Gauge parameter dependence and gauge invariance in the Abelian Higgs model

We analyze gauge parameter dependence by using an algebraic method which relates the gauge parameter dependence of Green functions to an enlarged Slavnov-Taylor identity. In the course of the renormalization it turns out that gauge parameter dependence of physical parameters is already restricted at the level of Green functions. In a first step we consider the on-shell conditions which we find to be in complete agreement with these restrictions to all orders of perturbation theory. The fixing of the coupling, however, is much more involved outside the complete on-shell scheme. In the Abelian Higgs model we prove that this fixing can be properly chosen by requiring the Ward identity of gauge invariance to hold in its tree form to all orders of perturbation theory.Comment: 28 pages, 2 figure

A physics-based compact model of SiC power MOSFETs

The presented compact model of SiC power MOSFETs is based on a thorough consideration of the physical phenomena which are important for the device characteristics and its electrothermal behavior. The model includes descriptions of the dependence of channel charge and electron mobility on the charge of interface traps and a simple but effective calculation of the voltage-dependent drain resistance. Comparisons with both physical 2-D device simulations and experiments validate the correctness of the modeling approach and the accuracy of the results

SiC MOSFET device parameter spread and ruggedness of parallel multichip structures

This paper presents a preliminary study of the impact of device electro-thermal parameter spread and temperature variation on the robustness of SiC MOSFET parallel multi-chip power switch architectures. Reference is made to 1200 V – 80 mΩ rated commercial devices. Some major parameters are identified and selected, presenting experimental evidence of their impact during transient overload events. An advanced physics-based simulation model is then employed to extend the analysis to a more comprehensive set of parameters and operational conditions

Gauge parameter dependence in the background field gauge and the construction of an invariant charge

By using the enlarged BRS transformations we control the gauge parameter dependence of Green functions in the background field gauge. We show that it is unavoidable -- also if we consider the local Ward identity -- to introduce the normalization gauge parameter $\xi_o$, which enters the Green functions of higher orders similarly to the normalization point $\kappa$. The dependence of Green functions on $\xi_o$ is governed by a further partial differential equation. By modifying the Ward identity we are able to construct in 1-loop order a gauge parameter independent combination of 2-point vector and background vector functions. By explicit construction of the next orders we show that this combination can be used to construct a gauge parameter independent RG-invariant charge. However, it is seen that this RG-invariant charge does not satisfy the differential equation of the normalization gauge parameter $\xi_o$, and, hence, is not $\xi_o$-independent as required.Comment: 29 pages, LaTe

Effectiveness of an app-based intervention to reduce substance use, gambling, and digital media use in vocational school students: study protocol for a randomized controlled trial

Background: Substance-related and addictive disorders are among the most common mental disorders in adolescence and young adulthood. Vocational school students are a risk group for problematic substance use and addictive behavior. However, the availability of evidence-based prevention concepts and programs is underdeveloped in the vocational school setting. Methods/design: A two-arm cluster randomized waitlist-controlled trial will be conducted to evaluate the effectiveness of an app-based intervention to decrease substance use, gambling, and digital media use in vocational school students in Germany. Vocational students will participate in an app-based intervention that is designed to support voluntary commitment to abstain from or reduce substance or digital media use over a period of 2 weeks. The "education-as-usual" control arm will have access to the intervention after data collection is completed. One of the primary outcome measures will be the use of alcohol, nicotine, and digital media 30 days after the intervention. Several secondary outcome measures will also be included, such as cannabis consumption, gambling, symptoms of stress, physical activity, mindfulness, well-being, impulsivity and sensation seeking, and readiness to change. A total of 4500 vocational students from 225 classes will be recruited and randomized across three German federal states. Discussion: This study protocol describes the design of an RCT testing the effectiveness of an app-based intervention to reduce addictive behaviors in vocational school students. It is expected that this approach will be feasible for and effective in the vocational school setting and that the study provides comprehensive information on the key factors involved in temporary abstaining or reducing substance or digital media use. Trial registration: German Clinical Trials Register DRKS00023788. Registered on 20 January 2021

Family firm configurations for high performance: The role of entrepreneurship and ambidexterity

The performance drivers of family firms have spawned considerable research interest. Almost exclusively this research has relied on independent sets of explanatory variables in linear analyses. These analyses mask the complex interdependencies that are likely to exist among key success factors, leading to faulty theory and misspecified implications for practice. As treatment, we propose a configuration approach to family firm performance that accounts for complex interdependencies among entrepreneurial, innovation and family influence conditions. Using a fuzzy set qualitative comparative analysis (fsQCA) of a sample of 129 Finnish family firms, we identify sufficient conditions with regards to the existence or absence of antecedent conditions to family firm performance. These conditions include entrepreneurial orientation, exploration and exploitation activities that form causal paths towards family firm performance. To enrich our analysis, we theorize and empirically analyse how these conditions might differ in family firms with high and low levels of family influence. We deepen the current understanding of configurations that promote the performance of family firms, offer important implications for theory and practice, and set new directions for future research on the strategic management of family firms. Our results are also virtually identical and insensitive to change across subjective and objective performance measures

Quantum field theory on a discrete space and noncommutative geometry

We analyse in detail the quantization of a simple noncommutative model of spontaneous symmetry breaking in zero dimensions taking into account the noncommutative setting seriously. The connection to the counting argument of Feyman diagrams of the corresponding theory in four dimensions is worked out explicitly. Special emphasis is put on the motivation as well as the presentation of some well-known basic notions of quantum field theory which in the zero-dimensional theory can be studied without being spoiled by technical complications due to the absence of divergencies.Comment: 111 pages, 6 figures, Habilitationsschrif

The chloride channel CFTR is not required for cyst growth in an ADPKD mouse model

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by the development of bilateral renal cysts which enlarge continuously, leading to compression of adjacent intact nephrons. The growing cysts lead to a progressive decline in renal function. Cyst growth is driven by enhanced cell proliferation and chloride secretion into the cyst lumen. Chloride secretion is believed to occur mainly by the cAMP-activated cystic fibrosis transmembrane conductance regulator (CFTR), with some contribution by the calcium-activated chloride channel TMEM16A. However, our previous work suggested TMEM16A as a major factor for renal cyst formation. The contribution of CFTR to cyst formation has never been demonstrated in an adult ADPKD mouse model. We used mice with an inducible tubule-specific Pkd1 knockout, which consistently develop polycystic kidneys upon deletion of Pkd1. Cellular properties, ion currents, and cyst development in these mice were compared with that of mice carrying a co-deletion of Pkd1 and Cftr. Knockout of Cftr did not reveal any significant impact on cyst formation in the ADPKD mouse model. Furthermore, knockout of Cftr did not attenuate the largely augmented cell proliferation observed in Pkd1 knockout kidneys. Patch clamp analysis on primary renal epithelial cells lacking expression of Pkd1 indicated an only marginal contribution of CFTR to whole cell Cl− currents, which were clearly dominated by calcium-activated TMEM16A currents. In conclusion, CFTR does not essentially contribute to renal cyst formation in mice caused by deletion of Pkd1. Enhanced cell proliferation and chloride secretion is caused primarily by upregulation of the calcium-activated chloride channel TMEM16A