GUTs and Exceptional Branes in F-theory - I

Motivated by potential phenomenological applications, we develop the necessary tools for building GUT models in F-theory. This approach is quite flexible because the local geometrical properties of singularities in F-theory compactifications encode the physical content of the theory. In particular, we show how geometry determines the gauge group, matter content and Yukawa couplings of a given model. It turns out that these features are beautifully captured by a four-dimensional topologically twisted N=4 theory which has been coupled to a surface defect theory on which chiral matter can propagate. From the vantagepoint of the four-dimensional topological theory, these defects are surface operators. Specific intersection points of these defects lead to Yukawa couplings. We also find that the unfolding of the singularity in the F-theory geometry precisely matches to properties of the topological theory with a defect.Comment: v2: 121 pages, 5 figures, reference and clarification adde

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Do Not-For-Profits Make a Difference in Social Services? A Survey Study

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Pathogenesis of Aryl Hydrocarbon Receptor-Mediated Development of Lymphoma Is Associated with Increased Cyclooxygenase-2 Expression

Epidemiological studies indicate that exposure to environmental pollutants such as pesticides and dioxins leads to the pathogenesis of lymphoma and leukemia. Here, we show that activation of the aryl hydrocarbon receptor (AhR) by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) resulted in loss of the programmed cell death (apoptosis) response in three different lymphoma cell lines, which plays a key role in the development of cancer, especially lymphoma and leukemia. The AhR-mediated inhibition of apoptosis in vitro was associated with a clear increase of cyclooxygenase-2 (COX-2) and deregulation of genes of the B-cell lymphoma-2 (Bcl-2) family involved in apoptosis including Bcl-xl and Mcl-1 in several lymphoma cell lines. Treatment with the COX-2 inhibitor NS-398 and the AhR antagonist 3′-methoxy-4′-nitroflavone abolished the TCDD-induced resistance of apoptosis in vitro. Furthermore, using micropositron emission tomography imaging, in vivo findings demonstrated that exposure to TCDD promotes the development of lymphoma in superficial lymph nodes of C57BL/10J mice, which was associated with a marked increase of COX-2 expression in the affected lymph nodes. The results indicate that AhR activation and COX-2 overexpression likely represent a mechanism of resistance to apoptosis in lymphoma cell lines that might be relevant for the development of lymphoma in vivo