Anti-de Sitter branes with Neveu-Schwarz and Ramond-Ramond backgrounds

We review some facts about AdS2xS2 branes in AdS3xS3 with a Neveu-Schwarz background, and consider the case of Ramond-Ramond backgrounds. We compute the spectrum of quadratic fluctuations in the low-energy approximation and discuss the open-string geometry.Comment: 8 pages, uses JHEP3.cl

D-branes and orientifolds of SO(3)

We study branes and orientifolds on the group manifold of SO(3). We consider particularly the case of the equatorial branes, which are projective planes. We show that a Dirac-Born-Infeld action can be defined on them, although they are not orientable. We find that there are two orientifold projections with the same spacetime action, which differ by their action on equatorial branes.Comment: 11 pages, no figure, uses JHEP3.cls. V2 : minor correction

Seeking cyclonic activity records in speleothems from central Pacific: preliminary sample screening

PosterInternational audienceIdeal cyclone-sensitive speleothems would have the following properties: active at the time of sampling and recording the past few millenia, with fast growth rate, made of clean primary calcite, precipitated without kinetic fractionation, and fed by water with a short residence time allowing for the isotopic signal of short events like cyclones to be transferred but long enough for the drip water to be supersaturated. The screening for this type of speleothem is still in progress and the results presented here are very preliminary. U-Th dating: low U concentration (9-40ng/g; host rock is reef limestone) ; significant detrital content, involving large corrections and large final age uncertainties. Growth rate is highly variable, from ~0.12 mm/yr to ~0.03mm/yr. Tau12A: δ 18 O profile shows some quite large variations (~3‰), with several abrupt events that we will try to identify in other archives. δ 13 C signal amplitude is very large (~-4 to ~-14‰) suggesting the effect of prior calcite precipitation. The δ 18 O signal gets heavier when the δ 13 C does, which could reflect the rainfall amount in this context. Var12C: δ 18 O profile shows values between-3.1 and-6.3‰, with decadal or centennial fluctuations, superimposed on a general trend which is consistent with the one of the δ 13 C profile without being correlated, which implies that calcite precipitation could occur in conditions close to isotopic equilibrium. Once properly dated, this record should provide interesting information about past rainfall regimes on the island

Speleothem growth intervals reflect New Zealand montane vegetation response to temperature change over the last glacial cycle

Flowstone speleothem growth beneath Mount Arthur, New Zealand shows a clear relationship to vegetation density and soil development on the surface above. Flowstone does not currently form beneath sub-alpine Nothofagus forest above ca. 1000–1100 m altitude but U-Th dating shows it has formed there during past intervals of warmer-than-present conditions including an early–mid Holocene optimum and the last interglacial from ca. 131–119 ka. Some flowstones growing beneath ca. 600 m surface altitude, currently mantled with dense broadleaf-podocarp forest, grew during full glacial conditions, indicating that local tree line was never below this altitude. This implies that Last Glacial Maximum annual temperature was no more than ca. 4 °C cooler than today. Flowstone growth appears to be a robust indicator of dense surface vegetation and well-developed soil cover in this setting, and indicates that past interglacial climates of MIS 7e, 5e, the early–mid Holocene and possibly MIS 5a were more conducive to growth of trees than was the late Holocene, reflecting regional temperature changes similar in timing to Antarctic temperature changes. Here, flowstone speleothem growth is a sensitive indicator of vegetation density at high altitude, but may respond to other factors at lower altitudes

Probing Orientifold Behavior Near NS Branes

The effect of NS 5 branes on an orientifold is studied. The orientifold is allowed to pass through a pile of k NS branes forming a regularized CHS geometry. Its effect on open strings in its vicinity is used to study the change in the orientifold charge induced by the NS branes.Comment: Important references added, 30 pages, 8 figure

Crosscap States for Orientifolds of Euclidean AdS_3

Crosscap states for orientifolds of Euclidean AdS_3 are constructed. We show that our crosscap states describe the same orientifolds which were obtained by the classical analysis. The spectral density of open strings in the system with orientifold can be read from the M"obius strip amplitudes and it is compared to that of the open strings stretched between branes and their mirrors. We also compute the Klein bottle amplitudes.Comment: 17 pages, LaTeX2e, v2: clarification and discussion added, v3: minor changes, to appear in JHE

Synchronous timing of abrupt climate changes during the last glacial period.

Abrupt climate changes during the last glacial period have been detected in a global array of palaeoclimate records, but our understanding of their absolute timing and regional synchrony is incomplete. Our compilation of 63 published, independently dated speleothem records shows that abrupt warmings in Greenland were associated with synchronous climate changes across the Asian Monsoon, South American Monsoon, and European-Mediterranean regions that occurred within decades. Together with the demonstration of bipolar synchrony in atmospheric response, this provides independent evidence of synchronous high-latitude-to-tropical coupling of climate changes during these abrupt warmings. Our results provide a globally coherent framework with which to validate model simulations of abrupt climate change and to constrain ice-core chronologies

Supersymmetric D-branes in the D1-D5 background

We construct supersymmetric D-brane probe solutions in the background of the 2-charge D1-D5 system on M, where M is either K3 or T^4. We focus on `near-horizon bound states' that preserve supersymmetries of the near-horizon AdS_3 x S^3 x M geometry and are static with respect to the global time coordinate. We find a variety of half-BPS solutions that span an AdS_2 subspace in AdS_3, carry worldvolume flux and can wrap an S^2 within S^3 and/or supersymmetric cycles in M.Comment: Latex, 24 pages. v2: references added, modified Discussion, published versio

Synchronous timing of abrupt climate changes during the last glacial period

Many geographically dispersed records from across the globe reveal the occurrence of abrupt climate changes, called interstadial events, during the last glacial period. These events appear to have happened at the same time, but the difficulty of determining absolute dates in many of the records have made that proposition difficult to prove. Corrick et al. present results from 63 precisely dated speleothems that confirm the synchrony of those interstadial events. Their results also provide a tool with which to validate model simulations of abrupt climate change and calibrate other time series such as ice-core chronologies.Science, this issue p. 963Abrupt climate changes during the last glacial period have been detected in a global array of palaeoclimate records, but our understanding of their absolute timing and regional synchrony is incomplete. Our compilation of 63 published, independently dated speleothem records shows that abrupt warmings in Greenland were associated with synchronous climate changes across the Asian Monsoon, South American Monsoon, and European-Mediterranean regions that occurred within decades. Together with the demonstration of bipolar synchrony in atmospheric response, this provides independent evidence of synchronous high-latitude–to-tropical coupling of climate changes during these abrupt warmings. Our results provide a globally coherent framework with which to validate model simulations of abrupt climate change and to constrain ice-core chronologies