487 research outputs found
Six-dimensional (1,0) effective action of F-theory via M-theory on Calabi-Yau threefolds
The six-dimensional effective action of F-theory compactified on a singular
elliptically fibred Calabi-Yau threefold is determined by using an M-theory
lift. The low-energy data are derived by comparing a circle reduction of a
general six-dimensional (1,0) gauged supergravity theory with the effective
action of M-theory on the resolved Calabi-Yau threefold. The derivation
includes six-dimensional tensor multiplets for which the (anti-) self-duality
constraints are imposed on the level of the five-dimensional action. The vector
sector of the reduced theory is encoded by a non-standard potential due to the
Green-Schwarz term in six dimensions. This Green-Schwarz term also contains
higher curvature couplings which are considered to establish the full map
between anomaly coefficients and geometry. F-/M-theory duality is exploited by
moving to the five-dimensional Coulomb branch after circle reduction and
integrating out massive vector multiplets and matter hypermultiplets. The
associated fermions then generate additional Chern-Simons couplings at
one-loop. Further couplings involving the graviphoton are induced by quantum
corrections due to excited Kaluza-Klein modes. On the M-theory side integrating
out massive fields corresponds to resolving the singularities of the Calabi-Yau
threefold, and yields intriguing relations between six-dimensional anomalies
and classical topology.Comment: 55 pages, v2: typos corrected, discussion of loop corrections
improve
D=7 / D=6 Heterotic Supergravity with Gauged R-Symmetry
We construct a family of chiral anomaly-free supergravity theories in D=6
starting from D=7 supergravity with a gauged noncompact R-symmetry, employing a
Horava-Witten bulk-plus-boundary construction. The gauged noncompact R-symmetry
yields a positive (de Sitter sign) D=6 scalar field potential. Classical
anomaly inflow which is needed to cancel boundary-field loop anomalies requires
careful consideration of the gravitational, gauge, mixed and local
supersymmetry anomalies. Coupling of boundary hypermultiplets requires care
with the Sp(1) gauge connection required to obtain quaternionic Kahler target
manifolds in D=6. This class of gauged R-symmetry models may be of use as
starting points for further compactifications to D=4 that take advantage of the
positive scalar potential, such as those proposed in the scenario of
supersymmetry in large extra dimensions.Comment: 43 pages, plain Latex; Clarification of discussion and references
adde
Non-supersymmetric extremal multicenter black holes with superpotentials
Using the superpotential approach we generalize Denef's method of deriving
and solving first-order equations describing multicenter extremal black holes
in four-dimensional N = 2 supergravity to allow non-supersymmetric solutions.
We illustrate the general results with an explicit example of the stu model.Comment: 17 pages, v2: some clarifications adde
An Exact Fluctuating 1/2-BPS Configuration
This work explores the role of thermodynamic fluctuations in the two
parameter giant and superstar configurations characterized by an ensemble of
arbitrary liquid droplets or irregular shaped fuzzballs. Our analysis
illustrates that the chemical and state-space geometric descriptions exhibit an
intriguing set of exact pair correction functions and the global correlation
lengths. The first principle of statistical mechanics shows that the possible
canonical fluctuations may precisely be ascertained without any approximation.
