Axial-vector Resonances Research Articles

τ decay and the structure of the [formula omitted

We analyse the decay τ→πππν based on the recently developed techniques to generate axial-vector resonances dynamically. Under the assumption that the a1 is generated entirely through coupled-channel dynamics, one gets a reasonable description of the spectral function. Including, in addition, an explicit elementary a1 does not improve the results.

Information on the structure of thea1fromτdecay

The decay $\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\pi}\ensuremath{\pi}\ensuremath{\pi}\ensuremath{\nu}$ is analyzed using different methods to account for the resonance structure, which is usually ascribed to the ${a}_{1}$. One scenario is based on the recently developed techniques to generate axial-vector resonances dynamically, whereas in a second calculation the ${a}_{1}$ is introduced as an explicit resonance. We investigate the influence of different assumptions on the result. In the molecule scenario the spectral function is described surprisingly well by adjusting only one free parameter. This result can be systematically improved by adding higher-order corrections to the iterated Weinberg-Tomozawa interaction. Treating the ${a}_{1}$ as an explicit resonance on the other hand leads to peculiar properties.

Form-factors and current correlators: chiral couplingsL10r(μ) andC87r(μ) at NLO in 1/NC

Using the resonance chiral theory Lagrangian, we perform a calculation of the vector and axial-vector two-point functions at the next-to-leading order (NLO) in the 1/NC expansion. We have analyzed these correlators within the single-resonance approximation and have also investigated the corrections induced by a second multiplet of vector and axial-vector resonance states. Imposing the correct QCD short-distance constraints, one determines the difference of the two correlators Π(t) ≡ ΠVV(t)−ΠAA(t) in terms of the pion decay constant and resonance masses. Its low momentum expansion fixes then the low-energy chiral couplings L10 and C87 at NLO, keeping full control of their renormalization scale dependence. At μ0 = 0.77 GeV, we obtain L10r(μ0) = (−4.4±0.9) · 10−3 and C87r(μ0) = (3.1±1.1) · 10−5.

Low lying axial-vector mesons as dynamically generated resonances

We make a theoretical study of the $s$-wave interaction of the nonet of vector mesons with the octet of pseudoscalar mesons starting from a chiral invariant Lagrangian and implementing unitarity in coupled channels. By looking for poles in the unphysical Riemann sheets of the unitarized scattering amplitudes, we get two octets and one singlet of axial-vector dynamically generated resonances. The poles found can be associated with most of the low lying axial-vector resonances quoted by the Particle Data Group: ${b}_{1}(1235)$, ${h}_{1}(1170)$, ${h}_{1}(1380)$, ${a}_{1}(1260)$, ${f}_{1}(1285)$, and two poles to the ${K}_{1}(1270)$ resonance. We evaluate the couplings of the resonances to the $VP$ states and the partial decay widths in order to reinforce the arguments in the discussion.

Four-point correlator constraints on electromagnetic chiral parameters and resonance effective Lagrangians

We pursue the analysis of a set of generalized DGMLY sum rules for the electromagnetic chiral parameters at order $e^2p^2$ and discuss implications for effective Lagrangians with resonances. We exploit a formalism in which charge spurions are introduced and treated as sources. We show that no inconsistency arises from anomalies up to quadratic order in the spurions. We focus on the sum rules associated with QCD 4-point correlators which were not analyzed in detail before. Convergence properties of the sum rules are deduced from a general analysis of the form of the counterterms in the presence of electromagnetic spurions. Following the approach in which vector and axial-vector resonances are described with antisymmetric tensor fields and have a chiral order, we show that the convergence constraints are violated at chiral order four and can be satisfied by introducing a set of terms of order six. The relevant couplings get completely and uniquely determined from a set of generalized Weinberg sum-rule relations. An update on the corrections to Dashen's low-energy theorem is given.

