The gradient flow in a twisted box

We study the perturbative behavior of the gradient flow in a twisted box. We apply this information to define a running coupling using the energy density of the flow field. We study the step-scaling function and the size of cutoff effects in SU(2) pure gauge theory. We conclude that the twisted gradient flow running coupling scheme is a valid strategy for step-scaling purposes due to the relatively mild cutoff effects and high precision.Comment: LaTeX. 7 pages. Proceedings of the 31st International Symposium on Lattice Field Theory - LATTICE 2013. July 29 - August 3, 2013. Mainz, German

FK/Fpi in full QCD

We determine the ratio FK/Fpi in QCD with Nf=2+1 flavors of sea quarks, based on a series of lattice calculations with three different couplings, large volumes and a simulated pion mass reaching down to about 190 MeV. We obtain FK/Fpi = 1.192 +- 0.007(stat) +- 0.006(sys) with all the sources of systematic uncertainty under control.Comment: 8 pages, 9 figures, 1 table. Presented at the XXVII International Symposium on Lattice Field Theory (2009

A meta-analysis of the magnetic line broadening in the solar atmosphere

A multi-line Bayesian analysis of the Zeeman broadening in the solar atmosphere is presented. A hierarchical probabilistic model, based on the simple but realistic Milne-Eddington approximation to the solution of the radiative transfer equation, is used to explain the data in the optical and near infrared. Our method makes use of the full line profiles of a more than 500 spectral lines from 4000 $\AA$ to 1.8 $\mu$m. Although the problem suffers from a strong degeneracy between the magnetic broadening and any other remaining broadening mechanism, the hierarchical model allows to isolate the magnetic contribution with reliability. We obtain the cumulative distribution function for the field strength and use it to put reliable upper limits to the unresolved magnetic field strength in the solar atmosphere. The field is below 160-180 G with 90% probability.Comment: 9 pages, 6 figures, accepted for publication in A&A. Fixed reference

Image Reconstruction with Analytical Point Spread Functions

The image degradation produced by atmospheric turbulence and optical aberrations is usually alleviated using post-facto image reconstruction techniques, even when observing with adaptive optics systems. These techniques rely on the development of the wavefront using Zernike functions and the non-linear optimization of a certain metric. The resulting optimization procedure is computationally heavy. Our aim is to alleviate this computationally burden. To this aim, we generalize the recently developed extended Zernike-Nijboer theory to carry out the analytical integration of the Fresnel integral and present a natural basis set for the development of the point spread function in case the wavefront is described using Zernike functions. We present a linear expansion of the point spread function in terms of analytic functions which, additionally, takes defocusing into account in a natural way. This expansion is used to develop a very fast phase-diversity reconstruction technique which is demonstrated through some applications. This suggest that the linear expansion of the point spread function can be applied to accelerate other reconstruction techniques in use presently and based on blind deconvolution.Comment: 10 pages, 4 figures, accepted for publication in Astronomy & Astrophysic