Magnetic and electric properties of quantum vacuum

In this report we show that vacuum is a nonlinear optical medium and we discuss what are the optical phenomena that should exist in the framework of the standard model of particle physics. We pay special attention to the low energy limit. The predicted effects for photons of energy smaller than the electron rest mass are of such a level that none has been observed experimentally yet. Progresses in field sources and related techniques seem to indicate that in few years vacuum nonlinear optics will be accessible to human investigation.Comment: Reports on Progress in Physics (2013) in pres

Limits on Non-Linear Electrodynamics

In this paper we set a framework in which experiments whose goal is to test QED predictions can be used in a more general way to test non-linear electrodynamics (NLED) which contains low-energy QED as a special case. We review some of these experiments and we establish limits on the different free parameters by generalizing QED predictions in the framework of NLED. We finally discuss the implications of these limits on bound systems and isolated charged particles for which QED has been widely and successfully tested

Characterization of the Vacuum Birefringence Polarimeter at BMV: Dynamical Cavity Mirror Birefringence

We present the current status and outlook of the optical characterization of the polarimeter at the Bir\'{e}fringence Magn\'etique du Vide (BMV) experiment. BMV is a polarimetric search for the QED predicted anisotropy of vacuum in the presence of external electromagnetic fields. The main challenge faced in this fundamental test is the measurement of polarization ellipticity on the order of ${10^{-15}}$ induced in linearly polarized laser field per pass through a magnetic field having an amplitude and length ${B^{2}L=100\,\mathrm{T}^{2}\mathrm{m}}$. This challenge is addressed by understanding the noise sources in precision cavity-enhanced polarimetry. In this paper we discuss the first investigation of dynamical birefringence in the signal-enhancing cavity as a result of cavity mirror motion.Comment: To appear in the 2019 CPEM special issue of IEEE Transactions on Instrumentation and Measuremen

Les oasis du Jérid, des ressources naturelles et idéelles

http://vbat.orgIn the Jerid of palm grove, there is a feeling of crisis about the land and hydraulic resources, and a first identification shows the problem of availability and especially management of resources. But each actor (gardeners, State) sees his own field of competence limited, and waits for the other actor the movement needed for a better management of resources.The use of resources is in correlation with the perception of environment. I have identified three ‘ideal-types' (paradigms) of the relation to the environment, and they condition the way to deal with the natural world. The actors of the oasian stage are differentiated by their relationship, more or less tight, with those ideal-types. So, we have to take into consideration the kind of actor, his own concepts to imagine his resources management.But this is still too simple: the oasian actors negotiate permanently their relationship with the three ideal-types. The main proposal of this paper is to include in the notion of resource this resource, no more material or natural but also conceptual. The way to deal with environment is itself a resource. It is organically linked with the natural resources.For the Development, this proposal can represent a new perspective of work, a synthetic approach which connects the systems of representation of the world, the manners of management of resources, the use of different scale of space and time and dynamic categories of agent of evolution of ecosystems.Au Jérid des palmeraies, on identifie un sentiment de crise dans les ressources foncières et aquifères, qui tient à la disponibilité et surtout à la gestion des ressources. Mais, des divers acteurs (jardiniers et État), chacun voit midi à sa porte : si sa propre gestion est critiquable, c'est l'autre qui peut évoluer et non soi.L'usage de ressources tient de la perception de l'environnement. J'ai identifié trois idéaux-types de la relation au milieu qui conditionnent trois manières de traiter avec le monde naturel. Les acteurs de la scène oasienne se différencient par leurs rapports plus ou moins étroits avec ces trois idéaux-types. Cela demande donc de prendre en considération le type d'acteurs, ces représentations propres, pour imaginer sa gestion des ressources. Mais cela est encore trop simple : ces agents oasiens ne se laissent pas, hors de la réalité intellectuelle, enfermer dans des caricatures rigides. Ils négocient en permanence leurs rapports avec ces trois pôles idéaux-typiques. Aussi, la proposition principale ici est d'inclure dans la notion de ressource cette ressource qui n'est plus matérielle et naturelle mais aussi idéelle. C'est-à-dire qu'une manière de traiter avec le monde, y compris les modes de gestion des ressources, est elle-même une ressource. Un ensemble de représentations, une manière de prendre en compte la productivité ou la sauvegarde et la préservation doit être considéré comme une ressource organiquement liée aux naturelles et matérielles.Pour le développement, cela représente une nouvelle perspective de travail, perspective synthétique qui fait le lien entre des systèmes de représentation du monde, des modes de gestion des ressources, des usages d'échelles d'espaces et de temps différenciés et des catégories dynamiques d'agents d'évolution d'écosystèmes

Noise characterization for resonantly-enhanced polarimetric vacuum magnetic-birefringence experiments

In this work we present data characterizing the sensitivity of the Bir\'{e}fringence Magnetique du Vide (BMV) instrument. BMV is an experiment attempting to measure vacuum magnetic birefringence (VMB) via the measurement of an ellipticity induced in a linearly polarized laser field propagating through a birefringent region of vacuum in the presence of an external magnetic field. Correlated measurements of laser noise alongside the measurement in the main detection channel allow us to separate measured sensing noise from the inherent birefringence noise of the apparatus. To this end we model different sources of sensing noise for cavity-enhanced polarimetry experiments, such as BMV. Our goal is to determine the main sources of noise, clarifying the limiting factors of such an apparatus. We find our noise models are compatible with the measured sensitivity of BMV. In this context we compare the phase sensitivity of separate-arm interferometers to that of a polarimetry apparatus for the discussion of current and future VMB measurements

