Zee Model Confronts SNO Data

We reexamine the solution of the minimal Zee model by comparing with the data of the SNO experiment, and conclude that the model is strongly disfavored but not yet excluded by the observations. Two extensions of the Zee model are briefly discussed both of which introduce additional freedom and can accommodate the data.Comment: 16 pages LaTeX including 7 figure

Implications of a Massless Neutralino for Neutrino Physics

We consider the phenomenological implications of a soft SUSY breaking term BN at the TeV scale (here B is the U(1)_Y gaugino and N is the right-handed neutrino field). In models with a massless (or nearly massless) neutralino, such a term will give rise through the see-saw mechanism to new contributions to the mass matrix of the light neutrinos. We treat the massless neutralino as an (almost) sterile neutrino and find that its mass depends on the square of the soft SUSY breaking scale, with interesting consequences for neutrino physics. We also show that, although it requires fine-tuning, a massless neutralino in the MSSM or NMSSM is not experimentally excluded. The implications of this scenario for neutrino physics are discussed.Comment: 14 pages, latex, no figure

(S)fermion Masses in Fat Brane Scenario

We discuss the fermion mass hierarchy and the flavor mixings in the fat brane scenario of a five dimensional SUSY theory. Assuming that the matter fields lives in the bulk, their zero mode wave functions are Gaussians, and Higgs fields are localized on the brane, we find simple various types of the matter configurations generating the mass matrices consistent with experimental data. Sfermion mass spectrum is also discussed using the matter configurations found above. Which type of squark mass spectra (the degeneracy, the decoupling and the alignment) is realized depends on the relative locations of SUSY breaking brane and the brane where Higgs fields are localized.Comment: 18 pages, LaTe

Constraints On Radiative Neutrino Mass Models From Oscillation Data

The three neutrino Zee model and its extension including three active and one sterile species are studied in the light of new neutrino oscillation data. We obtain analytical relations for the mixing angle in solar oscillations in terms of neutrino mass squared differences. For the four neutrino case, we obtain the result $\mathsf{sin^2 2 \theta_\odot \approx 1 - [ (\Delta m^2_{Atm})^2/(4 \Delta m^2_{LSND} \Delta m^2_\odot) ]^2}$, which can accommodate both the large and small mixing scenarios. We show that within this framework, while both the SMA-MSW and the LMA-MSW solutions can easily be accommodated, it would be difficult to reconcile the LOW-QVO solutions. We also comment on the active-sterile admixture within phenomenologically viable textures.Comment: The paper has been substantially rewritten, especially in Section IV, though the basic results are unchanged. Some new references and an appendix have been adde

Present and Future Bounds on Non-Standard Neutrino Interactions

We consider Non-Standard neutrino Interactions (NSI), described by four-fermion operators of the form $(\bar{\nu}_{\alpha} \gamma {\nu}_{\beta}) (\bar{f} \gamma f)$, where $f$ is an electron or first generation quark. We assume these operators are generated at dimension $\geq 8$, so the related vertices involving charged leptons, obtained by an SU(2) transformation $\nu_{\delta} \to e_{\delta}$, do not appear at tree level. These related vertices necessarily arise at one loop, via $W$ exchange. We catalogue current constraints from $\sin^2 \theta_W$ measurements in neutrino scattering, from atmospheric neutrino observations, from LEP, and from bounds on the related charged lepton operators. We estimate future bounds from comparing KamLAND and solar neutrino data, and from measuring $\sin^2 \theta_W$ at the near detector of a neutrino factory. Operators constructed with $\nu_\mu$ and $\nu_e$ should not confuse the determination of oscillation parameters at a $\nu$factory, because the processes we consider are more sensitive than oscillations at the far detector. For operators involving $\nu_\tau$, we estimate similar sensitivities at the near and far detector.Comment: Erratum added at the end of the documen

