arXiv subjects

Zhi-Hui Guo

Publications and source records attributed to Zhi-Hui Guo.

At least 73 records · Page 4Linked to original sources

arXiv2015

Scrutinizing the eta-eta' mixing, masses and pseudoscalar decay constants in the framework of U(3) chiral effective field theory

We study the $η$-$η'$ mixing up to next-to-next-to-leading-order in $U(3)$ chiral perturbation theory in the light of recent lattice simulations and phenomenological inputs. A general treatment for the $η$-$η'$ mixing at higher orders, with the higher-derivative, kinematic and mass mixing terms, is addressed. The connections between the four mixing parameters in the two-mixing-angle scheme and the low energy constants in the $U(3)$ chiral effective theory are provided both for the singlet-octet and the quark-flavor bases. The axial-vector decay constants of pion and kaon are studied in the same order and confronted with the lattice simulation data as well. The quark-mass dependences of $m_η$, $m_{η'}$ and $m_K$ are found to be well described at next-to-leading order. Nonetheless, in order to simultaneously describe the lattice data and phenomenological determinations for the properties of light pseudoscalars $π, K, η$ and $η'$, the next-to-next-to-leading order study is essential. Furthermore, the lattice and phenomenological inputs are well reproduced for reasonable values of low the energy constants, compatible with previous bibliography.

hep-ph↗

arXiv2014

Unified study of $J/ψ\to PV$, $Pγ^{(*)}$ and light hadron radiative processes

Within the framework of the effective Lagrangian approach, we perform a thorough analysis of the $J/ψ\to Pγ(γ^*)$, $J/ψ\to VP$, $V\to Pγ(γ^*)$, $P\to Vγ(γ^*)$ and $P\toγγ(γ^*)$ processes, where $V$ stand for light vector resonances, $P$ stand for light pseudoscalar mesons, and $γ^*$ subsequently decays into lepton pairs. The processes with light pseudoscalar mesons $η$ and $η'$ are paid special attention to and the two-mixing-angle scheme is employed to describe their mixing. The four mixing parameters both in singlet-octet and quark-flavor bases are updated in this work. We confirm that the $J/ψ\to η(η^{\prime})γ^{(*)}$ processes are predominantly dominated by the $J/ψ\to η_c γ^{*} \to η(η^{\prime})γ^{(*)}$ mechanism. Predictions for the $J/ψ\to P μ^+μ^-$ are presented. A detailed discussion on the interplay between electromagnetic and strong transitions in the $J/ψ\to VP$ decays is given.

hep-ph↗

arXiv2014

Radiative transition processes of light vector resonances in a chiral framework

Within the framework of chiral effective field theory, we study various electromagnetic processes with light vector resonances: $K^{\ast}(892)\to Kγ$, $e^{+}e^{-}\to K^{\ast}(892)K $ and the $ωπγ^\ast$ form factors. With two multiplets of vector resonances being introduced, we fit the decay widths of $K^{\ast0}\to K^{0}γ$, $K^{\ast+}\to K^{+}γ$, and the pertinent measurements from the $e^{+}e^{-}\to K^{\ast \pm}(892)K^{\mp} $ cross sections, such as moduli and relative phases between the isoscalar and isovector components from BABAR collaboration, together with the $ωπ$ form factors from NA60, SND and CLEO collaborations. The values of resonance couplings, masses and widths of the excited vector states $ρ'$ and $ϕ'$ are then determined. The $ω'$-$ϕ'$ mixing angle is discussed and turns out to be quite different from the ideal mixing case. Three sources of $SU(3)$ symmetry breaking effects in the $Γ(K^{\ast}\to Kγ)$ decays are identified and analyzed in detail.

