Mediterranean afterlives and the memory of Black presence

This article constitutes a long commentary on the section 'geographies of the Black Mediterranean', special issue in this Journa

Vite postume del Mediterraneo e il ricordo della presenza Nera

Questo intervento discute la prospettiva del Mediterraneo nero dal punto di vista empirci ed analitic

Recurrent adaptation in a low-dispersal trait

The study of natural populations from contrasting environments has greatly enhanced our understanding of ecological-dependent selection, adaptation and speciation. Cases of parallel evolution in particular have facilitated the study of the molecular and genetic basis of adaptive variation. This includes the type and number of genes underlying adaptive traits, as well as the extent to which these genes are exchanged among populations and contribute repeatedly to parallel evolution. Yet, surprisingly few studies provide a comprehensive view on the evolutionary history of adaptive traits from mutation to widespread adaptation. When did key mutations arise, how did they increase in frequency, and how did they spread? In this issue of Molecular Ecology, Van Belleghem et al. () reconstruct the evolutionary history of a gene associated with wing size in the salt marsh beetle Pogonus chalceus. Screening the entire distribution range of this species, they found a single origin for the allele associated with the short-winged ecotype. This allele seemingly evolved in an isolated population and rapidly introgressed into other populations. These findings suggest that the adaptive genetic variation found in sympatric short- and long-winged populations has an allopatric origin, confirming that allopatric phases may be important at early stages of speciation

Simple holographic duals to boundary CFTs

By relaxing the regularity conditions imposed in arXiv:1107.1722 on half-BPS solutions to six-dimensional Type~4b supergravity, we enlarge the space of solutions to include two new half-BPS configurations, which we refer to as the \kap\ and the \funnel. We give evidence that the \kap\ and \funnel\ can be interpreted as fully back-reacted brane solutions with respectively $AdS_2$ and $AdS_2\times S^2$ world volumes. \kap\ and \funnel\ solutions with a single asymptotic $AdS_3 \times S^3$ region are constructed analytically. We argue that \kap\ solutions provide simple examples of holographic duals to boundary CFTs in two dimensions and present calculations of their holographic boundary entropy to support the BCFT dual picture.Comment: 37 pages, pdflatex, 5 figure

Tachyon Vacuum in Cubic Superstring Field Theory

In this paper we give an exact analytic solution for tachyon condensation in the modified (picture 0) cubic superstring field theory. We prove the absence of cohomology and, crucially, reproduce the correct value for the D-brane tension. The solution is surprising for two reasons: First, the existence of a tachyon vacuum in this theory has not been definitively established in the level expansion. Second, the solution {\it vanishes} in the GSO$(-)$ sector, implying a ``tachyon vacuum'' solution exists even for a {\it BPS} D-brane.Comment: 16 pages, 2 figure

Self-duality of the D1-D5 near-horizon

We explore fermionic T-duality and self-duality in the geometry AdS3 x S3 x T4 in type IIB supergravity. We explicitly construct the Killing spinors and the fermionic T-duality isometries and show that the geometry is self-dual under a combination of two bosonic AdS3 T-dualities, four fermionic T-dualities and either two additional T-dualities along T4 or two T-dualities along S3. In addition, we show that the presence of a B-field acts as an obstacle to self-duality, a property attributable to S- duality and fermionic T-duality not commuting. Finally, we argue that fermionic T-duality may be extended to CY2 = K3, a setting where we cannot explicitly construct the Killing spinors.Comment: 24 pages, references added, changes made to reinforce the point that S-duality and fermionic T-duality generically do not commute, version accepted to JHE

String theory duals of Lifshitz-Chern-Simons gauge theories

We propose candidate gravity duals for a class of non-Abelian z=2 Lifshitz Chern-Simons (LCS) gauge theories studied by Mulligan, Kachru and Nayak. These are nonrelativistic gauge theories in 2+1 dimensions in which parity and time-reversal symmetries are explicitly broken by the presence of a Chern-Simons term. We show that these field theories can be realized as deformations of DLCQ N=4 super Yang-Mills theory. Using the holographic dictionary, we identify the bulk fields that are dual to these deformations. The geometries describing the groundstates of the non-Abelian LCS gauge theories realized here exhibit a mass gap.Comment: 25+14 pages, 3 figures; v2: significant corrections regarding IR geometry, resulting in new section 5; journal versio

Entropy Function for Non-extremal D1D5 and D2D6NS5-branes

We apply the entropy function formalism to non-extremal D1D5 and D2D6NS5-branes whose throat approximation is given by the Schwarzschild black hole in AdS_3\times S^3\times T^4 and AdS_3\times S^2\times S^1\times T^4, respectively. We find the Bekenstein-Hawking entropy and the (alpha')^3R^4 corrections from the value of the entropy function at its saddle point. While the higher derivative terms have no effect on the temperature, they decrease the value of the entropy.Comment: 17 Pages, Latex file; Minor additions, version published in JHE

Cosmology of the Tachyon in Brane Inflation

In certain implementations of the brane inflationary paradigm, the exit from inflation occurs when the branes annihilate through tachyon condensation. We investigate various cosmological effects produced by this tachyonic era. We find that only a very small region of the parameter space (corresponding to slow-roll with tiny inflaton mass) allows for the tachyon to contribute some e-folds to inflation. In addition, non-adiabatic density perturbations are generated at the end of inflation. When the brane is moving relativistically this contribution can be of the same order as fluctuations produced 55 e-folds before the end of inflation. The additional contribution is very nearly scale-invariant and enhances the tensor/scalar ratio. Additional non-gaussianities will also be generated, sharpening current constraints on DBI-type models which already predict a significantly non-gaussian signal.Comment: 30 pages, 2 figures; v3, minor revision, JCAP versio