When overconfident traders meet feedback traders

In this paper, we develop a model in which overconfident market participants and rational speculators trade against trend-chasers. We exhibit the unique linear equilibrium and assess the quality of prices according to the proportion of the different types of agents. We highlight how speculative bubbles arise when a large number of traders adopt a trend-chasing behavior. We show that overconfident traders can obtain positive expected profits. In particular, over-confident traders can outperform rational traders. The positive feedback trading enhances the negative correlation between the back-to-back prices changes and the volatility of prices as well. We show that positive feedback traders destabilize prices more than their overconfident opponents. Generally, overconfidence increases the volatility of prices and worsens the market efficiency. But, we show that in the presence of positive feedback trading, overconfidence improves the market efficiency and dampens the excess volatility

When Overconfident Traders Meet Feedback Traders

We develop a model in which informed overconfident market participants and informed rational speculators trade against trend-chasers. In this model positive feedback traders act as Computer Based Trading (CBT) and lead to positive feedback loops. In line with empirical findings we find a positive relationship between the volatility of prices and the size of the price reversal. The presence of positive feedback traders leads to a higher degree of trading activity by both types of informed traders. Overconfidence can lead to less price volatility and more efficient prices. Moreover, overconfident traders may be better off than their rational counterparts

Heterogeneous Noisy Beliefs and Dynamic Competition in Financial Markets

This paper analyzes the competition of heterogeneously informed traders in a multi-auction setting. We obtain that the competition can take different forms depending on the number of traders, trading rounds and the noise in the information. When the number of traders is small and the number of trading rounds is large, traders may trade very aggressively at the opening and at the end of the trading day with lower trading intensity in between. Hence, we can explain volume patterns by the nature of the competition between traders rather than by pattern in the level of liquidity. We find that the noise in the signal may be beneficial for traders when the competition is strong as it gives them a monopolistic position on their private information. The amount of noise maximizing the trader’s expected profit increases with the number of trading rounds as well as the number of traders. This implies that the value of information is closely related to the market where that information is subsequently being used

When Overconfident Traders Meet Feedback Traders

We develop a model in which informed overconfident market participants and informed rational speculators trade against trend-chasers. In this model positive feedback traders act as Computer Based Trading (CBT) and lead to positive feedback loops. In line with empirical findings we find a positive relationship between the volatility of prices and the size of the price reversal. The presence of positive feedback traders leads to a higher degree of trading activity by both types of informed traders. Overconfidence can lead to less price volatility and more efficient prices. Moreover, overconfident traders may be better off than their rational counterparts

Nostaljascee: Nostalgia e Memoria Post-comunista nella Russia del nuovo millennio.

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Perceptions of local populations on the state of phytodiversity in the subwatershed of Kossi river in the municipalities of Dassa-Zoumé and Glazoué in the Center of Benin