hep-ph↗

arXiv2014

Resonance effects in pion and kaon decay constants

In this article we study impact of the lightest vector and scalar resonance multiplets in the pion and kaon decay constants up to next-to-leading order in the $1/N_C$ expansion, i.e., up to the one-loop level. The $F_π$ and $F_K$ predictions obtained within the framework of Resonance Chiral Theory are confronted with lattice simulation data. The vector loops (and the $ρ-ππ$ coupling $G_V$ in particular) are found to play a crucial role in the determination of the Chiral Perturbation Theory couplings $L_4$ and $L_5$ at next-to-leading order in $1/N_C$. Puzzling, values of $G_V < 40$ MeV seem to be necessary to agree with current phenomenological results for $L_4$ and $L_5$. Conversely, a value of $G_V > 60$ MeV compatible with standard $ρ-ππ$ determinations turns these chiral couplings negative. However, in spite of the strong anti-correlation with $L_4$, the $SU(3)$ chiral coupling $F_0$ remains stable all the time and stays within the range $78 \sim 86$ MeV when $G_V$ is varied in a wide range, from $40$ up to $70$ MeV. Finally, we would like to remark that the leading order expressions used in this article for the $η-η'$ mixing, mass splitting of the vector multiplet masses and the quark mass dependence of the $ρ(770)$ mass are found in reasonable agreement with the lattice data.

hep-ph↗

arXiv2014

Nucleon-Nucleon scattering from the dispersive N/D method: next-to-leading order study

We consider nucleon-nucleon ($NN$) interactions from Chiral Effective Field Theory applying the $N/D$ method. The dynamical input is given by the discontinuity of the $NN$ partial-wave amplitudes across the left-hand cut (LHC) calculated in Chiral Perturbation Theory (ChPT) by including one-pion exchange (OPE), once-iterated OPE and leading irreducible two-pion exchange (TPE). We discuss both uncoupled and coupled partial-waves. We show algebraically that the resulting integral equation has a unique solution when the input is taken only from OPE because it is of the Fredholm type with a squared integrable kernel and an inhomogeneous term. Phase shifts and mixing angles are typically rather well reproduced, and a clear improvement of the results obtained previously with only OPE is manifest. We also show that the contributions to the discontinuity across the LHC are amenable to a chiral expansion. Our method also establishes correlations between the $S$-wave effective ranges and scattering lengths based on unitarity, analyticity and chiral symmetry.

nucl-th↗

arXiv2013

Meson-baryon reactions with strangeness -1 within a chiral framework

We study meson-baryon scattering with strangeness -1 in unitary chiral perturbation theory. Ten coupled channels are considered in our work, namely $π^0 Λ$, $π^0 Σ^0$, $π^- Σ^+$, $π^+ Σ^-$, $K^- p$, $\bar{K}^0 n$, $ηΛ$, $ηΣ^0$, $K^0 Ξ^0$ and $K^+ Ξ^-$. A large amount of experimental data are analyzed, including the recent precise measurement by the SIDDHARTA Collaboration of the energy shift and width of the $1s$ state of kaonic hydrogen. This leads to a strong constraint on the free parameters in our theory and of the resulting meson-baryon scattering amplitudes. We also analyze the uncertainty that stems by using several different strategies to perform the fits to data. It is found that large uncertainties in the subthreshold extrapolation of the $K^-p$ scattering amplitude arise by employing either only one common weak pseudoscalar decay constant or distinguishing between $f_π$, $f_K$ and $f_η$. However, in both cases a good reproduction of experimental data is obtained. We also discuss the pole content of the resulting $S$-wave amplitudes, particularly in connection with the two-pole structure of the $Λ(1405)$ resonance.

hep-ph↗

arXiv2012

Chiral dynamics in form factors, spectral-function sum rules, meson-meson scattering and semilocal duality

In this work, we perform the one-loop calculation of the scalar and pseudoscalar form factors in the framework of U(3) chiral perturbation theory with explicit tree level exchanges of resonances. The meson-meson scattering calculation from Ref.[1] is extended as well. The spectral functions of the nonet scalar-scalar (SS) and pseudoscalar-pseudoscalar (PP) correlators are constructed by using the corresponding form factors. After fitting the unknown parameters to the scattering data, we discuss the resonance content of the resulting scattering amplitudes. We also study spectral-function sum rules in the SS-SS, PP-PP and SS-PP sectors as well as semi-local duality from scattering. The former relate the scalar and pseudoscalar spectra between themselves while the latter mainly connects the scalar spectrum with the vector one. Finally we investigate these items as a function of Nc for Nc > 3. All these results pose strong constraints on the scalar dynamics and spectroscopy that are discussed. They are successfully fulfilled by our meson-meson scattering amplitudes and spectral functions.

hep-ph↗

arXiv2012

Recent developments in U(3) ChPT: meson-meson scattering and finite energy sum rules

We discuss the meson-meson scattering and finite energy sum rule(FESR), based on the one-loop calculation within U(3) chiral perturbation theory. First we obtain the pertinent resonance spectroscopy from the unitarized partial wave scattering amplitudes. Then we investigate how well the FESR can be satisfied in the physical situation at Nc=3. Further discussions on the extrapolation of Nc are also given.

