Cosmology with strongly coupled quintessence

The cosmological constant problem motivates alternative approaches for explaining the observed accelerated expansion of the Universe. Quintessence models describe a dynamical dark energy component in terms of a scalar field, the cosmon; in contrast to the cosmological constant scenario, the predicted amount of present dark energy is, generically, comparable to that of matter. The simplest models lack, however, a natural explanation why the dark energy has started to dominate the energy budget of the Universe just around the present cosmic epoch. Growing neutrino quintessence, proposing a coupling between the cosmon and the neutrinos, is a potential solution to this coincidence problem. At the level of perturbations in the energy densities, this coupling mediates an attractive force between the neutrinos stronger than gravity. This has drastic consequences for quantitative analyses of the model. The standard technical repertoire of linear perturbation theory and Newtonian N-body simulations fails. Even the evolution of the Friedmann-Lemaître-Robertson-Walker background depends on the nonlinear perturbations by virtue of a backreaction effect. We present a comprehensive method, accompanied with an improved physical understanding, for a quantitatively reliable investigation of the model and open the door to a systematic exploration of its parameter space and a confrontation with observational constraints

Four Essays on the Role of Personality in the Transition from the Education System to the Labor Market

This dissertation studies the role of personality in the transition from the education system to the labor market, based on person-environment fit theory. Four empirical studies are conducted that use psychological and sociological constructs to enrich economic research on education. The first study focuses on students at university and examines the role of personality traits and field of study for experimentally assessed positional preferences, that is, preferences concerning the relative position in comparison to others. It shows that narcissism differentially predicts positional preferences depending on the type of narcissism, and that students majoring in business administration or economics have a significantly lower tendency to exhibit positional preferences than other students. The second study turns to the transition to the labor market and examines the relationship between civic virtue – the wish to contribute to society – and public versus private sector employment, based on a representative dataset of the population in Germany. It shows that civic virtue relates positively to public sector employment when holding other motives and personality traits constant, that this association holds within various job branches, and that it is explained by (self-) selection before the start of the career. The third study focuses on teachers and analyzes the relationship between risk aversion and the teaching profession. It shows that working as a teacher is positively associated with risk aversion and especially with occupation-related risk aversion – that is, teachers tend to avoid risks in their occupational career. Teachers’ higher risk aversion already holds at career outset, and the results suggest that additional socialization processes may reinforce this relationship. The fourth study is concerned with economic effects of the field choice at university and investigates to what extent the relationships between field of study and later earnings are due to (self-) selection by abilities, personality, and socioeconomic background, using a longitudinal dataset with a cohort design spanning 14 years. It shows that psychological and sociological conditions at the end of high school predict earnings even when holding field of study constant, and the results suggest that (self-) selection by these individual characteristics may account for 15.9–47.0% of the significant associations between field of study and earnings. The four studies have implications for educational policy, educational leadership, and employers’ human resource management, and they inform students’ decision-making

Justinian und das Volk im Nikaaufstand

Die Arbeit geht der Frage nach, warum es unter Kaiser Justinian im Jahre 532 zur schwersten Erhebung des spätantiken Konstantinopel kam. Sie verfolgt die These, daß der Nikaaufstand die Folge eines spezifischen Verhältnisses zwischen Justinian und verschiedenen Bevölkerungsgruppen innerhalb des Hauptstadt des oströmischen Reiches war. Um dies zu zeigen, werden in einem ersten Schritt die Entwicklungen im Verhältnis zwischen Kaiser und Volk seit der Etablierung des Residenzkaisertums im späten vierten Jahrhundert nachgezeichnet, bevor im folgenden die verschiedenen Facetten der Beziehung zwischen Justinian und den verschiedenen Bevölkerungsgruppen in der Hauptstadt untersucht werden. Eine besondere Rolle nehmen dabei die Zirkusparteien als Hauptakteure während des Aufstandes ein, doch richtet die Arbeit den Blick ebenso auf weitere Teile der Bevölkerung wie die Mönche und einzelne Mitglieder der hauptstädtischen Eliten, deren Beziehung zum Kaiser Ausbruch und Verlauf des Nikaaufstands entscheidend mitbestimmte

