3,059 research outputs found
Conformal Field Theories: From Old to New
In a short review of recent work, we discuss the general problem of
constructing the actions of new conformal field theories from old conformal
field theories. Such a construction follows when the old conformal field theory
admits new conformal stress tensors in its chiral algebra, and it turns out
that the new conformal field theory is generically a new spin-two gauge theory.
As an example we discuss the new spin-two gauged sigma models which arise in
this fashion from the general conformal non-linear sigma model.Comment: 7 pages, LaTeX, to appear in a memorial issue of Theoretical and
Mathematical Physics in memory of F.A. Lune
An analysis of some mistakes, miracles and myths in supplier selection
This paper analyzes some consequences of formal methods and procedures for supplier selection. It argues that many mistakes and miracles may occur in frequently used procedures. Practical examples are given. In the analysis it turns out that preventing these unwanted effects from occurring may be tackled by methodological improvements. Some examples and guidelines for these are given as well. But another important point lies in the perspectives of the actors in supplier selection: governments and industry policy makers, purchasers, suppliers and (management) researchers. The analysis shows that these different actors often operate from quite different and sometimes conflicting attitudes, assumptions and principles. On the one hand this analysis leads to the conclusion that using some sort of formal approach for supplier selection may be necessary. On the other hand it clarifies the criticism on such an approach and the difficulties associated with its use. The paper concludes with recommendations and implications for policy makers, researchers, and practitioners
Entanglement, Holography and Causal Diamonds
We argue that the degrees of freedom in a d-dimensional CFT can be
re-organized in an insightful way by studying observables on the moduli space
of causal diamonds (or equivalently, the space of pairs of timelike separated
points). This 2d-dimensional space naturally captures some of the fundamental
nonlocality and causal structure inherent in the entanglement of CFT states.
For any primary CFT operator, we construct an observable on this space, which
is defined by smearing the associated one-point function over causal diamonds.
Known examples of such quantities are the entanglement entropy of vacuum
excitations and its higher spin generalizations. We show that in holographic
CFTs, these observables are given by suitably defined integrals of dual bulk
fields over the corresponding Ryu-Takayanagi minimal surfaces. Furthermore, we
explain connections to the operator product expansion and the first law of
entanglement entropy from this unifying point of view. We demonstrate that for
small perturbations of the vacuum, our observables obey linear two-derivative
equations of motion on the space of causal diamonds. In two dimensions, the
latter is given by a product of two copies of a two-dimensional de Sitter
space. For a class of universal states, we show that the entanglement entropy
and its spin-three generalization obey nonlinear equations of motion with local
interactions on this moduli space, which can be identified with Liouville and
Toda equations, respectively. This suggests the possibility of extending the
definition of our new observables beyond the linear level more generally and in
such a way that they give rise to new dynamically interacting theories on the
moduli space of causal diamonds. Various challenges one has to face in order to
implement this idea are discussed.Comment: 84 pages, 12 figures; v2: expanded discussion on constraints in
section 7, matches published versio
Thermodynamics of Higher Spin Black Holes in AdS
We discuss the thermodynamics of recently constructed three-dimensional
higher spin black holes in SL(N,R)\times SL(N,R) Chern-Simons theory with
generalized asymptotically-anti-de Sitter boundary conditions. From a
holographic perspective, these bulk theories are dual to two-dimensional CFTs
with W_N symmetry algebras, and the black hole solutions are dual to thermal
states with higher spin chemical potentials and charges turned on. Because the
notion of horizon area is not gauge-invariant in the higher spin theory, the
traditional approaches to the computation of black hole entropy must be
reconsidered. One possibility, explored in the recent literature, involves
demanding the existence of a partition function in the CFT, and consistency
with the first law of thermodynamics. This approach is not free from
ambiguities, however, and in particular different definitions of energy result
in different expressions for the entropy. In the present work we show that
there are natural definitions of the thermodynamically conjugate variables that
follow from careful examination of the variational principle, and moreover
agree with those obtained via canonical methods. Building on this intuition, we
derive general expressions for the higher spin black hole entropy and free
energy which are written entirely in terms of the Chern-Simons connections, and
are valid for both static and rotating solutions. We compare our results to
other proposals in the literature, and provide a new and efficient way to
determine the generalization of the Cardy formula to a situation with higher