The CDF dijet excess from intrinsic quarks

The CDF collaboration reported an excess in the production of two jets in association with a $W$. We discuss constraints on possible new particle state interpretations of this excess. The fact of no statistically significant deviation from the SM expectation for {$Z$+dijet} events in CDF data disfavors the new particle explanation. We show that the nucleon intrinsic strange quarks provide an important contribution to the $W$ boson production in association with a single top quark production. Such {$W$+t} single top quark production can contribute to the CDF {$W$+dijet} excess, thus the nucleon intrinsic quarks can provide a possible explanation to the CDF excess in {$W$+dijet} but not in {$Z$+dijet} events.Comment: 4 latex pages, 1 figure. Version for journal publicatio

Weak Isospin Violations in Charged and Neutral Higgs Couplings from SUSY Loop Corrections

Supersymmetric QCD and supersymmetric electroweak loop corrections to the violations of weak isospin to Yukawa couplings are investigated. Specifically it involves an analysis of the supersymmetric loop corrections to the Higgs couplings to the third generation quarks and leptons. Here we analyze the SUSY loop corrections to the charged Higgs couplings which are then compared with the supersymmetric loop corrections to the neutral Higgs couplings previously computed. It is found that the weak isospin violations can be quite significant, i.e, as much as 40-50% or more of the total loop correction to the Yukawa coupling. The effects of CP phases are also studied and it is found that these effects can either enhance or suppress the weak isospin violations. We also investigate the weak isospin violation effects on the branching ratio $BR(H^-\to\bar t b)/ BR(H^-\to \bar\nu_{\tau}\tau^-)$ and show that the effects are sensitive to CP phases. Thus an accurate measurement of this branching ratio along with the branching ratio of the neutral Higgs boson decays can provide a measure of weak isospin violation along with providing a clue to the presence of supersymmetry.Comment: 20 pages, 9 figure

B_s --> mu+ mu- decay in the R-parity violating minimal supergravity

We study B_s --> mu+ mu- in the context of the R-parity violating minimal supergravity in the high tan beta regime. We find that the lowest value of the branching ratio can go well below the present LHCb sensitivity and hence B_s --> mu+ mu- can even be invisible to the LHC. We also find that the present upper bound on Br(B_s --> mu+ mu-) puts strong constraint on the minimal supergravity parameter space. The constraints become more severe if the upper bound is close to its standard model prediction.Comment: 18 pages, 10 figures; version to be published in European Physical Journal

Neutrino masses in R-parity violating supersymmetric models

We study neutrino masses and mixing in R-parity violating supersymmetric models with generic soft supersymmetry breaking terms. Neutrinos acquire masses from various sources: Tree level neutrino--neutralino mixing and loop effects proportional to bilinear and/or trilinear R-parity violating parameters. Each of these contributions is controlled by different parameters and have different suppression or enhancement factors which we identified. Within an Abelian horizontal symmetry framework these factors are related and specific predictions can be made. We found that the main contributions to the neutrino masses are from the tree level and the bilinear loops and that the observed neutrino data can be accommodated once mild fine-tuning is allowed.Comment: 18 pages; minor typos corrected. To be published in Physical Review

CP Violation in Supersymmetric U(1)' Models

The supersymmetric CP problem is studied within superstring-motivated extensions of the MSSM with an additional U(1)' gauge symmetry broken at the TeV scale. This class of models offers an attractive solution to the mu problem of the MSSM, in which U(1)' gauge invariance forbids the bare mu term, but an effective mu parameter is generated by the vacuum expectation value of a Standard Model singlet S which has superpotential coupling of the form SH_uH_d to the electroweak Higgs doublets. The effective mu parameter is thus dynamically determined as a function of the soft supersymmetry breaking parameters, and can be complex if the soft parameters have nontrivial CP-violating phases. We examine the phenomenological constraints on the reparameterization invariant phase combinations within this framework, and find that the supersymmetric CP problem can be greatly alleviated in models in which the phase of the SU(2) gaugino mass parameter is aligned with the soft trilinear scalar mass parameter associated with the SH_uH_d coupling. We also study how the phases filter into the Higgs sector, and find that while the Higgs sector conserves CP at the renormalizable level to all orders of perturbation theory, CP violation can enter at the nonrenormalizable level at one-loop order. In the majority of the parameter space, the lightest Higgs boson remains essentially CP even but the heavier Higgs bosons can exhibit large CP-violating mixings, similar to the CP-violating MSSM with large mu parameter.Comment: 29 pp, 3 figs, 2 table