Axial-vector Transition Form Factors Research Articles

Axial-vector transition form factors and e+e− → f1π+π−

We study the transition form factors (TFFs) of axial-vector mesons in the context of currently available experimental data, including new constraints from e+e− → f1(1285)π+π− that imply stringent limits on the high-energy behavior and, for the first time, allow us to provide an unambiguous determination of the couplings corresponding to the two antisymmetric TFFs. We discuss how these constraints can be implemented in a vector-meson-dominance picture, and, in combination with contributions from the light-cone expansion, construct TFFs as input for the evaluation of axial-vector contributions to hadronic light-by-light scattering in the anomalous magnetic moment of the muon.

Axial-vector transition form factors of the singly heavy baryons

We investigate the axial-vector transition form factors of the lowest-lying singly heavy baryons within the framework of the chiral quark-soliton model. We consider the linear ${m}_{\mathrm{s}}$ corrections, dealing with the strange current quark mass ${m}_{\mathrm{s}}$ as a small perturbation. Since we have various relations between different transitions because of isospin symmetry and flavor SU(3) symmetry breaking, only two axial-vector transition form factors are independent. We present the numerical results for these form factors. The effects of the flavor SU(3) symmetry breaking turn out tiny, so we neglect them. We also compute the decay rates for several strong decays of the singly heavy baryons and compare the results with the experimental data and those from other models. While the results for the ${\mathrm{\ensuremath{\Sigma}}}_{c}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Lambda}}}_{c}^{+}+\ensuremath{\pi}$ and ${\mathrm{\ensuremath{\Sigma}}}_{c}^{*}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Lambda}}}_{c}^{+}+\ensuremath{\pi}$ decays are slightly overestimated in comparison with the corresponding experimental data, those for the ${\mathrm{\ensuremath{\Xi}}}_{c}^{*}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Xi}}}_{c}+\ensuremath{\pi}$ are in remarkable agreement with the data.

Axial-vector transition form factors of the baryon octet to the baryon decuplet with flavor SU(3) symmetry breaking

We investigate the axial-vector transition form factors of the baryon octet to the baryon decuplet within the framework of the chiral quark-soliton model, with the effects of flavor SU(3) symmetry breaking included. We consider the rotational $1/{N}_{c}$ corrections and regard the strange current quark mass as a perturbation. We compare the present results for the $\mathrm{\ensuremath{\Delta}}\ensuremath{\rightarrow}N$ axial-vector transition with those from other models and lattice QCD. We also compute all possible axial-vector transitions from the baryon decuplet to the octet with the strangeness changed, i.e., $|\mathrm{\ensuremath{\Delta}}S|=1$. We obtain the value of the essential form factor ${C}_{5}^{A}$ for the $\mathrm{\ensuremath{\Delta}}\ensuremath{\rightarrow}N$ axial-vector transition at the zero momentum transfer (${Q}^{2}=0$). Furthermore, the present results are in good agreement with those fitted with the T2K data. We extract the value of the axial-vector mass ${M}_{A}$ compared to the data.

$${\bar{\nu }}_{\mu }$$ induced quasielastic production of hyperons leading to pions

The quasielastic production cross sections and polarizations of the hyperons induced by ${\bar\nu}_\mu$ on the free nucleon as well as from $^{40}$Ar in the sub-GeV energy region has been reviewed [1-5]. The effects of the second class currents in the axial vector sector with and without T-invariance as well as the effect of SU(3) symmetry breaking are also studied. We find that the cross sections and the various polarization components can effectively be used to determine the axial vector transition form factors in the strangeness sector and to test the validity of various symmetries of the weak hadronic currents like G-invariance, T-invariance and SU(3) symmetry. These hyperons decay dominantly into pions giving an additional contribution to the weak pion production induced by the antineutrinos. In the case of nuclear targets like $^{40}$Ar, this contribution is shown to be significant when compared with the pion production by the $\Delta$ excitations in the energy range of $E_{\bar{\nu}_{\mu}} \le 0.7$ GeV [1]. This study could be useful for the DUNE experiment where argon will be used as the target material and the electronic imaging of particles is possible and the particle tracks can be identified.

