Wigner Function and Entanglement Entropy for Bosons from Non-Equilibrium Field Theory

We propose a new method of calculating entanglement entropy of a many-body interacting Bosonic system (open or closed) in a field theoretic approach without replica methods. The Wigner function and Renyi entropy of a Bosonic system undergoing arbitrary non-equilibrium dynamics can be obtained from its Wigner characteristic function, which we identify with the Schwinger Keldysh partition function in presence of quantum sources turned on at the time of measurement. For non-interacting many body systems, starting from arbitrary density matrices, we provide exact analytic formulae for Wigner function and entanglement entropy in terms of the single particle Green's functions. For interacting systems, we relate the Wigner characteristic to the connected multi-particle correlators of the system. We use this formalism to study the evolution of an open quantum system from a Fock state with negative Wigner function and zero entropy, to a thermal state with positive Wigner function and finite entropy. The evolution of the Renyi entropy is non-monotonic in time for both Markovian and non-Markovian dynamics. The entropy is also found to be anti-correlated with negativity of the Wigner function of a $2$ -mode open quantum system.Comment: 5+7 Pages, 2+2 Figure

Efficiency, scale economies and valuation effects : evidence from bank mergers in India

Original article can be found at : http://www.inderscience.com/ Copyright Inderscience PublishersThis paper examines two important issues related to bank mergers in India. First, we estimate potential economic gains of state owned banks if they undergo consolidation. Scale economies, returns to scale and profit efficiency of state owned banks during 1986 to 2003 are estimated based on stochastic frontier analysis. We find that many Indian banks exhibit potential cost savings from mergers provided they rationalize their branch networks although profit efficiency may not rise immediately. Second we measure the realized impact of bank mergers on shareholders’ wealth based on event study analysis. We find that in the case of forced mergers, shareholders of neither the bidder nor the target banks benefited. In the case of voluntary mergers, the bidder banks’ shareholders gained more than the target banks’ shareholders.Peer reviewe

Does monetary policy matter for corporate governance? Firm-level evidence for India

The paper assembles data on over 1,000 manufacturing and services firms in India for the entire post-reform period from 1992 through 2002 to examine the association between corporate governance and monetary policy. The findings suggests that (a) public firms are relatively more responsive to a monetary contraction vis-à-vis their private counterparts; and, (b) quoted firms lower their long-term bank borrowings in favour of short-term borrowings, post monetary tightening, as compared with unquoted firms. A disaggregated analysis based on firm size and leverage above a certain threshold validates these findings. The study concludes by analyzing the broad policy implications of these findings.monetary policy; corporate governance; relationship lending; leverage; India