Narrow Results

Limits on the anomalous magnetic moment and the electric dipole moment of the τ lepton are calculated through the reaction e⁺e^-→τ⁺τ^-γ at the Z₁-pole and in the framework of a left–right symmetric model. The results are based on the recent data reported by the L3 collaboration at CERN LEP. Due to the stringent limit of the model mixing angle ϕ, the effect of this angle on the dipole moments is quite small.

Recent results in searches for high transverse momentum leptons in events with large missing transverse momentum in electron–proton collisions at HERA are reviewed. These searches have implications for searches for physics beyond the Standard Model. The most recent results on searches for single top production via Flavour Changing Neutral Currents are reviewed. The consistency of results from the H1 and ZEUS collaborations and prospects of discovering new physics during the final year of HERA running are discussed.

The charged and the neutral currents are obtained by using a formal algebraical approach (developed and applied by the author) within the exact solution of a 3-3-1 gauge model with right-handed neutrinos. The entire Standard Model phenomenology is recovered without imposing any supplemental condition, but only by choosing an adequate set of parameters from the very beginning of the calculus. A new and rich phenomenology regarding the particles and their currents occurs as well. The appealing feature of our results resides in the exact expressions of the currents which need not the adjustment usually due to the small mixing angle ϕ between neutral bosons Z and Z′ (like in most of the papers in the literature treating the same issue). The required mixing was considered and already performed as an intermediate step by the solving method itself, since the physical eigenstates of those bosons were determined and then identified in the neutral currents.

The Pisano–Pleitez–Frampton 3-3-1 model is revisited here within the framework of the general method for solving gauge models with high symmetries. This exact algebraical approach — proposed several years ago by one of us — was designed to include a minimal Higgs mechanism that spontaneously breaks the gauge symmetry up to the universal U(1)_em electromagnetic one and, consequently, to supply the mass spectrum and the couplings of the currents for all the particles in the model. We prove in this paper that this powerful tool, when is applied to the PPF 3-3-1 model, naturally recovers the whole Standard Model phenomenology and, in addition, predicts — since a proper parametrization is employed — viable results such as: (i) the exact expressions for the boson and fermion masses, (ii) the couplings of the charged and neutral currents and (iii) a plausible neutrino mass pattern. A generalized Weinberg transformation is implemented, while the mixing between the neutral bosons Z and Z′ is performed as a necessary step by the method itself. Some phenomenological consequences are also sketched, including the strange possibility that simultaneously m(Z) = m(Z′) and m(W) = m(V) hold.

Using the experimental value for the rate , we derive constraints on the number of light neutrino species with the invisible width method in the framework of a left–right symmetric model (LRSM) and a E₆ superstring model as a function of their respective mixing angles for the neutral vector gauge bosons. Using the above LEP result we get the constraints -1.6×10^-3≤ ϕ ≤ 1.1 × 10^-3 and -1.3 × 10^-2 ≤ ϕ_E6 ≤ 0.4 × 10^-2, which are stronger than those obtained in previous studies of these models.

The boson mass spectrum of the electroweak SU(4)_L ⊗ U(1)_Y model with exotic electric charges is investigated by using the algebraical approach supplied by the method of solving gauge models with high symmetries. Our approach predicts for the boson sector a one-parameter mass scale to be tuned in order to match the data obtained at LHC, LEP, CDF.

The weak currents with respect to the diagonal neutral bosons Z, Z′ and Z^′′ of a specific SU(4)_L⊗U(1)_Y gauge model are computed in detail for all the fermion families involved therein. Our algebraical approach, which is based on the general method of solving gauge models with high symmetries proposed several years ago by Cotăescu, recovers in a nontrivial way all the Standard Model values for current couplings of the traditional leptons and quarks, and predicts plausible values for those of the exotic fermions in the model.

From the total cross-section for the reaction e⁺e^-→τ⁺τ^-γ at the Z₁ pole and in the framework of a simplest little Higgs model (SLHM), we get a limit on the characteristic energy scale of the model f, f ≥ 5.4 TeV, which in turn induces bounds on the electromagnetic and weak dipole moments of the tau–lepton. Our bounds on the electromagnetic moments are consistent with the bounds obtained by the L3 and OPAL collaborations for the reaction e⁺e^-→τ⁺τ^-γ. We also obtained bounds on the tau weak dipole moments which are consistent with the bounds obtained recently by the DELPHI and ALEPH collaborations from the reaction e⁺e^-→τ⁺τ^-.

