Test of the gravitational redshift with stable clocks in eccentric orbits: application to Galileo satellites 5 and 6

The Einstein Equivalence Principle (EEP) is one of the foundations of the theory of General Relativity and several alternative theories of gravitation predict violations of the EEP. Experimental constraints on this fundamental principle of nature are therefore of paramount importance. The EEP can be split in three sub-principles: the Universality of Free Fall (UFF), the Local Lorentz Invariance (LLI) and the Local Position Invariance (LPI). In this paper we propose to use stable clocks in eccentric orbits to perform a test of the gravitational redshift, a consequence of the LPI. The best test to date was performed with the Gravity Probe A (GP-A) experiment in 1976 with an uncertainty of $1.4\times10^{-4}$. Our proposal considers the opportunity of using Galileo satellites 5 and 6 to improve on the GP-A test uncertainty. We show that considering realistic noise and systematic effects, and thanks to a highly eccentric orbit, it is possible to improve on the GP-A limit to an uncertainty around $(3-4)\times 10^{-5}$ after one year of integration of Galileo 5 and 6 data.Comment: 13 pages, 5 figures, accepted in Classical and Quantum Gravity as a Fast Track Communicatio

Violation of the equivalence principle from light scalar fields: from Dark Matter candidates to scalarized black holes

Tensor-scalar theory is a wide class of alternative theory of gravitation that can be motivated by higher dimensional theories, by models of dark matter or dark ernergy. In the general case, the scalar field will couple non-universally to matter producing a violation of the equivalence principle. In this communication, we review a microscopic model of scalar/matter coupling and its observable consequences in terms of universality of free fall, of frequencies comparison and of redshifts tests. We then focus on two models: (i) a model of ultralight scalar dark matter and (ii) a model of scalarized black hole in our Galactic Center. For both these models, we present constraints using recent measurements: atomic clocks comparisons, universality of free fall measurements, measurement of the relativistic redshift with the short period star S0-2 orbiting the supermassive black hole in our Galactic Center.Comment: 8 pages, 1 figure, contribution to the 2019 Gravitation session of the 54th Rencontres de Morion

The vulnerability of the European agriculture and food system for calamities and geopolitics : a stress test

During the 1960s and 1970s, the EU succeeded in becoming largely self-sufficient in food production, thus assuring its food security for the most part. However, it is unclear which areas of food security are still vulnerable and/or whether there are there new vulnerabilities. In this report we have focused on emergencies and geopolitical shocks that can have a major impact on food security, i.e. food volume. We have not included emergencies that affect food safety (such as a nuclear disaster) or emergencies that have a much broader effect than on food chains alone (such as a flu pandemic or power failure)

Renormalization in Self-Consistent Approximation schemes at Finite Temperature III: Global Symmetries

We investigate the symmetry properties for Baym's $\Phi$-derivable schemes. We show that in general the solutions of the dynamical equations of motion, derived from approximations of the $\Phi$-functional, do not fulfill the Ward-Takahashi identities of the symmetry of the underlying classical action, although the conservation laws for the expectation values of the corresponding Noether currents are fulfilled exactly for the approximation. Further we prove that one can define an effective action functional in terms of the self-consistent propagators which is invariant under the operation of the same symmetry group representation as the classical action. The requirements for this theorem to hold true are the same as for perturbative approximations: The symmetry has to be realized linearly on the fields and it must be free of anomalies, i.e., there should exist a symmetry conserving regularization scheme. In addition, if the theory is renormalizable in Dyson's narrow sense, it can be renormalized with counter terms which do not violate the symmetry.Comment: 32 papges, 3 figures, uses ReVTeX 4, V2: Added one more reference, V3: Corrected some typos, added two more sections about the large-N expansio

Trekkers naast de trap : een zoektocht naar de dynamiek in de relatie tussen boer en overheid

