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Bing-Lin Young

Publications and source records attributed to Bing-Lin Young.

36 records · Page 2Linked to original sources
arXiv1999

Implications of LEP/SLD Data for New Physics in Zbb_bar Couplings

The combined LEP/SLD data on the b\bar b forward-backward asymmetry from the Z-pole measurements may imply the presence of new physics in the $Zb\bar b$ couplings. In general, the effect of new physics can be parameterized by $SU_C(3)\times SU_L(2)\times U_Y(1)$ invariant higher dimensional operators. By fitting the recently announced LEP/SLD data on A_b and R_b, the size of the coupling strengths of these operators can be determined. We also found that the new physics operators can be divided into two types, depending on their Higgs field content. The ones involving the Higgs have very mild effects at higher energy colliders, while the other type which do not contain the Higgs field can show significantly large effects on $b\bar b$ production at LEP II, $t\bar t$ production at the NLC and single top production at the Tevatron. The preliminary data from the LEP II measurements disfavors the second type of operators.

hep-ph↗
arXiv1999

R-parity violation and top quark polarization at the Fermilab Tevatron collider

The lepton or baryon number violating top quark interactions in the supersymmetric standard model with R parity violation contribute to the process d dbar to t tbar at the tree level via the t- or u-channel sfermion exchange. Since these interactions are chiral, they induce polarization to the top quark in the t tbar events at hadron colliders. We show in this article that the polarization can be a useful observable for probing these interactions at the upgraded Fermilab Tevatron collider, because the polarization is expected to be very small in the standard model.

hep-ph↗
arXiv1999

Neutrino Mixing, CP/T Violation and Textures in Four-Neutrino Models

We examine the prospects for determining the neutrino mixing matrix and for observing CP and T violation in neutrino oscillations in four-neutrino models. We focus on a general class of four-neutrino models with two pairs of nearly degenerate mass eigenstates separated by approximately 1 eV, which can describe the solar, atmospheric and LSND neutrino data. We present a general parametrization of these models and discuss in detail the determination of the mixing parameters and the mass matrix texture from current and future neutrino data in the case where $ν_e$ and $ν_μ$ each mix primarily with one other neutrino. We find that measurable CP/T violation in long-baseline experiments, with amplitude at the level of the LSND signal, is possible given current experimental constraints. Also, additional oscillation effects in short- and long-baseline experiments may be measurable in many cases. We point out that, given separate scales for the mass-squared differences of the solar and atmospheric oscillations, observable CP/T violation effects in neutrino oscillations signals the existence of a sterile neutrino. We examine several textures of the neutrino mass matrix and determine which textures can have measurable CP/T violation in neutrino oscillations in long-baseline experiments. We also briefly discuss some possible origins of the neutrino mass terms in straightforward extensions of the Standard Model.

hep-ph↗
arXiv1998

Probing anomalous top quark couplings at eγcolliders

We study in the effective Lagrangian approach the possibility of probing anomalous top quark charged current couplings in the single top production at a high energy eγcollider. We analyzed all possible dimension-six CP-conserving operators which can give rise to an anomalous Wtb coupling which represent new physics effect generated at a higher energy scale. For those operators which also give rise to anomalous Zbb_bar or right-handed Wtb couplings, we find that they are strongly constrained by the existing R_b and b->sγdata. As a result, a collider with a luminosity of the order of 100 fb^{-1} is required to observe the anomalous effects. For other operators which currently subject to no strong constraints, the high energy eγcollider can probe their couplings effectively because of the clean environment of such a collider.

hep-ph↗
arXiv1998

Probing anomalous top quark interactions at the Fermilab Tevatron Collider

We study the effects of dimension-six operators contributing to the $gt\bar t$ vertex in top quark pair production at the Tevatron collider. We derive both the limits from Run 1 data and the potential bounds from future runs (Run 2 and 3). Although the current constraints are not very strong, the future runs are quite effective in probing these operators. We investigate the possibility of disentangling different operators with the $t\bar t$ invariant mass distribution and the top quark polarization asymmetry. We also study the effects of a different set of operators contributing to single top production via the $Wt\bar b$ coupling. We derive the current and potential future bounds on these anomalous operators and find that the upgraded Tevatron can improve the existing constraints from $R_b$ for one of the operators.

