arXiv subjects

X. -G. He

Publications and source records attributed to X. -G. He.

17 recordsLinked to original sources

arXiv2011

$μ- e$ Conversion With Four Generations

We study $μ- e$ conversion with sequential four generations. A large mass for the fourth generation neutrino can enhance the conversion rate by orders of magnitude. We compare constraints obtained from $μ- e$ conversion using experimental bounds on various nuclei with those from $μ\to e γ$ and $μ\to e\bar e e$. We find that the current bound from $μ- e$ conversion with Au puts the most stringent constraint in this model. The relevant flavor changing parameter $λ_{μe} = V^*_{μ4}V_{e4}^{}$ is constrained to be less than $1.6\times 10^{-5}$ for the fourth generation neutrino mass larger than 100 GeV. Implications for future $μ-e$ conversion, $μ\to eγ$ and $μ\to e\bar e e$ experiments are discussed.

hep-ph↗

arXiv2003

SU(3) and Nonet Breaking Effects in $K_L \to γγ$ Induced by $s \to d + 2{gluon}$ due to Anomaly

In this paper we study the effects of $s\to d + 2{gluon}$ on $K_L \to γγ$ in the Standard Model. We find that this interaction can induce new sizeable SU(3) and U(3) nonet breaking effects in $K_L - η, η'$ transitions and therefore in $K_L\to γγ$ due to large matrix elements of $<η(η')|α_s G^a_{μν} \tilde G_a^{μν}|0>$ from QCD anomaly. These new effects play an important role in explaining the observed value. We also study the effects of this interaction on the contribution to $Δm_{K_L-K_S}$.

hep-ph↗

arXiv2003

$A^b_{FB}$ and $R_b$ at LEP and New Right-Handed Gauge Bosons

We explore models with additional right-handed gauge bosons that couple predominantly to the third generation in the context of $b\bar{b}$ production at LEP. In particular we investigate potential new contributions to $δg_{Rb}$ that are needed if the measured $A^b_{FB}$ at the $Z$ peak is interpreted as a signal of new physics. We identify two sources of large $δg_{Rb}$ corrections: $Z-Z^\prime$ mixing at tree-level, and one-loop effects from a new $SU_R(2)$ triplet of gauge bosons. We find that the latter can contribute to $δg_{Rb}$ at the 1%-level. We place bounds on the mass of the additional $Z^\prime$ gauge boson that occurs in these models using the $R_b$ measurements from LEP-II. We find that even in cases where the $Z^\prime$ couples almost exclusively to the $b$ and $t$-quarks, masses lighter than about 500 GeV are already excluded.

hep-ph↗

arXiv2003

Neutrino Masses with "Zero Sum" Condition: $m_{ν_1} + m_{ν_2} + m_{ν_3} = 0$

It is well known that the neutrino mass matrix contains more parameters than experimentalists can hope to measure in the foreseeable future even if we impose CP invariance. Thus, various authors have proposed ansatzes to restrict the form of the neutrino mass matrix further. Here we propose that $m_{ν_1} + m_{ν_2} + m_{ν_3} = 0$; this ``zero sum'' condition can occur in certain class of models, such as models whose neutrino mass matrix can be expressed as commutator of two matrices. With this condition, the absolute neutrino mass can be obtained in terms of the mass-squared differences. When combined with the accumulated experimental data this condition predicts two types of mass hierarchies, with one of them characterized by $m_{ν_3} \approx -2m_{ν_1} \approx -2 m_{ν_2} \approx 0.063$ eV, and the other by $m_{ν_1} \approx -m_{ν_2} \approx 0.054$ eV and $m_{ν_3} \approx 0.0064$ eV. The mass ranges predicted is just below the cosmological upper bound of 0.23 eV from recent WMAP data and can be probed in the near future. We also point out some implications for direct laboratory measurement of neutrino masses, and the neutrino mass matrix.

hep-ph↗

arXiv2003

Some Simple Mixing and Mass Matrices for Neutrinos

We argue that the accumulated neutrino data, including recent results from KamLAND and K2K, point to a neutrino mixing matrix with (V_{11}, V_{21}, V_{31}; V_{21}, V_{22}, V_{32}; V_{13}, V_{23}, V_{33}) = (-2/\sqrt{6}, 1/\sqrt{6}, 1/\sqrt{6}; 1/\sqrt{3}, 1/\sqrt{3}, 1/\sqrt{3}; 0, 1/\sqrt{2}, -1/\sqrt{2}). We propose some simple neutrino mass matrices which predict such a mixing matrix.

hep-ph↗

arXiv2002

CP Violating Rate Difference Relations for $B\to PP$ and $B \to PV$ in Broken SU(3)