This book describes a sociological expedition to the core of the relationship between farmers and government in the Netherlands. It focuses on the concept of mediation of agricultural policies between government and the farming target group. A starting point in this expedition is the rejection of the idea of policy-formation as a rational-synoptical chronology, in which policy is the result of a well-defined rational choice by politicians and administrators from different scenario's. Instead, policy formation in this context is understood as an incremental process: policies as a result of interaction between context induced actors. However, instead of being coincidental the interactions show up patterns of regularity that formed the motivation for this study.Policy mediation is defined as:the interrelated moments of preparation, formation, implementation and evaluation of policies,which by means of interactive processes, in which various actors (public servants, politicians, citizens, farmers, etc.) participate with their groups and projects (strategically),are geared to one another in such a manner, thatexactly therefore a legitimacy is obtained which otherwise would definitely be absent.The target group of agricultural policies is a so-called difuse one. That is, in need of intermediary structures able to mediate policies. The Dutch Agricultural Board (Landbouwschap) played this intermediary structure role between 1954 en 1996, when it promptly disappeared.In the meantime, several farmers' cooperative initiatives in one way or another have assumed the role of intermediary organizations. Central government tended to standardize their attitude towards these structures, in order to manage the policy mediation fluently. The objective of this investigation, however, is to analize and maintain the diversity of intermediary organizations. The reason is the assumption that succesful policy mediation depends on the taking account of the specifity of each structure.The central questions therefore are:in which different arrangements has the mediation of agricultural policies taken place so far,by which means could be obtained more success in terms of dynamic and legitimated policy mediation.Chapter 2 provides a theoretical approach of the relation between farmer and government, defining it as a particularisation of the relation between actor and structure. Instead of adhering to dualistic theories, which focus upon the complete determination of the individual by its surrounding structure (determinism) or upon the complete absence of such a determination (voluntarism), this study prefers duality as a key concept. Duality focuses upon the co-existence of contraint and enableness of the individual versus itssurrounding structure. Individuals actively make and remake social structure.The relation between citizen and government is subject of a process of legitimation. Public administration and policies are legitimized by:the procedure, with given objectives (the instrumental side of legitimation);the objectives of policies (the social contract side); andthe interchange of both.The chapter ends up presenting a social scientific tool to capture this legitimation process: policy-mediation.In chapter 3 policy mediation is surveyed in the Dutch socio-cultural heritage. In the Netherlands a strong tradition of subsidiarity and functional decentralization was founded in past centuries. The social charter of neo-corporatism is known because of its emphasis on consensus, compromise and consultation.Growing claims, policy overload, role distortions between public and private parties and he public opinion have shocked the traditional charter and caused a legitimation problem. Different answers are possible, varying from enforcening the state to enforcening the consensus model. In this report, there is a strong case for investing more in interdependency and participative democracy. The Dutch case shows different examples: coproduction of local policies, convenants between public governement and private parties, the socalled Green Polder Model. Although there is room for doubt because of (a) gaps between frontiers ans crowds, (b) interaction used only for self-interest. That is the risks of pseudo-participation. Therefore, field investigations are urgently needed.In chapter 4 an overview is given of the legitimation of agricultural policies in the Netherlands since the 19th century. The co-production tradition of farmers' organizations and central government, founded on a consensus about (a) the type of agricultural development to be nagestreefd, and (b) the need of consultation and compromise, ended up in a policy-community or - more precisely - iron triangle between farmers-leaders, ministry of agriculture and national politicians. From the late 60's, tensions grew between these parties and the iron triangle eroded. A vacuum in policy mediation became clear. Farmers reacted by protest, adaptation, individual initiatives and creating new collectivities, that became seeds of new arrangements. The following chapters describe the investigation of these new arrangements.Chapter 5 is a methodological intermezzo. It motivates why the sociological expedition is founded in daily reality, by describing caracteristics of factual initiatives as many and as detailed as necessary to get a sharp distinction between policy arrangements.In chapter 6 and 7 an inventory is made of the variation of possible arrangements, making use of 14 real collectivities in the Dutch countryside between 1980 and 1997. By adopting a cluster analysis 6 different arrangements are identified: product cooperative, horzelorganisation, farmers' association, policy cooperative, investigation cooperative and sindical organisation.Describing various cases in the Netherlands, in chapter 8 each arrangement is examined on its potential in terms of producing more dynamics in policy mediation. Chapter 9 also examines this potential, but now by evaluating an official policy experiment with 8 socalled environmental cooperatives (milieucoöperaties) from 1995 to 1999.In chapter 10, the conclusions of the expedition are summarized. The experiences of farmers' collectivities up to 1997 make clear that the state and its institutions (first of all the ministry of agriculture) are rather confused when defining an attitude against the calls for self-regulation that come from below. The state seems to get paralyzed by pleas for self-regulation on one side and the necessity to maintain principles of Good Governance on the other, one of which is gelijkberechtiging. Tailor-made policy solutions may come in conflict with the tendency to govern unilaterally from a cockpit.By way of recommendations, several triggers are derived from the expedition process, triggers that may give impetus to a more dynamic and prosperous relation between government and farmers. First of all, the actual situation should be understood better and more systematically by all of the parties involved. Potentials for succesful policy-mediation often aren't recognized as such.Next, cooperative initiatives shouldn't be put in one category too soon. Regionality, local culture and specifity are important factors for succes in policy-mediation along more selfregulation. The recognition and admission of the role local initiatives can play in succesful policy-arrangements should result in more incentives instead of penalties. State institutions should provoke and belonen a more entrepreneurial attitude of farmers. Another factor that may trigger a more dynamic relationship is the maintenance of the face-to-face caracter of policy-mediation. The personal committment of the parties involved, crucial within the agricultural population with so many individual interests and responsabilities, depends on the involvement of face-to-face contacts. This means more emphasis should be laid on local government instead of national.</p

Quantum state of a free spin-1/2 particle and the inextricable dependence of spin and momentum under Lorentz transformations

We revise the Dirac equation for a free particle and investigate Lorentz transformations on spinors. We study how the spin quantization axis changes under Lorentz transformations, and evince the interplay between spin and momentum in this context.Comment: 14 pages, 3 figures, published as a Review in the IJQ

Probing collectivity in ultra-relativistic heavy ion collision by leptons and photons