hep-ph↗
arXiv1998

Single Top Quark Production via FCNC Couplings at Hadron Colliders

We calculate single top-quark production at hadron colliders via the chromo-magnetic flavor-changing neutral current couplings $\bar tcg$ and $\bar tug$. We find that the strength for the anomalous $\bar tcg$ ($\bar tug$) coupling may be probed to $κ_c / Λ= 0.092 {TeV}^{-1}$ ($κ_u / Λ= 0.026 {TeV}^{-1}$) at the Tevatron with $2 {fb}^{-1}$ of data and $κ_c / Λ= 0.013 {TeV}^{-1}$ ($κ_u / Λ= 0.0061 {TeV}^{-1}$) at the LHC with $10 {fb}^{-1}$ of data. The two couplings may be distinguished by a comparision of the single top signal with the direct top and top decay signals for these couplings.

hep-ph↗
arXiv1998

Effective CP-violating operators of the tau lepton and some of their phenomenologies

The dimension-six CP-violating SU_L(2)\times U_Y(1) invariant operators involving the tau lepton are studied. The constraints from the available experimental data on tau dipole moments are derived. Under the current constraints, the induced CP-violating effects could possibly be observed in tau -> 3πν_τ at the future tau-charm factory.

hep-ph↗
arXiv1997

R-parity-violating SUSY effects and signals in single top production at the Tevatron

We discuss single top quark production via u^i+\bar d^j \to t+\bar b at the Fermilab Tevatron in the minimal supersymmetric model with R-parity violation. We find that within the allowed range of coupling constants, the lepton-number violating couplings can give rise to observable effects when the slepton mass lies in a specific narrow range. For the baryon-number violating couplings, the contribution to the production rate can be quite large in the presently allowed range of the coupling constants. We show that the measurement of single top production at the upgraded Tevatron can be used to constrain a linear combination of products of the R-parity violating couplings.

hep-ph↗
arXiv1997

b b-bar Production on the Z Resonance and Implications for LEP2

In terms of an effective lagrangian, we examine the effect of new physics associated with third-generation fermions on b b-bar production at the Z resonance and study its implications for LEP2. We obtain the constraints on such operators with derivative couplings at LEP1 and the SLC, and determine the prospects for detecting their presence at LEP2. We find that despite the small observed deviations from the standard model on the Z resonance, much larger deviations from standard model predictions are possible at LEP2, and the corresponding couplings can be determined rather precisely.

hep-ph↗
arXiv1997

Dimension-six CP-violating operators of the third-family quarks and their effects at colliders

We listed all possible dimension-six CP-violating $SU_c(3)\times SU_L(2)\times U_Y(1)$ invariant operators involving the third-family quarks, which can be generated by new physics at a higher energy scale. The expressions of these operators after electroweak symmetry breaking and the induced effective couplings $Wt\bar b$, $Xb\bar b$ and $Xt\bar t$ $(X=Z,γ,g,H)$ are also presented. We have evaluated sample contributions of these operators to CP-odd asymmetries of transverse polarization of top quark in single top production at the upgraded Tevatron, the similar effect in top-antitop pair production at the NLC, and the CP-odd observables of momentum correlations among the top quark decay products at the NLC. The energy and luminosity sensitivity in probing these CP-violating new physics has also been studied.

hep-ph↗
arXiv1997

Dimension-six CP-conserving operators of the third-family quarks and their effects on collider observables

