Imprint of DESI fiber assignment on the anisotropic power spectrum of emission line galaxies

The Dark Energy Spectroscopic Instrument (DESI), a multiplexed fiber-fed spectrograph, is a Stage-IV ground-based dark energy experiment aiming to measure redshifts for 29 million Emission-Line Galaxies (ELG), 4 million Luminous Red Galaxies (LRG), and 2 million Quasi-Stellar Objects (QSO). The survey design includes a pattern of tiling on the sky and the locations of the fiber positioners in the focal plane of the telescope, with the observation strategy determined by a fiber assignment algorithm that optimizes the allocation of fibers to targets. This strategy allows a given region to be covered on average five times for a five-year survey, but with coverage varying between zero and twelve, which imprints a spatially-dependent pattern on the galaxy clustering. We investigate the systematic effects of the fiber assignment coverage on the anisotropic galaxy clustering of ELGs and show that, in the absence of any corrections, it leads to discrepancies of order ten percent on large scales for the power spectrum multipoles. We introduce a method where objects in a random catalog are assigned a coverage, and the mean density is separately computed for each coverage factor. We show that this method reduces, but does not eliminate the effect. We next investigate the angular dependence of the contaminated signal, arguing that it is mostly localized to purely transverse modes. We demonstrate that the cleanest way to remove the contaminating signal is to perform an analysis of the anisotropic power spectrum $P(k,\mu)$ and remove the lowest $\mu$ bin, leaving $\mu>0$ modes accurate at the few-percent level. Here, $\mu$ is the cosine of the angle between the line-of-sight and the direction of $\vec{k}$. We also investigate two alternative definitions of the random catalog and show they are comparable but less effective than the coverage randoms method.Comment: Submitted to JCA

Stability in a population model without random deaths by the Verhulst factor

A large amount of population models use the concept of a carrying capacity. Simulated populations are bounded by invoking finite resources through a survival probability, commonly referred to as the Verhulst factor. The fact, however, that resources are not easily accounted for in actual biological systems makes the carrying capacity parameter ill-defined. Henceforth, we deem it essential to consider cases for which the parameter is unnecessary. This work demonstrates the possibility of Verhulst-free steady states using the Penna aging model, with one semelparous birth per adult. Stable populations are obtained by setting a mutation threshold that is higher than the reproduction age

Naissances de pensée

International audienceOffrant aux cliniciens et chercheurs français de nouveaux moyens de travail grâce à la traduction de l'Introduction aux idées psychanalytiques de Bion, Didier Anzieu (1976, XII) rappelait que, « s'il y a pour Bion un impensant, il n'y a pas d'impensable ». Et il regroupait,- sous la notion de « pensée primaire », tout à la fois la première « activité de penser », celle qui « à l'origine se confond avec un processus destiné à décharger le psychisme de l'excès de stimuli » et les pensées, qui ne sont alors « rien de plus que des impressions sensorielles et des vivances émotionnelles très primitives » (Grinberg et al., 1972, 51). Cette « pensée-acte », « je suis tenté, écrivait Anzieu, de l'appe- ler l'impensante : la pensée-mort psychique » (XI). Voilà pour « l'impensant » : celui qui ne peut être transformé chez le nourrisson que grâce à la « capacité de rêverie » de la mère (au sens de « capacité d'imagination non appuyée sur le raisonnement », Grinberg et al., 1972, 54), et celui qui est offert au travail psychanalytique, lorsque celui-ci se développe dans l'interaction avec des patients psycho- tiques ou souffrant de failles narcissiques : travail psychique « à la frontière de l'impensant et du premier pensant symbolisable » (XIII). La naissance de la pensée trouve alors son origine dans un travail effectué, selon Anzieu, « à la place du patient » (ou du bébé), puisque l'un et l'autre sont « hors d'état d'y pourvoir » (XIII). Remarque qui insiste sur la nécessité de l'engagement d'un appareil psychique extérieur à celui qui ne peut naître à la pensée sans l'aide d'un autre psychisme (Meltzer, 1984)

The effective field theory of multi-field inflationary fluctuations

We build an effective field theory of multi-field inflationary fluctuations based on the adiabatic perturbation and on any number of matter fluctuations in the non-adiabatic sector, without imposing extra symmetries on the latter. Focusing on terms with at most two derivatives in fields' fluctuations, we argue that taking the decoupling limit -- in which gravitational interactions are neglected -- is justified in a quasi de Sitter spacetime with slow-varying Hubble scale. With these working hypotheses, we find simple forms of multi-field mixings (quadratic order) and interactions (cubic order). We explain how to break degeneracies amongst various terms, and we compare the predictions of the effective field theory to those of non-linear sigma models of inflation and more general multi-field Lagrangian in the traditional model approach. We stress that several multi-field cubic interactions are dictated by non-linearly realised spacetime symmetries and are therefore given in terms of parameters already present in the quadratic action. We propose various directions to systematically explore the phenomenology generic to multi-field inflation and beyond the lamppost of known models.Comment: 6 pages + appendices, no figur