: Construction of the first stage of the Pierre Auger Observatory has begun. The aim of the Observatory is to collect unprecedented information about cosmic rays above 10(18) eV. The first phase of the project, the construction and operation of a prototype system, known as the engineering array, has now been completed. It has allowed all of the sub-systems that will be used in the full instrument to be tested under field conditions. In this paper, the properties and performance of these sub-systems are described and their success illustrated with descriptions of some of the events recorded thus far. (C) 2003 Elsevier B.V

We present in detail the scientific objectives in fundamental physics of the Space-Time Explorer and QUantum Equivalence Space Test (STE-QUEST) space mission. STE-QUEST was pre-selected by the European Space Agency together with four other missions for the cosmic vision M3 launch opportunity planned around 2024. It carries out tests of different aspects of the Einstein Equivalence Principle using atomic clocks, matter wave interferometry and long distance time/frequency links, providing fascinating science at the interface between quantum mechanics and gravitation that cannot be achieved, at that level of precision, in ground experiments. We especially emphasize the specific strong interest of performing equivalence principle tests in the quantum regime, i.e. using quantum atomic wave interferometry. Although STE-QUEST was finally not selected in early 2014 because of budgetary and technological reasons, its science case was very highly rated. Our aim is to expose that science to a large audience in order to allow future projects and proposals to take advantage of the STE-QUEST experience.

Presents a brief review of the theory and applications of Regge calculus in classical and quantum gravity, followed by a comprehensive bibliography which the author hopes will be of use to workers in the subject.

The role of Regge calculus as a tool for numerical relativity is discussed, and a parallelizable implicit evolution scheme described. Because of the structure of the Regge equations, it is possible to advance the vertices of a triangulated spacelike hypersurface in isolation, solving at each vertex a purely local system of implicit equations for the new edge-lengths involved. (In particular, equations of global "elliptic-type" do not arise.) Consequently, there exists a parallel evolution scheme which divides the vertices into families of non-adjacent elements and advances all the vertices of a family simultaneously. The relation between the structure of the equations of motion and the Bianchi identities is also considered. The method is illustrated by a preliminary application to a 600-cell Friedmann cosmology. The parallelizable evolution algorithm described in this paper should enable Regge calculus to be a viable discretization technique in numerical relativity. Much current activity in numerical relativity is centered around making predictions which can be tested by the proposed Laser Interferometry Gravitational Observatory (LIGO).1,2 There is a need to solve Einstein's equations numerically for many physical situations which could give rise to gravitational waves, so that data from LIGO can be interpreted, and used, if appropriate, as evidence for the existence of black holes. More generally, numerical solutions of Einstein's equations are invaluable for the understanding of astrophysical data, and for guidance as to what experiments to undertake.Methods of solving Einstein's equations numerically include finite difference schemes and finite element schemes. Regge calculus is a type of finite element method, and in this paper we shall describe a way of casting it into the form of a highly efficient tool of numerical relativity.The basic idea of Regge calculus is the division of spacetime into simplicial cells with flat interior geometry.3 The dynamical variables are the edge-lengths of the simplices, and the curvature, which is restricted to the "hinge simplices" of codimension two, can be expressed in terms of the defect angles at these hinges, where the flat cells meet. Variation of the action leads to the simplicial form of Einstein's equations. The convergence of the Regge action and equations to the corresponding continuum quantities has been investigated thoroughly and has been shown to be satisfactory under quite general conditions. [4][5][6][7][8][9]22,30 Regge calculus has been applied to a large variety of problems in classical and quantum gravity (see Ref. 10 for a review). Numerical applications in 3+1 dimensions have been mainly to problems with symmetry and no general code has been developed. [11][12][13][14][15]37 This is also the case in the alternative approach known as null-strut calculus, which builds a spacelike-foliated spacetime with the maximal number of null edges.16−20 Although null-strut calculus was used first to demonstrate numerically the approximate diffeomorphism fr...

We search for transient variations of the fine structure constant using data from a European network of fiber-linked optical atomic clocks. By searching for coherent variations in the recorded clock frequency comparisons across the network, we significantly improve the constraints on transient variations of the fine structure constant. For example, we constrain the variation to |δα/α| < 5 × 10−17 for transients of duration 103 s. This analysis also presents a possibility to search for dark matter, the mysterious substance hypothesised to explain galaxy dynamics and other astrophysical phenomena that is thought to dominate the matter density of the universe. At the current sensitivity level, we find no evidence for dark matter in the form of topological defects (or, more generally, any macroscopic objects), and we thus place constraints on certain potential couplings between the dark matter and standard model particles, substantially improving upon the existing constraints, particularly for large (≳104 km) objects.