457 research outputs found
Improved Holographic QCD
We provide a review to holographic models based on Einstein-dilaton gravity
with a potential in 5 dimensions. Such theories, for a judicious choice of
potential are very close to the physics of large-N YM theory both at zero and
finite temperature. The zero temperature glueball spectra as well as their
finite temperature thermodynamic functions compare well with lattice data. The
model can be used to calculate transport coefficients, like bulk viscosity, the
drag force and jet quenching parameters, relevant for the physics of the
Quark-Gluon Plasma.Comment: LatEX, 65 pages, 28 figures, 9 Tables. Based on lectures given at
several Schools. To appear in the proceedinds of the 5th Aegean School
(Milos, Greece
The Bethe-Ansatz for N=4 Super Yang-Mills
We derive the one loop mixing matrix for anomalous dimensions in N=4 Super
Yang-Mills. We show that this matrix can be identified with the Hamiltonian of
an integrable SO(6) spin chain with vector sites. We then use the Bethe ansatz
to find a recipe for computing anomalous dimensions for a wide range of
operators. We give exact results for BMN operators with two impurities and
results up to and including first order 1/J corrections for BMN operators with
many impurities. We then use a result of Reshetikhin's to find the exact
one-loop anomalous dimension for an SO(6) singlet in the limit of large bare
dimension. We also show that this last anomalous dimension is proportional to
the square root of the string level in the weak coupling limit.Comment: 35 pages, 3 figures, LaTeX; v2 references added, typos corrected,
\Lambda fixed; v3 expanded discussion of higher loops in conclusion, matches
published versio
Orbiting Membranes in M-theory on AdS_7 x S^4 Background
We study classical solutions describing rotating and boosted membranes on
AdS_7 x S^4 background in M-theory. We find the dependence of the energy on the
spin and R-charge of these solutions. In the flat space limit we get E ~
S^{2/3}, while for AdS at leading order E-S grows as S^{1/3}. The membranes on
AdS_4 x S^7 background have briefly been studied as well.Comment: 13 pages, latex, v2: a note and refs. added, some typos correcte
String interactions and discrete symmetries of the pp-wave background
Free string theory on the plane-wave background displays a discrete Z2
symmetry exchanging the two transverse SO(4) rotation groups. This symmetry
should be respected also at the interacting level. We show that the zero mode
structure proposed in hep-th/0208148 can be completed to a full kinematical
vertex, contrary to claims appeared in the previous literature. We also comment
on the relation with recent works on the string-bit formalism and on the
comparison with the field theory side of the correspondence.Comment: Proceeding of the 35th Symposium Ahrenshoop Aug 2002 and the Leuven
RTN-workshop Sept 200
Genome-Wide Transcriptional Reorganization Associated with Senescence-to-Immortality Switch during Human Hepatocellular Carcinogenesis
Cataloged from PDF version of article.Senescence is a permanent proliferation arrest in response to cell stress such as DNA damage. It contributes strongly to tissue aging and serves as a major barrier against tumor development. Most tumor cells are believed to bypass the senescence barrier (become "immortal") by inactivating growth control genes such as TP53 and CDKN2A. They also reactivate telomerase reverse transcriptase. Senescence-to-immortality transition is accompanied by major phenotypic and biochemical changes mediated by genome-wide transcriptional modifications. This appears to happen during hepatocellular carcinoma (HCC) development in patients with liver cirrhosis, however, the accompanying transcriptional changes are virtually unknown. We investigated genome-wide transcriptional changes related to the senescence-to-immortality switch during hepatocellular carcinogenesis. Initially, we performed transcriptome analysis of senescent and immortal clones of Huh7 HCC cell line, and identified genes with significant differential expression to establish a senescence-related gene list. Through the analysis of senescence-related gene expression in different liver tissues we showed that cirrhosis and HCC display expression patterns compatible with senescent and immortal phenotypes, respectively; dysplasia being a transitional state. Gene set enrichment analysis revealed that cirrhosis/senescence-associated genes were preferentially expressed in non-tumor tissues, less malignant tumors, and differentiated or senescent cells. In contrast, HCC/immortality genes were up-regulated in tumor tissues, or more malignant tumors and progenitor cells. In HCC tumors and immortal cells genes involved in DNA repair, cell cycle, telomere extension and branched chain amino acid metabolism were up-regulated, whereas genes involved in cell signaling, as well as in drug, lipid, retinoid and glycolytic metabolism were down-regulated. Based on these distinctive gene expression features we developed a 15-gene hepatocellular immortality signature test that discriminated HCC from cirrhosis with high accuracy. Our findings demonstrate that senescence bypass plays a central role in hepatocellular carcinogenesis engendering systematic changes in the transcription of genes regulating DNA repair, proliferation, differentiation and metabolism
Conformal Dimensions of Two-Derivative BMN Operators
We compute the anomalous dimensions of BMN operators with two covariant
derivative impurities at the planar level up to first order in the effective
coupling lambda'. The result equals those for two scalar impurities as well as
for mixed scalar and vector impurities given in the literature. Though the
results are the same, the computation is very different from the scalar case.