This review considers models with extended Higgs sectors in which there are tree-level flavor-changing neutral currents (FCNC) mediated by scalars. After briefly reviewing models without tree-level FCNC, several models with such currents are discussed. A popular mass-matrix ansatz, in which the flavor-changing couplings are the geometric mean of the individual flavor couplings, is presented. While it provided a target for experimentalists for three decades, it is now being severely challenged by experiments. Couplings expected to be of $O(1)$ must be substantially smaller and the ansatz is now not favored. The minimal flavor violation hypothesis is introduced. Then specific models are presented, including the Branco–Grimus–Lavoura models. These models are not yet excluded experimentally, but they are highly predictive and will be tested once heavy Higgs bosons are discovered. We then turn to flavorful models and flavor-changing decays of heavy Higgs bosons, and it is shown that in many of these models, the heavy Higgs could predominantly decay in a flavor-changing manner (such as $ct$ or $\mu \tau$) and experimentalists are encouraged to include these possibilities in their searches.

We obtain limits on the electromagnetic and weak dipole moments of the tau-lepton in the framework of a left–right symmetric model (LRSM) and a class of E₆ inspired models with an additional neutral vector boson Z_θ. Using as an input the data obtained by the L3 and OPAL collaborations for the reaction e⁺e^- → τ⁺τ^-γ, we get a stringent limit on the LRSM mixing angle ϕ, -1.66 × 10^-3 < ϕ<1.22×10^-3, which in turn induces bounds on the tau weak dipole moments which are consistent with the bounds obtained recently by the DELPHI and ALEPH collaborations from the reaction e⁺e^-→τ⁺τ^-. We also get similar bounds for the weak dipole moments of the tau lepton in the framework of E₆ superstring models.

This paper presents the physics case for a new high-energy, ultra-high statistics neutrino scattering experiment, NuSOnG (Neutrino Scattering on Glass). This experiment uses a Tevatron-based neutrino beam to obtain over an order of magnitude higher statistics than presently available for the purely weak processes ν_μ + e^- → ν_μ + e^- and ν_μ + e^- → ν_e + μ^-. A sample of Deep Inelastic Scattering events which is over two orders of magnitude larger than past samples will also be obtained. As a result, NuSOnG will be unique among present and planned experiments for its ability to probe neutrino couplings to Beyond the Standard Model physics. Many Beyond Standard Model theories physics predict a rich hierarchy of TeV-scale new states that can correct neutrino cross-sections, through modifications of Zνν couplings, tree-level exchanges of new particles such as Z′'s, or through loop-level oblique corrections to gauge boson propagators. These corrections are generic in theories of extra dimensions, extended gauge symmetries, supersymmetry, and more. The sensitivity of NuSOnG to this new physics extends beyond 5 TeV mass scales. This paper reviews these physics opportunities.

For the particular class of SU(4)_L ⊗ U(1)_Y electroweak models without exotic electric charges, some plausible phenomenological predictions — such as the boson mass spectrum and charges of all the fermions involved therein — are made by using the algebraical approach of the exactly solving method for gauge models with high symmetries. Along with the one-parameter resulting mass scale (to be confirmed at TeV scale in LHC) our approach predicts the exact expressions of the charges (both electric and neutral) in the fermion sector, while all the Standard Model phenomenology is naturally recovered.

We calculate the emissivity due to neutrino-pair production in e⁺e^- annihilation in the context of a left–right symmetric model in a way that can be used in supernova calculations. We also present some simple estimates which show that such process can act as an efficient energy-loss mechanism in the shocked supernova core. We find that the emissivity is dependent on the mixing angle ϕ of the model in the allowed range for this parameter.

mixing offers a profound probe into the effects of new physics beyond the Standard Model. In this paper, and mass differences are considered taking the effect of both Z- and Z′-mediated flavor-changing neutral currents in the mixing (q = d, s). Our estimated mass of Z′ boson is accessible at the experiments LHC and B-factories in near future.

