Resolving the QCD phase structure

This thesis discusses the quantitative description of the phase structure of Quantum Chromo- dynamics (QCD). We find that, in strongly correlated theories such as QCD, even a qualitative investigation of the phase structure can require highly quantitative methods. Hence, the de- velopment of a method with systematic error control is essential. In the present work, we use functional renormalisation group (fRG) method to this aim. This work focusses on three ideas: Firstly, we identify quantitatively dominating and sub-leading scattering-processes in our approximations. This allows a formulation of low energy effective theories of the four-quark interaction, as well as the description of gluon condensation. For the former, we present results for meson and quark masses. The latter provides an estimate of the Yang-Mills mass gap. Secondly, we further develop the use of highly precise numerical methods from fluid-dynamics in the fRG. In particular we use Discontinuous Galerkin methods, which are able to capture shock-development. Shock-waves are found to play a big role in a possible creation-mechanism of first-order phase transitions. Lastly, we focus on general RG-transformations (gRGt). For example, they allow a real time formulation of fRG flows and hence give access to spectral functions. Furthermore, we use them to formulate complex RG-flows, which enables us to locate Lee-Yang singularities in the complex plane and extrapolate the position of (real) phase transitions. Finally, we also use gRGts to formulate significant qualitative improvements of current fRG approximation schemes by means of dynamical field transformations

A Reward and Incentive-Sensitization Perspective on Compulsive Use of Social Networking Sites - Wanting but not Liking Predicts Checking Frequency and Problematic Use Behavior

The use of Social Networking Sites (SNSs) has exponentially increased over the past decade, leading to warnings about the addictive potential of this technology. Yet, the idea of SNS addiction remains controversial and more theory-driven research is required to understand the mechanisms of excessive and compulsive SNS use and to facilitate the development of targeted interventions helping affected users. In the present article we propose to utilize a reward-based approach to further our understanding of these behaviors. In particular, we suggest that concepts borrowed from the drug addiction literature that focus on incentive processes (incentive-sensitization and cue reactivity) can explain some SNS behaviors, such as compulsive checking. One elemental finding of the neurobiological drug addiction literature is that repeated exposure to a rewarding substance can render the brain’s reward system oversensitive to cues related to the drug. We report preliminary findings from 358 participants showing that cue-elicited urges to use SNSs characterized both excessive and problematic use behaviors. Moreover, desires and urges to use SNSs (wanting responses) could be reliably dissociated from the enjoyment and pleasure (liking responses) associated with SNSs, with the latter being less predictive of the intensity and problematicity of behaviors than the former. Such divergence between motivational and hedonic processes is another hallmark finding in the literature on drug and food rewards. Together our initial findings thus suggest that examining alterations of reward processes holds promise to explain the compulsive use of SNSs and to identify potential avenues to help affected individuals

Functional flows for complex effective actions

In the present work we set up a general functional renormalisation group framework for the computation of complex effective actions. For explicit computations we consider both flows of the Wilsonian effective action and the one-particle irreducible (1PI) effective action. The latter is based on an appropriate definition of a Legendre transform for complex actions, and we show its validity by comparison to exact results in zero dimensions, as well as a comparison to results for the Wilsonian effective action. In the present implementations of the general approaches, the flow of the Wilsonian effective action has a wider range of applicability and we obtain results for the effective potential of complex fields in $\phi^4$-theories from zero up to four dimensions. These results are also compared with results from the 1PI effective action within its range of applicability. The complex effective action also allows us to determine the location of the Lee-Yang zeros for general parameter values. We also discuss the extension of the present results to general theories including QCD.Comment: 29 pages, 24 figure

Flowing fields and optimal RG-flows

Renormalisation group approaches are tailor made for resolving the scale-dependence of quantum and statistical systems, and hence their phase structure and critical physics. Usually this advantage comes at the price of having to truncate the full theory at hand, which asks for optimal expansion schemes. In the present work we use a functional renormalisation group (fRG) approach for the effective action which includes general scale-dependent reparametrisations of the theory [1]. This approach is used in an O(N)-theory to set up adaptive RG-flows that correspond to an optimal systematic expansion of the theory about the ground state or rather its full covariance or propagator. These parametrisations are induced by flowing fields that encode the differential reparametrisation steps. The approach is put to work for an investigation of the thermal phase transition in the O(4)-theory in view of applications to QCD. The respective results are compared with those obtained in standard fRG computations.Comment: 15 pages, 10 figures. Improved equation (28) for the anomalous dimension leading to a simplification of the numerical treatment. Only quantitative changes in the results. Figures have been updated accordingl

Restricting social networking site use for one week produces varied effects on mood but does not increase explicit or implicit desires to use SNSs: Findings from an ecological momentary assessment study

Recent research on the addictive potential of modern technologies such as the internet, smartphones, or social networking sites (SNSs) has suggested that emotional and motivational changes associated with the sudden discontinuation of engagement with the technology mirror the aversive consequences seen when drug use is ceased abruptly. This has been observed even in moderate users and interpreted as a manifestation of withdrawal, an important marker of physical dependence in substance use disorders. On the other hand, a growing literature emphasises the positive effects of “digital detox” on mental health and well-being. Using a battery of affective and motivational measures, both explicit and implicit, the present study tracked the effects of a week of significantly reduced SNS use in moderate to heavy SNS users (N = 51). Our pre-registered analyses showed that the intervention elicited affective changes neither consistent with a general withdrawal syndrome (i.e., increased negative affect and cravings) nor with a general beneficial effect on well-being: While our data indicated some abstinence-related decreases of negative affect and boredom, they also showed a reduction of positive affect. These changes occurred regardless of problematic/addictive use behaviours. Importantly, restricting SNS use for one week had no effect on implicit measures of SNS use motivation (i.e., approach biases, time distortion and effort expenditure for SNS access) nor did it influence explicit cravings and SNS cue-reactivity. Together our findings suggest that restricting SNS use has nuanced and potentially offsetting effects on well-being. These could arise because use reduction may concurrently remove experiences that trigger negative emotions (e.g., upward social comparisons or Fear of Missing Out) but also those that elicit positive emotions (e.g., social approval). The hypothesised lack of a net effect on well-being would be consistent with our finding that voluntary reduction of SNS use does not mitigate or exacerbate SNS-related urges