Within the standard model there exist certain relations between CP violating rate differences in B decays in the SU(3) limit. We study SU(3) breaking corrections to these relations in the case of charmless, hadronic, two body $B$ decays using the improved factorization model of Ref.\cite{3}. We consider the cases $B \to PP$ and $B \to PV$ for both $B_d$ and $B_s$ mesons. We present an estimate for $A_{CP}(π^- π^+)$ in terms of $A_{CP}(K^- π^+)$.

hep-ph↗

arXiv2002

SU(3) Predictions of $B\to PP$ Decays in the Standard Model

With SU(3) symmetry one only needs 13 hadronic parameters to describe $B\to PP$ decays in the Standard Model. When annihilation contributions are neglected, only 7 hadronic parameters are needed. These parameters can be determined from existing experimental data and some unmeasured branching ratios and CP asymmetries of the type $B\to PP$ can be predicted. In this talk we present SU(3) predictions of branching ratios and CP asymmetries for $B\to PP$ decays in the Standard Model.

hep-ph↗

arXiv2002

Radiative Decay of $Υ$ into a Scalar Glueball

We study the radiative decay of $Υ$ into a scalar glueball $Υ\to γG_s$ using QCD factorization. We find that for this process the non-perturbative effects can be factorized into a matrix element well defined in non-relativistic QCD (NRQCD) and the gluon distribution amplitude. The same NRQCD matrix element appears also in leptonic decay of $Υ$ and therefore can be determined from data. In the asymptotic limit the gluon distribution amplitude is known up to a normalization constant. Using a QCD sum-rule calculation for the normalization constant, we obtain $Br(Υ\to γG_s)$ to be in the range $(1\sim 2)\times 10^{-3}$. We also discuss some of the implications for $Υ\to γf_i$ decays. Near future data from CLEO-III can provide crucial information about scalar glueball properties.

hep-ph↗

arXiv2002

$\bar B^0 \to π^+ X$ in the Standard Model

In this paper we investigate the possibility of studying $B\to π$ form factor using the semi-inclusive decays $\bar B^0 \to π^+ + X_q$. In general $B\to PX$ semi-inclusive decays involve several hadronic parameters. But for $\bar B^0 \to π^+ X_q$ decays we find that in the factorization approximation, the only unknown hadronic parameters are the form factors $F^{B\to π}_{0,1}$. Therefore these form factors can be studied in $\bar B^0 \to π^+ X_q$ decays. Using theoretical model calculations for the form factors the branching ratios for $\bar B^0 \to π^+ X_d(ΔS = 0) $ and $\bar B^0 \to π^+ X_s (ΔS = -1)$, with the cut $E_π > 2.1$ GeV, are estimated to be in the ranges of $(3.1\sim 4.9) \times 10^{-5}(F^{B\to π}_1(0)/0.33)^2$ and $(2.5\sim 4.2)\times 10^{-5}(F_1^{B\to π}(0)/0.33)^2$, respectively, depending on the value of $γ$. The combined branching ratio for $\bar B^0 \to π^+ (X_d+ X_s)$ is about $7.4\times 10^{-5} (F^{B\to π}_1(0)/0.33)^2$ and is insensitive to $γ$. We also discuss CP asymmetries in these decay modes.

hep-ph↗

arXiv2001

Muon Anomalous $g -2$ and Gauged $L_μ- L_τ$ Models

In this paper we study $Z'$ contribution to $g -2$ of the muon anomalous magnetic dipole moment in gauged $U(1)_{L_μ- L_τ}$ models. Here $L_i$ are the lepton numbers. We find that there are three classes of models which can produce a large value of $g-2$ to account for possible discrepancy between the experimental data and the Standard Model prediction. The three classes are: a) Models with an exact $U(1)_{L_μ- L_τ}$. In these models, $Z'$ is massless. The new gauge interaction coupling $e a/\cosθ_W$ is constrained to be $ 0.8\times 10^{-3} < |a| < 2.24\times 10^{-3}$. b) Models with broken $U(1)_{L_μ- L_τ}$ and the breaking scale is not related to electroweak symmetry breaking scale. The $Z'$ gauge boson is massive. The allowed range of the coupling and the $Z'$ mass are constrained, but $Z'$ mass can be large; And c) The $U(1)_{L_μ-L_τ}$ is broken and the breaking scale is related to the electroweak scale. In this case the $Z'$ mass is constrained to be $\sim 1.2$ GeV. We find that there are interesting experimental signatures in $μ^+μ^-\to μ^+μ^-, τ^+τ^-$ in these models.

