232 research outputs found
Philippinischer Bücherherbst
No full textAls im Februar 1986 der philippinische Diktator Ferdinand Marcos im zwanzigsten Jahr seiner Herrschaft durch eine Mischung von Militärrevolte und ziviler Massenerhebung gestürzt wurde, kam dies nicht nur für die Hauptströmung der philippinischen Linken, für die NDF, überraschend. Weltweit war die Solidaritätsbewegung mit dem philippinischen Volk geraume Zeit fast sprachlos und unsicher, wie die neue Entwicklung zu bewerten sei. Sicher gab es diese oder jene Prognose, doch der erste Jahrestag der "Februarrevolution” verging, ohne daß sich jemand mit einem Buch an die Würdigung der Aquino-Präsidentschaft ”herangewagt” hätte. Dieses Indiz zeigt vielleicht deutlicher als vieles andere, wie tief die - oft uneingestandene - Verunsicherung auch bei den besten ”Philippinen-Kenner(inne)n” gereicht hat. Doch nun, rund achtzehn Monate "danach” sind gleich drei Bücher auf deutsch erschienen, ein weiteres, das "Parlament der Straße” vom in Manila arbeitenden Journalisten und Sozialwissenschaftler Heinz Kotte, ist angekündigt, lag aber bei Redaktionsschluß noch nicht vor. Frank Braßel und Frithjof Schmidt haben sich mit den drei folgenden, von der Herangehensweise sehr unterschiedlichen Arbeiten auseinandergesetzt
Hundert Jahre Basler Friedenskongress (1912-2012) : die erhoffte "Verbrüderung der Völker"
No full text
DFT and TD-DFT studies to elucidate the configurational isomers of ferric aerobactin, ferric petrobactin, and their ferric photoproducts
No full textAuthor contributions: Sasha Gardner carried out all calculations and composed the original draft of the manuscript including tables and figures. Carl J. Carrano suggested the project, provided the original experimental data, and provided early guidance on the interpretation of the experimental work. Yuezhi Mao and Andrew Cooksy provided guidance and resources for the calculations. Frithjof Küpper provided guidance on the context of the work and on the original experimental work and drafted relevant sections of the manuscript. All authors save Carrano edited the manuscript.Peer reviewe
On the phase structure of two flavor QCD with improved actions
No full textOevers M, Karsch F, Laermann E, Schmidt P. On the phase structure of two flavor QCD with improved actions. 1999
Calculating Quark Number Susceptibilities with Domain-Wall Fermions
No full textHegde P, Karsch F, Schmidt C. Calculating Quark Number Susceptibilities with Domain-Wall Fermions. In: PoS LATTICE2008. 2008: 187
Higher order cumulants of net baryon-number distributions at non-zero μ
No full textBollweg D, Karsch F, Mukherjee S, Schmidt C. Higher order cumulants of net baryon-number distributions at non-zero μ. Nuclear Physics A. 2021;1005: 121835
Quasiparticle pictures and graphs - from perturbative to non-perturbative linked-cluster expansions
No full textA fundamental principle in condensed matter physics is the effective description in terms of quasiparticles. The high-energy part of the system is accounted for by renormalized properties of the quasiparticles, providing both, an accurate description and interpretation of the relevant low-energy physics. We consider two classes of methods suited to provide effective quasiparticle descriptions in the thermodynamic limit: (non-perturbative) linked-cluster expansions ((N)LCEs) and continuous unitary transformations (CUTs). We focus specifically on the combination of both methods, providing a different perspective and solutions to existing challenges.
LCEs provide high-order series expansions in a perturbation parameter, by combining effective Hamiltonians determined on finite clusters. We introduce a white-graph expansion for the method of perturbative continuous unitary transformations when implemented as an LCE. The essential idea behind an expansion in white graphs is to perform an optimized bookkeeping during the calculation by exploiting the model-independent effective Hamiltonian in second quantization and the associated inherent cluster additivity. This approach is shown to be especially well suited for microscopic models with many coupling constants, since the total number of relevant graphs is drastically reduced. The white-graph expansion is exemplified for a two-dimensional quantum spin model, illustrating its efficiency.
In NLCEs, the perturbative treatment of finite clusters is replaced by a numerical exact (block) diagonalization. While LCEs are restricted due to their perturbative nature, the non-perturbative variant is not.
In graph-based continuous unitary transformations (gCUTs), the block diagonalization is achieved by a non-perturbative CUT performed on finite clusters. The central objective of this thesis is a modification of the gCUT scheme, allowing to treat two kinds of major issues, denoted by pseudo and genuine decay, occuring for NLCEs due to the non-perturbative treatment of clusters.
Indeed, one finds surprising effects caused by the non-perturbative renormalization. In particular, we identify a fundamental challenge for any non-perturbative approach based on finite clusters resulting from the reduced symmetry on graphs, most importantly the breaking of translational symmetry when targeting the properties of excited states. This can be traced back to the appearance of intruder states in the low-energy spectrum, which represent a major obstacle in quasi-degenerate perturbation theory. Here, a generalized notion of cluster additivity is introduced, which is used to formulate an optimized scheme of gCUTs, allowing to solve and to physically understand this major issue. Most remarkably, our improved scheme demands to go beyond the paradigm of using the exact eigenvectors on graphs. We demonstrate that the modified scheme is correct in the non-perturbative regime.
Even at quantum criticality, the scheme gives valid results. To determine the critical behavior, one must rely on extrapolation schemes. We introduce a generic approach to extract critical properties from sequences of numerical data which is directly relevant for NLCEs. The scheme is applied to the quantum phase transition between the dimerized and the isotropic spin 1/2 Heisenberg chain.
Finally, we investigate a scenario where the gapped quasiparticle excitation is not stable for all momenta, i.e., the one-particle mode merges with the continuum for certain momenta and one observes quasiparticle decay. In this case, intruder states merging with the low-energy spectrum on finite clusters represent genuine physics of the system. Again, a proper renormalization on finite clusters satisfies the generalized cluster additivity. Our adjusted renormalization approach performed on finite clusters does not necessarily lead to a full decoupling of the quasiparticle subspaces and the remaining interactions are part of the effective description. The resulting effective Hamiltonian can be analyzed to describe quasiparticle decay in the thermodynamic limit. The modified scheme is applied to four-leg spin 1/2 Heisenberg ladders, providing insights into the spectral properties.
Overall, this thesis presents several important developments for the derivation of effective quasiparticle pictures in quantum spin models via perturbative and non-perturbative LCEs, opening various opportunities for future investigations
Dataset for "Lee-Yang and Langer edge singularities from analytic continuation of scaling functions"
No full textSchmidt-Sonntag C, Karsch F, Singh S. Dataset for "Lee-Yang and Langer edge singularities from analytic continuation of scaling functions". Bielefeld University; 2024.This data set contains all necessary data to reproduce plots in the publication "Lee-Yang and Langer edge singularities from analytic continuation of scaling functions", Phys.Rev.D 109 (2024) 1, 014508 [arXiv:2311.13530[hep-lat]]. The plot scripts are are also included
QCD thermodynamics with 2 and 3 quark flavors
No full textKarsch F, Laermann E, Peikert A, Schmidt C, Stickan S. QCD thermodynamics with 2 and 3 quark flavors. 2000
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