ad hoc finite symmetry. This makes the B-L MSSM very attractive from both a theoretical and phenomenological perspective.The B-L MSSM was introduced from a "bottom-up" phenomenological point of view in Refs. 1 and 2. It was also found from a "top-down" viewpoint to be the low-energy theory associated with a class of smooth vacua of the E 8 × E 8 heterotic superstring. 3-5 In addition, it was shown 6-8 that the "soft" supersymmetry breaking operators associated with this low-energy theory can radiatively induce -via a nonvanishing vacuum expectation value for a right-handed sneutrino -the breakdown of the U(1) B-L symmetry. Since the sneutrino has odd B-L charge, R-parity is spontaneously broken at a scale that is naturally consistent with both electroweak breaking and the bounds on proton decay. In Ref. 9, an analysis ...
The existence of R-parity in supersymmetric models can be naturally explained as being a discrete subgroup of gauged baryon minus lepton number (B − L). The most minimal supersymmetric B − L model triggers spontaneous R-parity violation, while remaining consistent with proton stability. This model is well-motivated by string theory and makes several interesting, testable predictions.Furthermore, R-parity violation contributes to neutrino masses, thereby connecting the neutrino sector to the decay of the lightest supersymmetric particle (LSP). This paper analyzes the decays of third generation squark LSPs into a quark and a lepton. In certain cases, the branching ratios into charged leptons reveal information about the neutrino mass hierarchy, a current goal of experimental neutrino physics, as well as the θ 23 neutrino mixing angle. Furthermore, optimization of leptoquark searches for this scenario is discussed. Using currently available data, the lower bounds on the third generation squarks are computed.
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