Quantum loops in the Resonance Chiral Theory: improving the vector form factor

Quantum loops in the Resonance Chiral Theory are needed to improve the implementation of non-perturbative QCD. Furthermore, the one-loop computations can predict chiral low-energy couplings at next-to-leading order, a very appealing task. We present a first calculation of the vector form factor of the pion at subleading order in the 1/N_C expansion. From the analysis of the result at large energies we justify the requirement of considering short-distance constraints from form factors with resonances in the final state. The long-distance limit of our results allows to get a next-to-leading order estimate of \ell_6.Comment: Talk given at the International Workshop e+e- Collisions from phi to J/psi, 27th February-2nd March (2006), Novosibirsk (Russia

Improving the Hadronization of QCD currents in TAUOLA and PHOKHARA

We present our study of the hadronization structure of both vector and axial-vector currents leading to decays of the tau into two kaons and a pion. The cornerstones of our framework are the large-N_C limit of QCD, the chiral structure exhibited at low energies and the proper asymptotic behaviour, ruled by QCD, that is demanded to the associated form factors. The couplings of the theory are mostly constrained by this procedure and upon the analysis of BaBar data on e^+e^- -> KK pi we are able to predict the hadronic spectra.Comment: 4 pages, 1 figure. To appear in the Proceedings of QCD 08: 14th International QCD Conference, 7-12th July 2008 Montpellier (France). To be published by Elsevier in Nuclear Physics B (Proceedings Supplement

Long distance contribution to K+→π+ννˉK^+ \to \pi^+ \nu {\bar \nu} decay and O(p4)O(p^4) terms in CHPT

The long distance contribution to $K^+ \to \pi^+ \nu {\bar \nu}$ is calculated using chiral perturbation theory. The leading contribution comes from $O(p^4)$ tree terms. The branching ratio of the $O(p^4)$ long distance contribution is found to be of order $10_{-3}$ smaller than the short distance contributions.Comment: 12 pages, 1 figure (available upon request

One-loop Renormalization of Resonance Chiral Theory with Scalar and Pseudoscalar Resonances

The divergent part of the generating functional of the Resonance Chiral Theory is evaluated up to one loop when one multiplet of scalar an pseudoscalar resonances are included and interaction terms which couple up to two resonances are considered. Hence we obtain the renormalization of the couplings of the initial Lagrangian and, moreover, the complete list of operators that make this theory finite, at this order.Comment: 4 pages, no figures. Talk given at the High-Energy Physics International Conference on Quantum Chromodynamics, 2-9 July (2005), Montpellier (France). To appear in the Proceeding

Hadronic Contributions to the Muon g−2g-2 and Low-Energy QCD

The contributions to the muon anomalous magnetic moment from hadronic vacuum polarization and from hadronic light-by-light scattering are reexamined within the frame work of chiral perturbation theory; the $1/N_c$-expansion; and the extended Nambu Jona-Lasinio model of low-energy QCD.Comment: 17 pages, CPT-93/P.2962, 4 figures available by request from the autho

Role of Scalar Meson Resonances in $K_{L}^{0} \rightarrow \pi^{0} \gamma \gamma Decay

Corrections to $K_{L}^{0}\rightarrow \pi^{0} \gamma \gamma$ decay induced by scalar meson exchange are studied within chiral perturbation theory. In spite of bad knowledge of scalar-mesons parameters, the calculated branching ratio can be changed by a few percent.Comment: 18 pages of text, 2 figures (available upon request); preprint IJS-TP-16-94 , TUM-T31-63-94

Low-Energy Photon-Photon Collisions to Two-Loop Order

We evaluate the amplitude for $\gamma \gamma \rightarrow \pi^0 \pi^0$ to two loops in chiral perturbation theory. The three new counterterms which enter at this order in the low-energy expansion are estimated with resonance saturation. We find that the cross section agrees rather well with the available data and with dispersion theoretic calculations even substantially above threshold. Numerical results for the Compton cross section and for the neutral pion polarizabilities are also given to two-loop accuracy.Comment: 48 pages, LaTex, 11 figs. (figures not included; available upon request from [email protected]),BUTP-93/18,LNF-93/077(P),PSI-PR-93-1

Isospin violation and the proton's neutral weak magnetic form factor

The effects of isospin violation on the neutral weak magnetic form factor of the proton are studied using two-flavour chiral perturbation theory. The first nonzero contributions appear at O(p^4) in the small-momentum expansion, and the O(p^5) corrections are also calculated. The leading contributions from an explicit Delta(1232) isomultiplet are included as well. At such a high order in the chiral expansion, one might have expected a large number of unknown parameters to contribute. However, it is found that no unknown parameters can appear within loop diagrams, and a single tree-level counterterm at O(p^4) is sufficient to absorb all divergences. The momentum dependence of the neutral weak magnetic form factor is not affected by this counterterm.Comment: 26 pages including 9 figure

τ−→ηπ−π0ντ\tau^-\to\eta\pi^-\pi^0\nu_\tau and σ(e+e−→ηπ+π−)\sigma(e^+e^-\to \eta\pi^+\pi^-) at low energies

We analyze the hadronization structure of $\tau \to \eta \pi^- \pi^0 \nu_\tau$ decays. In the isospin limit only the vector current contributes to this process. We compute the relevant form factor within Resonance Chiral Theory, at leading order in the $1/N_C$ expansion, and considering only the contribution of the lightest vector resonances. The couplings in the resonance theory are constrained by imposing the asymptotic behaviour of vector spectral functions ruled by $QCD$. We reproduce the branching ratio of this mode and predict the low-energy behaviour of $\sigma\left(e^+e^-\to\eta\pi^+\pi^-\right)$ using isospin symmetry.Comment: 4 pages, 3 figures. To appear in the Proceedings of the QCD10 (25th anniversary) 15th International QCD Conference. 28th June - 3rd July 2010 Montpellier (France) (Nucl. Phys. Proc. Suppl.

Ubiquitous CP violation in a top-inspired left-right model

We explore CP violation in a Left-Right Model that reproduces the quark mass and CKM rotation angle hierarchies in a relatively natural way by fixing the bidoublet Higgs VEVs to be in the ratio m_b:m_t. Our model is quite general and allows for CP to be broken by both the Higgs VEVs and the Yukawa couplings. Despite this generality, CP violation may be parameterized in terms of two basic phases. A very interesting feature of the model is that the mixing angles in the right-handed sector are found to be equal to their left-handed counterparts to a very good approximation. Furthermore, the right-handed analogue of the usual CKM phase delta_L is found to satisfy the relation delta_R \approx delta_L. The parameter space of the model is explored by using an adaptive Monte Carlo algorithm and the allowed regions in parameter space are determined by enforcing experimental constraints from the K and B systems. This method of solution allows us to evaluate the left- and right-handed CKM matrices numerically for various combinations of the two fundamental CP-odd phases in the model. We find that all experimental constraints may be satisfied with right-handed W and Flavour Changing Neutral Higgs masses as low as about 2 TeV and 7 TeV, respectively.Comment: 37 pages, 13 figure