Topological tunneling with Dynamical overlap fermions

Tunneling between different topological sectors with dynamical chiral fermions is difficult because of a poor mass scaling of the pseudo-fermion estimate of the determinant. For small fermion masses it is virtually impossible using standard methods. However, by projecting out the small Wilson eigenvectors from the overlap operator, and treating the correction determinant exactly, we can significantly increase the rate of topological sector tunneling and reduce substantially the auto-correlation time. We present and compare a number of different approaches, and advocate a method which allows topological tunneling even at low mass with little addition to the computational cost.Comment: 17 pages; v2 as accepted in computer Physics Communication

The solution of multi-scale partial differential equations using wavelets

Wavelets are a powerful new mathematical tool which offers the possibility to treat in a natural way quantities characterized by several length scales. In this article we will show how wavelets can be used to solve partial differential equations which exhibit widely varying length scales and which are therefore hardly accessible by other numerical methods. As a benchmark calculation we solve Poisson's equation for a 3-dimensional Uranium dimer. The length scales of the charge distribution vary by 4 orders of magnitude in this case. Using lifted interpolating wavelets the number of iterations is independent of the maximal resolution and the computational effort therefore scales strictly linearly with respect to the size of the system

Scaling study for 2 HEX smeared fermions: hadron and quark masses

The goal of this study is to investigate the scaling behaviour of our 2 HEX action. For this purpose, we compute the $N_f=3$ spectrum and compare the results to our 6 EXP action. We find a large scaling window up to $\sim 0.15\,\mathrm{fm}$ along with small scaling corrections at the 2%-level and full compatibility with our previous study. As a second important observable to be tested for scaling, we chose the non-perturbatively renormalized quenched strange quark mass. Here we find a fairly flat scaling with a broad scaling range up to $\simeq 0.15\,\mathrm{fm}$ and perfect agreement with the literature.Comment: PoS for the XXVIII International Symposium on Lattice Field Theory, Lattice2010, 7 pages, 4 figure

Leptonic decay-constant ratio fK/fπf_K/f_\pi from lattice QCD using 2+1 clover-improved fermion flavors with 2-HEX smearing

We present a calculation of the leptonic decay-constant ratio $f_K/f_\pi$ in 2+1 flavor QCD. Our data set includes five lattice spacings and pion masses reaching down below the physical one. Special emphasis is placed on a careful study of all systematic uncertainties, especially the continuum extrapolation. Our result is perfectly compatible with the first-row unitarity constraint of the Standard Model.Comment: 19 pages, 6 figures, 3 tables; v2: added supplementary analysis, version published in Phys. Rev.

Information exchange patterns and technology adoption behavior of cattle farmers in the Colombian Amazon

Colombia's cattle sector, characterised by extensive production systems, plays an important role in the national economy, contributing 19.8% to the agricultural GDP and providing employment and income to around one million people. However, the sector is associated with low productivity and negative environmental impacts such as land degradation, greenhouse gas emissions, and deforestation. This is particularly true in the Caquetá Department, located in the Colombian Amazon, which has the country's fifth largest cattle herd and the highest deforestation rate. Although efforts have been made in recent decades to introduce improved production practices to intensify cattle farming in a sustainable manner (e.g., improved forages or silvo-pastoral systems), corresponding adoption rates remain low. While several studies have analysed the cattle sector in Caquetá and have identified key adoption barriers, such as poor access to finance, inputs, technical assistance, and knowledge, the importance of interconnections, and information exchange between different actor groups in facilitating innovation diffusion, has received only marginal attention. There is a broad consensus that the structure and composition of social networks can affect information flows, learning processes, capabilities, preferences, and decision-making processes and that social networks can both facilitate and impede access to information. To address the identified knowledge gap, a social network analysis (SNA) using egocentric network methods will be conducted in June 2023 with 150 cattle farmers in the Caquetá Department to study the structure, composition, and strength of personal information exchange networks as well as their influence on technology adoption behaviour. Information will be elicited about the interviewed farmers’ relationships with other farmers, and with other actors such as input and service providers, buyers, extension agents, researchers, and NGO staff. First results will be presented during the Tropentag. Heterogeneous patterns of information exchange are expected to exist in the Caquetá Department, depending on, among others, the degree of remoteness of the farmers. It is also expected that farmers with larger, more diverse, and more fragmented networks are more likely to adopt improved practices. The findings will be useful for designing more context-specific policies to improve information flows and promote the sustainable transformation of the cattle sector

Systematic errors in partially-quenched QCD plus QED lattice simulations

At the precision reached in current lattice QCD calculations, electromagnetic effects are becoming numerically relevant. Here, electromagnetic effects are included by superimposing $\mathrm{U}(1)$ degrees of freedom on $N_f = 2+1$ QCD configurations from the Budapest-Marseille-Wuppertal Collaboration. We present preliminary results for the electromagnetic corrections to light pseudoscalars mesons masses and discuss some of the associated systematic errors.Comment: 7 pages, 2 figures, The XXIX International Symposium on Lattice Field Theory, July 10-16, 2011, Squaw Valley, Lake Tahoe, California, US

High-precision scale setting in lattice QCD

Scale setting is of central importance in lattice QCD. It is required to predict dimensional quantities in physical units. Moreover, it determines the relative lattice spacings of computations performed at different values of the bare coupling, and this is needed for extrapolating results into the continuum. Thus, we calculate a new quantity, $w_0$, for setting the scale in lattice QCD, which is based on the Wilson flow like the scale $t_0$ (M. Luscher, JHEP 1008 (2010) 071). It is cheap and straightforward to implement and compute. In particular, it does not involve the delicate fitting of correlation functions at asymptotic times. It typically can be determined on the few per-mil level. We compute its continuum extrapolated value in 2+1-flavor QCD for physical and non-physical pion and kaon masses, to allow for mass-independent scale setting even away from the physical mass point. We demonstrate its robustness by computing it with two very different actions (one of them with staggered, the other with Wilson fermions) and by showing that the results agree for physical quark masses in the continuum limit.Comment: 15 pages, 7 figures, 2 tables; Version published in JHE