Three-sphere free energy for classical gauge groups

In this note, we calculate the S [superscript 3] free energy F of 3-d N  ≥ 4 supersymmetric gauge theories with U(N), O(N), and USp(2N) gauge groups and matter hypermultiplets in the fundamental and two-index tensor representations. Supersymmetric localization reduces the computation of F to a matrix model that we solve in the large N limit using two different methods. The first method is a saddle point approximation first introduced in [1], which we extend to next-to-leading order in 1/N. The second method generalizes the Fermi gas approach of [2] to theories with symplectic and orthogonal gauge groups, and yields an expression for F valid to all orders in 1/N . In developing the second method, we use a non-trivial generalization of the Cauchy determinant formula.United States. Dept. of Energy (Cooperative Research Agreement Contract DE-FG02-05ER41360)MIT Department of Physics Pappalardo Progra

A refinement of entanglement entropy and the number of degrees of freedom

We introduce a “renormalized entanglement entropy” which is intrinsically UV finite and is most sensitive to the degrees of freedom at the scale of the size R of the entangled region. We illustrated the power of this construction by showing that the qualitative behavior of the entanglement entropy for a non-Fermi liquid can be obtained by simple dimensional analysis. We argue that the functional dependence of the “renormalized entanglement entropy” on R can be interpreted as describing the renormalization group flow of the entanglement entropy with distance scale. The corresponding quantity for a spherical region in the vacuum, has some particularly interesting properties. For a conformal field theory, it reduces to the previously proposed central charge in all dimensions, and for a general quantum field theory, it interpolates between the central charges of the UV and IR fixed points as R is varied from zero to infinity. We conjecture that in three (spacetime) dimensions, it is always non-negative and monotonic, and provides a measure of the number of degrees of freedom of a system at scale R. In four dimensions, however, we find examples in which it is neither monotonic nor non-negative.United States. Dept. of Energy (Cooperative Research Agreement DE-FG0205ER41360

Some results on the shape dependence of entanglement and Renyi entropies

We study how the universal contribution to entanglement entropy in a conformal field theory depends on the entangling region. We show that for a deformed sphere the variation of the universal contribution is quadratic in the deformation amplitude. We generalize these results for Renyi entropies. We obtain an explicit expression for the second order variation of entanglement entropy in the case of a deformed circle in a three-dimensional conformal field theory with a gravity dual. For the same system, we also consider an elliptic entangling region and determine numerically the entanglement entropy as a function of the aspect ratio of the ellipse. Based on these three-dimensional results and Solodukhin’s formula in four dimensions, we conjecture that the sphere minimizes the universal contribution to entanglement entropy in all dimensions.United States. Dept. of Energy (Cooperative Research Agreement Contract DE-FG02-05ER41360

Semi-local quantum liquids

Gauge/gravity duality applied to strongly interacting systems at finite density predicts a universal intermediate energy phase to which we refer as a semi-local quantum liquid. Such a phase is characterized by a finite spatial correlation length, but an infinite correlation time and associated nontrivial scaling behavior in the time direction, as well as a nonzero entropy density. For a holographic system at a nonzero chemical potential, this unstable phase sets in at an energy scale of order of the chemical potential, and orders at lower energies into other phases; examples include superconductors, and antiferromagnetic-type states. In this paper we give examples in which it also orders into Fermi liquids of “heavy” fermions. While the precise nature of the lower energy state depends on the specific dynamics of the individual system, we argue that the semi-local quantum liquid emerges universally at intermediate energies through deconfinement (or equivalently fractionalization). We also discuss the possible relevance of such a semi-local quantum liquid to heavy electron systems and the strange metal phase of high temperature cuprate superconductors.United States. Dept. of Energy (Cooperative Research Agreement DE-FG0205ER41360

Quantum phase transitions in semilocal quantum liquids

We consider several types of quantum critical phenomena from finite-density gauge-gravity duality which to different degrees lie outside the Landau-Ginsburg-Wilson paradigm. These include: (i) a “bifurcating” critical point, for which the order parameter remains gapped at the critical point, and thus is not driven by soft order parameter fluctuations. Rather it appears to be driven by “confinement” which arises when two fixed points annihilate and lose conformality. On the condensed side, there is an infinite tower of condensed states and the nonlinear response of the tower exhibits an infinite spiral structure; (ii) a “hybridized” critical point which can be described by a standard Landau-Ginsburg sector of order parameter fluctuations hybridized with a strongly coupled sector; (iii) a “marginal” critical point which is obtained by tuning the above two critical points to occur together and whose bosonic fluctuation spectrum coincides with that postulated to underly the “Marginal Fermi Liquid” description of the optimally doped cuprates.United States. Dept. of Energy (Cooperative Research Agreement DE-FG0205ER41360)United States. Dept. of Energy. Outstanding Junior Investigator Progra