Axial vector transition form factors in holographic QCD and their contribution to the anomalous magnetic moment of the muon

We evaluate axial vector transition form factors in holographic QCD models that have been shown to reproduce well recent experimental and theoretical results for the pion transition form factor. Comparing with L3 data on $f_1\to\gamma\gamma^*$ we find remarkable agreement regarding the shape of single-virtual form factors. In the double-virtual case, the holographic results differ strongly from a simple dipole form, and this has an important impact on the corresponding estimate of the axial vector contribution to the anomalous magnetic moment of the muon $a_\mu$ through hadronic light-by-light scattering. We demonstrate that hard-wall models satisfy the Melnikov-Vainshtein short-distance constraint for the latter, if and only if the infinite tower of axial vector states is included. The results for $a_\mu$, however, are strongly dominated by the first few resonances. Numerically, these results turn out to be surprisingly large: (2.9 - 4.1)$\times 10^{-10}$ in the hard-wall models, 57-58% of which are due to the longitudinal contribution, which is the one responsible for the Melnikov-Vainshtein short-distance constraint. Rescaling the holographic result to obtain an optimal fit of L3 data, but then matching only 52% of the asymptotic constraint, the result is reduced to $2.2(5)\times 10^{-10}$, which is still significantly larger than most previous phenomenological estimates of the axial vector exchange contribution.

Weak Quasielastic Hyperon Production Leading to Pions in the Antineutrino-Nucleus Reactions

In this review, we have studied the quasielastic production cross sections and polarization components of $\Lambda$, $\Sigma^0$ and $\Sigma^-$ hyperons induced by the weak charged currents in the antineutrino reactions on the nucleon and the nuclear targets like $^{12}$C, $^{16}$O, $^{40}$Ar and $^{208}$Pb. It is shown that the energy and the $Q^2$ dependence of the cross sections and the various polarization components can be effectively used to determine the axial vector transition form factors in the strangeness sector and test the validity of various symmetry properties of the weak hadronic currents like G-invariance, T-invariance and SU(3) symmetry. In particular, the energy and the $Q^2$ dependence of the polarization components of the hyperons is found to be sensitive enough to determine the presence of the second class current with or without T-invariance. These hyperons decay dominantly into pions giving an additional contribution to the weak pion production induced by the antineutrinos. This contribution is shown to be quantitatively significant as compared to the pion production by the $\Delta$ excitation in the nuclear targets in the sub-GeV energy region relevant for the $\bar{\nu}_\mu$ cross section measurements in the oscillation experiments. We have also included a few new results, based on our earlier works, which are in the kinematic region of the present and future (anti)neutrino experiments being done with the accelerator (anti)neutrinos at T2K, MicroBooNE, MiniBooNE, NO$\nu$A, MINER$\nu$A and DUNE, as well as for the atmospheric (anti)neutrino experiments in this energy region.

Weak quasielastic electroproduction of hyperons with polarization observables

With the availability of high luminosity electron beam at the accelerators, there is now the possibility of studying weak quasielastic hyperon production off the proton, i.e. $e^-p \to \nu_e Y(Y=\Lambda,\Sigma^0)$, which will enable the determination of the nucleon-hyperon vector and axial-vector transition form factors at high $ Q^2$ in the strangeness sector and provide test of the Cabibbo model, G-invariance, CVC, PCAC hypotheses and SU(3) symmetry. In this work, we have studied the total cross section, differential cross section as well as the longitudinal and perpendicular components of polarization of the final hyperons ($ \Lambda$ and $\Sigma^0$ produced in these reactions) and presented numerical results for these observables and their sensitivity to the transition form factors.

Axial vector transition form factors of N → Δ in QCD

The isovector axial vector form factors of N→Δ transition are calculated by employing Light-cone QCD sum rules. The analytical results are analyzed by both the conventional method, and also by a Monte Carlo based approach which allows one to scan all of the parameter space. The predictions are also compared with the results in the literature, where available. Although the Monte Carlo analysis predicts large uncertainties in the predicted results, the predictions obtained by the conventional analysis are in good agreement with other results in the literature.

Electroweak radiative corrections to parity-violating electroexcitation of theΔ

We analyze the degree to which parity-violating (PV) electroexcitation of the $\Delta(1232)$ resonance may be used to extract the weak neutral axial vector transition form factors. We find that the axial vector electroweak radiative corrections are large and theoretically uncertain, thereby modifying the nominal interpretation of the PV asymmetry in terms of the weak neutral form factors. We also show that, in contrast to the situation for elastic electron scattering, the axial $N\to\Delta$ PV asymmetry does not vanish at the photon point as a consequence of a new term entering the radiative corrections. We argue that an experimental determination of these radiative corrections would be of interest for hadron structure theory, possibly shedding light on the violation of Hara's theorem in weak, radiative hyperon decays.