In Africa, since several decades a rarefaction of many plant species because of their daily use by people can be observed. This study which was conducted in the subwatershed of the Kossi River aims to collect peasant perceptions about the state of phytodiversity. The data were collected through an individual survey in 10 villages with 492 households. The software CAP version 2.15. and R version 3.3.3. were used for the statistical analysis. In total, 94 species belonging to 83 genera and 38 families were identified. The dominant genera are Ficus, Ocimum, Acacia and Blighia. Forty-six (46) species of the listed species (48.94%) are currently rare and 9 species (19.57%) of those rare species are threatened in Benin. Value of importance (IV) of activity and the consensus value (UCs) of the choice of activity show that logging, agriculture and breeding have greatest influence on species loss. This study gives information on the most used species by the populations and those we can select for reforestation campaigns. As a perspective, a work on the temporal dynamics of the land use units of this sub-basin will be done to better appreciate their evolution over time. En Afrique, on assiste depuis plusieurs décennies à la raréfaction de plusieurs espèces végétales du fait de leur utilisation quotidienne par les populations. La présente étude conduite dans le sous-bassin versant de la rivière Kossi vise à recueillir les perceptions des populations locales sur l’état de la phytodiversité. Les données ont été collectées à travers une enquête individuelle dans 10 villages auprès de 492 ménages. Les logiciels CAP version 2.15. et R version 3.3.3. ont été utilisés pour les analyses statistiques. Au total, 94 espèces reparties en 83 genres et 38 familles ont été recensées. Les genres dominants sont Ficus, Ocimum, Acacia et Blighia et les familles les mieux représentées sont les Caesalpiniaceae, les Papilionaceae et les Combretaceae. Quarante-six des espèces recensées (48,94%) sont actuellement rares et 9 de ces espèces rares (19,57%) sont menacées au Bénin. La Valeur d’Importance (IV) de l’activité et la valeur consensuelle (UCs) du choix de l’activité ont révélé que l’exploitation forestière, l’agriculture et la transhumance sont les principaux facteurs responsables de cette raréfaction. Cette étude renseigne sur les espèces les plus utiles pour les populations et celles à apporter en cas d’enrichissement. Comme perspective, la dynamique temporelle des unités d’occupation du sol de ce sous-bassin sera abordée pour mieux apprécier leur évolution dans le temps

Gravitational waves throughout galaxy evolution: stellar BH mergers and heavy SMBH seeds.

The main goal of my thesis is to carefully characterize different astrophysical processes leading to gravitational wave (GW) emission, strongly relying on theoretical and observational astrophysical basis. From an observational point of view, current interferometers (Advanced Laser Interferometer Gravitational wave Observatory/Virgo (AdvLIGO/Virgo)) and future detectors (Einstein Telescope (ET), Cosmic Explorer (CE), Deci-hertz Interferometer Gravitational wave Observatory (DECIGO), Laser Interferometer Space Antenna (LISA)) will greatly enlarge the number of detected GW events. However, in order to extract meaningful information about various astrophysical phenomena and improve our knowledge on cosmology and fundamental physics from this large sample of observational data, a correct modelization of the impact of different astrophysical processes on GWs rates is necessary. The marking feature of all the work is an accurate and deep study of the galactic environment, making use of classic theoretical arguments and recent observational results in the galaxy formation and evolution field. Galactic properties, such as star formation rate, gas and stellar density, metallicity, can have a profound impact on stellar and compact object evolution and on the ensuing GW emissions. In particular, throughout the thesis I focused on the study of 2 different channels of GW production: merging of isolated double compact object binaries of stellar origin (neutron stars and stellar black holes) and dynamical merging of stellar and, eventually, primordial black holes in the central regions of early-type galaxy progenitors. In the context of double compact object merging binaries, given the relevance of gas-phase metallicity for all the stellar and binary evolution processes, the main effort of my work is in the characterization of a metallicity dependent cosmic star formation rate density. I compute this term in various ways, highlighting the impact of different galactic prescriptions, such as galaxy statistics and metallicity scaling relations. In particular I focus on the gas-phase metallicity, showing that the two main empirical scaling relations present in literature, the Mass Metallicity Relation and the Fundamental Metallicity Relation, hold substantially different results at high redshift ( > 2), with the Fundamental Metallicity Relation featuring relatively high metallicitites ∼ 0.4 − 0.5 Z⊙ and the Mass Metallicity Relation predicting a significant metallicity drop below 0.1 Z⊙. I discuss the reasons and possible biases originating this discrepancy, arguing in favor of the Fundamental Metallicity Relation or of a slowly declining Mass Metallicity Relation. I also present a chemical evolution model to deal with metallicity from a theoretical point of view and I find a pleasant agreement between the model and the Fundamental Metallicity Relation. Finally, I show the impact of these different astrophysical prescriptions on the merging rates and on the properties of compact objects binaries, such as their chirp mass or time delay distribution. I complete the work forecasting the ensuing GW detection rates with present and future detectors, as well as the expected lensed event rates and the stochastic GW background. As for the dynamical merging channel, recent observations of the extremely star-forming and gas-dense environments in the central regions of early-type galaxy progenitors at z bigger than 1, inspired the idea for the proposal of a new mechanism for the growth of supermassive black hole seeds. This envisages the migration and merging of compact objects via gaseous dynamical friction toward the galactic center where a central black hole accumulates mass thanks to these continuous merging events. I show that, under reasonable assumptions, the process can build up central BH masses of order 10^4 − 10^5 M⊙ within some 10^7 yr, so effectively providing heavy seeds before standard (Eddington-like) disk accretion takes over to become the dominant process for further BH growth. Remarkably, such a mechanism may provide an explanation, alternative or complementary to other processes, for the buildup of billion solar masses black holes in quasar hosts at z bigger than 7, when the age of the Universe less than 0.8 Gyr constitutes a demanding constraint. This process naturally present a possibility to be tested via detections of the gravitational waves produced by mergers between the migrating compact objects and the growing central black hole. I also make predictions for the produced stochastic GW background which extends over a wide range of frequencies [10^(−6) Hz, 10 Hz], very different from the typical range originated by mergers of isolated binaries. I show that both the single events and the background could be revealed by future ground- and space-based interferometers as ET, DECIGO and LISA

