65 research outputs found

    A Summer with the Large Hadron Collider: The Search for Fundamental Physics

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    The B-L MSSM from Strings to the LHC

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    We develop connections between a string-motivated realization of the minimal B â?? L extension of the MSSM and LHC-observable phenomenology. Using a random scan of the high-scale parameter space, together with numerical solution of the renormalization group equations, we connect the modelâ??s roots in String Theory to its phenomenological implications for the LHC. One predictive result of this approach is a limited set of possible lightest supersymmetric particles (LSPs). Motivated by this result, we study the implications of a stop or sbottom LSP at the LHC. This yields predictive connections between the neutrino sector and the LHC. We present lower bounds on the mass of stop and sbottom LSPs

    The RR-parity Violating Decays of Charginos and Neutralinos in the B-L MSSM

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    The B−LB-L MSSM is the MSSM with three right-handed neutrino chiral multiplets and gauged B−LB-L symmetry. The B−LB-L symmetry is broken by the third family right-handed sneutrino acquiring a VEV, thus spontaneously breaking RR-parity. Within a natural range of soft supersymmetry breaking parameters, it is shown that a large and uncorrelated number of initial values satisfy all present phenomenological constraints; including the correct masses for the W±W^{\pm}, Z0Z^0 bosons, having all sparticles exceeding their present lower bounds and giving the experimentally measured value for the Higgs boson. For this "valid" set of initial values, there are a number of different LSPs, each occurring a calculable number of times. We plot this statistically and determine that among the most prevalent LSPs are chargino and neutralino mass eigenstates. In this paper, the RR-parity violating decay channels of charginos and neutralinos to standard model particles are determined, and the interaction vertices and decay rates computed analytically. These results are valid for any chargino and neutralino, regardless of whether or not they are the LSP. For chargino and neutralino LSPs, we will-- in a subsequent series of papers --present a numerical study of their RPV decays evaluated statistically over the range of associated valid initial points.Comment: 62 pages, 12 figures, added references in section 1, corrected some calculation error

    The Minimal SUSY B−LB-L Model: From the Unification Scale to the LHC

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    This paper introduces a random statistical scan over the high-energy initial parameter space of the minimal SUSY B−LB-L model--denoted as the B−LB-L MSSM. Each initial set of points is renormalization group evolved to the electroweak scale--being subjected, sequentially, to the requirement of radiative B−LB-L and electroweak symmetry breaking, the present experimental lower bounds on the B−LB-L vector boson and sparticle masses, as well as the lightest neutral Higgs mass of ∼\sim125 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 low-energy 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−LB-L MSSM is shown to generically require less fine-tuning.Comment: 65 pages, 18 figure

    Spontaneous R-Parity Breaking, Stop LSP Decays and the Neutrino Mass Hierarchy

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    The MSSM with right-handed neutrino supermultiplets, gauged B-L symmetry and a non-vanishing sneutrino expectation value is the minimal theory that spontaneously breaks R-parity and is consistent with the bounds on proton stability and lepton number violation. This minimal B-L MSSM can have a colored/charged LSP, of which a stop LSP is the most amenable to observation at the LHC. We study the R-parity violating decays of a stop LSP into a bottom quark and charged leptons--the dominant modes for a generic "admixture" stop. A numerical analysis of the relative branching ratios of these decay channels is given using a wide scan over the parameter space. The fact that R-parity is violated in this theory by a vacuum expectation value of a sneutrino links these branching ratios directly to the neutrino mass hierarchy. It is shown how a discovery of bottom-charged lepton events at the LHC can potentially determine whether the neutrino masses are in a normal or inverted hierarchy, as well as determining the theta_23 neutrino mixing angle. Finally, present LHC bounds on these leptoquark signatures are used to put lower bounds on the stop mass.Comment: 13 pages, 2 figures, upgraded stop lower bound analysis, version accepted by PL
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