The main aim of the project is the application of techniques from partial differential equations, microlocal analysis and scattering theory to the study of quantum matter interacting with spacetime geometry. The last decade has witnessed spectacular progress in the mathematical description of phenomena in relativistic physics. However, one of the great persisting challenges is to understand how does the presence of quantum matter alter the Einstein equations (and therefore, the geometry), and how do the dynamics of spacetimes give rise to quantum effects. This is a strong impulse for exploring topics including scattering theory of gauge fields, quantization of linearized gravity and renormalization problems in relation with PDEs and Lorentzian geometry, with the ultimate objective of establishing a rigorous formulation of theories where quantum degrees of freedom interact with gravity.

The global economy is subject to large and sudden changes in regimes, as evidenced by the severe crashes in the financial system during the last two decades, including the global financial crisis of 2008. A distinctive feature of the last crashes it that these are episodes during which previously unrelated financial markets can become extremely dependent, which makes the global economy very risky for all stakeholders. A better understanding of such episodes of the economy is hence of primary importance. In this research program, we develop and implement quantitative tools that explicitly take into account the sometimes abruptly changing nature of the economic environment. In particular, our research agenda centers on three axes that are central to our understanding of risk in times of crises. The first axis focuses on models in which the economy can oscillate between several regimes, characterized by different laws of motion, as well as models of structural change. These models reflect the notion that the behavior of the economy may differ across periods of crisis and calmer periods. Existing regime switching models have the drawback that all parameters change when there is a regime switch. First, we propose a methodology for multiple breaks, where we relax the assumption that all parameters need to change when there is a structural break. This is done by shrinking irrelevant break-parameters towards zero. Estimation is based on a sampling scheme tailored to change-point and Markov Switching models. Second, we develop a framework for off-line multiple change-point problems in one-parameter exponential family observation-driven time series models. Third, we propose a monitoring procedure for sequential change-point detection for integer-valued time series. Finally we check for the presence of breaks in an extended version of the heterogeneous autoregressive model of realized volatility and we assess the model's in- and out-of-sample performance. Our second broad topic is models of correlations in default risk, whose deficiency was at the epicenter of the subprime crisis. We propose two new bottom-up models of credit risk. The first tackles the default dependence of securitized subprime mortgages. On top of a classical multinomial logistic framework, we use composite likelihood to estimate a pairwise copula model of default, where dependence is a function of physical distance between mortgages, pairwise averages and differences in mortgage characteristics, as well as interest rates and past local default rates. The second introduces default correlations in the forward-intensity model of \citeasnoun{duan2012multiperiod}, which predicts corporate defaults over multiple horizons and is the methodological basis for the non-profit credit rating initiative at the National University of Singapore that provides default forecasts for 60000 firms worldwide. Finally we propose a multivariate equidependent copula regime-switching model to analyze how dependence in local house prices in the U.S., and thus the benefits of geographic diversification of real estate portfolios, change with conditions on the credit market. Finally, we analyze the behavior of the risk premia that investors require as a compensation for carrying variance risk. First, we propose a joint regime-switching model of realized and risk-neutral variances in a state-space framework with three regimes, designed to capture heteroskedasticity, jumps, and time varying dependence between the variance risk premium, the risk neutral and physical variances. Second, we propose a particle-based Bayesian method to estimate a very general model of dynamic volatility with both underlying and derivative observations, that encompasses many specifications that have been proposed in the literature. Finally, we will build a state space model for the joint dynamics of the 'efficient' price as well as for a set of parameters that capture the shape of the limit order book,

LAMARTINE aims at measuring building and land use regulations and evaluate their socioeconomic and environmental impact. Starting from the observation that the share of land in housing value has been constantly increasing, this project aims to understand the potential role of land use regulation in this rise. To this end, we first propose to build a dataset shared with the scientific community and a broader audience to measure all the regulations applied on land parcels and conditioning their construction potential, Second, using this data set, we are willing to decompose the value of parcels between their structure and land components. This should allow us assess the value of Land in France, its distribution between households and the redistributive potential of land tax. Third, we also want to investigate the drivers of land use regulation and its consequences on real estate market dynamics as prices, construction and city shape. Finally, these data will be used to develop spatial equilibrium models to document the nationwide spillovers of land use regulation, their welfare and redistributive effects to help the design of acceptable environmental policies.