We list all possible dimension-six CP-conserving $SU_c(3)\times SU_L(2) \times U_Y(1)$ invariant operators involving the third-family quarks which could be generated by new physics at a higher scale. Expressions for these operators after electroweak gauge symmetry breaking and the induced effective couplings $Wt\bar b$, $Xb\bar b$ and $Xt\bar t$ $( X=Z,γ,g,H)$ are presented. Analytic expressions for the tree level contributions of all these operators to the observables $R_b$ and $A^b_{FB}$ at LEP I, $σ(e^+e^-\rightarrow b\bar b)$ and $A^b_{FB}$ at LEP II, $σ(e^+e^-\rightarrow t\bar t)$ and $A_{FB}^t$ at the NLC, as well as $σ(p\bar p\rightarrow t\bar b+X)$ at the Tevatron upgrade, are provided. The effects of these operators on different electroweak observables are discussed and numerical examples presented. Numerical analyses show that in the coupling region allowed by $R_b$ and $A^b_{FB}$ at LEP I, some of the new physics operators can still have significant contributions at LEP II, the Tevatron and the NLC.

hep-ph↗
arXiv1996

Unitarity Constraints on Anomalous Top Quark Couplings to Weak Gauge Bosons

If there is new physics associated with the top quark, it could show up as anomalous couplings of the top quark to weak gauge bosons, such as $Z\ttbar$ and $W\tbbar$ vector and axial-vector couplings. We use the processes $\ttbar\to Z^0Z^0$, $\ttbar\to W^+W^-$, and $\ttbar\to Z^0H$ to obtain the unitarity constraints on these anomalous couplings, and combine these constraints with those from precision electroweak data. The unitarity constraints can impose additional limits on the anomalous couplings when the scale of new physics is as low as 2 TeV. A nonzero measurement of such an anomalous coupling leads to an upper limit on the new physics scale from the unitarity condition.

hep-ph↗
arXiv1995

Some Recent Developments in Sphalerons

We review briefly the sphaleron and list some of its properties. We summarize some of the results in models which have an extended scalar sector. We also present our work on models dealing with physics beyond the standard model. We focus on the energy of the sphaleron which is important in determining the rate of baryon number violation at the electroweak scale.

hep-ph↗
arXiv1994

Unitarity And Anomalous Top-Quark Yukawa Couplings

Unitarity constraints on anomalous top-Higgs couplings are examined. We also compare the unitarity constraints with the constraints from electroweak baryogenesis and electric dipole moments derived earlier.

hep-ph↗
arXiv1994

On the vacuum theta angle in Yang-Mills field theories

Recently, MIT group found a numerical solution to non-abelian gauge fields which is shown to contain non-integer topological number. Using this fact, V.V.Khoze has argued that the vacuum theta angle is zero. Here, we study this in a complimentary way--its physical respect. The key point is MIT solution has an infinite action. Using this, we prove the vacuum theta angle is zero at semiclassical level.

hep-ph↗
arXiv1994

Dual solutions of Yang-Mills field theories in Minkowski space

Using spherical ansatz, we construct dual equations for non-abelian gauge fields in Minkowski space. The analytically continued instanton is shown to satisfy the dual equations but assumes a more ansatz. It is not the solution of MIT second order differential equation. The symmetries of the solution function space are examined. The relevant physics is reviewed.

hep-ph↗
arXiv1993

Electroweak Sphaleron in Large Higgs Boson Mass Limit

Since the TRIVIALITY argument of the Higgs sector requires the existence of new physics beyond the standard model, there should exist a cutoff $Λ$ beyond which the standard model will breakdown. The cutoff can be determined from the position of the Landau pole. We study the effects of this cutoff on the energy of the electroweak sphaleron, $E^{spha}$, in the large Higgs boson mass limit. We found that $E^{spha}$ becomes arbitrarily large as the Higgs boson mass increases. This is in contrast to the well-known result, which is held in the standard model and a wide class of its extensions, that $E^{spha}$ is stable against the variation of the {\it bare} Higgs boson mass. The physical meaning of this result is discussed.

hep-ph↗