In recent years, B_s →τ⁺τ^- rare decay has attracted a lot of attention since it is very sensitive to the structure of standard model (SM) and potential source of new physics beyond SM. In this paper, we study the effect of both Z and Z′-mediated flavor-changing neutral currents on the B_s →τ⁺τ^- decay. We find the branching ratio B(B_s→τ⁺τ^-) is enhanced relative to SM prediction, which would help to explain the recently observed CP-violation from like-sign dimuon charge asymmetry in the B system.

The recent observation of the same-sign dimuon charge asymmetry in the B system by the D0 collaboration has 3.9σ deviation from the standard model prediction. However, the recent LHCb data on B_s neutral-meson mixing do not accommodate the D0 collaboration result. In this paper, considering the effect of Z′-mediated flavor-changing neutral currents in the mixing, the same-sign dimuon charge asymmetry is calculated. We find the same-sign dimuon charge asymmetry is enhanced from its SM prediction and provides signals for new physics beyond the SM.

We investigate the dipole moments of the tau-neutrino at high-energy and high luminosity at linear electron–positron colliders, such as CLIC or ILC through the analysis of the reaction $e^{+}{e}^{-}\to \nu \bar{\nu }\gamma$ in the framework of the $SU{(4)}_L\times U{(1)}_X$ model. The limits on dipole moment were obtained for integrated luminosity of ${ℒ}=250\text{–}1000{\mathrm{\text{fb}}}^{-1}$ and mass ranging from 0.25 to 1.0 TeV. The estimated limits for the tau-neutrino magnetic and electric dipole moments at 95% of confidence level are ${\mu }_{{\nu }_{\tau }}\le 4.83\times 10^{-9}$ and $d_{{\nu }_{\tau }}\le 2.04\times 10^{-19}$ improved by 2–3 orders of magnitude compared to L3 and complement previous studies on the dipole moments.

We evaluate the stellar energy-loss rates ${𝒬}$ due to the production of neutrino pair in 3-3-1 models. The energy loss rate ${𝒬}$ is evaluated for different values of $\beta =\pm \frac{1}{\sqrt{3}},\pm \frac{2}{\sqrt{3}},\pm \sqrt{3}$ in which $\beta$ is a parameter used to define the charge operator in the 331 models. We show that the contribution of dipole moment to the energy loss rate is small compared to the contribution of new natural gauge boson $Z^{\prime }$. The correction ${𝒬}$ compared with that of Standard Model is evaluated and do not exceed 14% and is highest with $\beta =-\sqrt{3}$. Of all the evaluated models, model with $\beta =-\sqrt{3}$ give a relative large ${𝒬}$ correction for the mass of $Z^{\prime }$$m_{Z^{\prime }}\le 4000$ GeV. This mass range is within the searching range for $Z^{\prime }$ boson at LHC.

The detection of galactic supernova (SN) neutrinos represents one of the future frontiers of low energy neutrino physics and astrophysics. The neutron coherence of neutral currents (NCs) allows quite large cross-sections in the case of neutron rich targets, which can be exploited in detecting earth and sky neutrinos by measuring nuclear recoils. They are relatively cheap and easy to maintain. These (NC) cross-sections are not dependent on flavor conversions and, thus, their measurement will provide useful information about the neutrino source. In particular, they will yield information about the primary neutrino fluxes and perhaps about the spectrum after flavor conversions in neutrino sphere. They might also provide some clues about the neutrino mass hierarchy. The advantages of large gaseous low threshold and high resolution time projection counters (TPC) detectors are discussed.

The detection of galactic supernova (SN) neutrinos represents one of the future frontiers of low energy neutrino physics and astrophysics. The neutron coherence of neutral currents (NCs) allows quite large cross-sections in the case of neutron rich targets, which can be exploited in detecting earth and sky neutrinos by measuring nuclear recoils. They are relatively cheap and easy to maintain. These (NC) cross-sections are not dependent on flavor conversions and, thus, their measurement will provide useful information about the neutrino source. In particular, they will yield information about the primary neutrino fluxes and perhaps about the spectrum after flavor conversions in neutrino sphere. They might also provide some clues about the neutrino mass hierarchy. The advantages of large gaseous low threshold and high resolution time projection counters (TPC) detectors are discussed.