Observables in theories with a varying fine structure constant

We show how two seemingly different theories with a scalar multiplicative coupling to electrodynamics are actually two equivalent parametrisations of the same theory: despite some differences in the interpretation of some phenemenological aspects of the parametrisations, they lead to the same physical observables. This is illustrated on the interpretation of observations of the Cosmic Microwave Background.Comment: 14 pages, matched published versio

Breaking of the equivalence principle in the electromagnetic sector and its cosmological signatures

This paper proposes a systematic study of cosmological signatures of modifications of gravity via the presence of a scalar field with a multiplicative coupling to the electromagnetic Lagrangian. We show that, in this framework, variations of the fine structure constant, violations of the distance duality relation, evolution of the cosmic microwave background (CMB) temperature and CMB distortions are intimately and unequivocally linked. This enables one to put very stringent constraints on possible violations of the distance duality relation, on the evolution of the CMB temperature and on admissible CMB distortions using current constraints on the fine structure constant. Alternatively, this offers interesting possibilities to test a wide range of theories of gravity by analysing several datasets concurrently. We discuss results obtained using current data as well as some forecasts for future data sets such as those coming from EUCLID or the SKA.Comment: 14 pages, 4 figures, matched published version. Note: title changed upon suggestion of PRD editor

Big Bang nucleosynthesis in scalar tensor gravity: the key problem of the 7^7Li abundance

Combined with other CMB experiments, the WMAP survey provides an accurate estimate of the baryon density of the Universe. In the framework of the standard Big Bang Nucleosynthesis (BBN), such a baryon density leads to predictions for the primordial abundances of $^{4}$He and D in good agreement with observations. However, it also leads to a significant discrepancy between the predicted and observed primordial abundance of $^{7}$Li. Such a discrepancy is often termed as 'the lithium problem'. In this paper, we analyze this problem in the framework of scalar-tensor theories of gravity. It is shown that an expansion of the Universe slightly slower than in General Relativity before BBN, but faster during BBN, solves the lithium problem and leads to $^4$He and D primordial abundances consistent with the observational constraints. This kind of behavior is obtained in numerous scalar-tensor models, both with and without a self-interaction potential for the scalar field. In models with a self-interacting scalar field, the convergence towards General Relativity is ensured without any condition, thanks to an attraction mechanism which starts to work during the radiation-dominated epoch.Comment: Revised version. CMB and matter power spectrum constraints added. Accepted for publication in Ap

4-(Dimethyl-amino)phenyl ethynyl telluride

The title compound, C(10)H(11)NTe, is the first organyl ethynyl telluride, R-Te-C C-H, to be structurally characterized. In the L-shaped mol-ecule, the aryl moiety, viz. Me(2)NC(6)H(4)Te, is almost perpendicular to the Te-C C-H fragment. The Te-Csp(2) bond [2.115 (3) Å] is significantly longer than the Te-Csp bond [2.041 (4) Å]. The Te-C C group is approximately linear [Te-C-C = 178.5 (4)° and C C = 1.161 (5) Å], while the coordination at the Te atom is angular [C-Te-C = 95.92 (14)°]. In the crystal structure, there are Csp-H⋯N hydrogen bonds which are perpendicular to the CNMe(2) group; the N atom displays some degree of pyramidalization. Centrosymmetrically related pairs of mol-ecules are linked by Te⋯π(ar-yl) inter-actions, with Te⋯Cg = 3.683 (4) Å and Csp-Te⋯Cg = 159.1 (2)° (Cg is the centroid of the benzene ring). These inter-actions lead to the formation of zigzag ribbons which run along c and are approximately parallel to (110

Power-law cosmic expansion in f(R) gravity models

We show that within the class of f(R) gravity theories, FLRW power-law perfect fluid solutions only exist for R^n gravity. This significantly restricts the set of exact cosmological solutions which have similar properties to what is found in standard General Relativity.Comment: 4 pages, 2 figure

Dynamics of a lattice Universe : the dust approximation in cosmology

We find a solution to Einstein field equations for a regular toroidal lattice of size L with equal masses M at the centre of each cell; this solution is exact at order M/L. Such a solution is convenient to study the dynamics of an assembly of galaxy-like objects. We find that the solution is expanding (or contracting) in exactly the same way as the solution of a Friedman–Lemaître–Robertson–Walker Universe with dust having the same average density as our model. This points towards the absence of backreaction in a Universe filled with an infinite number of objects, and this validates the fluid approximation, as far as dynamics is concerned, and at the level of approximation considered in this work