arXiv subjects

Yue-Liang Wu

Publications and source records attributed to Yue-Liang Wu.

At least 181 records · Page 10Linked to original sources

arXiv2006

Anomalous Action of QCD from the General Quark Propagator

The anomalous action of the chiral effective theory to $\mathcal{O}(p^4)$ is investigated by generalizing the consideration in \cite{ma02} with including the wave function part in the general quark propagator. It is found that the QCD dynamics dependence of the Wess-Zumino term is explicit and this dependence means that the QCD chiral symmetry must be broken dynamically in the low energy region for dynamically generating the Wess-Zumino term. In addition, we found that the next to leading order anomalous action in the momentum expansion of the chiral perturbation theory is gauge invariant and QCD dynamics dependent.

hep-ph↗

arXiv2006

Spin Polarisability of the Nucleon in the Heavy Baryon Effective Field Theory

We have constructed a heavy baryon effective field theory with photon as an external field in accordance with the symmetry requirements similar to the heavy quark effective field theory. By treating the heavy baryon and anti-baryon equally on the same footing in the effective field theory, we have calculated the spin polarisabilities $γ_i, i=1...4$ of the nucleon at third order and at fourth-order of the spin-dependent Compton scattering. At leading order (LO), our results agree with the corresponding results of the heavy baryon chiral perturbation theory, at the next-to-leading order(NLO) the results show a large correction to the ones in the heavy baryon chiral perturbation theory due to baryon-antibaryon coupling terms. The low energy theorem is satisfied both at LO and at NLO. The contributions arising from the heavy baryon-antibaryon vertex were found to be significant and the results of the polarisabilities obtained from our theory is much closer to the experimental data.

hep-ph↗

arXiv2005

Hidden Local Symmetry and Effective Chiral Theory for Vector and Axial-vector Mesons

The Lagrangian of pseudoscalar, vector, and axial-vector mesons is determined by the explicit global chiral symmetry and hidden local chiral symmetry. There are fourteen interacting terms up to the dimension-four of covariant derivatives rather than the usual eleven interacting terms given in literature from hidden local symmetry approach. There are only two independent parameters. The three new terms are important in phenomenology.

hep-ph↗

arXiv2005

Charmless decays B->pipi, piK and KK in broken SU(3)symmetry

Charmless B decay modes $B \to ππ, πK$ and $KK$ aresystematically investigated with and without flavor SU(3) symmetry. Independent analyses on $ππ$ and $πK$ modes both favor a large ratio between color-suppressed tree ($C$) and tree ($T)$ diagram, which suggests that they are more likely to originate from long distance effects. The sizes of QCD penguin diagrams extracted individually from $ππ$, $πK$ and $KK$ modes are found to follow a pattern of SU(3) breaking in agreement with the naive factorization estimates. Global fits to these modes are done under various scenarios of SU(3)relations. The results show good determinations of weak phase $γ$ in consistency with the Standard Model (SM), but a large electro-weak penguin $(P_{\tmop{EW}})$ relative to $T + C$ with a large relative strong phase are favored, which requires an big enhancement of color suppressed electro-weak penguin ($P_{\tmop{EW}}^C$) compatible in size but destructively interfering with $P_{\tmop{EW}}$ within the SM, or implies new physics. Possibility of sizable contributions from nonfactorizable diagrams such as $W$-exchange ($E$), annihilation($A$) and penguin-annihilation diagrams($P_A$) are investigated. The implications to the branching ratios and CP violations in $K K$modes are discussed.

hep-ph↗

arXiv2005

Exploring Final State Hadron Structure and SU(3) Flavor Symmetry Breaking Effects in D->PP and D->PV Decays

The nonleptonic two body decays $D\to PP$ and $D\to PV$ are investigated based on the diagrammatic decomposition in a generalized factorization formalism. It is shown that to fit the experimental data, the SU(3) flavor symmetry breaking effects of the coefficients $a_i$s should be considered in $D\to PP$ decay modes. In $D\to PV$ decays, the final state hadron structure due to the pseudoscalar and vector mesons has more important effects on the coefficients $a_i$s than the SU(3) symmetry breaking effects. It is found that the nonfactorizable contributions as well as that of the exchange and annihilation diagrams are significant in these decays.