hep-ph↗

arXiv2012

Chiral dynamics in U(3) unitary chiral perturbation theory

We perform a complete one-loop calculation of meson-meson scattering, and of the scalar and pseudoscalar form factors in U(3) chiral perturbation theory with the inclusion of explicit resonance fields. This effective field theory takes into account the low-energy effects of the QCD U_A(1) anomaly explicitly in the dynamics. The calculations are supplied by non-perturbative unitarization techniques that provide the final results for the meson-meson scattering partial waves and the scalar form factors considered. We present thorough analyses on the scattering data, resonance spectroscopy, spectral functions, Weinberg-like sum rules and semi-local duality. The last two requirements establish relations between the scalar spectrum with the pseudoscalar and vector ones, respectively. The Nc extrapolation of the various quantities is studied as well. The fulfillment of all these non-trivial aspects of the QCD dynamics by our results gives a strong support to the emerging picture for the scalar dynamics and its related spectrum.

hep-ph↗

arXiv2012

Study of η-η' mixing from radiative decay processes

We perform a thorough analysis of the VPγ(γ*) and Pγγ(γ*) decays in the resonance chiral theory, where V stand for the vector resonances ρ, K*, ω, ϕ, P stand for π, K, η, η' and γ* subsequently decays into lepton pairs. Upon imposing QCD short-distance constraints on resonance couplings, the ω-> πγ(γ*), ρ-> πγ(γ*), K^{*0} -> K^0γprocesses only depend on one free parameter and π-> γγ(γ*) can be completely predicted. The four mixing parameters of the η-η' system, i.e. two mixing angles \theta8, \theta0 and two decay constants F8, F0, are determined from radiative decays involving ηor η'. The higher order low energy constants of the pseudo-Goldstone Lagrangian in the chiral anomaly sector are predicted by integrating out heavy resonances. We also predict the decay widths of ρ-> πe^+ e^-, η' -> γe^+ e^- and ϕ-> ημ^+ μ^-, which can be compared with the future measurement in these channels.

hep-ph↗

arXiv2011

Exploration of resonance properties in chiral perturbation theory with explicit U_A(1) anomaly

We study the resonance properties within chiral perturbation theory by explicitly taking into account the U_A(1) anomaly effect. This assures we have the appropriate degrees of freedom of low energy QCD in the large Nc limit. We calculate the various resonance properties, such as mass, width and residues, for the physical case, i.e. Nc=3. Then we extrapolate the values of Nc to study the trajectories of resonance poles.

hep-ph↗

arXiv2011

Resonances from meson-meson scattering in U(3) CHPT

In this work, the complete one loop calculation of meson-meson scattering amplitudes within U(3)\otimes U(3) chiral perturbation theory with explicit resonance states is carried out for the first time. Partial waves are unitarized from the perturbative calculation employing a non-perturbative approach based on the N/D method. Once experimental data are reproduced in a satisfactory way we then study the resonance properties, such as the pole positions, corresponding residues and their N_C behaviors. The resulting N_C dependence is the first one in the literature that takes into account the fact that the η_1 becomes the ninth Goldstone boson in the chiral limit for large N_C. Within this scheme the vector resonances studied, ρ(770), K^*(892) and ϕ(1020), follow an N_C trajectory in agreement with their standard \bar{q}q interpretation. The scalars f_0(1370), a_0(1450) and K^*(1430) also have for large N_C a \bar{q}q pole position trajectory and all of them tend to a bare octet of scalar resonances around 1.4 GeV. The f_0(980) tends asymptotically to the bare pole position of a singlet scalar resonance around 1 GeV. The σ, κand a_0(980) scalar resonances have a very different N_C behavior. The case of the σresonance is analyzed with special detail.

hep-ph↗

arXiv2011

One meson radiative tau decays

We have studied the one meson radiative tau decays: tau- -> nu(tau) pi-(K-) gamma, computing the structure dependent contributions within a Lagrangian approach based on the large-N(C) limit of QCD that ensures the proper low-energy limit dictated by chiral symmetry. Upon imposing the short-distance QCD constraints to the form-factors we are able to predict without any free parameter the structure dependent radiation and, therefore, the relevant observables for the decay tau- -> nu(tau) pi- gamma: the photon energy spectrum, the invariant mass spectrum of the meson-photon system and the integrated decay rate. We also discuss the remaining uncertainties in these observables for the tau- -> nu(tau) K- gamma decay. According to our results, the present facilities could detect these rare decays for the first time in the near future allowing for a stringent test of our predictions.

