Linear Collider Signals of Anomaly Mediated Supersymmetry Breaking

Diagnostic signals of the minimal model of anomaly mediated supersymmetry breaking are discussed in the context of a $\sqrt{s}$ = 1 TeV $e^+e^-$ linear collider.Comment: Talk given at SUSY'01, Dubna, Russia, June 11-17, 2001. 4 pages, LaTeX, 1 postscript figure. Style file include

Neutrino masses and mixing, lightest neutralino decays and a solution to the μ\mu problem in supersymmetry

We examine in detail the neutrino masses and mixing patterns in an extension of the minimal supersymmetric standard model with three gauge-singlet neutrinos and R-parity violation. The Majorana masses for the gauge-singlet neutrinos as well as the usual $\mu$-term for the Higgs superfields are generated at the electroweak scale through the vacuum expectation values of the singlet sneutrinos. The resulting effective mass matrix for the three light neutrinos have contributions from the seesaw mechanism involving the singlet neutrinos as well as due to the mixing with the heavy neutralinos. This model is popularly known in the literature as the "$\mu$ from $\nu$ supersymmetric standard model" ($\mu\nu$SSM). We show that even with flavour diagonal neutrino Yukawa couplings, the global data on three-flavour neutrinos can be well accounted for in this scenario, at the tree level. We also analyze the mixing in the chargino and the Higgs sector and calculate the decays of the lightest supersymmetric particle in this model. The decay branching ratios show certain correlations with the neutrino mixing angles, which can be tested at the LHC. Some other phenomenological implications of such a model have been discussed.Comment: 49 pages, 19 figures, LaTex, JHEP style, short remarks added in the text, typos corrected, minor modifications in the abstract, to appear in JHE

Higgs boson mass, neutrino masses and mixing and keV dark matter in an U(1)R−U(1)_R- lepton number model

We discuss neutrino masses and mixing in the framework of a supersymmetric model with an $U(1)_{R}$ symmetry, consisting of a single right handed neutrino superfield with an appropriate R charge. The lepton number ($L$) of the standard model fermions are identified with the negative of their R-charges. As a result, a subset of leptonic R-parity violating operators can be present and are consistent with the $U(1)_R$ symmetry. This model can produce one light Dirac neutrino mass at the tree level without the need of introducing a very small neutrino Yukawa coupling. We analyze the scalar sector of this model in detail paying special attention to the mass of the lightest Higgs boson. One of the sneutrinos might acquire a substantial vacuum expectation value leading to interesting phenomenological consequences. Different sum rules involving the physical scalar masses are obtained and we show that the lightest Higgs boson mass receives a contribution proportional to the square of the neutrino Yukawa coupling $f$. This allows for a 125 GeV Higgs boson at the tree level for $f \sim {\cal O} (1)$ and still having a small tree level mass for the active neutrino. In order to fit the experimental results involving neutrino masses and mixing angles we introduce a small breaking of $U(1)_R$ symmetry, in the context of anomaly mediated supersymmetry breaking. In the presence of this small R-symmetry breaking, light neutrino masses receive contributions at the one-loop level involving the R-parity violating interactions. We also identify the right handed sterile neutrino as a warm dark matter candidate in our model. In the case of R-symmetry breaking, the large $f$ case is characterized by a few hundred MeV lightest neutralino as an unstable lightest supersymmetric particle (LSP) and we briefly discuss the cosmological implications of such a scenario.Comment: Minor corrections in the text, figure 9.6 and 9.7 modified, eq. (66) added, matches with the published version in JHE