Searching for anisotropic stochastic gravitational-wave backgrounds with constellations of space-based interferometers

Many recent works have shown that the angular resolution of ground-based detectors is too poor to characterize the anisotropies of the stochastic gravitational-wave background (SGWB). For this reason, we asked ourselves if a constellation of space-based instruments could be more suitable. We consider the Laser Interferometer Space Antenna (LISA), a constellation of multiple LISA-like clusters, and the Deci-hertz Interferometer Gravitational-wave Observatory (DECIGO). Specifically, we test whether these detector constellations can probe the anisotropies of the SGWB. For this scope, we considered the SGWB produced by two astrophysical sources: merging compact binaries and a recently proposed scenario for massive black-hole seed formation through multiple mergers of stellar remnants. We find that measuring the angular power spectrum of the SGWB anisotropies is almost unattainable. However, it turns out that it could be possible to probe the SGWB anisotropies through cross-correlation with the CMB fluctuations. In particular, we find that a constellation of two LISA-like detectors and CMB-S4 can marginally constrain the cross-correlation between the CMB lensing convergence and the SGWB produced by the black hole seed formation process. Moreover, we find that DECIGO can probe the cross-correlation between the CMB lensing and the SGWB from merging compact binaries.Comment: 17 pages, 9 figures, accepted by Ap

Discours des grands leaders politiques et catholiques du Bénin : critiques et propositions en vue d'une stratégie de communication pour le développement

