Weak Stability and a Bargaining Set for the Marriage Model

In this note we introduceweak stability, a relaxation of the concept of stability for the marriage model by assuming that the agents are no longer myopic in choosing a blocking pair. The new concept is based on threats within blocking pairs: an individually rational matching is weakly stable if for every blocking pair one of themembers can find a more attractive partner with whom he forms another blocking pair for the original matching. Our main result is that under the assumption of strict preferences, the set of weakly stable and weakly efficient matchings coincides with the bargaining set of Zhou (1994) for this context.matching;(weak) stability;bargaining set

Job creation and job destruction in Estonia: labour reallocation and structural changes

This paper documents and analyses gross job flows and their determinants in Estonia over the years 1995-2001, using a unique database from the Estonian Business Registry. This database contains all (including also micro and small firms) officially registered firms in Estonia, the total number being almost 52,000. There are several important findings in the paper. Our results show that job flows (job creation and job destruction rates) have been extremely high in Estonia and are comparable to the levels documented for the US. These rates have not decreased recently, although worker flows (transitions between labour market states) have dropped. We also found that the firm-specific component in job flows excess of employment change had relatively lower importance than in western studies due to the emergence of small and medium-sized enterprises and labour reallocation between the economic sectors. The high inter-sectoral mobility has helped maintain high levels of job flows, while both are high also due to a favourable institutional environment, especially due to low start-up costs and a large share of micro enterprises

Creative destruction and transition: the effects of firm entry and exit on productivity growth in Estonia

This paper presents one of the first studies of firm demographics in Estonia, particularly, on the processes of firm entry and exit as well as survival analysis of new firms. Also decompositions of productivity change into components consisting of resource reallocation, firm entry and exit, and productivity growth within continuing firms is carried out. Our results, derived from a novel database of the population of Estonian firms, show that firm turnover has been rather high in Estonia during the observed period from 1995 to 2001, resulting from low institutional entry barriers and emergence of the SME sector. The high survival rates for new firms and surviving firms' relatively fast growth could reflect their relatively high productivity compared to incumbent firms and changes in the sectoral structure of the economy. The decomposition of productivity change shows that the high productivity growth has been mostly from within-firm productivity growth (e.g. the adoption of new production technologies and organizational changes), but the reallocation of production factors (especially the exit of low productivity units) has played an important role as well

Renormalization of dimension-six operators relevant for the Higgs decays h→γγ,γZh\rightarrow \gamma\gamma,\gamma Z

The discovery of the Higgs boson has opened a new window to test the SM through the measurements of its couplings. Of particular interest is the measured Higgs coupling to photons which arises in the SM at the one-loop level, and can then be significantly affected by new physics. We calculate the one-loop renormalization of the dimension-six operators relevant for $h\rightarrow \gamma\gamma, \gamma Z$, which can be potentially important since it could, in principle, give log-enhanced contributions from operator mixing. We find however that there is no mixing from any current-current operator that could lead to this log-enhanced effect. We show how the right choice of operator basis can make this calculation simple. We then conclude that $h\rightarrow \gamma\gamma, \gamma Z$ can only be affected by RG mixing from operators whose Wilson coefficients are expected to be of one-loop size, among them fermion dipole-moment operators which we have also included.Comment: 21 pages. Improved version with h -> gamma Z results added and structure of anomalous-dimension matrix determined further. Conclusions unchange

Numerical evolution of matter in dynamical axisymmetric black hole spacetimes. I. Methods and tests

We have developed a numerical code to study the evolution of self-gravitating matter in dynamic black hole axisymmetric spacetimes in general relativity. The matter fields are evolved with a high-resolution shock-capturing scheme that uses the characteristic information of the general relativistic hydrodynamic equations to build up a linearized Riemann solver. The spacetime is evolved with an axisymmetric ADM code designed to evolve a wormhole in full general relativity. We discuss the numerical and algorithmic issues related to the effective coupling of the hydrodynamical and spacetime pieces of the code, as well as the numerical methods and gauge conditions we use to evolve such spacetimes. The code has been put through a series of tests that verify that it functions correctly. Particularly, we develop and describe a new set of testbed calculations and techniques designed to handle dynamically sliced, self-gravitating matter flows on black holes, and subject the code to these tests. We make some studies of the spherical and axisymmetric accretion onto a dynamic black hole, the fully dynamical evolution of imploding shells of dust with a black hole, the evolution of matter in rotating spacetimes, the gravitational radiation induced by the presence of the matter fields and the behavior of apparent horizons through the evolution.Comment: 42 pages, 20 figures, submitted to Phys Rev

Axions and their Relatives

A review of the status of axions and axion-like particles is given. Special attention is devoted to the recent results of the PVLAS collaboration, which are in conflict with the CAST data and with the astrophysical constraints. Solutions to the puzzle and the implications for new physics are discussed. The question of axion-like particles being dark matter is also addressed.Comment: Updated version of an invited talk at the Axion Training (CERN, December 2005). To appear as a Lecture Notes in Physics (Springer-Verlag), edited by B. Beltran, M. Kuster and G. Raffel