hep-ph↗

arXiv2010

$τ^-\toπ^-γν_τ$ as a source of background on the Lepton Flavour Violating decay $τ^-\toμ^-γ$

We calculate the decay of $τ^-\toπ^-γν_τ$ in the framework of Resonance Chiral Theory ($RχT$). By demanding the high energy constraints from QCD on the related form factors, we could predict the various physical observables of $τ^-\toπ^-γν_τ$ without any free parameter. Our results show that for a realistic cut on the photon energy (around $100$ MeV) this mode gives a branching ratio of roughly $0.1%$ that should have already been detected at the heavy-flavour factories. Another interesting subject we have studied based on our calculation of the decay $τ^-\toπ^-γν_τ$ is the experimental background estimation of the lepton flavour violation process $τ^- \to μ^- γ$. We point out that although the description of radiation that PHOTOS provides -which has been used by BaBar and Belle collaborations to estimate this source of background- is in excellent agreement with the theoretical expectations in the low energy region in $τ^-\toπ^-γν_τ$ decay, this is not the case in the high energy region, precisely where it is easier that this decay mimics the process $τ^-\toμ^-γ$.

hep-ph↗

arXiv2009

Positivity constraints on LECs of $χ$PT lagrangian at $\cO(p^6)$ level

Positivity constraints on the LECs of $\cO(p^6)$ $χ$PT lagrangian are discussed. We demonstrate that the constraints are automatically satisfied inside the Mandelstam triangle for $ππ$ scatterings, when $N_C$ is large. Numerical tests are made in the $N_C=3$ case, and it is found that these constraints are also well respected.

hep-ph↗

arXiv2009

Pi pi scattering lengths at O(p^6) revisited

This article completes a former work where part of the O(p^6) low-energy constants entering in the pi pi scattering were estimated. Some resonance contributions were missed in former calculations and slight differences appeared with respect to our outcome. Here, we provide the full results for all the contributing O(p^6) couplings. We also perform a reanalysis of the hadronic inputs used for the estimation (resonance masses, widths...). Their reliability was checked together with the impact of the input uncertainties on the determinations of the chiral couplings and the scattering lengths a^I_J. Our outcome is found in agreement with former works though with slightly larger errors. However, the effect in the final values of the a^I_J is negligible after combining them with the other uncertainties. Based on this consistency, we conclude that the previous scattering length determinations seem to be rather solid and reliable, with the cO(p^6) low-energy constants quite under control. Nevertheless, the uncertainties found in the present work point out the limitation on further improvements unless the precision of the O(p^6) couplings is properly increased.

hep-ph↗

arXiv2008

Update analysis of tau- --> V P- nu(tau): Theory and Experiment

Within the resonance chiral theory, we have studied the process of a tau lepton decaying into a vector resonance plus a pseudo-Goldstone meson and a tau neutrino. Two kinds of processes are discussed: (a) tau- --> (rho pi-,omega pi-, phi pi-, K*0 K-) nu(tau), belonging to Delta S=0 processes and (b) Delta S = 1 processes, such as tau- --> (rho K-, omega K-,phi K-,\bar{K*0} pi-) nu(tau). To fit the tau- --> omega pi- nu(tau) spectral function and the decay distribution of tau- --> omega K- nu(tau) to get unknown resonance couplings, we then make a prediction for branching ratios of all channels.

hep-ph↗

arXiv2008

Study of tau- --> V P- nu(tau) in the framework of resonance chiral theory

In this paper we study two kinds of tau decays: (a) tau- --> (rho pi-,omega pi-, phi pi-, K*0 K-) nu(tau), which belong to Delta S=0 processes and (b) Delta S = 1 processes, like tau- --> (rho K-, omega K-, phi K-, \bar{K*0} pi-) nu(tau), in the framework of resonance chiral theory. We fit the tau- --> omega pi- nu(tau) spectral function and the invariant mass distribution of omega K in the process of tau- --> omega K- nu(tau) to get the values of unknown resonance couplings. Then we make a prediction for branching ratios of all channels.

hep-ph↗