The temporal dependence of exploration on neotic style in birds

Exploration (interacting with objects to gain information) and neophobia (avoiding novelty) are considered independent traits shaped by the socio-ecology of a given species. However, in the literature it is often assumed that neophobia inhibits exploration. Here, we investigate how different approaches to novelty (fast or slow) determine the time at which exploration is likely to occur across a number of species. We presented four corvid and five parrot species with a touchscreen discrimination task in which novel stimuli were occasionally interspersed within the familiar training stimuli. We investigated the likelihood that an animal would choose novelty at different stages of its training and found evidence for a shift in the pattern of exploration, depending on neotic style. The findings suggest that faster approaching individuals explored earlier, whilst animals with long initial approach latencies showed similar amounts of exploration but did so later in training. Age rather than species might have influenced the amount of total exploration, with juveniles exploring more than adults. Neotic style varied consistently only for one species and seems to involve a strong individual component, rather than being a purely species-specific trait. This suggests that variation in behavioural phenotypes within a species may be adaptive

Histological assessment of paxgene tissue fixation and stabilization reagents

Within SPIDIA, an EC FP7 project aimed to improve pre analytic procedures, the PAXgene Tissue System (PAXgene), was designed to improve tissue quality for parallel molecular and morphological analysis. Within the SPIDIA project promising results were found in both genomic and proteomic experiments with PAXgene-fixed and paraffin embedded tissue derived biomolecules. But, for this technology to be accepted for use in both clinical and basic research, it is essential that its adequacy for preserving morphology and antigenicity is validated relative to formalin fixation. It is our aim to assess the suitability of PAXgene tissue fixation for (immuno)histological methods. Normal human tissue specimens (n = 70) were collected and divided into equal parts for fixation either with formalin or PAXgene. Sections of the obtained paraffin-embedded tissue were cut and stained. Morphological aspects of PAXgene-fixed tissue were described and also scored relative to formalin-fixed tissue. Performance of PAXgene-fixed tissue in immunohistochemical and in situ hybridization assays was also assessed relative to the corresponding formalin-fixed tissues. Morphology of PAXgene-fixed paraffin embedded tissue was well preserved and deemed adequate for diagnostics in most cases. Some antigens in PAXgene-fixed and paraffin embedded sections were detectable without the need for antigen retrieval, while others were detected using standard, formalin fixation based, immunohistochemistry protocols. Comparable results were obtained with in situ hybridization and histochemical stains. Basically all assessed histological techniques were found to be applicable to PAXgene-fixed and paraffin embedded tissue. In general results obtained with PAXgene-fixed tissue are comparable to those of formalin-fixed tissue. Compromises made in morphology can be called minor compared to the advantages in the molecular pathology possibilities

Targeted Therapy Resistance Mediated by Dynamic Regulation of Extrachromosomal Mutant EGFR DNA

Intratumoral heterogeneity contributes to cancer drug resistance, but the underlying mechanisms are not understood. Single-cell analyses of patient-derived models and clinical samples from glioblastoma patients treated with epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) demonstrate that tumor cells reversibly up-regulate or suppress mutant EGFR expression, conferring distinct cellular phenotypes to reach an optimal equilibrium for growth. Resistance to EGFR TKIs is shown to occur by elimination of mutant EGFR from extrachromosomal DNA. After drug withdrawal, reemergence of clonal EGFR mutations on extrachromosomal DNA follows. These results indicate a highly specific, dynamic, and adaptive route by which cancers can evade therapies that target oncogenes maintained on extrachromosomal DNA

Brain Tumor Stem Cells as Therapeutic Targets in Models of Glioma

At this time, brain tumor stem cells remain a controversial hypothesis while malignant brain tumors continue to present a dire prognosis of severe morbidity and mortality. Yet, brain tumor stem cells may represent an essential cellular target for glioma therapy as they are postulated to be the tumorigenic cells responsible for recurrence. Targeting oncogenic pathways that are essential to the survival and growth of brain tumor stem cells represents a promising area for developing therapeutics. However, due to the multiple oncogenic pathways involved in glioma, it is necessary to determine which pathways are the essential targets for therapy. Furthermore, research still needs to comprehend the morphogenic processes of cell populations involved in tumor formation. Here, we review research and discuss perspectives on models of glioma in order to delineate the current issues in defining brain tumor stem cells as therapeutic targets in models of glioma