Interestingly, our intrinsic geometric study exemplifies that there exist exact
fluctuating 1/2-BPS statistical configurations which involve an ensemble of
microstates describing the liquid droplets or fuzzballs. The Gaussian
fluctuations over an equilibrium chemical and state-space configurations
accomplish a well-defined, non-degenerate, curved and regular intrinsic
Riemannian manifolds for all physically admissible domains of black hole
parameters. An explicit computation demonstrates that the underlying chemical
correlations involve ordinary summations, whilst the state-space correlations
may simply be depicted by standard polygamma functions. Our construction
ascribes definite stability character to the canonical energy fluctuations and
to the counting entropy associated with an arbitrary choice of excited boxes
from an ensemble of ample boxes constituting a variety of Young tableaux.Comment: Minor changes, added references, 30 pages, 4 figures, PACS numbers:
04.70.-s: Physics of black holes; 04.70.-Bw: Classical black holes; 04.50.Gh
Higher-dimensional black holes, black strings, and related objects; 04.60.Cf
Gravitational aspects of string theory, accepted for publication in JHE
All the timelike supersymmetric solutions of all ungauged d=4 supergravities
We determine the form of all timelike supersymmetric solutions of all N
greater or equal than 2, d=4 ungauged supergravities, for N less or equal than
4 coupled to vector supermultiplets, using the $Usp(n+1,n+1)-symmetric
formulation of Andrianopoli, D'Auria and Ferrara and the spinor-bilinears
method, while preserving the global symmetries of the theories all the way. As
previously conjectured in the literature, the supersymmetric solutions are
always associated to a truncation to an N=2 theory that may include
hypermultiplets, although fields which are eliminated in the truncations can
have non-trivial values, as is required by the preservation of the global
symmetry of the theories. The solutions are determined by a number of
independent functions, harmonic in transverse space, which is twice the number
of vector fields of the theory (n+1). The transverse space is flat if an only
if the would-be hyperscalars of the associated N=2 truncation are trivial.Comment: v3: Some changes in the introduction. Version to be published in JHE
Combined Transfer of Human VEGF165 and HGF Genes Renders Potent Angiogenic Effect in Ischemic Skeletal Muscle
Increased interest in development of combined gene therapy emerges from results of recent clinical trials that indicate good safety yet unexpected low efficacy of “single-gene” administration. Multiple studies showed that vascular endothelial growth factor 165 aminoacid form (VEGF165) and hepatocyte growth factor (HGF) can be used for induction of angiogenesis in ischemic myocardium and skeletal muscle. Gene transfer system composed of a novel cytomegalovirus-based (CMV) plasmid vector and codon-optimized human VEGF165 and HGF genes combined with intramuscular low-voltage electroporation was developed and tested in vitro and in vivo. Studies in HEK293T cell culture, murine skeletal muscle explants and ELISA of tissue homogenates showed efficacy of constructed plasmids. Functional activity of angiogenic proteins secreted by HEK293T after transfection by induction of tube formation in human umbilical vein endothelial cell (HUVEC) culture. HUVEC cells were used for in vitro experiments to assay the putative signaling pathways to be responsible for combined administration effect one of which could be the ERK1/2 pathway. In vivo tests of VEGF165 and HGF genes co-transfer were conceived in mouse model of hind limb ischemia. Intramuscular administration of plasmid encoding either VEGF165 or HGF gene resulted in increased perfusion compared to empty vector administration. Mice injected with a mixture of two plasmids (VEGF165+HGF) showed significant increase in perfusion compared to single plasmid injection. These findings were supported by increased CD31+ capillary and SMA+ vessel density in animals that received combined VEGF165 and HGF gene therapy compared to single gene therapy. Results of the study suggest that co-transfer of VEGF and HGF genes renders a robust angiogenic effect in ischemic skeletal muscle and may present interest as a potential therapeutic combination for treatment of ischemic disorders
State-space Manifold and Rotating Black Holes
We study a class of fluctuating higher dimensional black hole configurations
obtained in string theory/ -theory compactifications. We explore the
intrinsic Riemannian geometric nature of Gaussian fluctuations arising from the
Hessian of the coarse graining entropy, defined over an ensemble of brane
microstates. It has been shown that the state-space geometry spanned by the set
of invariant parameters is non-degenerate, regular and has a negative scalar
curvature for the rotating Myers-Perry black holes, Kaluza-Klein black holes,
supersymmetric black holes, - configurations and the
associated BMPV black holes. Interestingly, these solutions demonstrate that
the principal components of the state-space metric tensor admit a positive
definite form, while the off diagonal components do not. Furthermore, the ratio
of diagonal components weakens relatively faster than the off diagonal
