arXiv subjects

John N. Ng

Publications and source records attributed to John N. Ng.

50 records · Page 3Linked to original sources

arXiv2002

Lepton Universality, Rare Decays and Split Fermions

We investigate the constraint on the split fermions in extra dimensions by considering the universality of $W$ leptonic decays $W\to l_i ν_i$, the charged lepton decays $l_i \ra l_jν_i\barν_j$, and the lepton flavor violating process $l_i\ra \bar{l}_j l_k l_h$ where $l_i= e,μ$ or $τ$. For the Standard Model (SM) background of $W\ra l_i ν_i$, we extended the one loop quantum correction to include effects of order $m_l^2/M_W^2$ and the Higgs mass dependence. We find that in general the split fermion scenarios give rise to a 4D effective Yukawa matrix of the Kaluza-Klein Higgs bosons is misaligned with respect to the fermion mass matrix. This holds true also for gauge bosons as well. This leads to decays of $l_i\ra \bar{l_j}l_k l_h$ at tree level and muonium antimuonium conversion. Interestingly the leptonic universality of $W$ boson decays are not affected at this level.

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arXiv2002

Minimal Schemes for Large Neutrino Mixings with Inverted Hierarchy

Existing oscillation data point to nonzero neutrino masses with large mixings. We analyze the generic features of the neutrino Majorana mass matrix with inverted hierarchy and construct realistic {\it minimal schemes} for the neutrino mass matrix that can explain the large (but not maximal) ν_e - ν_mu mixing of MSW-LAM as well as the nearly maximal ν_mu - ν_tau mixing and the small (or negligible) ν_e --> ν_tau transition. These minimal schemes are quite unique and turn out to be extremely predictive. Implications for neutrinoless double beta decay, tritium beta decay and cosmology are analyzed.

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arXiv2001

Neutrino-Lepton Masses, Zee Scalars and Muon g-2

Evidence for neutrino oscillations is pointing to the existence of tiny but finite neutrino masses. Such masses may be naturally generated via radiative corrections in models such as the Zee model where a singlet Zee-scalar plays a key role. We minimally extend the Zee model by including a right-handed singlet neutrino ν_R. The radiative Zee-mechanism can be protected by a simple U(1)_X symmetry involving only the ν_R and a Zee-scalar. We further construct a class of models with a single horizontal U(1)_FN (a la Frogatt-Nielsen) such that the mass patterns of the neutrinos and leptons are naturally explained. We then analyze the muon anomalous magnetic moment (g-2) and the flavor changing μ--> eγdecay. The ν_R interaction in our minimal extension is found to induce the BNL g-2 anomaly, with a light charged Zee-scalar of mass 100-300 GeV.

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arXiv1998

On the invisible decays of the Upsilon and J/Psi resonances

We estimate the most important corrections to the branching ratios for the invisible decays of quarkonium states, arising from possible extensions of the standard model. Among the possibilities considered are the presence of extra Z-bosons, minimal supersymmetric extensions of the standard model with R-parity violation, and decays into goldstinos. Prospects of detecting these corrections at existing and future B-factories and tau-charm factories are discussed.

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arXiv1997

Polarization Measurements and T-Violation in Exclusive Semileptonic B Decays

We provide a general analysis of time reversal invariance violation in the exclusive semileptonic B decays B to D l nu and B to D* l nu. Measurements of the lepton and D* polarizations can be used to search for and identify non-standard model sources of T violation. Upper limits are placed on the T-odd polarization observables in both the supersymmetric R-parity conserving and R-parity breaking theories, as well as in some non-supersymmetric extensions of the standard model, including multi-Higgs-doublet models, leptoquark models, and left-right symmetric models. It is noted that many of these models allow for large T-violating polarization effects which could be within the reach of the planned B factories.

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arXiv1997

Testing Time Reversal Invariance in Exclusive Semileptonic B Meson Decays

We demonstrate that polarization measurements in exclusive semileptonic B decays are powerful tools for unraveling non-standard model sources of T-violation. Measurements of the transverse polarization of the tau lepton in the B to D tau nu and B to D* tau nu decays probe separately effective scalar and pseudoscalar CP-violating four-Fermi interactions, whereas the D* polarization in the B to D* l nu (l=e,mu) decay is sensitive to an effective right-handed quark current interaction. Two T-odd polarization structures exist involving the D* polarization and they can be isolated and studied separately. An estimate of these T-odd effects is also given in the context of supersymmetric theories.

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arXiv1996

Supersymmetric Time Reversal Violation in Semileptonic Decays of Charged Mesons

We provide a general analysis of time reversal violation arising from misalignment between quark and squark mass eigenstates. In particular, we focus on the possibility of large enhancement effects due to the top quark mass. For semileptonic decays of the charged mesons, $K^+ \rightarrow π^0 μ^+ ν_μ$, $D^+ \rightarrow \overline{K}^0 μ^+ ν_μ$, and $B^+ \rightarrow \overline{D}^0 τ^+ ν_τ$, the transverse polarization of the lepton $P^{\bot}_l$ is a $T$-odd observable that is of great experimental interest. It is noted that under favorable choice of parameters, $P^{\bot}_μ$ in $K^+_{\mu3}$ decay can be detectable at the ongoing KEK experiment and it holds a promising prospect for discovery at the proposed BNL experiment. Furthermore, $P^{\bot}_τ$ in $B^{\pm}$ decay could well be within the reach of $B$ factories, but $P^{\bot}_μ$ in $D^{\pm}$ decay is not large enough for detection at the proposed $τ$-charm factory.