La République du Bénin, selon certains observateurs économiques, a de grands atouts pour figurer parmi les nations développées. Depuis plusieurs décennies, elle jouit d'une démocratie enviable et le taux de scolarisation des jeunes est très élevé. Depuis sa constitution comme peuple, elle n'a jamais connu de conflits armés ni de famine. Mais elle figure parmi les pays les plus endettés; car ayant bénéficié d'importants financements alors que les leaders catholiques et politiques, dont les discours sont presque tous similaires, font du développement le premier objectif de leurs discours. Or selon la théorie critique, les mass média influencent les récepteurs en les obligeant à agir tandis que pour la théorie fonctionnaliste les médias influencent ces mêmes récepteurs à cause de la présence en leur sein de certaines personnes dont la popularité, la notoriété ou la technicité permet de convaincre leur audience. Or au Bénin, l'ensemble aussi bien de la classe politique et que de la hiérarchie catholique sont souvent présent sur les médias. Ces deux classes bénéficient à elles seules de 40% du taux d'audience sur les grands medias du pays. Comment se fait-il que ces leaders catholiques et politiques, malgré le crédit -presque divin- dont ils bénéficient n'arrivent pas encore à faire adopter une attitude qui corresponde à leur vision surtout qu'ils bénéficient des audiences les plus grandes dans le pays? Ces audiences sur les medias et des grands rassemblements sont pourtant importantes. Comment se fait-il que le développement, objectif principal de leur mission commune, ne soit pas encore amorcé? Il se pose alors une question d'efficacité des communications des leaders politique et catholique du Bénin sur le développement. Nous nous sommes alors fixé trois objectifs à atteindre. D'abord analyser la place et l'importance réelle de ces leaders d'opinion dans les communications sociales et publiques. Ensuite faire « l'analyse diagnostic» des schémas de communication adoptés par ces leaders à Cotonou et enfin évaluer la place de «l'autre» dans les communications politiques et catholiques du Bénin. Pour y arriver, nous avons sélectionné un ensemble de discours politiques de trois grands partis politiques, de même qu'une série de lettres pastorales de la conférence épiscopale des évêques du Bénin que nous avons analysé à l'aide du logiciel Semato. Ceci nous a permis de dégager les grandes lignes communes et ensuite nous avons établi trois questionnaires d'enquête et fait un focus groupe afin de vérifier si ces discours sont méconnus ou simplement rejetés par les récepteurs. Le résultat auquel nous sommes parvenus dépassait nos attentes. Les personnes interrogées attendent des actes concrets pour amorcer le développement. Le contenu des discours politiques et catholiques sur le développement est inconnu. Les propositions de développement avancées par les personnes interrogées s'accordent avec celles avancées par les leaders catholiques et politiques. Certes, ces discours, sur la question du développement, attirent de grandes audiences qui aiment écouter ces leaders catholiques et politiques. Mais leurs propositions sur le développement ne sont pas mises pour autant en pratique. C'est la même observation qu'ont faite certains grands communicateurs sur le Pape Jean II : Pape populaire et aimé sur les médias mais dont les prises de position sont des plus contestées surtout sur les questions de morale et donc de comportement. ... Enfin, le schéma de communication adopté par les leaders gagne à partir des interrogations et des réalités que vivent les récepteurs à chaque moment; car il s'agit de l'autre. Cet autre doit être au cœur des préoccupations, des théories et méthodes de communication. Nous parlerons de mass media et de focus group. Ne pas les considérer comme des anglicismes. Ce sont des mots clefs précis qui désignent des réalités concrètent. On peut les comparer respectivement aux médias de masse et à des groupes de discutions, mais les réalités ne sont pas profondément identiques.\ud ______________________________________________________________________________ \ud MOTS-CLÉS DE L’AUTEUR : Leader, développement, communication pour le développement, récepteur, l'autre, analyse diagnostic, schéma de communication, discours, minimum social commun

The impact of the FMR and starburst galaxies on the (low metallicity) cosmic star formation history

The question how much star formation is occurring at low metallicity throughout the cosmic history appears crucial for the discussion of the origin of various energetic transients, and possibly double black hole mergers. We revisit the observation-based distribution of birth metallicities of stars (fSFR(Z,z)), focusing on several factors that strongly affect its low metallicity part: (i) the method used to describe the metallicity distribution of galaxies (redshift-dependent mass metallicity relation - MZR, or redshift-invariant fundamental metallicity relation - FMR), (ii) the contribution of starburst galaxies and (iii) the slope of the MZR. We empirically construct the FMR based on the low-redshift scaling relations, which allows us to capture the systematic differences in the relation caused by the choice of metallicity and star formation rate (SFR) determination techniques and discuss the related fSFR(Z,z) uncertainty. We indicate factors that dominate the fSFR(Z,z) uncertainty in different metallicity and redshift regimes. The low metallicity part of the distribution is poorly constrained even at low redshifts (even a factor of ∼200 difference between the model variations) The non-evolving FMR implies a much shallower metallicity evolution than the extrapolated MZR, however, its effect on the low metallicity part of the fSFR(Z,z) is counterbalanced by the contribution of starbursts (assuming that they follow the FMR). A non-negligible fraction of starbursts in our model may be necessary to satisfy the recent high-redshift SFR density constraints