Abstract:We extend the formalism developed in ref. [53] for the renormalisation of the chargino-neutralino sector to the most general case of the MSSM with complex parameters. We show that products of imaginary parts arising from MSSM parameters and from absorptive parts of loop integrals can already contribute to predictions for physical observables at the one-loop level, and demonstrate that the consistent treatment of such contributions gives rise to non-trivial structure, either in the field renormalisation constants or the corrections associated with the external legs of the considered diagrams. We furthermore point out that the phases of the parameters in the chargino-neutralino sector do not need to be renormalised at the one-loop level, and demonstrate that the appropriate choice for the mass parameters used as input for the on-shell conditions depends both on the process and the region of MSSM parameter space under consideration. As an application, we compute the complete one-loop results in the MSSM with complex parameters for the process h a →χ + iχ − j (Higgs-propagator corrections have been incorporated up to the two-loop level), which may be of interest for SUSY Higgs searches at the LHC, and for chargino pair-production at an e + e − Linear Collider, e + e − →χ + iχ − j . We investigate the dependence of the theoretical predictions on the phases of the MSSM parameters, analysing in particular the numerical relevance of the absorptive parts of loop integrals.

Complete one-loop results are obtained for the class of processesχ 0 i →χ 0 j h a in the MSSM where all parameters entering this process beyond lowest order are allowed to have arbitrary CP-violating phases. An on-shell renormalisation scheme is worked out for the chargino-neutralino sector that properly takes account of imaginary parts arising from complex parameters and from absorptive parts of loop integrals. The genuine vertex contributions to the neutralino decay amplitudes are combined with two-loop propagator-type corrections for the outgoing Higgs boson. In this way the currently most precise prediction for this class of processes is obtained. The numerical impact of the genuine vertex corrections is studied for several examples of CP-conserving and CPviolating scenarios. We find that significant effects on the decay widths and branching ratios are possible even in the CP-conserving MSSM. In the CP-violating CPX benchmark scenario the corrections to the decay width are found to be particularly large, namely, of order 45% for a Higgs mass of 40 GeV. This parameter region of the CPX scenario where a very light Higgs boson is unexcluded by present data is analysed in detail. We find that in this parameter region, which will be difficult to cover by standard Higgs search channels at the LHC, the branching ratio for the decayχ 0 2 →χ 0 1 h 1 is large. This may offer good prospects to detect such a light Higgs boson in cascade decays of supersymmetric particles.

Search for R-parity-violating supersymmetry in events with four or more leptons in √ s = 7 TeV pp collisions with the ATLAS detectorThe ATLAS collaboration E-mail: atlas.publications@cern.ch Abstract: A search for new phenomena in final states with four or more leptons (electrons or muons) is presented. The analysis is based on 4.7 fb −1 of √ s = 7 TeV proton-proton collisions delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in two signal regions: one that requires moderate values of missing transverse momentum and another that requires large effective mass. The results are interpreted in a simplified model of R-parity-violating supersymmetry in which a 95% CL exclusion region is set for charged wino masses up to 540 GeV. In an R-parity-violating MSUGRA/CMSSM model, values of m 1/2 up to 820 GeV are excluded for 10 < tan β < 40. Keywords: Hadron-Hadron ScatteringOpen Access, Copyright CERN, for the benefit of the ATLAS collaboration JHEP12(2012)1242 R-parity-violating supersymmetry SUSY postulates the existence of SUSY particles, or "sparticles", each with spin (S) differing by one-half unit from that of its SM partner. Gauge-invariant and renormalisable interactions introduced in SUSY models can violate the conservation of baryon (B) and lepton (L) number and lead to a proton lifetime shorter than current experimental limits [16]. This is usually solved by assuming that R-parity, defined by P R = (−1) 2S+3B+L , is conserved [17][18][19][20][21], which makes the lightest supersymmetric particle (LSP) stable. In P R -conserving models where the LSP is neutral and weakly interacting, sparticle production is characterised by large missing transverse momentum (E miss T ) due to LSPs escaping detection. Many SUSY searches at hadron colliders rely on this large E miss T signature. Alternatively, proton decay can be prevented by imposing other symmetries [22] that require the conservation of either lepton or baryon number, while allowing R-parity violation. Such models can accommodate non-zero neutrino masses and neutrino-mixing angles consistent with the observation of neutrino oscillations [23]. If R-parity is violated, the LSP decays into SM particles and the signature of large E miss T may be lost. Trilinear lepton-number-violating RPV interactions can generate both charged leptons and neutrinos during the LSP decay, and therefore lead to a characteristic signature with high lepton multiplicity and moderate values of E miss T compared to R-parity-conserving models. R-parity-violating modelsThe results of this analysis are interpreted in two Minimal Supersymmetric Standard Model (MSSM) scenarios with an RPV superpotential term given by W RP V = λ ijk L i L jĒk . The i, j, k indices of the λ ijk Yukawa couplings refer to the lepton generations. The lepton SU(2) doublet superfields are denoted by L i , while the corresponding singlet superfields are given by E k . Single coupling dominance is assumed with λ 121 as the only non-ze...

Complete one-loop results are obtained for the class of processesχ 0 i →χ 0 j h a in the MSSM where all parameters entering this process beyond lowest order are allowed to have arbitrary CP-violating phases. An on-shell renormalisation scheme is worked out for the chargino-neutralino sector that properly takes account of imaginary parts arising from complex parameters and from absorptive parts of loop integrals. The genuine vertex contributions to the neutralino decay amplitudes are combined with two-loop propagator-type corrections for the outgoing Higgs boson. In this way the currently most precise prediction for this class of processes is obtained. The numerical impact of the genuine vertex corrections is studied for several examples of CP-conserving and CPviolating scenarios. We find that significant effects on the decay widths and branching ratios are possible even in the CP-conserving MSSM. In the CP-violating CPX benchmark scenario the corrections to the decay width are found to be particularly large, namely, of order 45% for a Higgs mass of 40 GeV. This parameter region of the CPX scenario where a very light Higgs boson is unexcluded by present data is analysed in detail. We find that in this parameter region, which will be difficult to cover by standard Higgs search channels at the LHC, the branching ratio for the decayχ 0 2 →χ 0 1 h 1 is large. This may offer good prospects to detect such a light Higgs boson in cascade decays of supersymmetric particles.