Optical spectroscopy of a microsized Rb vapour sample in magnetic fields up to 58 tesla

We use a magnetometer probe based on the Zeeman shift of the rubidium resonant optical transition to explore the atomic magnetic response for a wide range of field values. We record optical spectra for fields from few tesla up to 60 tesla, the limit of the coil producing the magnetic field. The atomic absorption is detected by the fluorescence emissions from a very small region with a submillimiter size. We investigate a wide range of magnetic interactions from the hyperfine Paschen-Back regime to the fine one, and the transitions between them. The magnetic field measurement is based on the rubidium absorption itself. The rubidium spectroscopic constants were previously measured with high precision, except the excited state Land\'e $g$-factor that we derive from the position of the absorption lines in the transition to the fine Paschen-Back regime. Our spectroscopic investigation, even if limited by the Doppler broadening of the absorption lines, measures the field with a 20 ppm uncertainty at the explored high magnetic fields. Its accuracy is limited to 75 ppm by the excited state Land\'e $g$-factor determination

Les relations au désert des religions monothéistes

Article non publié, refusé par Archives de Sciences Sociales des Religions en 1994 Il s'agit d'une version modifiée de mon mémoire secondaire de DEA (1993), mémoire qui portait le même titre, sous la dir. du Pr. Philippe Laburthe-Tolra, Paris 5 - mention très bien. Cela dit, je ne revendique plus ces pages : je les ai certes écrites, mais si je devais les relire je sais que je ne serai plus d'accord avec moi-même.Note: je ne suis pas sûr de vouloir revendiquer (au jour du dépôt) ce travail « de jeunesse ». Parce que l'on me le demande, et pas transparence, je le dépose néanmoins en Archives ouvertes. Résumé: Cette étude propose d'explorer différents points de conjonction entre le désert et les religions monothéistes. Les textes fondant ces religions (Thora - Évangiles - Coran) fourniront un matériel de choix, mais aborder la réaction de l'homme face au désert aidera sans doute aussi à comprendre la place qu'occupe ce milieu minéral dans le contenu religieux. L'examen peut être poussé plus loin : l'existence même de ces religions monothéistes n'est- elle pas due à la fréquentation des milieux désertiques ? Quoiqu'il en soit, des traces de sables se relèvent tout au long de leur histoire, qu'il s'agisse de retours réels au désert ou de l'utilisation du symbole à des fins mystiques

Les relations équivoques et les oasis

Résumé de la thèse de doctorat.http://vbat.orgInternational audienceCet article est lui-même un résumé du travail de thèse : Les relations équivoques, Approches circonspectes pour une socio-écologie des oasis sahariennes, th. Anthropologie sociale, Uni. René Descartes-Sorbonne Paris V - MNHN, sept. 1998, bibl., 47 fig., 10 photog., 14 tab. + annexes, 357 p

La conception du travail et appréciation du paysage dans l'oasis saharienne

Cette conférence date un peu... mais apporte quelques petites idées.National audienceThe same environment, a landscape, the oasis, can concretely not be seen, understood or perceived in a similar way by different people. It is as if this system-object could display various faces or more convincingly as people can find various faces depending on his backgrounds, concerns, interests. This 'faces' are so different that they come to be nearly opposite. It is disturbing almost because I attribute to these 'lookers' ('regardeurs', in the meaning of M. Duchamp) the status of social agent of the palm-grove and the oasis world, i.e. taking obviously part, actively or passively, to the evolution of this environment.Un même milieu, un paysage, l'oasis en l'occurrence, peut concrètement ne pas être vu, perçu, de manière identique par diverses personnes. Comme si cet objet-système montrait des visages différents ou plutôt comme si selon ses origines, ses préoccupations, ses intérêts on lui trouvait des essences différentes. A ce point différentes dans le cas présent, qu'elles en deviennent opposées ce qui est troublant quand j'attribue à ces " regardeurs " (au sens de M. Duchamp) le statut d'acteur social du monde oasien c'est-à-dire prenant une part importante, passive ou active, dans l'évolution de ce milieu

Resources and Appropriations: Back to the Jerid Oases (Tunisia) after the Revolution

(Late) English version of a French paper: "Des ressources et des appropriations. Retour, après la révolution, dans les oasis du Jérid (Tunisie)" (2013)http://hal.archives-ouvertes.fr/hal-00832566International audienceIn the Jerid region of southwestern Tunisia, the dynamics governing the appropriation of resources vary depending on the type of resource. While it has yet to gain control of genes, the state has appropriated and secured control of key natural resources such as water and land. In the Jerid region, agriculture is concentrated in oasis areas (palm groves) forming unique ecosystems. Based on a field study conducted since the 2011 revolution in an area already examined prior to the revolution, this paper highlights the current dynamics at work in the region and provides a basis for rethinking the concept of “appropriation.” It is important to emphasize that appropriation is not simply a matter of appropriating material resources but that it also concerns the appropriation of uses, practices, and ways of relating to the world. This paper suggests that skills or competences such as these are more likely to be found among local farmers than among agricultural policy makers and bureaucrats, i.e., the official bearers of agronomic knowledge, power, and legitimacy