Pad\'e Approximants and Resonance Poles

Based on the mathematically well defined Pad\'e Theory, a theoretically safe new procedure for the extraction of the pole mass and width of a resonance is proposed. In particular, thanks to the Montessus de Ballore theorem we are able to unfold the Second Riemann Sheet of an amplitude to search for the position of the resonant pole in the complex plane. The method is systematic and provides a model-independent treatment of the prediction and the corresponding errors of the approximation.Comment: 12 pages, 17 figure

Quantum Zeno-based control mechanism for molecular fragmentation

A quantum control mechanism is proposed for molecular fragmentation processes within a scenario grounded on the quantum Zeno effect. In particular, we focus on the van der Waals Ne-Br$_2$ complex, which displays two competing dissociation channels via vibrational and electronic predissociation. Accordingly, realistic three dimensional wave packet simulations are carried out by using ab initio interaction potentials recently obtained to reproduce available experimental data. Two numerical models to simulate the repeated measurements are reported and analyzed. It is found that the otherwise fast vibrational predissociation is slowed down in favor of the slow electronic (double fragmentation) predissociation, which is enhanced by several orders of magnitude. Based on these theoretical predictions, some hints to experimentalists to confirm their validity are also proposed.Comment: 4 pages, 3 figure

Temperature crossover of decoherence rates in chaotic and regular bath dynamics

The effect of chaotic bath dynamics on the decoherence of a quantum system is examined for the vibrational degrees of freedom of a diatomic molecule in a realistic, constant temperature collisional bath. As an example, the specific case of I$_2$ in liquid xenon is examined as a function of temperature, and the results compared with an integrable xenon bath. A crossover in behavior is found: the integrable bath induces more decoherence at low bath temperatures than does the chaotic bath, whereas the opposite is the case at the higher bath temperatures. These results, verifying a conjecture due to Wilkie, shed light on the differing views of the effect of chaotic dynamics on system decoherence.Comment: 7 pages, 3 figure

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

Effect of ancilla's structure on quantum error correction using the 7-qubit Calderbank-Shor-Steane code

In this work we discuss the ability of different types of ancillas to control the decoherence of a qubit interacting with an environment. The error is introduced into the numerical simulation via a depolarizing isotropic channel. After the correction we calculate the fidelity as a quality criterion for the qubit recovered. We observe that a recovery method with a three-qubit ancilla provides reasonable good results bearing in mind its economy. If we want to go further, we have to use fault-tolerant ancillas with a high degree of parallelism, even if this condition implies introducing new ancilla verification qubits.Comment: 24 pages, 10 Figures included. Accepted in Phys. Rev. A 200

Coverage of Infertility Treatment and Fertility Outcomes: Do Women Catch Up?

The ageing of first-time mothers and the changes in women's labor market conditions have been accompanied by the introduction and subsequent increase in the use of assisted reproductive therapies (ART) that help extend women's reproductive lives. Considering the financial cost of infertility treatments, policy interventions that increase insurance coverage may significantly affect fertility trends, and ultimately, population age structures. However, policies have ignored the overall impact of ART coverage on fertility. In this paper, long-term effects of insurance coverage for infertility on the timing of first births and on total fertility rates are examined. Variation in the enactment of infertility insurance mandates over time and across U.S. states allows the estimation of both the short-term and long-term effects. We concentrate on the effects of the more demanding mandates enacted in six states in the later 80s and 90s. Our results show that the effect of these mandates to cover infertility treatment is positive on the average age at first birth and increases over time. The long-term estimates of the increase in age of first-time mothers range from 3 to 5 months. Importantly, we also show that these mandates do not increase the total fertility rates of women by the end of their reproductive lives.assisted reproductive technologies, infertility insurance mandates, total fertility, synthetic control methods