Trade liberalization was at the core of structural reforms in the last decades. A lot of attention has been paid recently to the microeconomic effects of trade openness on firms’ competitiveness and labor markets. On the production side, recent works (Verhoogen, 2008, Khandelwal, 2010) highlight alternative strategies to price competitiveness to improve firm efficiency in a globalized world: firms can increase their market shares abroad by upgrading the quality of their products (non-price competitiveness). Our recent work shows that trade liberalization creates incentives for firms to upgrade the quality of foreign inputs to improve the quality of exported final goods (Bas and Strauss-Kahn, 2015). On the labor market, the literature has shown that trade shocks induce large labor market adjustments that have important distributional consequences (Autor et al. 2013). This research program proposes several projects to understand the mechanisms at play. Conducting micro econometric analysis theoretically grounded using detailed firm-product data for several countries, this research program explores the heterogeneous effects of international trade on firm performance, quality upgrading and employment demand. The first two projects focus on the role of product quality on final prices and demand, on the one hand, and on the impact of input quality upgrading on product innovation and employment of different skills, on the other hand. The two other projects look at the relationship between firms’ exposure to international markets and different domestic labor market outcomes such as volatility of workers of different skills and gender differences in occupational status. The last project investigates the impact of resource misallocation on external competitiveness and asks whether firms optimizing their use of labor compete more successfully in international markets. The main contribution of this research program to the literature is to look at the different ways in which firms can enhance their non-price competitiveness in a globalized world and its effects on labor demand. The research projects proposed are innovative in several ways. First, all projects share one common ambition: they aim at identifying the causal relationship between international trade, firm performance and labor market outcomes relying on very detailed micro-data (at the firm-product and country level) and original econometric identification strategies based on variations of exogenous trade shocks. Second, the empirical analysis is always theoretically guided. All projects proposed a theoretical framework that rationalizes the mechanisms at play and the theoretical implications that will be tested. Third, the research topics of each project are novel and original and aim at contributing to the literature in several ways: (i) there is no evidence on the heterogeneous impact of tariff cuts on export prices depending on product quality at the micro level, (ii) there is no work that has explored the relationship between firms’ foreign input-quality upgrading and skilled bias technical change, (iii) there is a lack of evidence on the impact of firms’ export exposure on the employment volatility across workers of different skill, (iv) little is known about the impact of trade liberalization on informal employment depending on gender and occupations and (v) there is little micro-level evidence on the relationship between firm heterogeneity, external competitiveness and misallocation of resources within the firm. This research agenda does not lack of policy implications. By exploring the heterogeneous effects of trade openness on firms’ decisions to innovate, upgrade their quality and on changes in employment demand and in occupational status of different types of workers, this research program aims to identifying the firms and workers that win and lose from globalization. Leaving room for industrial, labor market and social policies to complement trade policies.

This project tackles the issue of the diversity of opinions in a society. It is grounded in Economics but is at the intersection with several other fields: Psychology, Statistics, Decision Theory, Analytical Philosophy, Social Choice, and Political Science. It goes beyond equating individuals' opinions with their probabilistic beliefs, a standard practice in Economics, and aims at encompassing notions like unawareness, ambiguity, and competence to analyze opinion heterogeneity more broadly. The general questions we will explore are the following ones: - How does diversity of opinions come about and how can it survive? - What is the impact of this diversity on economic arrangements? - How do individuals react when confronted with other's opinions? - How can one aggregate the various opinions to make the best decisions? These questions deserve to be treated both normatively and positively, calling for various analytical approaches (e.g. axiomatic treatment, modelling of markets, etc.) and experimental approaches (from psychophysics and social psychology). From a positive side, we will provide models explaining how individuals exposed to the same information can disagree. This requires to think outside of the usual Bayesian, common prior framework. Getting outside of this framework is also required to provide an understanding of how disagreements can survive in the long run, as we aim to show, contrary to a long-standing view in economics that "irrational" opinions get wiped out of the market. Experimentally, we will focus on how individuals integrate heterogeneous opinions when making decisions and, in particular, how social pressure affects individuals' opinions. We will finally analyze how opinion heterogeneity affects economic arrangements such as bargaining, risk sharing and financial markets, incentive provision, etc. From a normative side, we will concentrate on the many ways different opinions can be aggregated to form a social or group opinion. A particular attention will be given to procedures that allow one to extract a measure of competence or expertise from opinions expressed by members of a society or group. These degrees of competence will then be used to weight the various opinions in order to make the best informed decision for the group. We will provide an experimental assessment of these rules, compared with other rules studied in the literature. We will also go beyond taking opinions as exogenous and will see how correlations (and, possibly, failure to recognize these) among the sources of information accessible to individuals changes the way aggregating procedures like voting work. This study will fit into a more general research question which is how to aggregate "ill-defined" or "biased" opinions. The project's aim is mainly to advance scientific knowledge on these issues. It could lead to define practical ways of aggregating opinions or rankings that could be of interest for the private and public sectors. The team of researchers assembled for this project have expertise in the various fields the project is touching. They have already worked, produced scientific papers published in the best international outlets and organized events together.