It has been shown that the evolution of collectivity in ultra-relativistic heavy ion collision is manifested in the variation of various HBT radii with invariant mass ($M$) extracted from the correlation functions of two lepton pairs. The value of the radial velocity ($v_r$) can be estimated from the ratio of the $p_T$ distributions of single photons to lepton pairs for various $M$ windows. It has been argued that the variation of radial flow with appropriate kinematic variables can be used as an indicator of a phase transition from initially produced partons to hadrons. We also consider the elliptic flow ($v_2^{HF}$) of the matter as probed by the single electron spectra originating from the semileptonic decays of heavy mesons. The measured values of $v_2^{HF}$ and the nuclear suppression factor ($R_{\mathrm AA}$) at RHIC energy have been reproduced simultaneously by including both the collisional and radiative processes within the scope of perturbative quantum chromodynamics. The $R_{\mathrm AA}$ and $v_2^{HF}$ have been predicted for LHC energy.Comment: Plenary talk at ICPAQGP 2010, December 6-10, 2011, Goa, Indi

Collectieve versus individuele contracten voor natuurbeheer

In dit onderzoek staat de vraag centraal of collectieve contracten in vergelijking met individuele contracten efficiënter zijn en/of een grotere ecologische effectiviteit hebben. Daarbij is bijzondere aandacht gegeven aan de rol die agrarische natuurverenigingen kunnen spele

Improving Orbit Estimates for Incomplete Orbits with a New Approach to Priors -- with Applications from Black Holes to Planets

We propose a new approach to Bayesian prior probability distributions (priors) that can improve orbital solutions for low-phase-coverage orbits, where data cover less than approximately 40% of an orbit. In instances of low phase coverage such as with stellar orbits in the Galactic center or with directly-imaged exoplanets, data have low constraining power and thus priors can bias parameter estimates and produce under-estimated confidence intervals. Uniform priors, which are commonly assumed in orbit fitting, are notorious for this. We propose a new observable-based prior paradigm that is based on uniformity in observables. We compare performance of this observable-based prior and of commonly assumed uniform priors using Galactic center and directly-imaged exoplanet (HR 8799) data. The observable-based prior can reduce biases in model parameters by a factor of two and helps avoid under-estimation of confidence intervals for simulations with less than about 40% phase coverage. Above this threshold, orbital solutions for objects with sufficient phase coverage such as S0-2, a short-period star at the Galactic center with full phase coverage, are consistent with previously published results. Below this threshold, the observable-based prior limits prior influence in regions of prior dominance and increases data influence. Using the observable-based prior, HR 8799 orbital analyses favor lower eccentricity orbits and provide stronger evidence that the four planets have a consistent inclination around 30 degrees to within 1-sigma. This analysis also allows for the possibility of coplanarity. We present metrics to quantify improvements in orbital estimates with different priors so that observable-based prior frameworks can be tested and implemented for other low-phase-coverage orbits.Comment: Published in AJ. 23 pages, 14 figures. Monte Carlo chains are available in the published article, or are available upon reques

Rondom Kraaybeek: het groene hart

In het noordoostelijk deel van Driebergen ligt een open groene ruimte omsloten door bebouwing. Het gebied bezit cultuurhistorische waarden, is ecologisch van belang en is een plek waar bewoners uit het dorp recreëren. Een groep omwonenden, samengebracht in de Vereniging Rondom Kraaybeek (VRK), is bezorgd over de toekomst van het gebied. Zij vrezen dat de groene, educatieve en recreatieve functie verloren gaat. Kaders voor de toekomstige inrichting van het gebied ontbreken en verschillende betrokkenen hebben elk hun eigen plannen en wensenlijsten. Door het ontbreken van een gemeenschappelijke visie of overlegstructuur werken betrokkenen langs elkaar heen en worden deeloplossingen aangedragen, die niet altijd te verenigen zijn. Het onderzoek moet bijdragen aan het opstellen van een gemeenschappelijke visie van de gewenste ontwikkeling op lange termijn, die meer is dan de som der delen. Een tweede onderzoek (rapport 209) laat zien welke mogelijkheden de VRK kan benutten om haar doel te bereiken. Het onderzoek laat zien dat de situatie in het gebied erg complex is met veel verschillende betrokkenen met even zoveel belangen, die veelal niet meer goed naar elkaar luisteren. Door in werkateliers met elkaar te werken aan een gemeenschappelijke visie voor het gebied, is er meer het begrip gekomen voor elkaars standpunten. Dat maakt duidelijk dat partijen en hun belangen niet zover uit elkaar liggen als men oorspronkelijk dacht. Zo is er overeenstemming over het verbeteren van de verbindingen tussen landgoed de Kraaybeekerhof en Beukenstein. Ook is er consensus over het verbeteren van de waterhuishoudkundige situatie. Belangrijk voor de toekomst is het koesteren van de ecologische en recreatieve waarde van het gebied, zolang het gebied maar niet totaal op slot gaat. De waarde van het gebied voor het dorp is te vergroten door het gebied duidelijker zichtbaar en beleefbaar te maken. Ook de cultuurhistorie is belangrij