Hadronic charmed meson decays involving axial vector mesons

Cabibbo-allowed charmed meson decays into a pseudoscalar meson and an axial-vector meson are studied. The charm to axial-vector meson transition form factors are evaluated in the Isgur-Scora-Grinstein-Wise quark model. The dipole momentum dependence of the $\stackrel{\ensuremath{\rightarrow}}{D}K$ transition form factor and the presence of a sizable long-distance W exchange are the two key ingredients for understanding the data of $\stackrel{\ensuremath{\rightarrow}}{D}\overline{K}{a}_{1}.$ The ${K}_{1A}\ensuremath{-}{K}_{1B}$ mixing angle of the strange axial-vector mesons is found to be $\ensuremath{\approx}\ifmmode\pm\else\textpm\fi{}37\ifmmode^\circ\else\textdegree\fi{}$ or $\ifmmode\pm\else\textpm\fi{}58\ifmmode^\circ\else\textdegree\fi{}$ from $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\tau}}{K}_{1}{\ensuremath{\nu}}_{\ensuremath{\tau}}$ decays. The study of $\stackrel{\ensuremath{\rightarrow}}{D}{K}_{1}(1270)\ensuremath{\pi},$ ${K}_{1}(1400)\ensuremath{\pi}$ decays excludes the positive mixing-angle solutions. It is pointed out that an observation of the decay ${D}^{0}\ensuremath{\rightarrow}{K}_{1}^{\ensuremath{-}}(1400){\ensuremath{\pi}}^{+}$ at the level of $5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ will rule out $\ensuremath{\theta}\ensuremath{\approx}\ensuremath{-}37\ifmmode^\circ\else\textdegree\fi{}$ and favor the solution $\ensuremath{\theta}\ensuremath{\approx}\ensuremath{-}58\ifmmode^\circ\else\textdegree\fi{}.$ Though the decays ${D}^{0}\ensuremath{\rightarrow}{K}_{1}^{0}{\ensuremath{\pi}}^{0}$ are color suppressed, they are comparable to and even larger than the color-allowed counterparts ${K}_{1}^{0}(1270){\ensuremath{\pi}}^{0}\ensuremath{\sim}{K}_{1}^{\ensuremath{-}}(1270){\ensuremath{\pi}}^{+}$ and ${K}_{1}^{0}(1400){\ensuremath{\pi}}^{0}>{K}_{1}^{\ensuremath{-}}(1400){\ensuremath{\pi}}^{+}.$ The finite width effect of the axial-vector resonance is examined. It becomes important for ${a}_{1}(1260)$ in particular when its width is near 600 MeV.

Erratum: Polarization effects inB→K1(1270)+J/ψdecays [Phys. Rev. D65, 091501 (2002)

The joint angular distribution of the decay B \to J/\Psi V, where V is an axial vector or vector resonance, followed by the subsequent decay processes of the J/\Psi and V is calculated using the covariant density method. In particular, the case where V is the axial vector meson K_1(1270) which decays into K \rho is considered as well as the case that V is the vector meson K^\ast(890) which decays into K \pi.

Polarization effects inB→K1(1270)+J/ψdecays

The joint angular distribution of the decay B \to J/\Psi V, where V is an axial vector or vector resonance, followed by the subsequent decay processes of the J/\Psi and V is calculated using the covariant density method. In particular, the case where V is the axial vector meson K_1(1270) which decays into K \rho is considered as well as the case that V is the vector meson K^\ast(890) which decays into K \pi.

Long-distance contribution to the muon-polarization asymmetry inK+→π+μ+μ−

We revisit the calculation of the long-distance contribution to the muon-polarization asymmetry \Delta_{LR}, which arises, in K^+\to\pi^+\mu^+\mu^-, from the two-photon intermediate state. The parity-violating amplitude of this process, induced by the local anomalous K^+\pi^-\gamma^*\gamma^* 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 \Delta_{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.