Early cortical facilitation for emotionally arousing targets during the attentional blink

BACKGROUND: The present study aimed to investigate the time course of electrocortical facilitation for affectively arousing written words during the so-called 'attentional blink' (AB) period in a rapid serial visual presentation (RSVP) task. The AB refers to a period of reduced awareness for second-target stimuli following a first target by an interval of about 200–500 ms. Pleasant, neutral, and unpleasant written verbs were used as second targets in an 8.6-Hz RSVP paradigm that contained affectively neutral words as distractors. Replicating and extending behavioral studies, we expected that emotional second targets would be associated with better identification accuracy and greater electrocortical activity, compared with neutral targets. RESULTS: The steady-state visual evoked potential was recorded using 129 scalp electrodes. The time-varying energy at the presentation frequency of 8.6 Hz was extracted as a continuous measure of electrocortical activity related to the RSVP stream. Behavioral data showed that at an inter-target interval of 232 ms, the report for emotionally arousing (pleasant and unpleasant) words was more accurate than for neutral control words. This result was mirrored by the electrocortical response at posterior sensors, which showed rapid amplitude enhancement (120–270 ms after T2 onset) for pleasant and unpleasant targets specifically. CONCLUSION: The present data suggest that identification facilitation for emotionally arousing target words in the AB is related to rapid enhancement of sensory processing. Affectively arousing information is preferentially selected at the level of early perceptual analysis, leading to facilitation at later stages of processing, including consolidation in working memory and visual awareness

Bacillus pumilus laccase: a heat stable enzyme with a wide substrate spectrum

<p>Abstract</p> <p>Background</p> <p>Laccases are multi-copper oxidases that catalyze the one electron oxidation of a broad range of compounds. Laccase substrates include substituted phenols, arylamines and aromatic thiols. Such compounds are activated by the enzyme to the corresponding radicals. Owing to their broad substrate range laccases are considered to be versatile biocatalysts which are capable of oxidizing natural and non-natural industrial compounds, with water as sole by-product.</p> <p>Results</p> <p>A novel CotA-type laccase from <it>Bacillus pumilus </it>was cloned, expressed and purified and its biochemical characteristics are presented here. The molecular weight of the purified laccase was estimated to be 58 kDa and the enzyme was found to be associated with four copper atoms. Its catalytic activity towards 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS), 2,6-dimethoxyphenol (2,6-DMP) and syringaldazine (SGZ) was investigated. The kinetic parameters <it>K</it>_Mand <it>k</it>_catfor ABTS were 80 ± 4 μM and 291 ± 2.7 s^-1, for 2,6-DMP 680 ± 27 μM and 11 ± 0.1 s^-1and for SGZ only <it>k</it>_catcould be estimated to be 66 ± 1.5 s^-1. The pH optimum for ABTS was 4, for 2,6-DMP 7 and for SGZ 6.5 and temperature optima for ABTS and 2,6-DMP were found to be around 70°C. The screening of 37 natural and non-natural compounds as substrates for <it>B. pumilus </it>laccase revealed 18 suitable compounds. Three of them served as redox mediators in the laccase-catalyzed decolorization of the dye indigocarmine (IC), thus assessing the new enzyme's biotechnological potential.</p> <p>Conclusions</p> <p>The fully copper loaded, thermostable CotA laccase from <it>Bacillus pumilus </it>is a versatile laccase with potential applications as an industrial biocatalyst.</p

Neural evidence of motivational conflict between social values

Motivational interdependence is an organizing principle in Schwartz’s circumplex model of social values, which has received abundant cross-cultural support. We used fMRI to test whether motivational relations between social values predict different brain responses in a situation of choice between values. We hypothesized that differences in brain responses would become evident when the more important value had to be selected in pairs of congruent (e.g., wealth and success) as opposed to incongruent (e.g., curiosity and stability) values as they are described in Schwartz’s model, because the former serve mutually facilitating motives, whereas the latter serve mutually inhibiting motives. Consistent with the model, choosing between congruent values led to longer response times and more activation in conflict-related brain regions (e.g., the supplementary motor area, dorsolateral prefrontal cortex) than selecting between incongruent values. These results provide novel neural evidence supporting the circumplex model’s predictions about motivational interdependence between social values. In particular, our results show that the neural networks underlying social values are organized in a way that allows activation patterns related to motivational similarity between congruent values to be dissociated from those related to incongruent values

Towards quantitative precision for QCD at large densities

QCD at large density reveals a rich phase structure, ranging from a potential critical end point and inhomogeneous phases or moat regimes to color superconducting ones with competing order effects. Resolving this region in the phase diagram of QCD with functional approaches requires a great deal of quantitative reliability, already for a qualitative access. In the present work, we systematically extend the functional renormalisation group approach to low energy QCD by setting up a fully self-consistent approximation scheme in a low energy effective quark-meson theory. In this approximation, all pointlike multi-scattering events of the mesonic pion and the sigma mode are taken into account in terms of an effective potential as well as all higher quark-antiquark-mesonic scattering orders. As a first application we compute the phase structure of QCD including its low temperature - large chemical potential part. The quantitative reliability of the approximation and systematic extensions are also discussed