On the reduction of hypercubic lattice artifacts

This note presents a comparative study of various options to reduce the errors coming from the discretization of a Quantum Field Theory in a lattice with hypercubic symmetry. We show that it is possible to perform an extrapolation towards the continuum which is able to eliminate systematically the artifacts which break the O(4) symmetry.Comment: 15 pages. 4 figures. Minor changes (Appendix and refs added

Instanton dominance over αs\alpha_s at low momenta from lattice QCD simulations at Nf=0N_f=0, Nf=2+1N_f=2+1 and Nf=2+1+1N_f=2+1+1

We report on an instanton-based analysis of the gluon Green functions in the Landau gauge for low momenta; in particular we use lattice results for $\alpha_s$ in the symmetric momentum subtraction scheme (${\rm MOM}$) for large-volume lattice simulations. We have exploited quenched gauge field configurations, $N_f=0$, with both Wilson and tree-level Symanzik improved actions, and unquenched ones with $N_f=2+1$ and $N_f=2+1+1$ dynamical flavors (domain wall and twisted-mass fermions, respectively). We show that the dominance of instanton correlations on the low-momenta gluon Green functions can be applied to the determination of phenomenological parameters of the instanton liquid and, eventually, to a determination of the lattice spacing. We furthermore apply the Gradient Flow to remove short-distance fluctuations. The Gradient Flow gets rid of the QCD scale, $\Lambda_{\rm QCD}$, and reveals that the instanton prediction extents to large momenta. For those gauge field configurations free of quantum fluctuations, the direct study of topological charge density shows the appearance of large-scale lumps that can be identified as instantons, giving access to a direct study of the instanton density and size distribution that is compatible with those extracted from the analysis of the Green functions.Comment: Proceedings of the 35th International Symposium on Lattice Field Theory, Granada, Spai

Position-space gluon propagator from quenched lattice QCD

We report novel lattice QCD results for the position-space gluon propagator in Landau gauge from quenched simulations. Using standard Wilson action, we computed gluon propagator in position space with a detailed treatment of hypercubic errors. Gluon propagator is scrutinized in position-space, discussing on the usefulness of the long-distance behavior of gluon propagator for constraining the gluon spectral function or the deep infrared running of the gluon propagator in momentum-space

Phase diagram of bosonic hard rods in a one-dimensional optical lattice

We calculated the phase diagram of a pure one-dimensional system of hard-rod bosons when it is loaded in optical lattices of different depths by means of a diffusion Monte Carlo technique. The results were compared with those for a Bose-Hubbard model for the same range of densities and characteristic parameters. Both diagrams were found to be qualitatively similar in the regime in which a one-band Hubbard model is adequate, that comparison being poorer when this condition is not fulfilled.Universidad Pablo de Olavide. Departamento de Sistemas Físicos, Químicos y NaturalesVersión del edito

Testing OPE for ghosts, gluons and αs\alpha_s

We present here our results on extracting Wilson coefficients from different quantities such as ghost and gluon propagators which are calculated by means of Lattice QCD. The results confirm the validity of our method for the calculation of the strong coupling constant as well as allow to estimate the range of momenta where OPE is applicable.Comment: arXiv admin note: substantial text overlap with arXiv:1301.759

Zero-temperature phase diagram of hard-sphere bosons in asymmetric three-dimensional optical lattices

We studied the superfluid-to-Mott-insulator transition for bosonic hard spheres loaded in asymmetric three-dimensional optical lattices by means of diffusion Monte Carlo calculations. The onset of the transition was monitored through the change in the chemical potential around the density corresponding to one particle per potential well. With this method, we were able to reproduce the results given in the literature for three-dimensional symmetric lattices and for systems whose asymmetry makes them equivalent to a set of quasi-one-dimensional tubes. The location of the same transition for asymmetric systems akin to a stack of quasi-two-dimensional lattices will be also given. Our results were checked against those given by a Bose-Hubbard model for similar arrangements.Universidad Pablo de Olavide. Departamento de Sistemas Físicos, Químicos y NaturalesVersión del edito

Continuous model for bosonic hard spheres in quasi-one-dimensional optical lattices