components, and thus they swiftly come into an equilibrium statistical
configuration. Novel aspects of the scaling property suggest that the
brane-brane statistical pair correlation functions divulge an asymmetric
nature, in comparison with the others. This approach indicates that all above
configurations are effectively attractive and stable, on an arbitrary
hyper-surface of the state-space manifolds. It is nevertheless noticed that
there exists an intriguing relationship between non-ideal inter-brane
statistical interactions and phase transitions. The ramifications thus
described are consistent with the existing picture of the microscopic CFTs. We
conclude with an extended discussion of the implications of this work for the
physics of black holes in string theory.Comment: 44 pages, Keywords: Rotating Black Holes; State-space Geometry;
Statistical Configurations, String Theory, M-Theory. PACS numbers: 04.70.-s
Physics of black holes; 04.70.Bw Classical black holes; 04.70.Dy Quantum
aspects of black holes, evaporation, thermodynamics; 04.50.Gh
Higher-dimensional black holes, black strings, and related objects. Edited
the bibliograph
Biomechanical analyses of the performance of Paralympians: From foundation to elite level
Biomechanical analysis of sport performance provides an objective method of determining performance of a particular sporting technique. In particular, it aims to add to the understanding of the mechanisms influencing performance, characterization of athletes, and provide insights into injury predisposition. Whilst the performance in sport of able-bodied athletes is well recognised in the literature, less information and understanding is known on the complexity, constraints and demands placed on the body of an individual with a disability. This paper provides a dialogue that outlines scientific issues of performance analysis of multi-level athletes with a disability, including Paralympians. Four integrated themes are explored the first of which focuses on how biomechanics can contribute to the understanding of sport performance in athletes with a disability and how it may be used as an evidence-based tool. This latter point questions the potential for a possible cultural shift led by emergence of user-friendly instruments. The second theme briefly discusses the role of reliability of sport performance and addresses the debate of two-dimensional and three-dimensional analysis. The third theme address key biomechanical parameters and provides guidance to clinicians, and coaches on the approaches adopted using biomechanical/sport performance analysis for an athlete with a disability starting out, to the emerging and elite Paralympian. For completeness of this discourse, the final theme is based on the controversial issues on the role of assisted devices and the inclusion of Paralympians into able-bodied sport is also presented. All combined, this dialogue highlights the intricate relationship between biomechanics and training of individuals with a disability. Furthermore, it illustrates the complexity of modern training of athletes which can only lead to a better appreciation of the performances to be delivered in the London 2012 Paralympic Games
CD103 Deficiency Prevents Graft-versus-Host Disease but Spares Graft-versus-Tumor Effects Mediated by Alloreactive CD8 T Cells
Graft-versus-host disease (GVHD) remains the main barrier to broader application of allogeneic hematopoietic stem cell transplantation (alloSCT) as a curative therapy for host malignancy. GVHD is mediated by allogeneic T cells directed against histocompatibility antigens expressed by host tissues. Based on previous studies, we postulated that the integrin CD103 is required for CD8-mediated GVHD, but not for graft-versus-tumor effects (GVT).We herein provide evidence in support of this hypothesis. To circumvent the potentially confounding influence of donor CD4 T cells, we developed an alloSCT model in which GVHD mortality is mediated by purified CD8 T cells. In this model, host-reactive CD8 T cells receive CD4 T cell help at the time of initial activation but not in the effector phase in which mature CD8 T effectors migrate into host tissues. We show that donor CD8 T cells from wild-type BALB/c mice primed to host alloantigens induce GVHD pathology and eliminate tumors of host origin in the absence of host CD4 T cells. Importantly, CD103 deficiency dramatically attenuated GVHD mortality, but had no detectable impact on the capacity to eliminate a tumor line of host origin. We provide evidence that CD103 is required for accumulation of donor CD8 T cells in the host intestinal epithelium but not in the tumor or host lymphoid compartments. Consistent with these data, CD103 was preferentially expressed by CD8 T cells infiltrating the host intestinal epithelium but not by those infiltrating the tumor, lamina propria, or lymphoid compartments. We further demonstrate that CD103 expression is not required for classic CD8 effector activities including cytokine production and cytotoxicity.These data indicate that CD103 deficiency inhibits GVHD pathology while sparing anti-tumor effects mediated by CD8 T cells, identifying CD103 blockade as an improved strategy for GVHD prophylaxis
- …