Vacuum Stability Constraints on the Minimal Singlet TeV Seesaw Model

We consider the minimal seesaw model in which two gauge singlet right handed neutrinos with opposite lepton numbers are added to the Standard Model. In this model, the smallness of the neutrino mass is explained by the tiny lepton number violating coupling between one of the singlets with the standard left-handed neutrinos. This allows one to have the right handed neutrino mass at the TeV scale as well as appreciable mixing between the light and heavy states. This model is fully reconstructible in terms of the neutrino oscillation parameters apart from the overall coupling strengths. We show that the overall coupling strength $y_\nu$ for the Dirac type coupling between the left handed neutrino and one of the singlets can be restricted by consideration of the (meta)stability bounds on the electroweak vacuum. In this scenario the lepton flavor violating decays of charged leptons can be appreciable which can put further constraint on $y_\nu$, for right-handed neutrinos at TeV scale. We discuss the combined constraints on $y_\nu$ for this scenario from the process $\mu \rightarrow e \gamma$ and from the consideration of vacuum (meta)stability constraints on the Higgs self coupling. We also briefly discuss the implications for neutrinoless double beta decay and possible signatures of the model that can be expected at colliders.Comment: One loop effective potential due to heavy neutrino included, 20 pages, 9 figure

Stability constraints in triplet extension of MSSM

We study the stability constraints on the parameter space of a triplet extension of MSSM. Existence of unbounded from below directions in the potential can spoil successful Electroweak (EW) symmetry breaking by making the corresponding minimum unstable, and hence the model should be free from those directions. Avoiding those directions restricts the parameter space of the model. We derive four stability constraints, of which only three independent from each other. After scanning the model's parameter space for phenomenologically viable data points, we impose the stability constraints and find that only about a quarter of the data points features a stable EW minimum. At those data points featuring stability, $\mu$ and the up Higgs soft mass turn out to be smaller than about a TeV in absolute value, which make the mass of the lightest chargino and neutralino smaller than about 700 GeV. Two relevant phenomenological consequences of lifting the unbounded from below directions are that the lightest Higgs boson decay rate to diphoton predicted by the triplet extension of MSSM generally features larger deviations from MSSM and fine tuning is actually higher, that what each of the two would be without imposing stability constraints.Comment: 20 pages, 3 figure

h→γγh \rightarrow \gamma \gamma in U(1)R−U(1)_{R}- lepton number model with a right-handed neutrino

We perform a detailed study of the signal rate of the lightest Higgs boson in the diphoton channel ($\mu_{\gamma \gamma}$), recently analyzed by both the ATLAS and CMS collaborations at the Large Hadron Collider, in the framework of $U(1)_R-$ lepton number model with a right handed neutrino superfield. The corresponding neutrino Yukawa coupling, `$f$', plays a very important role in the phenomenology of this model. A large value of $f\sim\mathcal O(1)$ provides an additional tree level contribution to the lightest Higgs boson mass along with a very light (mass $\sim$ a few hundred MeV) bino like neutralino and a small tree level mass of one of the active neutrinos that is compatible with various experimental results. In the presence of this light neutralino, the invisible decay width of the Higgs boson can become important. We studied this scenario in conjunction with the recent LHC results. The signal rate $\mu_{\gamma\gamma}$ obtained in this scenario is compatible with the recent results from both the ATLAS and the CMS collaborations at 1$\sigma$ level. A small value of `$f$', on the other hand, is compatible with a sterile neutrino acting as a 7 keV dark matter that can explain the observation of a mono-energetic X-ray photon line by the XMM-Newton X-ray observatory. We also study the impact of $\mu_{\gamma\gamma}$ in this case.Comment: 45 pages, Corrected a sign error in the numerical code and included the correct symmetry factor in Eq.(B.8). One figure removed, some modifications in the text, conclusions partially changed. Erratum published in JHE

R parity violating supersymmetric explanation for the CDF Wjj excess

Recently CDF has reported a 4.1 sigma excess in the distribution of the dijet invariant mass between 120-160 GeV in Wjj event sample in 7.3 fb^{-1} of data, which has generated considerable interest. We offer a possible explanation of this observation in the general framework of MSSM with R-parity violation through resonance production of tau sneutrino decaying into the LSP stau_1 and W boson. We also give the predictions of this scenario for the LHC operating at 7 TeV center of mass energy.Comment: 4 pages, 2 ps figures, revtex4, typos corrected, one new reference added, version to appear in PR