hep-ph↗

arXiv2005

Higgs physics and CP violation

The CP violation in $K$ and B decays are discussed with the emphasize on the precise prediction for $ε'/ε$ and the new physics effects from a class of models with additional Higgs doublets and fermions. The contributions from standard model with two-Higgs-doublet (S2HDM) to $K$, $B$ mixing and decays are briefly reviewed. The possible large effects on CP violation in $B\to ϕK$ is discussed in an extended standard model with both an additional Higgs doublet and fourth generation quarks (S2HDM4). We show that although the S2HDM and the Standard model with fourth generation quarks alone are not likely to largely change the effective $\sin 2β$ from the decay of $B \to ϕK_S $, the S2HDM4 model can easily account for the possible large deviation of $\sin 2 β$ without conflicting with other experimental constraints.

hep-ph↗

arXiv2005

Implications of Charmless B Decays with Large Direct CP Violation

Based on the most recent data in charmless B decays including the very recently reported large direct CP violations, it is shown that the weak phase gamma can well be extracted without two-fold ambiguity even only from two decay modes pi^+pi^- and pi^+K^-, and its value is remarkably consistent with the global standard model fit at a compatible accuracy. A fit to all the pi pi, pi K data favor both large electroweak penguin and color-suppressed tree amplitude with large strong phases. It is demonstrated that the inclusion of small SU(3)symmetry breaking effects of strong phases and the inelastic rescattering effects can well improve the consistency of the data, while both effects may not be sufficient to arrive at a small electroweak penguin amplitude in the standard model. It is of interest to notice that large or small electroweak penguin amplitude becomes a testable prediction as they lead to significantly different predictions for the direct CP violations for pi^0 pi^0, pi^0 K^0 modes. Clearly, precise measurements on charmless B decays will provide a window for probing new physics.

hep-ph↗

arXiv2004

Hidden Local Symmetry and Chiral Effective Theory for Vector and Axial-vector Mesons

In this paper, we present the full Lagrangian of mesons (pseudoscalars, vectors and axial-vectors) to $O(p^4)$ by using the explicit global chiral symmetry and hidden local symmetry in the chiral limit. In this approach, we see that there are many other terms besides the usual eleven terms given in the literature from hidden local symmetry approach. Of particular, there are some terms in our full results which are important for understanding the vector meson dominance and $π-π$ scattering and providing consistent predictions on the decay rates of $a_1\toγπ$ and $a_1\toρπ$ as well as for constructing a consistent effective chiral Lagrangian with chiral perturbation theory. It is likely that the structures of the effective chiral Lagrangian for $O(p^4)$ given in the literature by using hidden local symmetry are incomplete and consequently the resulting couplings are not reliable. It is examined that the more general effective chiral Lagrangian given in present paper can provide more consistent predictions for the low energy phenomenology of $ρ-a_1$ system and result in more consistent descriptions on the low energy behavior of light flavor mesons.

hep-ph↗

arXiv2004

CP asymmetry in $B \to ϕK_S$ in a general two-Higgs-doublet model with fourth-generation quarks

We discuss the time-dependent CP asymmetry of decay $B \to ϕK_S$ in an extension of the Standard Model with both two Higgs doublets and additional fourth-generation quarks. We show that although the Standard Model with two-Higgs-doublet and the Standard model with fourth generation quarks alone are not likely to largely change the effective $\sin 2 β$ from the decay of $B \to ϕK_S $, the model with both additional Higgs doublet and fourth-generation quarks can easily account for the possible large negative value of $\sin 2 β$ without conflicting with other experimental constraints. In this model, additional large CP violating effects may arise from the flavor changing Yukawa interactions between neutral Higgs bosons and the heavy fourth generation down type quark, which can modify the QCD penguin contributions. With the constraints obtained from $b \to s \bar{s} s$ processes such as $B \to X_s γ$ and $Δm_{B_s^0}$, this model can lead to the effective $\sin 2 β$ to be as large as $- 0.4$ in the CP asymmetry of $B \to ϕK_S$.