Observation of pseudoscalar and axial vector resonances in π−p→K+K−π0n at 18 GeV

The number of pseudoscalar mesons in the mass range from 1400 to 1500 MeV/ c 2 has been a subject of considerable interest for many years, with several experiments having presented evidence for two closely spaced states. A new measurement of the reaction π − p → K + K − π 0 n has been made at a beam energy of 18 GeV. A partial wave analysis of the K + K − π 0 system shows evidence for three pseudoscalar resonances, η (1295), η (1416), and η (1485), as well as two axial vectors, f 1 (1285), and f 1 (1420). Their observed masses, widths and decay properties are reported. No signal was observed for C (1480), an I G J PC =1 + 1 −− state previously reported in φπ 0 decay.

Pole contributions in semileptonic decays of D mesons

The contributions of the axial-vector and vector resonance states to D → P(V)l\(\bar \nu\)l decays are investigated on the basis of phenomenological chiral Lagrangians. It is shown that inclusion of such intermediate states improves agreement with experimental data.

Bosonized Lagrangians in higher orders of the chiral expansion

The derivation of effective mesonLagrangians in higher orders of the chiral expansion from bosonization of the four-quark interaction of the extended Nambu–Jona-Lasinio (NJL) model, treated as a local approximation of low-energy QCD, is reviewed. The calculated heat-kernel coefficients for the quark determinant of the bosonized NJL model through seventh order are presented in a systematic way. The results are used to fix the structure coefficients of the effective chiral Lagrangians in orders p 4 and p 6 of the momentum expansion. Various aspects of the use of bosonized Lagrangians to describe low-energy meson processes are discussed: the reduction of vector, axial-vector, and scalar resonances, regularization of graphs with meson loops, and the dependence of the phenomenological structure coefficients on the renormalization scheme and regularization parameters. Questions related to the physical justification of the NJL model as a low-energy limit of QCD are also discussed. Nonlocal corrections to the structure coefficients of bosonized Lagrangians are studied in this context.

Tests for a strong electroweak sector at futuree +e- high-energy colliders

The study of the scattering at high energy of the gauge bosons W and Z, in particular longitudinally polarized W and Z, can clarify the mechanism of spontaneous symmetry breaking in the Standard Model of the electroweak interactions. Different models of strong electroweak sector, based on the effective lagrangian approach are briefly reviewed. They include models with no resonance, with scalar resonance, additional vector and axial-vector resonances. The effective Lagrangians are derived from the chiral symmetry of the symmetry breaking sector. Limits on these models from existing measurements, mainly LEP and Tevatron, are considered. We study also direct and indirect effects of the new interactions at high energy future e^+e^- linear colliders, through WW scattering and the direct production of these new vector gauge bosons.

Indirect effects of new resonances at future linear colliders

In this paper we consider a general SU(2) L ⊗ SU(2) R invariant Lagrangian describing scalar, vector and axial-vector resonances. By expanding the WW and the ZZ scattering amplitude up to the fourth order in the external momenta we can compare the parameters of our Lagrangian with the ones used in the effective chiral Lagrangian formalism. In the last approach there has been a recent study of the fusion processes at future e + e − colliders at energies above 1 TeV. We use these results to put bounds on the parameter space of our model and to show that for the case of vector resonances the bounds obtained from the annihilation channel in fermion pairs are by far more restrictive, already at energies of the order of 500 GeV.

One loop calculation of the ϵ3 parameter within the extended BESS model

The existence of a strongly interacting sector responsible for the electroweak symmetry breaking is assumed. As a consequence vector and axial-vector bound states may be formed. These resonances mix with the Standard Model gauge bosons and are of primary phenomenological importance for the LEP physics. The extended BESS model is an effective scheme based on the symmetry group SU(8) L ⊗ SU(8) R , describing in a consistent way the interactions among the pseudo-Goldstone bosons, vector and axial-vector resonances and the standard gauge bosons. In a previous paper, the contribution from extended BESS to the electroweak oblique corrections was evaluated. However, only an estimate of the effects coming from mass and wave function renormalization of the new resonances, was given. Here we complete the evaluation by computing explicitly these effects. We confirm the previous result, that is, in spite of the great precision of the present LEP measurements, the extended BESS parameter space is not very much constrained.

