Quantum field theory predicts a nonlinear response of the vacuum to strong electromagnetic fields of macroscopic extent. This fundamental tenet has remained experimentally challenging and is yet to be tested in the laboratory. A particularly distinct signature of the resulting optical activity of the quantum vacuum is vacuum birefringence. This offers an excellent opportunity for a precision test of nonlinear quantum electrodynamics in an uncharted parameter regime. Recently, the operation of the high-intensity Relativistic Laser at the X-ray Free Electron Laser provided by the Helmholtz International Beamline for Extreme Fields has been inaugurated at the High Energy Density scientific instrument of the European X-ray Free Electron Laser. We make the case that this worldwide unique combination of an X-ray free-electron laser and an ultra-intense near-infrared laser together with recent advances in high-precision X-ray polarimetry, refinements of prospective discovery scenarios and progress in their accurate theoretical modelling have set the stage for performing an actual discovery experiment of quantum vacuum nonlinearity.

We present radio observations of the galaxy cluster Abell S1136 at 888 MHz, using the Australian Square Kilometre Array Pathfinder radio telescope, as part of the Evolutionary Map of the Universe Early Science program. We compare these findings with data from the Murchison Widefield Array, XMM-Newton, the Wide-field Infrared Survey Explorer, the Digitised Sky Survey, and the Australia Telescope Compact Array. Our analysis shows the X-ray and radio emission in Abell S1136 are closely aligned and centered on the Brightest Cluster Galaxy, while the X-ray temperature profile shows a relaxed cluster with no evidence of a cool core. We find that the diffuse radio emission in the centre of the cluster shows more structure than seen in previous low-resolution observations of this source, which appeared formerly as an amorphous radio blob, similar in appearance to a radio halo; our observations show the diffuse emission in the Abell S1136 galaxy cluster contains three narrow filamentary structures visible at 888 MHz, between $\sim$80 and 140 kpc in length; however, the properties of the diffuse emission do not fully match that of a radio (mini-)halo or (fossil) tailed radio source.

We present kinematic, radiometric, geochemical and PT data, which help to constrain the tectonometamorphic evolution of the Tripolitza Unit (TPU). The age of both the metamorphic peak (P = 0.4 ±0.2 GPa, T = ca. 310 °C) and top-to-the WNW mylonitic thrusting, attributed to the emplacement of the hanging Pindos nappe, has been constrained at 19 ±2.5 Ma using Rb-Sr on synkinematic white mica of a basal mylonite of NW Crete. This early tectonic event is also documented by the oldest generation of veins, which cut through less metamorphic (T = 240 ±15 °C) late Bartonian/Priabonian Nummulite limestone exposed as olistolith in TPU flysch of central Crete. Calcite of these veins yielded a similar U-Pb age at 20 ±6 Ma. U-Pb dating of matrix calcite, on the other hand, reflect the time of sedimentation (38.4 ±5.7 Ma and 37.6 ±1.2 Ma), which is in line with the faunal content of the black limestone. Geochemical data and U-Pb calcite ages of fibres of the Nummulite test (32.3 ±3.1 Ma and 34.6 ±0.9 Ma) suggest unexpected pseudomorphic fibre replacement during late Priabonian/early Rupelian diagenesis. Additional calcite veins, which developed at ca. 10–11 and 7 – 9 Ma (U-Pb on calcite), are attributed to top-to-the S thrusting and subsequent extension, respectively. The resulting anticlockwise rotation of the shortening direction within the TPU from WNW-ESE at ca. 20 Ma to N-S at ca. 10 Ma has significant implications for the geodynamic evolution of the External Hellenides.