Light-front representation of chiral dynamics in peripheral transverse densities

The nucleon's electromagnetic form factors are expressed in terms of the transverse densities of charge and magnetization at fixed light-front time. At peripheral transverse distances $b = O(M_\pi^{-1})$ the densities are governed by chiral dynamics and can be calculated model-independently using chiral effective field theory (EFT). We represent the leading-order chiral EFT results for the peripheral transverse densities as overlap integrals of chiral light-front wave functions, describing the transition of the initial nucleon to soft pion-nucleon intermediate states and back. The new representation (a) explains the parametric order of the peripheral transverse densities; (b) establishes an inequality between the spin-independent and -dependent densities; (c) exposes the role of pion orbital angular momentum in chiral dynamics; (d) reveals a large left-right asymmetry of the current in a transversely polarized nucleon and suggests a simple interpretation. The light-front representation enables a first-quantized, quantum-mechanical view of chiral dynamics that is fully relativistic and exactly equivalent to the second-quantized, field-theoretical formulation. It relates the charge and magnetization densities measured in low-energy elastic scattering to the generalized parton distributions probed in peripheral high-energy scattering processes. The method can be applied to nucleon form factors of other operators, e.g. the energy-momentum tensor.Comment: 28 pages, 9 figure

Chiral dynamics and peripheral transverse densities

In the partonic (or light-front) description of relativistic systems the electromagnetic form factors are expressed in terms of frame-independent charge and magnetization densities in transverse space. This formulation allows one to identify the chiral components of nucleon structure as the peripheral densities at transverse distances b = O(M_pi^{-1}) and compute them in a parametrically controlled manner. A dispersion relation connects the large-distance behavior of the transverse charge and magnetization densities to the spectral functions of the Dirac and Pauli form factors near the two-pion threshold at timelike t = 4 M_pi^2. Using relativistic chiral effective field theory in the leading-order approximation, we (a) derive the asymptotic behavior (Yukawa tail) of the isovector transverse densities in the "chiral" region b = O(M_pi^{-1}) and the "molecular" region b = O(M_N^2/M_pi^3); (b) perform the heavy-baryon expansion; (c) explain the relative magnitude of the peripheral charge and magnetization densities in a simple mechanical picture; (d) include Delta intermediate states and study the densities in the large-N_c limit of QCD; (e) quantify the spatial region where the chiral components are numerically dominant; (f) calculate the chiral divergences of the b^2-weighted moments of the transverse densities (charge and magnetic radii) and determine their spatial support. Our approach provides a concise formulation of the spatial structure of the nucleon's chiral component and offers new insights into basic properties of the chiral expansion. It relates the information extracted from low-t elastic form factors to the generalized parton distributions probed in peripheral high-energy scattering processes.Comment: 52 pages, 13 figure

Estimating the impact of single pill combination therapy for hypertension: projections of patient outcomes in Italy

Introduction: Hypertension affects almost a third of the Italian population and is a major risk factor for cardiovascular disease. Management of hypertension is often hindered by poor adherence to complex treatment regimens. This analysis aimed to estimate the 10-year clinical outcomes associated with single pill combination (SPC) therapies compared with other treatment pathways for the management of hypertension in Italy. Methods: A microsimulation modeling approach was used to project health outcomes over a 10-year period for people with hypertension. Input data for four treatment pathways [current treatment practices (CTP), single drug with dosage titration then sequential addition of other agents (start low and go slow, SLGS), free choice combination with multiple pills (FCC) and SPC] were sourced from the Global Burden of Disease 2017 data set. The model simulated clinical outcomes for 1 000 000 individuals in each treatment pathway, including mortality, chronic kidney disease (CKD), stroke, ischemic heart disease (IHD) and disability-adjusted life years (DALYs). Results: Through improved adherence, SPC was projected to improve clinical outcomes versus CTP, SLGS, and FCC. SPC was associated with reductions in mortality, incidence of clinical events, and DALYs versus CTP of 5.4%, 11.5%, and 5.7%, respectively. SLGS and FCC were associated with improvements in clinical outcomes versus CTP, but smaller improvements than those associated with SPC. Conclusions: Over 10 years, combination therapies (including SPC and FCC) were projected to reduce the burden of hypertension compared with conventional management approaches in Italy. Due to higher adherence, SPC was associated with the greatest overall benefits versus other regimen

Space-time description of strong-field ionization and high-order-harmonic generation

We develop the spatiotemporal description of matter-field interaction within the strong-field approximation. We show that the space-time form of the ionized wave function has analogies with the diffraction phenomenon, allowing for the definition of two different regimes: Fresnel and Fraunhofer. We demonstrate that the standard saddle-point analysis corresponds to the paraxial approximation of the Fraunhofer case. The Fresnel number therefore appears as a useful parameter to characterize the validity of the saddle-point approach. We give a closed formula for the ionized wave function beyond the standard saddle-point analysis that takes the form of a chirped Volkov wave. We apply our results to the study of high-order-harmonic generation, demonstrating that the saddle-point approximation breaks down for extended systems, i.e., when the Fresnel number approaches or is above the unity. As a simple example, we analyze the harmonic generation of dissociating H2+ and demonstrate the Fresnel number as a useful parameter to determine the accuracy of the semiclassical saddle-point approach.We acknowledge support from Spanish MINECO through the research project FIS2009-09522; Junta de Castilla y León, through the research project SA116U13; and a grant from the European Research Council (ERC-2011-AdG-291561-HELIOS)

Invalidity of the Ehrenfest theorem in the computation of high-order-harmonic generation within the strong-field approximation

[EN]It is known that the strong-field approximations commonly used in models for computing high-order-harmonic generation invalidate the Ehrenfest theorem. Therefore, the time derivative of the atomic dipole or of the dipole velocity does not correspond to the dipole acceleration. We study the consequences of this invalidation for the quantitative evaluation of high-order-harmonic spectra in hydrogen at different wavelengths and intensities. As a main result, we propose a form for the time derivative of the kinetic momentum that allows a quantitatively accurate computation of the acceleration spectra using the dipole-velocity matrix elementWe acknowledge support from the Spanish Ministerio de Economıa y Competitividad through the Consolider program SAUUL (Grant No. CSD2007-0013) and Research Project No. FIS2009-09522 and also from the Centro de Laseres Pulsados (CLPU), Salamanca