104 research outputs found
Non-perturbative effects and the refined topological string
The partition function of ABJM theory on the three-sphere has
non-perturbative corrections due to membrane instantons in the M-theory dual.
We show that the full series of membrane instanton corrections is completely
determined by the refined topological string on the Calabi-Yau manifold known
as local P1xP1, in the Nekrasov-Shatashvili limit. Our result can be
interpreted as a first-principles derivation of the full series of
non-perturbative effects for the closed topological string on this Calabi-Yau
background. Based on this, we make a proposal for the non-perturbative free
energy of topological strings on general, local Calabi-Yau manifolds.Comment: 38 pages, 5 figure
Geometry of open strings ending on backreacting D3-branes
We investigate open string theory on backreacting D3-branes using a spacetime
approach. We study in detail the half-BPS supergravity solutions describing
open strings ending on D3-branes, in the near horizon of the D3-branes. We
recover quantitatively several non-trivial features of open string physics
including the appearance of D3-brane spikes, the polarization of fundamental
strings into D5-branes, and the Hanany-Witten effect. Finally we detail the
computation of the gravitational potential between two open strings, and
contrast it with the holographic computation of Wilson lines. We argue that the
D-brane backreaction has a large influence on the low-energy gravity, which may
lead to experimental tests for string theory brane-world scenarios.Comment: 64 pages, 20 figure
Bootstrapping the superconformal index with surface defects
The analytic properties of the N = 2 superconformal index are given a
physical interpretation in terms of certain BPS surface defects, which arise as
the IR limit of supersymmetric vortices. The residue of the index at a pole in
flavor fugacity is interpreted as the index of a superconformal field theory
without this flavor symmetry, but endowed with an additional surface defect.
The residue can be efficiently extracted by acting on the index with a
difference operator of Ruijsenaars-Schneider type. By imposing the
associativity constraints of S-duality, we are then able to evaluate the index
of all generalized quiver theories of type A, for generic values of the three
superconformal fugacities, with or without surface defects.Comment: 60 pages, 7 figure
The Tumorigenicity of Mouse Embryonic Stem Cells and In Vitro Differentiated Neuronal Cells Is Controlled by the Recipients' Immune Response
Embryonic stem (ES) cells have the potential to differentiate into all cell types and are considered as a valuable source of cells for transplantation therapies. A critical issue, however, is the risk of teratoma formation after transplantation. The effect of the immune response on the tumorigenicity of transplanted cells is poorly understood. We have systematically compared the tumorigenicity of mouse ES cells and in vitro differentiated neuronal cells in various recipients. Subcutaneous injection of 1Ă—106 ES or differentiated cells into syngeneic or allogeneic immunodeficient mice resulted in teratomas in about 95% of the recipients. Both cell types did not give rise to tumors in immunocompetent allogeneic mice or xenogeneic rats. However, in 61% of cyclosporine A-treated rats teratomas developed after injection of differentiated cells. Undifferentiated ES cells did not give rise to tumors in these rats. ES cells turned out to be highly susceptible to killing by rat natural killer (NK) cells due to the expression of ligands of the activating NK receptor NKG2D on ES cells. These ligands were down-regulated on differentiated cells. The activity of NK cells which is not suppressed by cyclosporine A might contribute to the prevention of teratomas after injection of ES cells but not after inoculation of differentiated cells. These findings clearly point to the importance of the immune response in this process. Interestingly, the differentiated cells must contain a tumorigenic cell population that is not present among ES cells and which might be resistant to NK cell-mediated killing
Exact Results on the ABJM Fermi Gas
We study the Fermi gas quantum mechanics associated to the ABJM matrix model.
We develop the method to compute the grand partition function of the ABJM
theory, and compute exactly the partition function Z(N) up to N=9 when the
Chern-Simons level k=1. We find that the eigenvalue problem of this quantum
mechanical system is reduced to the diagonalization of a certain Hankel matrix.
In reducing the number of integrations by commuting coordinates and momenta, we
find an exact relation concerning the grand partition function, which is
interesting on its own right and very helpful for determining the partition
function. We also study the TBA-type integral equations that allow us to
compute the grand partition function numerically. Surprisingly, all of our
exact results of the partition functions are written in terms of polynomials of
1/pi with rational coefficients.Comment: 41 pages, 4 figure
Optimized outcome prediction in breast cancer by combining the 70-gene signature with clinical risk prediction algorithms
Multigene prognostic tests in breast cancer: past, present, future
There is growing consensus that multigene prognostic tests provide useful complementary information to tumor size and grade in estrogen receptor (ER)-positive breast cancers. The tests primarily rely on quantification of ER and proliferation-related genes and combine these into multivariate prediction models. Since ER-negative cancers tend to have higher proliferation rates, the prognostic value of current multigene tests in these cancers is limited. First-generation prognostic signatures (Oncotype DX, MammaPrint, Genomic Grade Index) are substantially more accurate to predict recurrence within the first 5Â years than in later years. This has become a limitation with the availability of effective extended adjuvant endocrine therapies. Newer tests (Prosigna, EndoPredict, Breast Cancer Index) appear to possess better prognostic value for late recurrences while also remaining predictive of early relapse. Some clinical prediction problems are more difficult to solve than others: there are no clinically useful prognostic signatures for ER-negative cancers, and drug-specific treatment response predictors also remain elusive. Emerging areas of research involve the development of immune gene signatures that carry modest but significant prognostic value independent of proliferation and ER status and represent candidate predictive markers for immune-targeted therapies. Overall metrics of tumor heterogeneity and genome integrity (for example, homologue recombination deficiency score) are emerging as potential new predictive markers for platinum agents. The recent expansion of high-throughput technology platforms including low-cost sequencing of circulating and tumor-derived DNA and RNA and rapid reliable quantification of microRNA offers new opportunities to build extended prediction models across multiplatform data
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