By means of diffusion Monte Carlo calculations, we investigated the quantum phase transition between a superfluid and a Mott insulator for a system of hard-sphere bosons in a quasi-one-dimensional optical lattice. For this continuous Hamiltonian, we studied how the stability limits of the Mott phase changed with the optical lattice depth and the transverse confinement width. A comparison of these results to those of a one-dimensional homogeneous Bose-Hubbard model indicates that this last model describes accurately the phase diagram only in the limit of deep lattices. For shallow ones, our results are comparable to those of the sine-Gordon model in its limit of application. We provide an estimate of the critical parameters when none of those models are realistic descriptions of a quasi-one-dimensional optical lattice.Universidad Pablo de Olavide. Departamento de Sistemas Físicos, Químicos y NaturalesVersión del edito

234Th-derived particle fluxes and seasonal variability: when is the ss assumption reliable? Insights from a novel Approach for carbon flux simulation

Th measurements are widely used to estimate the downward carbon flux of particles via the oceanic Biological Pump. Carbon export is evaluated from 234Th-238U disequilibrium assuming either steady state (SS) conditions, or including a non-SS (NSS) correction. We use a novel stochastic simulation to quantify the temporal variation of vertical carbon and 234Th (dissolved and particulate) concentration profiles with high temporal resolution. We calculate seasonal export as if in situ measured with sediment trap and SS- and NSS-234ThapproachesandquantifytheperiodsofvalidityforSS/NSSconditionsdefinedinpreviousworks.The SS approach is valid throughout the entire season in oligotrophic regions. In temperate regions, the SS introduces a bias in the export if sampling takes place outside specific temporal windows. Windows of validity range from days in short blooms of ~15-day duration to weeks in blooms longer than ~30 days

Experiencias comparadas en autoevaluación y formación en competencias a través de la WebCT en Física

El EEES fomenta el uso por parte del estudiante de ejercicios de autoevaluación como complemento en el proceso de enseñanza-aprendizaje, y ejercitando de esta forma las distintas competencias asociadas a la asignatura y facilitando a la vez su evaluación final por parte del profesorado. Con este objetivo se implementaron en dos cursos sucesivos de la asignatura de Física en el grado de Ciencias Ambientales, 2009-2010 y 2010-2011, la autoevaluación formativa a través de exámenes virtuales utilizando la plataforma WebCT como retroalimentación por parte del alumno del propio proceso. El análisis de los resultados obtenidos tras la implantación vislumbra una alta participación y valoración de los alumnos del sistema de evaluación.Artículo revisado por pare

Lattice three-gluon vertex in extended kinematics: Planar degeneracy

We present novel results for the three-gluon vertex, obtained from an extensive quenched lattice simulation in the Landau gauge. The simulation evaluates the transversely projected vertex, spanned on a special tensorial basis, whose form factors are naturally parametrized in terms of individually Bose-symmetric variables. Quite interestingly, when evaluated in these kinematics, the corresponding form factors depend almost exclusively on a single kinematic variable, formed by the sum of the squares of the three incoming four-momenta, q, r, and p. Thus, all configurations lying on a given plane in the coordinate system (q2,r2,p2) share, to a high degree of accuracy, the same form factors, a property that we denominate planar degeneracy. We have confirmed the validity of this property through an exhaustive study of the set of configurations satisfying the condition q2=r2, within the range [0,5GeV]. This drastic simplification allows for a remarkably compact description of the main bulk of the data, which is particularly suitable for future numerical applications. A semi-perturbative analysis reproduces the lattice findings rather accurately, once the inclusion of a gluon mass has cured all spurious divergences.The authors thank A. C. Aguilar, G. Eichmann and C. D. Roberts for useful discussions. M.N.F. acknowledges financial support from the FAPESP projects 2017/05685-2 and 2020/12795-1, respectively. J.P. is supported by the Spanish MICINN grant PID2020-113334GB-I00 and the regional Prometeo/2019/087 from the Generalitat Va-lenciana; while F.D.S. and J.R.Q. are by the Spanish MICINN grant PID2019-107844GB-C22 and the regional Andalusian P18-FR-5057. All calculations have been performed at the UPO computing center, C3UPO