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arXiv1996

T-Violation in $K^+ \to μ^+ νγ$ Decay And Supersymmetry

Measurement of the transverse muon polarization $P^{\bot}_μ$ in the $K^+ \rightarrow μ^+νγ$ decay will be attempted for the first time at the ongoing KEK E246 experiment and also at a proposed BNL experiment. We provide a general analysis of how $P^{\bot}_μ$ is sensitive to the physical $CP$-violating phases in new physics induced four-Fermi interactions, and then we calculate the dominant contributions to $P^{\bot}_μ$ from squark family mixings in generic supersymmetric models. Estimates of the upper bounds on $P^{\bot}_μ$ are also given. It is found that a supersymmetry-induced right-handed quark current from $W$ boson exchange gives an upper limit on $P^{\bot}_μ$ as large as a few per cent, whereas with charged-Higgs-exchange induced pseudoscalar interaction, $P^{\bot}_μ$ is no larger than a few tenths of a per cent. Possible correlations between the muon polarization measurements in $K^+ \rightarrow μ^+νγ$ and $K^+ \rightarrow π^0μ^+ν$ decays are discussed, and distinctive patterns of this correlation from squark family-mixings and from the three-Higgs-doublet model are noted.

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arXiv1996

Supersymmetric Signatures at an $e$$γ$ Collider

High energy electron-photon colliders provide unique opportunities for probing physics beyond the standard model. We have studied the experimental signatures for two supersymmetric scenarios, with the lightest supersymmetric particle (LSP) being either the lightest neutralino or the gravitino. In the ``neutralino LSP'' scenario favored by the minimal supersymmetric standard model (MSSM), it is found that some basic parameters of the model, $μ$, $\tanβ$, $M_1$ and $M_2$, may be uniquely determined from the outgoing electron energy spectrum without assuming high scale unification of the masses or couplings. In the ``gravitino LSP'' scenario which occurs naturally in models of low energy dynamical supersymmetry breaking, it is possible to have background-free signatures if the next-to-lightest supersymmetric particle (NLSP) has a long decay length. In cases that the NLSP decays quickly, ways to distinguish among the experimental signatures of the two scenarios and of the standard model (SM) background are discussed.

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arXiv1995

A note on Majorana neutrinos, leptonic CKM and electron electric dipole moment

The electric dipole moment of the electron, $d_e$, is known to vanish up to thre e-loops in the standard model with massless neutrinos. However, if neutrinos are massive Majorana particles, we obtain the result that $d_e$ induced by leptonic CKM mechanism is non-vanishing at two-loop order, and it applies to all massive Majorana neutrino models.

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arXiv1994

Muon Number Violating Processes in Single Particle Extensions of the Standard Model

We study the one-loop induced muon number processes when the standard model is minimally extended to include a $\rm SU(2)$ singlet of a charged scalar $h^+$ and a neutral fermion $N$. We find that $μ\rightarrow e γ$ is more sensitive for the former model whereas $μ-e$ conversion in nuclei for the latter. Effects of a scalar leptoquark $y^{1/3}$ and a heavy vector fermion $E^-$, which induce tree level rare muon decays, are also discussed.

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arXiv1994

Phenomenological Consequences of Singlet Neutrinos

In this paper, we study the phenomenology of right-handed neutrino isosinglets. We consider the general situation where the neutrino masses are not necessarily given by $m_D^2/M$, where $m_D$ and $M$ are the Dirac and Majorana mass terms respectively. The consequent mixing between the light and heavy neutrinos is then not suppressed, and we treat it as an independent parameter in the analysis. It turns out that $μ-e$ conversion is an important experiment in placing limits on the heavy mass scale ($M$) and the mixing. Mixings among light neutrinos are constrained by neutrinoless double beta decay, as well as by solar and atmospheric neutrino experiments. Detailed one-loop calculations for lepton number violating vertices are provided.

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arXiv1993

Supersymmetric $b \rightarrow s γ$ with Large Chargino Contributions

Supersymmetric (SUSY) theories are often thought to give large branching ratios for $b \rightarrow s γ$ from charged Higgs loops. We show that in many cases chargino loop contributions can cancel those of the Higgs, and SUSY can give $B(b \rightarrow s γ)$ at or below the \SM\ prediction. We show this occurs because the large stop mass splittings usually found in SUSY break a GIM mechanism suppression. These effects are strongly enhanced by large $\tanβ$, so that $B(b \rightarrow s γ)$ is very sensitive to the value of $\tanβ$, contrary to what has been claimed. We also note that the supergravity relation $B_0 = A_0-1$ is somewhat disfavored over the general case.

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arXiv1992

What can the L3 $γγll$ events be?

We consider the 4 $γγll$ ($l=μ,\ e$) events reported by the L3 collaboration, and go through the logical possibilities which could explain the events. If they are not coincidental bremsstrahlung events, we find that the physics which they could point to is extremely limited. One possibility would be to have a new 60 GeV scalar (or pseudoscalar) particle $X^0$ with an off-diagonal coupling to a $Z$ and $Z'$ which is non-perturbative ($α> 1$), where the $Z'$ couplings to $ν\barν$ are suppressed. One could also construct a model involving $X^0$, and a second scalar $X'^0$ with a large $X'll$ coupling. We do not promote either of these models, but hope they would prove to be useful guidelines, should the L3 events turn out to be new physics.

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