R. Schäffer

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In this paper we set up a general formalism to deal with quantum theories on a Lobatchevski space, i.e. a spatial manifold that is homogeneous, isotropic and has negative curvature. The heart of our approach is the construction of a suitable basis of plane waves which are eigenfunctions of the Laplace-Beltrami operator relative to the geometry of the curved(More)
We examine the most recent observational constraints arising from i) small-scale and large-scale Galactic dy-namical properties, ii) star counts of population I and II stars at faint magnitude and iii) microlensing experiments towards the Large Magellanic Cloud and the Galactic centre. From these constraints, we determine the halo and disk stellar mass(More)
A series of studies using a Go versus No-go task examined the question of whether preliminary information available early in the recognition of a stimulus is made available to later processes before stimulus recognition is finished, a question relevant to the controversy between discrete and continuous models. Experiment 1 showed that a Go response is(More)
Experiment 1 utilized a choice reaction time paradigm to examine whether advance information about the second component of a movement has similar effects upon movement initiation and execution as advance information about the first component. Four stimuli were assigned to four goal keys. Subjects responded with the index finger of their preferred hand. They(More)
Several variants of a precued reaction time experiment were performed to assess preparation for Choice (Donders' type B) or Go/No-Go (type C) reaction tasks. On each trial, the imperative stimulus could necessitate either a keypress with the left forefinger, the right forefinger, or no response. A precue given at lead times of 50-750 ms either informed the(More)
We provide a method to decompose the two-point function of a quantum field on a warped manifold in terms of fields living on a lower-dimensional manifold. We discuss explicit applications to Minkowski, de Sitter and anti-de Sitter quantum field theories. This decomposition presents a remarkable analogy with the holography principle, in the sense that(More)
We provide a new general setting for scalar interacting fields on the covering of a d + 1– dimensional AdS spacetime. The formalism is used at first to construct a one-parameter family of field theories, each living on a corresponding spacetime submanifold of AdS, which is a cylinder R×S d−1. We then introduce a limiting procedure which directly produces(More)
In this letter we show that the " preferred " Klein–Gordon Quantum Field Theories (QFT's) on a d-dimensional de Sitter spacetime can be obtained from a Klein– Gordon QFT on a (d + 1)-dimensional " ambient " Minkowski spacetime satisfying the spectral condition and, conversely, that a Klein–Gordon QFT on a (d + 1)-dimensional " ambient " Minkowski spacetime(More)
We use the calculations derived in a previous paper (Méra, Chabrier and Schaeffer, 1997), based on observational constraints arising from star counts, microlensing experiments and kinematic properties, to determine the amount of dark matter under the form of stellar and sub-stellar objects in the different parts of the Galaxy. This yields the derivation of(More)
We investigate the variation of galaxy clustering with luminosity using the recently completed SSRS2 sample. Clustering measurements based on the two-point correlation function and the variance of counts in cells reveal a strong dependence of clustering on luminosity for galaxies brighter than L * , while no significant variation is detected for fainter(More)