Dual simulation of the massless lattice Schwinger model with topological term and non-zero chemical potential

We discuss simulation strategies for the massless lattice Schwinger model with a topological term and finite chemical potential. The simulation is done in a dual representation where the complex action problem is solved and the partition function is a sum over fermion loops, fermion dimers and plaquette-occupation numbers. We explore strategies to update the fermion loops coupled to the gauge degrees of freedom and check our results with conventional simulations (without topological term and at zero chemical potential), as well as with exact summation on small volumes. Some physical implications of the results are discussed.Comment: Proceedings, The 35th International Symposium on Lattice Field Theor

Discovery and detection of phase-II metabolites of exogenous steroids in anti-doping analysis

Anti-doping measures are an essential part of professional sports around the world. Anabolic androgenic steroids have been among the most widely used illicit substance classes since the early days of the fight against doping. The conventional method for analysing these substances is gas chromatography combined with mass spectrometry (GC-MS). This approach is sensitive and selective but also very time- and resource-consuming. The main goal of this work was to improve the detection of steroids in a time- and resource-efficient manner by shifting the analysis from GC-MS to liquid chromatography-MS (LC-MS). In the first part of this thesis, we present a novel, highly functional analytical method for the analysis of steroid phase-II glucuronides in which sample preparation is reduced to a minimum. For this purpose, we developed a simple but powerful online solid-phase extraction method coupled with LC-MS. Two comprehensive validation studies demonstrated the analytical performance of this method. Initially developed for rapid confirmation analysis, this method also showed high potential for identifying and characterizing novel steroid phase-II metabolites. The aim of the second part of this work was to identify and characterize novel phase-II metabolites of the anabolic androgenic steroids stanozolol and dehydrochloromethyltestosterone using the newly developed method. Both substances are among the most commonly used steroids in professional sports and are of great interest for anti-doping research. For stanozolol, we achieved for the first time to unequivocally confirm four different phase-II glucuronide conjugates using newly synthesized high-quality reference standards. Furthermore, using urine samples from excretion studies, we generated elimination curves for all four metabolites showing elimination windows of up to 28 days. The long excretion time makes this metabolite very interesting for the long-term detection of stanozolol. In the case of dehydrochloromethyltestosterone, we identified two different glucuronide conjugates of the important long-term metabolite M3 for the first time. Due to the lack of reference standards, we used a combination of different analytical approaches to characterize and elucidate the chemical structure of these conjugates. Since these metabolites are well suited for LC-MS analysis, we present for the first time a way to analyse metabolite M3 without requiring a laborious GC-MS approach

Kramers-Wannier duality and worldline representation for the SU(2) principal chiral model

In this letter we explore different representations of the SU(2) principal chiral model on the lattice. We couple chemical potentials to two of the conserved charges to induce finite density. This leads to a complex action such that the conventional field representation cannot be used for a Monte Carlo simulation. Using the recently developed Abelian color flux approach we derive a new worldline representation where the partition sum has only real and positive weights, such that a Monte Carlo simulation is possible. In a second step we transform the model to new dual variables in the Kramers-Wannier (KW) sense, such that the constraints are automatically fulfilled, and we obtain a second representation free of the complex action problem. We implement exploratory Monte Carlo simulations for both, the worldline, as well as the KW-dual form, for cross-checking the two dualizations and a first assessment of their potential for dual simulations.Comment: Comments and a new plot for the relative errors added. Version to appear in Physics Letters

Worldlines and worldsheets for non-abelian lattice field theories: Abelian color fluxes and Abelian color cycles

We discuss recent developments for exact reformulations of lattice field theories in terms of worldlines and worldsheets. In particular we focus on a strategy which is applicable also to non-abelian theories: traces and matrix/vector products are written as explicit sums over color indices and a dual variable is introduced for each individual term. These dual variables correspond to fluxes in both, space-time and color for matter fields (Abelian color fluxes), or to fluxes in color space around space-time plaquettes for gauge fields (Abelian color cycles). Subsequently all original degrees of freedom, i.e., matter fields and gauge links, can be integrated out. Integrating over complex phases of matter fields gives rise to constraints that enforce conservation of matter flux on all sites. Integrating out phases of gauge fields enforces vanishing combined flux of matter- and gauge degrees of freedom. The constraints give rise to a system of worldlines and worldsheets. Integrating over the factors that are not phases (e.g., radial degrees of freedom or contributions from the Haar measure) generates additional weight factors that together with the constraints implement the full symmetry of the conventional formulation, now in the language of worldlines and worldsheets. We discuss the Abelian color flux and Abelian color cycle strategies for three examples: the SU(2) principal chiral model with chemical potential coupled to two of the Noether charges, SU(2) lattice gauge theory coupled to staggered fermions, as well as full lattice QCD with staggered fermions. For the principal chiral model we present some simulation results that illustrate properties of the worldline dynamics at finite chemical potentials.Comment: Contribution to LATTICE 2017, 16 page

Simulation strategies for the massless lattice Schwinger model in the dual formulation

The dual form of the massless Schwinger model on the lattice overcomes the complex action problems from two sources: a topological term, as well as non-zero chemical potential, making these physically interesting cases accessible to Monte Carlo simulations. The partition function is represented as a sum over fermion loops, dimers and plaquette-surfaces such that all contributions are real and positive. However, these new variables constitute a highly constrained system and suitable update strategies have to be developed. In this exploratory study we present an approach based on locally growing plaquette-surfaces surrounded by fermion loop segments combined with a worm based strategy for updating chains of dimers, as well as winding fermion loops. The update strategy is checked with conventional simulations as well as reference data from exact summation on small volumes and we discuss some physical implications of the results