This is basically due to the existence of a non-vanishing overlap between the
derivative impurity and the ``background'' field Z. We present details of these
differences and their consequences.Comment: 27 pages, v2: references added, minor change
Holonomy from wrapped branes
Compactifications of M-theory on manifolds with reduced holonomy arise as the
local eleven-dimensional description of D6-branes wrapped on supersymmetric
cycles in manifolds of lower dimension with a different holonomy group.
Whenever the isometry group SU(2) is present, eight-dimensional gauged
supergravity is a natural arena for such investigations. In this paper we use
this approach and review the eleven dimensional description of D6-branes
wrapped on coassociative 4-cycles, on deformed 3-cycles inside Calabi-Yau
threefolds and on Kahler 4-cycles.Comment: 1+8 pages, Latex. Proceedings of the Leuven workshop, 2002. v2:
Corrected typos in equations (4)-(8
Chiral primary cubic interactions from pp-wave supergravity
We explicitly construct cubic interaction light-cone Hamiltonian for the
chiral primary system involving the metric fields and the self-dual four-form
fields in the IIB pp-wave supergravity. The background fields representing
pp-waves exhibit SO(4)*SO(4)*Z_2 invariance. It turns out that the interaction
Hamiltonian is precisely the same as that for the dilaton-axion system, except
for the fact that the chiral primary system fields have the opposite parity to
that of the dilaton-axion fields under the Z_2 transformation that exchanges
two SO(4)'s.Comment: 14 pages, A few comments are adde
Let's Twist Again: General Metrics of G(2) Holonomy from Gauged Supergravity
We construct all complete metrics of cohomogeneity one G(2) holonomy with S^3
x S^3 principal orbits from gauged supergravity. Our approach rests on a
generalization of the twisting procedure used in this framework. It corresponds
to a non-trivial embedding of the special Lagrangian three-cycle wrapped by the
D6-branes in the lower dimensional supergravity. There are constraints that
neatly reduce the general ansatz to a six functions one. Within this approach,
the Hitchin system and the flop transformation are nicely realized in eight
dimensional gauged supergravity.Comment: 31 pages, latex; v2: minor changes, references adde
Spacetime singularity resolution by M-theory fivebranes: calibrated geometry, Anti-de Sitter solutions and special holonomy metrics
The supergravity description of various configurations of supersymmetric
M-fivebranes wrapped on calibrated cycles of special holonomy manifolds is
studied. The description is provided by solutions of eleven-dimensional
supergravity which interpolate smoothly between a special holonomy manifold and
an event horizon with Anti-de Sitter geometry. For known examples of Anti-de
Sitter solutions, the associated special holonomy metric is derived. One
explicit Anti-de Sitter solution of M-theory is so treated for fivebranes
wrapping each of the following cycles: K\"{a}hler cycles in Calabi-Yau two-,
three- and four-folds; special lagrangian cycles in three- and four-folds;
associative three- and co-associative four-cycles in manifolds; complex
lagrangian four-cycles in manifolds; and Cayley four-cycles in
manifolds. In each case, the associated special holonomy metric is
singular, and is a hyperbolic analogue of a known metric. The analogous known
metrics are respectively: Eguchi-Hanson, the resolved conifold and the
four-fold resolved conifold; the deformed conifold, and the Stenzel four-fold
metric; the Bryant-Salamon-Gibbons-Page-Pope metrics on an
bundle over , and an bundle over or ;
the Calabi hyper-K\"{a}hler metric on ; and the
Bryant-Salamon-Gibbons-Page-Pope metric on an bundle
over . By the AdS/CFT correspondence, a conformal field theory is
associated to each of the new singular special holonomy metrics, and defines
the quantum gravitational physics of the resolution of their singularities.Comment: 1+52 page
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