hep-ph↗

arXiv2001

The CP violating phase $γ$ from global fit of rare charmless hadronic B decays

We study constraints on the CP violating phase $γ$ in the Kobayashi-Maskawa model using available experimental data. We first follow the conventional method to up date the constraint on $γ$ by performing a $χ^2$ analysis using data from $|ε_K|$, $Δm_{B_{d,s}}$ and $|V_{ub}/V_{cb}|$. We also include the recent information on $\sin2β$ in the analysis. We obtain the best fit for $γ$ to be $66^\circ$ and the 95% C.L. allowed range to be $42^\circ \sim 87^\circ$. We then develop a method to carry out a $χ^2$ analysis based on SU(3) symmetry using data from $B\to ππ$ and $B\to K π$. We also discuss SU(3) breaking effects from model estimate. We find that present data on $B\to ππ, K π$ can also give some constraint on $γ$ although weaker than the earlier method limited by the present experimental errors. Future improved data will provide more stringent constraint. Finally we perform a combined fit using data from $|ε_K|$, $Δm_{B_{d,s}}$, $|V_{ub}/V_{cb}|$, $\sin2β$ and rare charmless hadronic B decays. The combined analysis gives $γ=67^\circ$ for the best fit value and $43^\circ \sim 87^\circ$ as the 95% C.L. allowed range. Several comments on other methods to determine $γ$ based on SU(3) symmetry are also provided.

hep-ph↗

arXiv1998

CP Violation in Quasi-inclusive $B\to K^{(*)} X$ Decays

We consider the possibility of observing CP violation in quasi-inclusive decays of the type $B^-\to K^- X$, $B^-\to K^{*-} X$, $\bar B^0\to K^- X$ and $\bar B^0\to K^{*-} X$, where $X$ does not contain strange quarks. We present estimates of rates and asymmetries for these decays in the Standard Model and comment on the experimental feasibility of observing CP violation in these decays at future $B$ factories. We find the rate asymmetries can be quite sizeable.

hep-ph↗

arXiv1996

CP Violation in $Wγ$ and $Zγ$ Production

We study the capability of a $2 TeV$ $p\overline{p}$ collider with an integrated luminosity of $10 fb^{-1}$ to study CP violation in the processes $p \bar{p} \ra W^\pm γ$ and $p \bar{p} \ra Z γ$. We assume the existence of new CP violating interactions beyond the standard model which we describe with an effective Lagrangian. We find that the study of CP-odd observables would allow this machine to place bounds on CP violating anomalous couplings similar to the bounds that the same machine can place on $\cp$ conserving anomalous couplings. For example it could place the bound $|\tildeκ_γ|<0.1$ at the 95% confidence level.

hep-ph↗

arXiv1996

Discriminating between Higgs Boson models using $e^+e^-\to t \anti t \h$ and $Z\h$ at the NLC

We demonstrate that the process $e^+e^-\to t\anti t h$ at the NLC provides a powerful tool for extracting the $t\anti t$ (Yukawa) couplings of the $\h$. In combination with the $\epem\to Z\h$ process, an accurate determination of the $ZZ$ coupling of the $\h$ is also possible. The resulting ability to distinguish different models of the Higgs sector is illustrated by detailed studies for two-Higgs-doublet models.

hep-ph↗

arXiv1996

Determining the top-antitop and $ZZ$ Couplings of a Neutral Higgs Boson of Arbitrary CP Nature at the NLC

The optimal procedure for extracting the coefficients of different components of a cross section which takes the form of unknown coefficients times functions of known kinematical form is developed. When applied to $\epem\to t\anti t+$Higgs production at $\rts=1\tev$ and integrated luminosity of $200\fbi$, we find that the $t\anti t\to$Higgs CP-even and CP-odd couplings and, to a lesser extent, the $ZZ\to$Higgs (CP-even) coupling can be extracted with reasonable errors, assuming the Higgs sector parameter choices yield a significant production rate. Indeed, the composition of a mixed-CP Higgs eigenstate can be determined with sufficient accuracy that a SM-like CP-even Higgs boson can be distinguished from a purely CP-odd Higgs boson at a high level of statistical significance, and vice versa.

hep-ph↗

arXiv1994

Model for a Light Z' Boson

A model of a light $Z'$ boson is constructed and phenomenological bounds are derived. This $Z'$ boson arises from a very simple extension to the Standard Model, and it is constrained to be light because the vacuum expectation values which generate its mass also break the electroweak gauge group. It is difficult to detect experimentally because it couples exclusively or primarily (depending on symmetry breaking details) to second and third generation leptons. However, if the $Z'$ boson is sufficiently light, then there exists the possibility of the two-body decay $τ\rightarrow μZ'$ occuring. This will provide a striking signature to test the model.

hep-ph↗

arXiv1992

On the CP-odd Nucleon Potential

The CP-odd nucleon potential for different models of CP violation in the one meson exchange approximation is studied. It is shown that the main contribution is due to the $π$-meson exchange which leads to a simple one parameter CP-odd nucleon potential.

hep-ph↗