Bi-metric theory of gravity from the non-chiral Plebanski action

We study a modification of the Plebanski action for general relativity, which leads to a modified theory of gravity with eight degrees of freedom. We show how the action can be recasted as a bi-metric theory of gravity, and expanding around a bi-flat background we identify the six extra degrees of freedom with a second, massive graviton and a scalar mode.Comment: 28 pages. v2 minor typos correcte

Collective Bargaining under EMU: Lessons from the Italian and Spanish Experiences, CES Working Paper, no. 72, February 2000

This paper seeks to shed light on the question of the likely evolution of collective bargaining in Europe under EMU by considering the experiences of two countries (Italy and Spain) in which governments and social actors attempted to decentralized collective bargaining during the 1980s only to opt in favor of a re-centralization of bargaining during the 1990s. The paper argues that the experiences of Italy and Spain offer two kinds of insights for our understanding of the future evolution of wage bargaining in the EU. On the one hand, they illustrate why governments and social actors may come to favor a consolidation of the structure of bargaining under EMU rather than opt for a further decentralization of bargaining. On the other hand, they also suggest that any such process of consolidation faces great obstacles in moving beyond the national level. The recent experiences of Italy and Spain thus lead us to conclude that the most likely outcome in the EU is that of a reaffirmation of the national and national/sectoral-levels of bargaining within member states, rather than either a radical decentralization of bargaining across the EU, or an effective shift to EU-level bargaining

Neutrino-nucleon scattering rate in proto neutron star matter

We present a calculation of the neutrino-nucleon scattering cross section which takes into account the nuclear correlations in the relativistic random phase approximation. Our approach is based on a quantum hadrodynamics model with exchange of $\sigma$, $\omega$, $\pi$, $\rho$ and $\delta$ mesons. In view of applications to neutrino transport in the final stages of supernova explosion and protoneutron star cooling, we study the evolution of the neutrino mean free path as a function of density, proton-neutron asymmetry and temperature. Special attention was paid to the issues of renormalization of the Dirac sea, residual interactions in the tensor channel and meson mixing. It is found that RPA corrections, with respect to the mean field approximation, amount to only 10% to 15% at high density.Comment: 20 pages, 9 figures, subm. to EPJ