Fairness considerations are activated by social information

Die so genannte Feedback Negativity (FN) ist eine Komponente des ereigniskorrelierten Potentials (EKP), die nach Fehlern, negativem Leistungsfeedback und Geldverlusten in Glücksspielen generiert wird. Die kürzlich vorgeschlagene Reinforcement-Learning Theorie der FN nimmt an, die Einschätzung von Ereignissen als „schlechter als erwartet“ werde in der FN reflektiert. Die vorliegende Studie untersucht die Rolle besagter Komponente im Kontext des Ultimatumspiels. In diesem spieltheoretischen Paradigma erhalten zwei Personen einen bestimmten Geldbetrag (hier 10 Euro), wobei die erste (Proposer) der zweiten (Responder) einen Verteilungsvorschlag unterbreitet, den letztgenannte entweder annehmen oder ablehnen kann. Wir gingen der Frage nach, ob die Wahrnehmung von unterschiedlich fairen Angeboten sich in der Amplitude der FN widerspiegelt. Außerdem versuchten wir den Einfluss sozialer Distanz (manipuliert über das Ausmaß an Information, dass unseren Versuchspersonen über ihre Mitspieler zukam) auf Verhaltens- und neuronaler Ebene zu bestimmen. Elektroenzephalogramme (EEGs) wurden aufgezeichnet während unsere Probanden in der Rolle des Responders mit fairen (ein Verteilungsvorschlag von 5-5), midfairen (7-3) und unfairen (9-1) Angeboten konfrontiert waren. Wir versuchten, Erwartungen in unseren Versuchspersonen zu wecken über soziale Information, die sie über ihre mutmaßlichen Mitspieler erhielten. Diese Manipulation wurde durchgeführt um das Ausmaß an sozialer Distanz zwischen den Spielern zu reduzieren, was erwiesener Maßen erheblichen Einfluss auf ökonomisches Spielverhalten hat. Wir konnten beobachten, dass die Wahrnehmung unterschiedlicher Ultimatumspiel- Angebote eine FN generierte, wobei faire Angebote mit den niedrigsten Amplituden assoziiert waren. Der Grad an sozialer Distanz hat die neuronalen Antworten wesentlich beeinflusst: Unterschiede in der Amplitude der FN konnten nur festgestellt werden, wenn zuvor Informationen über den Mitspieler präsentiert wurden. Wir schlagen vor, dass die FN in dieser Studie die Verletzung von allgemeinen Erwartungen und Fairness-Überlegungen, die durch soziale Information aktiviert werden, darstellt. In diesem Sinne hängt die Amplitude der FN von der Größe des Vorhersagefehlers ab und wächst mit steigender Abweichung vom fairen 50-50 Verteilungsvorschlag.The feedback negativity (FN) is a component of the event-related brain potential (ERP) that is associated with stimuli indicating unfavorable outcomes like losses in monetary gambling tasks or negative performance feedback. A recently proposed theory of reinforcement learning holds that the FN is generated whenever ongoing events are evaluated as 'worse than expected'. The work at hand investigated the role of the FN in the context of the Ultimatum Game (UG). In this game, two players split a certain amount of money (10 Euros in the present research); one player (commonly entitled the proposer) suggests a division and the other (called the responder) can either accept or reject it. We were interested in the question whether the perception of (un)fairness, as experienced by responders being confronted with different types of UG offers, was reflected in the amplitude of the FN. Additionally, we tried to assess the impact of social distance (manipulated via information provided to the responders about their presumed counterparts) on behavioral and neural responses of our subjects. We recorded electroencephalograms (EEGs) while participants were in the role of the responder, facing fair (a proposed split of 5-5), midfair (7-3) or unfair (9-1) offers. We sought to generate (or additionally enforce) expectations in our UG subjects by providing information about their presumed counterparts in half of the trials. This manipulation was accomplished to reduce the degree of social distance among the players, which has been shown to have strong influence on economic game behavior. We found that the perception of different types of UG offers generated an FN, being less pronounced for fair as compared to midfair and unfair offers. Social distance crucially influenced brain responses to the three offers, as differences in the FN amplitude were only apparent when social information about the responders' counterparts was revealed. We propose that the FN in the context of this study reflects the violation of general expectations and fairness considerations of our subjects which are activated by social information. It is further suggested that the amplitude of the FN depends on the size of the prediction error, growing with the magnitude of deviation from the fair 50-50 split

A neural autoencoder approach for document ranking and query refinement in pharmacogenomic information retrieval

In this study, we investigate learning-to- rank and query refinement approaches for information retrieval in the pharmacogenomic domain. The goal is to improve the information retrieval process of biomedical curators, who manually build knowledge bases for personalized medicine. We study how to exploit the relationships be- tween genes, variants, drugs, diseases and outcomes as features for document ranking and query refinement. For a supervised approach, we are faced with a small amount of annotated data and a large amount of unannotated data. Therefore, we explore ways to use a neural document auto-encoder in a semi-supervised approach. We show that a combination of established algorithms, feature-engineering and a neural auto-encoder model yield promising results in this setting