On the instability of Reissner-Nordstrom black holes in de Sitter backgrounds

Recent numerical investigations have uncovered a surprising result: Reissner-Nordstrom-de Sitter black holes are unstable for spacetime dimensions larger than 6. Here we prove the existence of such instability analytically, and we compute the timescale in the near-extremal limit. We find very good agreement with the previous numerical results. Our results may me helpful in shedding some light on the nature of the instability.Comment: Published in Phys.Rev.

Dynamical friction in slab geometries and accretion disks

The evolution of planets, stars and even galaxies is driven, to a large extent, by dynamical friction of gravitational origin. There is now a good understanding of the friction produced by extended media, either collisionless of fluid-like. However, the physics of accretion or protoplanetary disks, for instance, is described by slab-like geometries instead, compact in one spatial direction. Here, we find, for the first time, the gravitational wake due to a massive perturber moving through a slab-like medium, describing e.g. accretion disks with sharp transitions. We show that dynamical friction in such environments can be substantially reduced relatively to spatially extended profiles. Finally, we provide simple and accurate expressions for the gravitational drag force felt by the perturber, in both the subsonic and supersonic regime.Comment: 10 pages, 8 figure

Drawing on the Innovative Moments Model during Career Construction Counseling to explain and foster client change

Career Construction Counseling (CCC) is a narrative intervention that supports individuals in the elaboration of narrative identity and career construction. The theory, research, and practice of this approach to career counseling has benefited from the Innovative Moments Model (IMM) to explain client change. Similar to CCC, the IMM is grounded on a narrative conception of human functioning, in which psychological difficulties arise from problematic self-narratives that constrain the meaning-making. Change takes place when clients challenge problematic self-narratives and construct new meanings that lead to new ways of behaving, thinking, or feeling. These novelties are termed innovative moments. The integration of IMM into the study of CCC has provided empirical evidence about the processes of client change throughout this intervention. Findings show that the transformation of a client’s self-narrative is associated with the aims of each session revealing a movement from a focus in structuring the past to an increased engagement in projecting the future. Moreover, results suggest the possibility of using IMs as process markers to guide counselors in facilitating client change during counseling sessions. The purpose of this chapter is to explain the contribution of IMM to CCC theory, research, and practice. We begin by presenting the Innovative Moments framework. Then we review CCC process research using the Innovative Moment’s framework. Finally, research implications for theory and practice of CCC are discussed

The provision of wage insurance by the firm: evidence from a longitudinal matched employer-employee dataset

We evaluate the impact of product market uncertainty on workers wages, addressing the questions: To what extent do firms provide insurance to their workforce, insulating their wages from shocks in product markets? How does the amount of insurance provided vary with firm and worker attributes? We use a longitudinal matched employer-employee dataset of remarkable quality. The empirical strategy is based on Guiso et al. (2005). We first estimate dynamic models of sales and wages to retrieve consistent estimates of shocks to firms’ sales and to workers’ earnings. We are then able to estimate the sensitivity of wages to permanent and transitory shocks to firm performance. Results point to the rejection of the full insurance hypothesis. Workers’ wages respond to permanent shocks to firm performance, whereas they are not sensitive to transitory shocks. Managers are not fully insured against transitory shocks, while they receive the same protection against permanent shocks as workers in other occupations. Firms with higher variability in their sales, and those operating in di?erent industries, o?er more insurance against permanent shocks. Comparison with Guiso et al. (2005) indicates that Portuguese firms provide less insurance than Italian firms, corroborating evidence on the high degree of wage flexibility in Portugal.

Essays in International Economics: the Trade-Creation Effect of Migration

My thesis consists of three chapters relating to topics in International Economics. My first two chapters study the effects of migration flows on the economic outcomes of stayers for both receiving and sending countries. In both these chapters I develop and calibrate two distinct general equilibrium (GE) models to study the quantitative effect of migration on the real income of workers. The third chapter empirically investigates the relationship between firm export behaviour and their composition of foreign-born workers. In my first chapter I develop a multi-country GE model where consumers choose where to reside, facing a trade-off between potentially earning a higher wage abroad but incurring a cost to migrating. The novel contribution in this paper is that estimating migration costs within a GE model allows me to quantify interesting policy experiments. In one experiment I consider the effects of an expansion of the European Economic Area (EEA), which allows free movement of labour for its member countries. I find that expanding the European Economic Area to include Turkey leads to a very small negative impact on the average wages in the rest of the member countries. I find the increase in migration from Turkey into the EEA is offset by a decrease in migration to EEA countries from other member countries. The empirical trade-literature has shown that members of migrant networks can reduce the information frictions that exist in bilateral trade costs and help firms increase exports to their country of origin. In my second chapter I utilize insights from this literature and add a new channel, a trade-creation effect, by which migrants affect economic outcomes across countries in a GE multi-country model with trade. In this setting the decision of workers on where to reside and the decisions of firms on which countries to export to are linked because where firms choose to sell their goods affects real income in a location which in turn affects a consumer’s decision to migrate. My results show that the trade creation effects are strong. It is particularly important in mitigating welfare losses for countries with large outflows in their population. For example, the average real income of a stayer in a net-emigration country is 1.4% higher due to the trade-creation effect. In my final chapter, which is joint work with Professor Ananth Ramanarayanan, we study the relationship between export behaviour and the foreign-born worker composition at Canadian manufacturing firms using unique Canadian administrative employer-employee tax data. We argue that if immigrants are lowering the informational, or language barriers to export to their home country, then we should see these effects at firms that employ these immigrants, and it should be evident at a country-specific level. Our results confirm this assertion; we find that firms have much higher export sales to a country if they employ immigrant workers from that country. The increase in export sales of these firms stems from the link between immigrant employment and a reduction in trade costs