Rho Meson Properties in the Chiral Theory Framework

We study the mass, width and couplings of the lightest resonance multiplet with I(J^{PC})=1(1^{--}) quantum numbers. Effective field theories based on chiral symmetry are employed in order to describe the form factor associated with the two-pseudoscalar matrix element of the QCD vector current. The bare poles of the intermediate resonances are regularized through a Dyson-Schwinger-like summation. We explore the role of the resonance width in physical observables and make a coupled-channel analysis of final-state interactions. This provides many interesting properties, as the pole mass M_rho{pole}= 764.1 +- 2.7 +4.0-2.5 MeV. At energies E~1 GeV, a second 1(1^{--}) resonance multiplet is considered in order to describe the data in a more consistent way. From the phenomenologically extracted resonance couplings, we obtain the chiral coupling L_9^r(mu0)= (7.04 +- 0.05 +0.19-0.27)* 10^{-3}, at mu0=770$ MeV, and show how the running with the scale mu affects the resonance parameters. A 1/N_C counting is adopted in this work and the consistency of the large--N_C expansion is tested. Finally, we make an estimation of the contribution from diagrams with resonances in crossed channels.Comment: 26 pages, 8 figures, Latex fil

Pseudoscalar pole light-by-light contributions to the muon (g−2)(g-2) in Resonance Chiral Theory

We have studied the $P\to\gamma^\star\gamma^\star$ transition form-factors ($P=\pi^0,\eta,\eta'$) within a chiral invariant framework that allows us to relate the three form-factors and evaluate the corresponding contributions to the muon anomalous magnetic moment $a_\mu$, through pseudoscalar pole contributions. We use a chiral invariant Lagrangian to describe the interactions between the pseudo-Goldstones from the spontaneous chiral symmetry breaking and the massive meson resonances. We will consider just the lightest vector and pseudoscalar resonance multiplets. Photon interactions and flavor breaking effects are accounted for in this covariant framework. This article studies the most general corrections of order $m_P^2$ within this setting. Requiring short-distance constraints fixes most of the parameters entering the form-factors, consistent with previous determinations. The remaining ones are obtained from a fit of these form-factors to experimental measurements in the space-like ($q^2\le0$) region of photon momenta. The combination of data, chiral symmetry relations between form-factors and high-energy constraints allows us to determine with improved precision the on-shell $P$-pole contribution to the Hadronic Light-by-Light scattering of the muon anomalous magnetic moment: we obtain $a_{\mu}^{P,HLbL}=(8.47\pm 0.16)\cdot10^{-10}$ for our best fit. This result was obtained excluding BaBar $\pi^0$ data, which our analysis finds in conflict with the remaining experimental inputs. This study also allows us to determine the parameters describing the $\eta-\eta'$ system in the two-mixing angle scheme and their correlations. Finally, a preliminary rough estimate of the impact of loop corrections ($1/N_C$) and higher vector multiplets (asym) enlarges the uncertainty up to $a_\mu^{P,HLbL} = (8.47\pm 0.16_{\rm sta}\pm0.09_{1/N_C}{}^{+0.5}_{-0.0}{}_{\rm asym})\cdot 10^{-10}$.Comment: 43 pages, 5 figures. Accepted for publication in JHEP. New subsection involving error analysis and some minor change

Form-factors and current correlators: chiral couplings L_10(mu) and C_87(mu) at NLO in 1/N(C)

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/N(C) 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 Pi(t) = Pi_VV(t)- Pi_AA(t) in terms of the pion decay constant and resonance masses. Its low momentum expansion fixes then the low-energy chiral couplings L_10 and C_87 at NLO, keeping full control of their renormalization scale dependence. At mu_0=0.77 GeV, we obtain L_10(mu_0) = (-4.4 \pm 0.9)10^{-3} and C_87^r(mu_0)=(3.1 \pm 1.1)10^{-5}

On-chip quantum tomography of mechanical nano-scale oscillators with guided Rydberg atoms

Nano-mechanical oscillators as well as Rydberg-atomic waveguides hosted on micro-fabricated chip surfaces hold promise to become pillars of future quantum technologies. In a hybrid platform with both, we show that beams of Rydberg atoms in waveguides can quantum-coherently interrogate and manipulate nanomechanical elements, allowing full quantum state tomography. Central to the tomography are quantum non-demolition measurements using the Rydberg atoms as probes. Quantum coherent displacement of the oscillator is also made possible, by driving the atoms with external fields while they interact with the oscillator. We numerically demonstrate the feasibility of this fully integrated on-chip control and read-out suite for quantum nano-mechanics, taking into account noise and error sources.Comment: 11 pages, 5 figures, 1 tabl