Contributions of the C-odd axial-vector resonances to eta --> pi 0 gamma gamma and gamma gamma --> pi 0 pi 0.

We consider the contributions of the $C$-odd axial-vector resonances (${b}_{1}$, ${h}_{1}$) to $\ensuremath{\eta}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}\ensuremath{\gamma}\ensuremath{\gamma}$, as well as those of the usual $C$-odd vector resonances ($\ensuremath{\rho}$, $\ensuremath{\omega}$) and chiral loops. Inclusion of ${b}_{1}(1235)$, ${h}_{1}(1170)$, ${h}_{1}(1380)$ increases the decay width of $\ensuremath{\eta}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}\ensuremath{\gamma}\ensuremath{\gamma}$, improving the theoretical prediction. The measurement of the $\ensuremath{\gamma}\ensuremath{\gamma}$ spectrum can test our model. We also discuss the effects of these $C$-odd axial-vector resonances on electromagnetic interactions of neutral pions: $\ensuremath{\gamma}\ensuremath{\gamma}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}$ and electric and magnetic polarizabilities of ${\ensuremath{\pi}}^{0}$.

Experimental study of the axial-vector resonances of a 1 and h 1 in the π-p charge exchange reaction

A high-statistics experiment on the reaction π −p→ π + π − π 0n at 8.06 GeV/ c has been performed using a spectrometer detecting both charged particles and gamma rays. A partial-wave analysis based on the isobar model has been carried out for π +π −π 0 data in the mass range between 0.86 and 1.50 GeV for four t′ regions: 0.0–0.1, 0.1–0.25, 0.25–0.45 and 0.45–0.95 (GeV/ c 2). Two axial-vector resonances, a 1(1260) and h 1(1170), were observed in the analysis. The masses and widths of a 1 and h 1 were determined to be M(a 1 = 1121 ± 8 MeV, Λ(a 1 = 239± 11 MeV, M(h 1 = 1168±4 MeV and Λ(h 1 = 345±6 MeV, respectively, by fitting the Breit-Wigner formula to the partial wave amplitude. A fit including the Deck type background was also tried in each t′ region. The results showed a small effect on these resonance parameters and were consistent with those obtained by the simple Breit-Wigner fitting.

EFFECTIVE ACTION FOR COMPOSITE HIGGS MODELS

We derive the effective action for composite Higgs models in electroweak theory from Nambu-Jona-Lasinio model. This action contains vector and axial vector mesons together with Higgs, W, Z and photon. Due to the interaction of the techni-quark with SU(2) L × U(1) gauge fields, mixing terms of SU(2) L × U(1) gauge fields and vector and axial vector resonances develop in the kinetic term of the effective action. Mass relation of the techni-rho and the Higgs is obtained.

The axial vector resonances, a 1 and h 1, in the π−p charge exchange reaction

A partial-wave analysis based on the isobar model has been carried out for a high statistics π + π − π 0 data in the π −p charge exchange reaction in the mass range between 0.88 and 1.44 GeV. Two axial-vector resonances, a 1(1260) and h 1(1170), were observed in the analysis. The masses and widths of a 1 and h 1 were determined by fitting the partial-wave amplitude to the Breit Wigner formula at four t' regions.

Mixing of P wave axial vector resonances

An analysis is given of the mixing of the axial vector kaon resonances by use of new data from SLAC. Mass values, decay widths and branching ratios of the SLAC work may be compatible with SU(3) and/or “pair creation model” classifications for a mixing angle λ ≈ −35° ± 10°. The mass values and coupling strengths proposed by Basdevant and Berger, from a different parametrization of the same data, can be fitted in an SU(3) and/or broken SU(6) w model with a larger mixing angle λ ≈ −80°. Such a mixing would mean that the lower kaonic state is closely related to the 1 +− nonet in contrast to expectations from duality and/or one-gluon exchange mixing schemes. We also discuss the mixing of the charmed D meson states.