hep-ph↗

arXiv2004

Symmetry-preserving Loop Regularization and Renormalization of QFTs

A new symmetry-preserving loop regularization method proposed in \cite{ylw} is further investigated. It is found that its prescription can be understood by introducing a regulating distribution function to the proper-time formalism of irreducible loop integrals. The method simulates in many interesting features to the momentum cutoff, Pauli-Villars and dimensional regularization. The loop regularization method is also simple and general for the practical calculations to higher loop graphs and can be applied to both underlying and effective quantum field theories including gauge, chiral, supersymmetric and gravitational ones as the new method does not modify either the lagrangian formalism or the space-time dimension of original theory. The appearance of characteristic energy scale $M_c$ and sliding energy scale $μ_s$ offers a systematic way for studying the renormalization-group evolution of gauge theories in the spirit of Wilson-Kadanoff and for exploring important effects of higher dimensional interaction terms in the infrared regime.

hep-th↗

arXiv2004

Conformal Scaling Gauge Symmetry and Inflationary Universe

Considering the conformal scaling gauge symmetry as a fundamental symmetry of nature in the presence of gravity, a scalar field is required and used to describe the scale behavior of universe. In order for the scalar field to be a physical field, a gauge field is necessary to be introduced. A gauge invariant potential action is constructed by adopting the scalar field and a real Wilson-like line element of the gauge field. Of particular, the conformal scaling gauge symmetry can be broken down explicitly via fixing gauge to match the Einstein-Hilbert action of gravity. As a nontrivial background field solution of pure gauge has a minimal energy in gauge interactions, the evolution of universe is then dominated at earlier time by the potential energy of background field characterized by a scalar field. Since the background field of pure gauge leads to an exponential potential model of a scalar field, the universe is driven by a power-law inflation with the scale factor $a(t) \sim t^p$. The power-law index $p$ is determined by a basic gauge fixing parameter $g_F$ via $p = 16πg_F^2[1 + 3/(4πg_F^2) ]$. For the gauge fixing scale being the Planck mass, we are led to a predictive model with $g_F=1$ and $p\simeq 62$.

hep-th↗

arXiv2004

Dynamically Spontaneous Symmetry Breaking and Masses of Lightest Nonet Scalar Mesons as Composite Higgs Bosons

Based on the (approximate) chiral symmetry of QCD Lagrangian and the bound state assumption of effective meson fields, a nonlinearly realized effective chiral Lagrangian for meson fields is obtained from integrating out the quark fields by using the new finite regularization method. As the new method preserves the symmetry principles of the original theory and meanwhile keeps the finite quadratic term given by a physically meaningful characteristic energy scale $M_c$, it then leads to a dynamically spontaneous symmetry breaking in the effective chiral field theory. The gap equations are obtained as the conditions of minimal effective potential in the effective theory. The instanton effects are included via the induced interactions discovered by 't Hooft and found to play an important role in obtaining the physical solutions for the gap equations. The lightest nonet scalar mesons($σ$, $f_0$, $a_0$ and $κ$) appearing as the chiral partners of the nonet pseudoscalar mesons are found to be composite Higgs bosons with masses below the chiral symmetry breaking scale $Λ_χ \sim 1.2$ GeV. In particular, the mass of the singlet scalar (or the $σ$) is found to be $m_σ \simeq 677$ MeV.

hep-ph↗

arXiv2004

More Precise Determination of V_{cb} & V_{ub} and Direct CP Violation in Charmless B Decays

More precise extractions on the two important CKM matrix elements $|V_{cb}|$ and $|V_{ub}|$ are presented up to $1/m_Q^2$ corrections based on the complete heavy quark effective field theory (HQEFT) of QCD. The HQEFT as a large component QCD provides us a complete theoretical framework for correctly and systematically evaluating the subleading and higher order contributions in $1/m_Q$ expansion of heavy quarks. A global analysis on charmless B decays is made based on the isospin and SU(3) flavor symmetry. An isospin relation is found to be very useful for studying SU(3) symmetry breaking effects of strong phases and exploring new type of electroweak penguin effects. The direct CP violation in charmless B decays is predicted and its precise measurement is helpful either for testing SU(3) symmetry breaking effects of strong phases or for probing new physics beyond standard model.

hep-ph↗

arXiv2003

Isospin relation and SU(3) breaking effects of strong phases in Charmless B decays

