RESUMO
Superconformal field theories (SCFTs) in dimensions greater than 4 have become an integral part in the general understanding of quantum field theory, with many interesting implications in lower dimensions. They are hard to define using traditional methods, but can be engineered in string theory. Recently, a large class of AdS/CFT dualities has been constructed for five-dimensional SCFTs, which further supports their existence and allows for quantitative studies. We confront these dualities with a decisive test. We obtain the partition functions and central charges in gauge theory deformations of the SCFTs and extrapolate the results to the conformal fixed points. In the appropriate large N limits, this precisely matches the AdS/CFT predictions, providing strong support for the proposed dualities.
RESUMO
We construct global solutions to type IIB supergravity with 16 residual supersymmetries whose space-time is AdS_{6}×S^{2} warped over a Riemann surface. Families of solutions are labeled by an arbitrary number L≥3 of asymptotic regions, in each of which the supergravity fields match those of a (p,q) five-brane, and may therefore be viewed as near-horizon limits of fully localized intersections of five-branes in type IIB string theory. These solutions provide compelling candidates for holographic duals to a large class of five-dimensional superconformal quantum field theories which arise as nontrivial UV fixed points of perturbatively nonrenormalizable Yang-Mills theories, thereby making them more directly accessible to quantitative analysis.
RESUMO
We put AdS/CFT dualities involving probe branes to a precision test. On the holographic side we use a new class of supersymmetric D7-brane embeddings into AdS(5)×S(5), which allow us to describe N=4 super Yang-Mills theory coupled to massive N=2 supersymmetric flavors on S(4). With these embeddings we can compare holographic results to a field theory analysis of the free energy using supersymmetric localization. Localization allows us to get results at strong coupling, and hence to compare in detail to AdS/CFT. We find analytically matching results: a phase transition at the same critical mass in both calculations and matching free energies up to a scheme-dependent constant in both phases.
RESUMO
BACKGROUND: DNA and chromatin modifications are critical mediators in the establishment and maintenance of cell type-specific gene expression patterns that constitute cellular identities. One type of modification, the acetylation and deacetylation of histones, occurs reversibly on lysine ε-NH3(+) groups of core histones via histone acetyl transferases (HAT) and histone deacetylases (HDAC). Hyperacetylated histones are associated with active chromatin domains, whereas hypoacetylated histones are enriched in non-transcribed loci. METHODS: We analyzed global histone H4 acetylation and HDAC activity levels in mature lineage marker-positive (Lin(+)) and progenitor lineage marker-negative (Linâ») hematopoietic cells from murine bone marrow (BM). In addition, we studied the effects of HDAC inhibition on hematopoietic progenitor/stem cell (HPSC) frequencies, cell survival, differentiation and HoxB4 dependence. RESULTS: We observed that Linâ» and Lin(+) cells do not differ in global histone H4 acetylation but in HDAC activity levels. Further, we saw that augmented histone acetylation achieved by transient Trichostatin A (TSA) treatment increased the frequency of cells with HPSC immunophenotype and function in the heterogeneous pool of BM cells. Induction of histone hyperacetylation in differentiated BM cells was detrimental, as evidenced by preferential death of mature BM cells upon HDAC inhibition. Finally, TSA treatment of BM cells from HoxB4(-/-) mice revealed that the HDAC inhibitor-mediated increase in HPSC frequencies was independent of HoxB4. CONCLUSIONS: Overall, these data indicate the potential of chromatin modifications for the regulation of HPSC. Chromatin-modifying agents may provide potential strategies for ex vivo expansion of HPSC.