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Dao-Neng Gao

Publications and source records attributed to Dao-Neng Gao.

36 records · Page 2Linked to original sources
arXiv2005

Angular distribution asymmetry in tau^- --> pi^- pi^0 nu_tau decay in the two-Higgs-doublet model with large tan beta

We study possible scalar type interactions in tau^- -->pi^- pi^0 nu_tau decay. One finds that an angular distribution asymmetry, A(s), can be induced from the interference between the scalar part and vector part amplitudes in this decay. Our analysis shows that, in the two-Higgs-doublet model of type II with large tan beta, the charged Higgs contribution could make A(s) up to 10^{-3} without conflict with present experimental constraints. Thus in the future precise experiments in tau-charm factories, this angular distribution asymmetry may be an interesting observable either to be helpful in searching for the signal of the charged Higgs boson or to impose the significant bound on it.

hep-ph↗
arXiv2004

On the electron-positron energy asymmetry in K_L --> pi0 e+ e-

Motivated by some new experimental and theoretical efforts, we update the theoretical analysis of the electron-positron energy asymmetry, which arises, in K_L --> pi0 e+ e-, from the two-photon intermediate state in the standard model. It is found that the measurement of this asymmetry in future experiments may increase our understanding of the K_{L, S} --> pi0 e+ e- decays, which would thus provide some useful information on quark flavor physics. Meanwhile, in the standard model the electron-positron energy asymmetry in the decay of K_S --> pi0 e+ e- is expected to be vanishingly small, therefore the asymmetry in K_S --> pi0 e+ e- might be a very interesting quantity to explore new physics scenarios.

hep-ph↗
arXiv2003

Long-distance contribution to the forward-backward asymmetry in decays K+ --> pi+ l+ l-

The long-distance contribution via the two-photon intermediate state to the forward-backward asymmetries in decays K+ --> pi+ l+ l- (l=e and mu) has been studied within the standard model. In order to evaluate the dispersive part of the K+ --> pi+ gamma* gamma* --> pi+ l+ l- amplitude, we employ a phenomenological form factor to soften the ultraviolet behavior of the transition. It is found that, this long-distance transition, although subject to some theoretical uncertainties, can lead to significant contributions to the forward-backward asymmetries, which could be tested in the future high-precise experiments.

hep-ph↗
arXiv2003

Charge asymmetry in K+- --> π+-γγinduced by the electromagnetic penguin operators

The CP-violating charge asymmetry in decays K+- --> π+- γγ, which is induced by the electromagnetic penguin operators, has been studied both in thestandard model and in its extensions. Because of a large enhancement of the Wilson coefficients of the electromagnetic penguin operators in the supersymmetric extensions of the standard model, a significant upper bound on this charge asymmetry could be expected, and thus high precision measurements of this interesting CP-violating quantity might explore new physics effects beyond the standard model.

hep-ph↗
arXiv2003

$K_L \to γν> \barν$ decay beyond the standard model

The decay $K_L \to γν\barν$ is investigated beyond the standard model. Interestingly, the upper limit of the CP-conserving and CP-violating branching ratios of the decay, induced from the possible extensions of the standard model, would be larger than the corresponding branching ratios given in the standard model respectively, and it is expected that the CP-violating part could be enhanced.

hep-ph↗
arXiv2002

Electromagnetic penguin operators and direct CP violation in K --> pi l^+ l^-

Supersymmetric extensions of the Standard Model predict a large enhancement of the Wilson coefficients of the dimension-five electromagnetic penguin operators affecting the direct CP violation in K_L --> pi^0 e^+ e^- and the charge asymmetry in K^\pm --> pi^\pm l^+ l^-. Here we compute the relevant matrix elements in the chiral quark model and compare these with the ones given by lattice calculations

hep-ph↗
arXiv2002

The CP-violating asymmetry in η\toπ^+ π^- e^+e^-

We study the CP-violating asymmetry {\cal A}_{\rm CP}, which arises, in η\toπ^+π^- e^+e^-, from the angular correlation of the e^+ e^- and π^+π^- planes due to the interference between the magnetic and electric decay amplitudes. With the phenomenologically determined magnetic amplitude and branching ratio as input, the asymmetry, induced by the electric bremsstrahlung amplitude through the CP-violating decay η\toπ^+π^-, and by an unconventional tensor type operator, has been estimated respectively. The upper bound of {\cal A}_{\rm CP} from the former is about 10^{-3}, and the asymmetry from the latter might be up to O(10^{-2}). One can therefore expect that this CP asymmetry would be an interesting CP-violating observable for the future precise measurements in the ηfactories.

hep-ph↗
arXiv2001

Long-distance contribution to the muon-polarization asymmetry in K^+\to π^+ μμ

We revisit the calculation of the long-distance contribution to the muon-polarization asymmetry Δ_{LR}, which arises, in K^+\toπ^+μ^+μ^-, from the two-photon intermediate state. The parity-violating amplitude of this process, induced by the local anomalous K^+π^-γ^*γ^* transition, is analysed; unfortunately, one cannot expect to predict its contribution to the asymmetry by using chiral perturbation theory alone. Here we evaluate this amplitude and its contribution to Δ_{LR} by employing a phenomenological model called the FMV model, in which the utility of the vector and axial-vector resonances exchange is important to soften the ultraviolet behaviour of the transition. We find that the long-distance contribution is of the same order of magnitude as the standard model short-distance contribution.

hep-ph↗
arXiv2001

The diquark model: New Physics effects for charm and kaon decays

Motivated by diquark exchange, we construct a class of extensions of the standard model. These models can generate large CP conserving and CP violating contributions to the doubly Cabbibo suppressed decays D^0\to K^+π^- without affecting D^0-\overline{D^0} mixing, contrary to what is usually believed in the literature. We find an interesting specific realization of these models, which has the LR chiral structure and can induce novel density \times density operators. It is new for non-leptonic kaon decays, and particularly, may provide a possible solution to the ΔI=1/2 rule and direct CP violation, without inducing large flavour changing neutral currents.

