Francisco Guerrero

Effective field theory description of the pion form factor

Abstract Using our present knowledge on effective hadronic theories, short-distance QCD information, the 1 N C expansion, analyticity and unitarity, we derive an expression for the pion form factor, in terms of mπ, mK, Mϱ and fπ. This parameter-free prediction provides a surprisingly good description of the experimental data up to energies of the order of 1 GeV.

KK scattering amplitude to one loop in chiral perturbation theory, its unitarization and pion form factors

We have calculated the KK → KK scattering amplitude to next-to-leading order in chiral perturbation theory. Then, making use of a unitarization procedure with one or several coupled channels (ππ, KK in our case) we have calculated the ππ → ππ, ππ → KK and KK → KK S- and P-waves in good agreement with the experiment up to √s ⋍ 1.2 GeV. The ππ scattering lengths with isospin and spin (I, J) equal to (0,0), (1,1) and (2,0) are also calculated in agreement with experiment and former chiral perturbation theory calculations. Finally we have employed these amplitudes, making use of an Omnes representation, to calculate the scalar and the vector pion form factors, obtaining a good agreement with the available experimental data.

Analysing the Spanish smoke-free legislation of 2006: A new method to quantify its impact using a dynamic model

BACKGROUND There are many models that study aspects of smoking habits: the influence of price, tax, relapse time, and the effects of prohibition. There are also studies examining the effects of the Spanish smoke-free law. We wanted to build a model able to separate the effect of the law from the pre-law evolution of smoking habits. METHODS Using data from the Spanish Ministry of Health and Social Policy, we developed a dynamic model of tobacco use. The model projects the evolution over time of the number of non-smokers, smokers and ex-smokers before 2006. Then, we compared the predictions of the model with data for the years after the law came into force, 2006 and 2009. RESULTS We show that smoke-free law has had a significant impact on different sub-populations. The number of ex-smokers increased significantly in 2006 and this increase was maintained in 2009. The number of smokers also decreased significantly in 2006, but in 2009 this returned to its value before the law. Simultaneously, the number of non-smokers decreased in 2009. CONCLUSIONS When the law came into force (2006), its restriction on smoking in public and work places made many smokers decide to give up smoking, decreasing the number of smokers and increasing the number of ex-smokers. In 2009, the majority of those who succeeded in giving up smoking did not return to the habit. However, the smoke-free law had no effect on new smokers and the number of smokers returned to previous levels, whereas the number of non-smokers decreased. Therefore, we can conclude that the law had a very positive effect in the first few years but this has dissipated over time, with the exception of ex-smokers, whose number is still higher than before the law.

Study of the resummation of chiral logarithms in the exponentiated expression for the pion form factor 1

From the properties of analyticity and unitarity it has been recently obtained an exponentiated expression for the pion form factor. In this work I show the validity of this expression comparing its order p 6 term with the one exactly calculated in ChPT.

Kaon polarizabilities in chiral perturbation theory

Abstract We study the kaon polarizabilities in the framework of chiral perturbation theory to order p 4 . For the neutral kaon we find that they vanish and have a first non-zero contribution of order p 6 . We also emphasize the theoretical potential of an eventual measurement of the kaon polarizabilities, in particular of the neutral kaon ones.

Solving a model for 1-D, three-phase flow vertical equilibrium processes in a homogeneous porous medium by means of a Weighted Essentially Non Oscillatory numerical scheme

Mathematical models of multi-phase flow are useful in some engineering applications like enhanced oil recovery, filtration of pollutants into subsurface, etc. In this work, we derive a mathematical model for the motion of one-dimensional three-phase flow in a porous medium under the condition of vertical equilibrium, which can be viewed as an extension of some two-phase flow models described in the literature. Our model involves a system of two partial differential equations in the form of viscous conservation laws, whose solutions may contain very sharp transitions. We show that a high-order/high resolution Weighted Essentially Non Oscillatory scheme is an appropriate tool to discretize the buoyancy flux and obtain a well resolved representation of the solution of the model. In addition, we show that the efficiency of the scheme may be improved by using Implicit-Explicit (IMEX) strategies, where the parabolic terms are handled by an implicit discretization.

Implicit-explicit methods for models for vertical equilibrium multiphase flow

In this paper we provide a derivation of a 1D N-phase flow model in a porous medium under the condition of vertical equilibrium which generalizes the three-phase flow model developed in Guerrero et al. (2013). We identify, from a mathematical point of view, a set of conditions on the capillary pressures that ensure that the linearized, purely parabolic, initial value problem is well-posed. For the numerical simulation of the model, we advocate the use of Implicit-Explicit (IMEX)-Runge-Kutta (RK) schemes for time evolution with a Weighted-Essentially Non-Oscillatory (WENO) spatial discretization of the convective terms. In previous papers (Donat et al., 2013), (Guerrero et al., 2013), we showed that IMEX-RK methods can be useful in the numerical simulation of 1D two-phase and three-phase flows, since the stability restrictions for the time-step of these schemes are less severe than those of fully explicit schemes. On the other hand, their implementation requires, in general, a fairly intensive use of a nonlinear system solver, so that the efficiency and robustness of IMEX schemes for multi-phase flow is directly related to this nonlinear technique. In this paper we describe an efficient nonlinear system solver, based on an appropriate fixed-point iteration technique, in order to find the solution of the nonlinear systems that result from the implicit discretization of the nonlinear diffusive terms in the model. In addition, we implement zero-flux boundary conditions fully consistent with the vertical equilibrium assumptions. A set of numerical examples confirm the efficiency, robustness and reliability of the proposed numerical technique.

Recent progress on the chiral unitary approach to meson meson and meson baryon interactions

We report on recent progress on the chiral unitary approach, analogous to the effective range expansion in Quantum Mechanics, which is shown to have a much larger convergence radius than ordinary chiral perturbation theory, allowing one to reproduce data for meson meson interaction up to 1.2 GeV. Applications to physical processes so far unsuited for a standard chiral perturbative approach are presented. Results for the extension of these ideas to the meson baryon sector are discussed, together with applications to kaons in a nuclear medium and K- atoms.

A Non-Perturbative Chiral Approach for Meson-Meson Interactions *

A non-perturbative method [1] which combines constraints from chiral symmetry breaking and coupled channel unitarity is used to describe meson-meson interactions up to √s<_~1.2 GeV, extending in this way the range of applicability of the information contained in Chiral Perturbation Theory (X PT) [2], since this perturbative series is typically restricted to √s<_500 MeV. The approach uses the O(p²) and O(p^4) Lagrangians. The seven free parameters resulting from the O(p^4) Lagrangian are fitted to the experimental data. The approach makes use of the expansion of T^(-1) instead of the amplitude itself as done in X PT. The former expansion is suggested by analogy with the effective range approximation in Quantum Mechanics and it appears to be very useful. The results, in fact, are in good agreement with a vast amount of experimental analyses [3,4]. The amplitudes develop poles corresponding to the fₒ(980), aₒ(980), ρ(770), K*(890), the octet contribution to the φ , fₒ(400 −1200) ≡ σ and κ [4]. The total and partial decay widths of the resonances are also well reproduced.