Chiral symmetry breaking transitions in holographic duals

Generalisations of the AdS/CFT Correspondence are used to study chiral symmetry breaking in dual gauge theories. We use the D3/D7 and D3/D5 systems to model both 3+1 and 2+1 dimensional, strongly coupled, gauge theories with quark fields. We show that chiral symmetry breaking is induced by either an imposed running coupling/dilaton profile or a background magnetic field. We explore the low energy effective theory of the pions of these models deriving simple integral equations for low energy parameters in the spirit of constituent quark model results. We also explore the phase structure of these models, with respect totemperature, chemical potential and applied electric field. The phase diagrams contain regions with broken and restored chiral symmetry separated by first order, second order and BKT transitions. There is an extra transition associated with the melting of the meson states into the background plasma. Finally we use the phenomenological dilaton profile to engineer holographic descriptions of theories with QCD-like phase diagrams

E, B, \mu, T Phase Structure of the D3/D7 Holographic Dual

The large N_c N=4 gauge theory with quenched N=2 quark matter displays chiral symmetry breaking in the presence of a magnetic field. We previously studied the temperature and chemical potential phase structure of this theory in the grand canonical ensemble - here we, in addition, include the effect of an electric field which acts to counter chiral symmetry breaking by disassociating mesons. We compute using the gravity dual based on the D3/probe-D7 brane system. The theory displays two transition at one of which chiral symmetry is restored. At the other transition density switches on, the mesons of the theory become unstable and a current forms, making it a conductor-insulator transition. Through the temperature, electric field, chemical potential volume (at fixed magnetic field parallel to the electric field) these transitions can coincide or separate at critical points, and be first order or second order. We map out this full phase structure which provides varied computable examples relevant to strongly coupled gauge theories and potentially condensed matter systems.Comment: 20 pages, 7 figure

Phase diagram of the D3/D5 system in a magnetic field and a BKT transition

We study the full temperature and chemical potential dependence of the D3/D5 2+1 dimensional theory in the presence of a magnetic field. The theory displays separate transitions associated with chiral symmetry breaking and melting of the bound states. We display the phase diagram which has areas with first and second order transitions meeting at two critical points similar to that of the D3/D7 system. In addition there is the recently reported BKT transition at zero temperature leading to distinct structure at low temperatures.Comment: 5 pages, 3 figures, V2: references adde

Wirkungsanalyse bestehender Klimaschutzmaßnahmen und -programme sowie Identifizierung möglicher weiterer Maßnahmen eines Energie- und Klimaschutzprogramms der Bundesregierung

Eine Analyse der deutschen Energie- und Klimapolitik hat ergeben: Nur im Maßnahmenfeld "Ausbau der Erneuerbaren Energien im Strombereich" wird voraussichtlich das Ziel ereicht. Dagegen wird in allen anderen Maßnahmenfeldern das Ziel verfehlt oder es bestehen Wirkungsdefizite der eingesetzten Politikinstrumente. Das betrifft insbesondere die Energieeffizienz auf der Nachfrageseite, aber auch die Kraft-Wärme-Kopplung und Erneuerbare Energien-Wärme. Für die Maßnahmenfelder "Fluorierte Treibhausgase", "Industrieprozesse" und "Landwirtschaft" müssen überhaupt erst verbindliche Reduktionsziele festgelegt und Politikinstrumente eingeführt werden

Towards a Holographic Model of the QCD Phase Diagram

We describe the temperature-chemical potential phase diagrams of holographic models of a range of strongly coupled gauge theories that display chiral symmetry breaking/restoration transitions. The models are based on the D3/probe-D7 system but with a phenomenologically chosen running coupling/dilaton profile. We realize chiral phase transitions with either temperature or density that are first or second order by changing the dilaton profile. Although the models are only caricatures of QCD they show that holographic models can capture many aspects of the QCD phase diagram and hint at the dependence on the running coupling.Comment: 11 pages, 9 figures, v2: minor corrections, Invited contribution to an AdS/CFT edition of Journal of Physics

Situated learning in in-service teacher training

Bisherige Forschungsergebnisse zur Wirksamkeit von Lehrerfortbildungen zeigen, dass die Nutzung der Fortbildungsinhalte in der Unterrichtspraxis fragwürdig bleibt. Konzepte, die auf Ansätzen des situierten Lernens basieren, erscheinen hier erfolgversprechend. Im Rahmen einer von der DFG geförderten Studie wurde untersucht, inwiefern sich mittels unterschiedlicher Situierungsqualitäten von Lernsituationen förderdiagnostische Kompetenzen von Lehrkräften im Schriftspracherwerb erhöhen lassen. Die Ergebnisse weisen deutliche Vorzüge der beiden situiert konzipierten Experimentalgruppen gegenüber einer traditionell-textbasierten Kontrollgruppe auf. Diese Vorzüge betreffen eine Kompetenzsteigerung im anwendungsbezogenen Wissen in einer eher moderat situierten Experimentalgruppe ("konstruiert-situiert"), eine höhere intrinsische Motivation sowie tendenziell bessere Schülerleistungen in einer "voll-situierten" Experimentalgruppe. In der Zusammenfassung und Diskussion werden mögliche Ursachen für die Unterschiede erörtert. (DIPF/Orig.)Previous research about the effectiveness of in-service teacher training tends to reveal a deficient effectiveness of traditional forms of in-service teacher training. Especially the transfer of knowledge into practice is questioned. However, concepts based on the principles of situated learning seem to be promising. In the context of an empirical study, funded by the DFG, it was investigated to what extent the diagnostic competence of teachers of literacy can be increased by situated learning. For that purpose training programmes that provided different degrees of situated learning opportunities were compared. The results show that the two experimental groups that were based on situated concepts have clear advantages over the traditional control group that was mainly taught on a textual basis. These advantages relate to increased competencies in the field of knowledge application in the moderately situated experimental group, a higher level of intrinsic motivation and better pupil achievements in the completely situated experimental group. In the article it is tried to analyse possible reasons for these results. (DIPF/Orig.

E, B, µ, T Phase Structure of the D3/D7 Holographic Dual

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