hep-ph↗
arXiv2000

A phenomenological description of $K\toππγ$ magnetic transitions

A phenomenological analysis of $K\to ππγ$ ($K_L\toπ^+π^-γ$ and $K^+\toπ^+π^0γ$) with the direct emission photon is carried out beyond the leading order in the chiral perturbation theory. We show that the experimental evidence for the large photon energy dependence of the magnetic amplitude in $K_L\toπ^+π^-γ$ seems to indicate an interesting consequence: vector meson dominance must be implemented at $O(p^4)$, which is not a general feature of the chiral perturbation theory. The phenomenology of $K^+\toπ^+π^0γ$ is also analyzed using the same scheme.

hep-ph↗
arXiv1999

Electromagnetic self-energies of the neutral pions: Contributions from vector resonances

By employing vector meson dominance to establish the electromagnetic interactions of hadrons, the electromagnetic self-energy of the neutral pions, which receives the contributions from the vector resonances due to chiral anomaly, is evaluated. This part of the electromagentic mass, which can contribute to the mass difference of $π^\pm-π^0$, is finite and as expected, is smaller than the contributions due to isospin symmetry breaking and electromagnetic chiral logs corrections, however, could be compared with the contribution from the short distance QCD.

hep-ph↗
arXiv1999

Electromagnetic self-energies of vector mesons and electromagnetic mass anomaly of the massive Yang-Mills particles

A systematic method developed by the authors to evaluate the one-loop electromagnetic self-energies of the low-lying mesons is extended to the calculation of the vector sector including $ρ$, $ω$, and $ϕ$-mesons. The theoretical result of $ρ^0-ρ^\pm$ electromagnetic mass difference is in agreement with the measurements. An interesting effect called as electromagnetic mass anomaly of the massive Yang-Mills particles is further discussed. There is no new parameter in this study.

hep-ph↗
arXiv1998

$ρ^0-ω$ mixing in U(3)}$_L\times$ U(3)$_R$ chiral theory of mesons

In this paper, U(3)$_L\times$ U(3)$_R$ chiral theory of mesons is extended to the leading order in quark mass expansion in order to evaluate the $ρ^0-ω$ mixing. It is shown that the use of path integral method to integrate out the quark fields naturally leads to the $ρ^0-ω$ mixing vertices, and this mixing is entirely from the quark loop in this theory. The off-shell behaviour of the mixing amplitude is analyzed. The on-shell mixing amplitude is obtained from the decay $ω\to π^+π^-$. Furthermore, the constraints on the light quark mass parameters are extracted from the $ρ^0-ω$ mixing and the mesons masses, and the mass splitting of $K^*(892)$-mesons is predicted.

hep-ph↗
arXiv1997

Electromagnetic masses of the mesons and the generalization of Dashen's theorem

In the framework of $U(3)_L\times U(3)_R$ chiral field theory, Dashen's theorem is reexamined, and the well-known result of $m_{π^\pm}^2-m_{π^0}^2$ obtained by Das, Guralnik, Mathur, Low, and Young is reproduced. We find that Dashen's theorem, which automatically holds for pseudoscalar mesons in this theory, can be generalized to the sector of axial-vector mesons, however, fails for the sector of vector mesons.

hep-ph↗
arXiv1997

Electromagnetic mass splittings of $π, a_1, K, K_1(1400)$ and $K^*(892)$

To one-loop order and $O(α_{em})$, the electromagnetic mass splittings of $π$, $a_1$, $K$, $K_1(1400)$, and $K^*(892)$ are calculated in the framework of $U(3)_L\times U(3)_R$ chiral field theory. The logarithmic divergences emerging in the Feynman integrations of the mesonic loops are factorized by using an intrinsic parameter $g$ of this theory. No other additional parameters or counterterms are introduced to absorb the mesonic loop divergences. When $f_π$,$m_ρ$ and $m_a$ are taken as inputs, the parameter $g$ will be determined and all the physical results are finite and fixed. Dashen's theorem is satisfied in the chiral SU(3) limit of this theory, and a rather large violation of the theorem is revealed at the order of $m_s$ or $m_K^2$. Mass ratios of light quarks have been determined. A relation for electromagnetic corrections to masses of axial-vector mesons is obtained. It could be regarded as a generalization of Dashen's theorem. Comparing with data, it is found that the non-electromagnetic mass difference of $K^*$ is in agreement with the estimation of Schechter, Subbaraman, Weigel.

hep-ph↗
arXiv1996

Electromagnetic Masses of the Massive Yang-Mills Particles K^*(892)

Electromagnetic mass difference between neutral $K^*$ and charged $K^*$ has been calculated in the $U(3)_L\times U(3)_R$ chiral fields theory of mesons. It has been revealed that the non-abelian gauge structure of the massive Yang-Mills lagrangian obeyed by $K^*$ plus VMD (vector meson dominace) causes the EM-mass of neutral one larger than charged one. Experiment supports this effect.

hep-ph↗
arXiv1995

Intrinsic Regularization Method in QCD

There exist certain intrinsic relations between the ultraviolet divergent graphs and the convergent ones at the same loop order in renormalizable quantum field theories. Whereupon we may establish a new method, the intrinsic regularization method, to regularize those divergent graphs. In this paper, we apply this method to QCD at the one loop order. It turns out to be satisfactory:The gauge invariance is preserved manifestly and the results are the same as those derived by means of other regularization methods.

hep-th↗