Isospin and flavor SU(3) relations in charmless hadronic B decays $B\to ππ, πK$ are investigated in detail with paying attention to the SU(3) symmetry breaking effects in both amplitudes and strong phases. In general, the isospin and the flavor SU(3) structure of the effective Hamiltonian provide several relations among the amplitudes and strong phases. Whereas a global fit to the latest data shows that some relation seems not to be favorable for a consistent explanation to the current data within the standard model (SM). By considering several patterns of SU(3) breaking, the amplitudes and the corresponding strong phases are extracted and compared with the theoretical estimations. It is found that in the case of SU(3) limits and also the case with SU(3) breaking only in amplitudes, the fitting results lead to an unexpected large ratio between two isospin amplitudes $a^{c}_{3/2}/a^{u}_{3/2}$, which is about an order of magnitude larger than the SM prediction. The results are found to be insensitive to the weak phase $γ$. By including SU(3) breaking effects on the strong phases, one is able to obtain a consistent fit to the current data within the SM, which implies that the SU(3) breaking effect on strong phases may play an important role in understanding the observed charmless hadronic B decay modes $B\to ππ$ and $πK$. It is possible to test those breaking effects in the near future from more precise measurements of direct CP violation in B factories.

hep-ph↗

arXiv2002

B --> pi l nu Decay and |V_{ub}|

B --> pi l nu decay is studied in the effective theory of heavy quark with infinite mass limit. The leading order heavy flavor-spin independent universal wave functions which parametrize the relevant matrix elements are evaluated via light cone sum rule method in the effective theory. The important quark mixing matrix element |V_{ub}| is then extracted via B --> pi l nu decay mode.

hep-ph↗

arXiv2001

Muon anomalous magnetic moment in the standard model with two Higgs doublets

The muon anomalous magnetic moment is investigated in the standard model with two Higgs doublets (S2HDM) motivated from spontaneous CP violation. Thus all the effective Yukawa couplings become complex. As a consequence of the non-zero phase in the couplings, the one loop contribution from the neutral scalar bosons could be positive and negative relying on the CP phases. The interference between one and two loop diagrams can be constructive in a large parameter space of CP-phases. This will result in a significant contribution to muon anomalous magnetic moment even in the flavor conserving process with a heavy neutral scalar boson ($m_h \sim$ 200 GeV) once the effective muon Yukawa coupling is large ($|ξ_μ|\sim 50$). In general, the one loop contributions from lepton flavor changing scalar interactions become more important. In particular, when all contributions are positive in a reasonable parameter space of CP phases, the recently reported 2.6 sigma experiment vs. theory deviation can be easily explained even for a heavy scalar boson with a relative small Yukawa coupling in the S2HDM.

hep-ph↗

arXiv2001

Implications from recent measurements on sin 2βand muon g-2

The recent data on CP asymmetry in $B->J/ΨK_S$ and muon g-2 are discussed in the framework of standard model and beyond. Possible new phase effects besides the CKM phase are discussed in the processes concerning CP violation in B decays and muon anomalous magnetic moment (muon g-2). It is found that the new phases will result in difference between angles $beta$ measured from $B->J/ΨK_S$ and the one from global fit. The ration between them serves as a probe of not only new physics but also new phase besides the CKM phase In the case of muon g-2, the new phase may change the interferences between various contributions. By including the new phases, some cancelations in the real coupling cases can be avoided and the large value of muon g-2 observed in the recent measurements can be understood.

hep-ph↗

arXiv2001

Consistent Prediction for Direct CP Violation and ΔI = 1/2 Rule

The theoretical status of direct CP violation $ε'/ε$ is briefly reviewed. Special attention is paid to the recent new consistent predictions for both the ratio $ε'/ε$ and the $ΔI = 1/2$ rule within the standard model. In particular, two matching conditions resulting from the matching between the QCD and chiral perturbation theory(ChPT), and also some algebraic relations of chiral operators are found to be very useful. It is of interest that the new predictions are no longer sensitive to the strange quark mass, and are also renormalization scale and scheme independent in the leading QCD and chiral loop approximation with large $N_c$ approach. The new prediction for the direct CP violation with the value $ε'/ε= (20 \pm 4) \times 10^{-4} [Imλ_t /1.2\times 10^{-4}]$ is consistent with the most recent experimental results reported by the NA48 and KTeV groups.

hep-ph↗