spin charges.Comment: 30 pages, PDFLaTeX; v2: typos corrected, explicit expressions for the
free energy adde
Je omgeving bepaalt je lot
Slim ontworpen materialen zetten straks lichaamseigen cellen aan tot spontaan herstel van weefsels. Onderzoeksinstituut Mira zoekt verbanden tussen celgroei en oppervlaktestructuren van metaal of kunststof
A link between the accumulation of DNA damage and loss of multi-potency of human mesenchymal stromal cells
Human mesenchymal stromal cells (hMSCs) represent an attractive cell source for clinic applications. Besides being multi-potent, recent clinical trials suggest that they secrete both trophic and immunomodulatory factors, allowing allogenic MSCs to be used in a wider variety of clinical situations. The yield of prospective isolation is however very low, making expansion a required step toward clinical applications. Unfortunately, this leads to a significant decrease in their stemness. To identify the mechanism behind loss of multi-potency, hMSCs were expanded until replicative senescence and the concomitant molecular changes were characterized at regular intervals. We observed that, with time of culture, loss of multi-potency was associated with both the accumulation of DNA damage and the respective activation of the DNA damage response pathway, suggesting a correlation between both phenomena. Indeed, exposing hMSCs to DNA damage agents led to a significant decrease in the differentiation potential. We also showed that hMSCs are susceptible to accumulate DNA damage upon in vitro expansion, and that although hMSCs maintained an effective nucleotide excision repair activity, there was a progressive accumulation of DNA damage. We propose a model in which DNA damage accumulation contributes to the loss of differentiation potential of hMSCs, which might not only compromise their potential for clinical applications but also contribute to the characteristics of tissue agein
Near Horizon Limits of Massless BTZ and Their CFT Duals
We consider the massless BTZ black hole and show that it is possible to take
its "near horizon" limit in two distinct ways. The first one leads to a null
self-dual orbifold of AdS3 and the second to a spacelike singular AdS3/Z_K
orbifold in the large K limit, the "pinching orbifold". We show that from the
dual 2d CFT viewpoint, the null orbifold corresponds to the p^+=0 sector of the
Discrete Light-Cone Quantisation (DLCQ) of the 2d CFT where a chiral sector of
the CFT is decoupled, while the pinching orbifold corresponds to taking an
infinite mass gap limit in both the right and left sectors of the 2d CFT,
essentially leaving us with the states L_0=\bar L_0=c/24 only. In the latter
case, one can combine the near horizon limit with sending the 3d Planck length
l_P to zero, or equivalently the dual CFT central charge c to infinity. We
provide preliminary evidence that in that case some nontrivial dynamics may
survive the limit.Comment: 22 pages, no figures, v2: minor improvements, references adde
The chiral ring of AdS3/CFT2 and the attractor mechanism
We study the moduli dependence of the chiral ring in N = (4,4) superconformal
field theories, with special emphasis on those CFTs that are dual to type IIB
string theory on AdS3xS3xX4. The chiral primary operators are sections of
vector bundles, whose connection describes the operator mixing under motion on
the moduli space. This connection can be exactly computed using the constraints
from N = (4,4) supersymmetry. Its curvature can be determined using the tt*
equations, for which we give a derivation in the physical theory which does not
rely on the topological twisting. We show that for N = (4,4) theories the
chiral ring is covariantly constant over the moduli space, a fact which can be
seen as a non-renormalization theorem for the three-point functions of chiral
primaries in AdS3/CFT2. From the spacetime point of view our analysis has the
following applications. First, in the case of a D1/D5 black string, we can see
the matching of the attractor flow in supergravity to RG-flow in the boundary
field theory perturbed by irrelevant operators, to first order away from the
fixed point. Second, under spectral flow the chiral primaries become the Ramond
ground states of the CFT. These ground states represent the microstates of a
small black hole in five dimensions consisting of a D1/D5 bound state. The
connection that we compute can be considered as an example of Berry's phase for
the internal microstates of a supersymmetric black hole.Comment: 72 pages (60 + appendices
Anomalous Breaking of Anisotropic Scaling Symmetry in the Quantum Lifshitz Model
In this note we investigate the anomalous breaking of anisotropic scaling
symmetry in a non-relativistic field theory with dynamical exponent z=2. On
general grounds, one can show that there exist two possible "central charges"
which characterize the breaking of scale invariance. Using heat kernel methods,
we compute these two central charges in the quantum Lifshitz model, a free
field theory which is second order in time and fourth order in spatial
derivatives. We find that one of the two central charges vanishes.
Interestingly, this is also true for strongly coupled non-relativistic field
theories with a geometric dual described by a metric and a massive vector
field.Comment: 26 pages; major revision (results were unaffected), published versio
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