Too few spots in the cosmic microwave background

We investigate the abundance of large-scale hot and cold spots in the WMAP-5 temperature maps and find considerable discrepancies compared to Gaussian simulations based on the LCDM best-fit model. Too few spots are present in the reliably observed cosmic microwave background (CMB) region, i.e., outside the foreground-contaminated parts excluded by the KQ75 mask. Even simulated maps created from the original WMAP-5 estimated multipoles contain more spots than visible in the measured CMB maps. A strong suppression of the lowest multipoles would lead to better agreement. The lack of spots is reflected in a low mean temperature fluctuation on scales of several degrees (4 to 8), which is only shared by less than 1% (0.16%-0.62%) of Gaussian LCDM simulations. After removing the quadrupole, the probabilities change to 2.5%-8.0%. This shows the importance of the anomalously low quadrupole for the statistical significance of the missing spots. We also analyze a possible violation of Gaussianity or statistical isotropy (spots are distributed differently outside and inside the masked region).Comment: 12 pages; changes in the abstract, extended discussion of the quadrupole and the significances, minor clarifications, one added figure (behavior of typical simulations), one added referenc

Extreme value statistics of smooth random Gaussian fields

We consider the Gumbel or extreme value statistics describing the distribution function p_G(x_max) of the maximum values of a random field x within patches of fixed size. We present, for smooth Gaussian random fields in two and three dimensions, an analytical estimate of p_G which is expected to hold in a regime where local maxima of the field are moderately high and weakly clustered. When the patch size becomes sufficiently large, the negative of the logarithm of the cumulative extreme value distribution is simply equal to the average of the Euler Characteristic of the field in the excursion x > x_max inside the patches. The Gumbel statistics therefore represents an interesting alternative probe of the genus as a test of non Gaussianity, e.g. in cosmic microwave background temperature maps or in three-dimensional galaxy catalogs. It can be approximated, except in the remote positive tail, by a negative Weibull type form, converging slowly to the expected Gumbel type form for infinitely large patch size. Convergence is facilitated when large scale correlations are weaker. We compare the analytic predictions to numerical experiments for the case of a scale-free Gaussian field in two dimensions, achieving impressive agreement between approximate theory and measurements. We also discuss the generalization of our formalism to non-Gaussian fields.Comment: 10 pages, 2 figures, accepted for publication in MNRA

Anomalous variance in the WMAP data and Galactic Foreground residuals

A previous work (Monteser\'in et al. 2008) estimated the CMB variance from the three-year WMAP data, finding a lower value than expected from Gaussian simulations using the WMAP best-fit cosmological model. We repeat the analysis on the five-year WMAP data using a new estimator with lower bias and variance. Our results confirm this anomaly at higher significance, namely with a p-value of 0.31%. We perform the analysis using different exclusion masks, showing that a particular region of the sky near the Galactic plane shows a higher variance than 95.58% of the simulations whereas the rest of the sky has a lower variance than 99.96% of the simulations. The relative difference in variance between both regions is bigger than in 99.64% of the simulations. This anisotropic distribution of power seems to be causing the anomaly since the model assumes isotropy. Furthermore, this region has a clear frequency dependence between 41GHz and 61GHz or 94GHz suggesting that Galactic foreground residuals could be responsible for the anomaly. Moreover, removing the quadrupole and the octopole from data and simulations the anomaly disappears. The variance anomaly and the previously reported quadrupole and octopole alignment seem therefore to be related and could have a common origin. We discuss different possible causes and Galactic foreground residuals seem to be the most likely one. These residuals would affect the estimation of the angular power spectrum from the WMAP data, which is used to generate Gaussian simulations, giving rise to an inconsistency between the estimated and expected CMB variance. If the presence of residuals is confirmed, the estimation of the cosmological parameters could be affected.Comment: Accepted for publication in MNRAS. Analysis section rewritten. New exclusion masks are used finding a high variance region. Relation to the Quadrupole-Octopole alignment foun