Mu + N --> Tau + N at a Muon or Neutrino Factory

The experimental discovery of large nu_mu-nu_tau mixing indicates that analogous mixing in the charged lepton sector could be substantial. We consider the possibility that if a high intensity muon beam, perhaps at the early stages of a muon or neutrino factory, strikes a nuclear target, then conversion of some of the muons into tau leptons could occur (similar to the conversion of muons to electrons at MECO). Using current experimental limits on rare tau decays to bound the size of the relevant operators, we find that a 50 GeV muon beam, with 10^20 muons on target per year, could yield as many as 10^7 mu + N --> tau + N events per year. Backgrounds could be substantial, and we comment on the possibility of detection of this process.Comment: Paragraph on theoretical models added. Version to be published in Phys. Rev.

Production and Decays of WRW_R bosons at the LHC

With the advent of the LHC, it is important to devise clear tests for Physics Beyond the Standard Model. Such physics could manifest itself in the form of new charged bosons, whose presence is most naturally occurring in left-right symmetric models (LRSM). We analyze the single $W_R$ boson production in an asymmetric left-right model, where the left and right quark mixing matrices are not constrained to be equal. We investigate the cross sections as well as branching ratios of $W_R$ bosons at the LHC, including constraints from low energy phenomenology. We then look for most likely signals in $pp \to W_R\ t \to t ~(dijet)$ production. Including the background, we find that LHC could show significant signals for the new charged bosons. We compare our results throughout with the manifest left-right symmetric model and comment on similarities and differences.Comment: 22 pages, 9 figure

Neutrino Masses in the Effective Rank-5 Subgroups of E_6 I: Non-supersymmetric Case

The neutral fermion sectors of E_6-inspired low energy models, in particular the Alternative Left-Right and Inert models, are considered in detail within the non-supersymmetric scenario. We show that in their simplest form, these models always predict, for each generation, the lightest neutrino to be an SU(2)_L singlet, as well as two extra neutrinos with masses of the order of the up-quark mass. In order to recover Standard Model phenomenology, additional assumptions in the form of discrete symmetries and/or new interactions are needed. These are classified as the Discrete Symmetry (DS), Higher Dimensional Operators (HDO), and Additional Neutral Fermion (ANF) methods. The DS method can solve the problem, but requires additional Higgs doublets that do not get vacuum expectation values. The HDO method predicts no sterile neutrino, and that the active neutrinos mix with a heavy isodoublet neutrino, thus slightly suppressing the couplings of active neutrinos, with interesting phenomenological implications. The ANF method also predicts this suppression, and also naturally includes one or more "sterile" neutrinos. This scenario allows the existence of sterile neutrino(s) in either a 3+1 or 2+2 structure at low energies, which are favored by the LSND result.Comment: 25 pages, 1 figure; typos corrected, version to be published in Physical Review

Neutrino Masses in the Effective Rank-5 Subgroups of E_6 II: Supersymmetric Case

We present a complete analysis of the neutral fermion sector of supersymmetric E_6-inspired low energy models containing an extra SU(2), concentrating on the Alternate Left-Right and Inert models. We show that the R-parity conserving scenario always exhibits a large Dirac mass for \nu_L with maximal mixing with an isosinglet neutrino, and that R-parity violating scenarios do not change the picture other than allowing further mixing with another isosinglet. In order to recover Standard Model phenomenology, additional assumptions in the form of discrete symmetries and/or new interactions are needed. We introduce and investigate Discrete Symmetry method and Higher Dimensional Operators as mechanisms for solving the neutrino mass and mixing problems in these models.Comment: 27 pages, 2 figures; typos correted, version to be published in Physical Review

Collider Effects of Unparticle Interactions in Multiphoton Signals

A new model of physics, with a hidden conformal sector which manifests itself as an unparticle coupling to Standard Model particles effectively through higher dimensional operators, predicts strong collider signals due to unparticle self-interactions. We perform a complete analysis of the most spectacular of these signals at the hadron collider, pp -> 4photon and pp ->2photon,2gluon. These processes can go through the three-point unparticle self interactions as well as through some s and t channel diagrams with one and/or two unparticle exchanges. We study the contributions of individual diagrams classified with respect to the number of unparticle exchanges and discuss their effect on the cross sections at the Tevatron and the LHC. We also restrict the Tevatron bound on the unknown coefficient of the three-point unparticle correlator. With the availability of data from Tevatron, and the advent of the data emerging from the LHC, these interactions can provide a clear and strong indication of unparticle physics and distinguish this model from other beyond the standard model scenarios.Comment: 28 pages, 16 figure

Lorentz and CPT Violation in the Higgs Sector

Colladay and Kostelecky have proposed a framework for studying Lorentz and CPT violation in a natural extension of the Standard Model. Although numerous bounds exist on the Lorentz and CPT violating parameters in the gauge boson and fermion sectors, there are no published bounds on the parameters in the Higgs sector. We determine these bounds. The bounds on the CPT-even asymmetric coefficients arise from the one-loop contributions to the photon propagator, those from the CPT-even symmetric coefficients arise from the equivalent c_{\mu\nu} coefficients in the fermion sector, and those from the CPT-odd coefficient arise from bounds on the vacuum expectation value of the Z-boson.Comment: 17 pages, 1 figure, 1 table; Clarifications and changes to text, results unchanged. References added. Version to be published in Physical Review

Neutralino Dark Matter in the Left-Right Supersymmetric Model

We study the neutralino sector of the left-right supersymmetric model. In addition to the possibilities available in the minimal supersymmetric model, the neutralino states can be superpartners of the U(1)_{B-L} gauge boson, the neutral SU(2)_R neutral gauge boson, or of the Higgs triplets. We analyze neutralino masses and determine the parameter regions for which the lightest neutralino can be one of the new pure states. We then calculate the relic density of the dark matter for each of these states and impose the constraints coming from the rho parameter, the anomalous magnetic moment of the muon, b -> s gamma, as well as general supersymmetric mass bounds. The lightest neutralino can be the bino, or the right-wino, or the neutral triplet higgsino, all of which have different couplings to the standard model particles from the usual neutralinos. A light bino satisfies all the experimental constraints and would be the preferred dark matter candidate for light supersymmetric scalar masses, while the right-wino would be favored by intermediate supersymmetric mass scales. The neutral triplet Higgs fermion satisfies the experimental bounds only in a small region of the parameter space, for intermediate to heavy supersymmetric scalar masses.Comment: 31 pages, 8 figures, one table and references added, to be published in Phys. Rev.

B Decays in an Asymmetric Left-Right Model

Motivated by recently observed disagreements with the SM predictions in $B$ decays, we study $b \to d, s$ transitions in an asymmetric class of $SU(2)_L \times SU(2)_R \times U(1)_{B-L}$ models, with a simple one-parameter structure of the right handed mixing matrix for the quarks, which obeys the constraints from kaon physics. We use experimental constraints on the branching ratios of $b \to s \gamma$, $b \to c e {\bar \nu}_e$, and $B_{d,s}^0 -\bar{B}^0_{d,s}$ mixing to restrict the parameters of the model: $\displaystyle {g_R}/{g_L}, M_{W_2}, M_{H^\pm}, \tan \beta$ as well as the elements of the right-handed quark mixing matrix $V^R_{CKM}$. We present a comparison with the more commonly used (manifest) left-right symmetric model. Our analysis exposes the parameters most sensitive to $b$ transitions and reveals a large parameter space where left- and right-handed quarks mix differently, opening the possibility of observing marked differences in behaviour between the standard model and the left-right model.Comment: 32 pages and 8 figure