Two-loop Wess-Zumino model with exact supersymmetry on the lattice

We consider a lattice formulation of the four dimensional N=1 Wess-Zumino model in terms of the Ginsparg-Wilson relation. This formulation has an exact supersymmetry on the lattice. The lattice action is invariant under a deformed supersymmetric transformation which is non-linear in the scalar fields and it is determined by an iterative procedure in the coupling constant to all orders in perturbation theory. We also show that the corresponding Ward-Takahashi identity is satisfied at fixed lattice spacing. The calculation is performed in lattice perturbation theory up to order $g^3$ (two-loop) and the Ward-Takahashi identity (containing 110 connected non-tadpole Feynman diagrams) is satisfied at fixed lattice spacing thanks to this exact lattice supersymmetry.Comment: PRD (Rapid Communication) to appea

The Study of the Continuum Limit of the Supersymmetric Ward-Takahashi Identity for N=1 Super Yang-Mills Theory

The one-loop corrections to the supersymmetric Ward-Takahashi identity (WTi) are investigated in the off-shell regime in the Wilson formulation of the discretized N=1 Super Yang-Mills (SYM) theory. The study of the continuum limit as well as the renormalization procedure for the supercurrent are presented.Comment: Talk at Confinement 200

Efficiency gains and mergers

In the theoretical literature, strong arguments have been provided in support of the efficiency defense in antitrust merger policy. One of the most often cited results is due to Williamson (1968) that shows how relatively small reduction in cost could offset the deadweight loss of a large price increase. Furthermore, Salant et al. (1983) demonstrate that (not for monopoly) mergers are unprofitable absent efficiency gains. The general result, drawn in a Cournot framework by Farrell and Shapiro (1990), is that (not too large) mergers that are profitable are always welfare improving. In the present work we challenge the conclusions of this literature in two aspects. First, we show that Williamson's results underestimate the welfare loss due to a price increase and overestimate the effect of efficiency gains. Then, we prove that the conditions for welfare improving mergers defined by Farrell and Shapiro (1990) hold true only when consumers are adversely affected. This seems an argument to disregard their policy prescriptions when antitrust authorities are more "consumers-oriented". In this respect, we provide a necessary and sufficient condition for a consumer surplus improving merger: in a two firm merger, efficiency gains must be larger than the pre-merger average markup

The High Density Region of QCD from an Effective Model

We study the high density region of QCD within an effective model obtained in the frame of the hopping parameter expansion and choosing Polyakov-type loops as the main dynamical variables representing the fermionic matter. This model still shows the so-called sign problem, a difficulty peculiar to non-zero chemical potential, but it permits the development of algorithms which ensure a good overlap of the simulated Monte Carlo ensemble with the true one. We review the main features of the model and present results concerning the dependence of various observables on the chemical potential and on the temperature, in particular of the charge density and the Polykov loop susceptibility, which may be used to characterize the various phases expected at high baryonic density. In this way, we obtain information about the phase structure of the model and the corresponding phase transitions and cross over regions, which can be considered as hints about the behaviour of non-zero density QCD.Comment: 7 pages, 5 figures, talk presented at the XXVth International Symposium on Lattice Field Theory, July 30 - August 4 2007, Regensburg, German

Is competition for FDI bad for regional welfare?

We investigate the impact on regional welfare of policy competition for FDI when a multinational firm can strategically react to differences in statutory corporate tax rates and shift taxable profits to lower-tax jurisdictions. We show that competing governments may have an incentive to tax discriminate between domestic and multinational firms even in the presence of profit shifting opportunities for the latter. In particular, tax discrimination leads to higher welfare for the region as a whole than lump-sum subsidy competition when the difference in statutory corporate tax rates and/or their average is high enough. We also find that policy competition increases regional welfare by changing the firm's investment decision when profit shifting motivations might induce the firm to locate in the least profitable country

Endogenous timing in a mixed duopoly

This paper addresses the issue of endogenizing the equilibrium solution when a private - domestic or foreign - firm competes in the quantities with a public, welfare maximizing firm. Theoretical literature on mixed oligopolies, in fact, provides results and policy implications that crucially rely on the notion of equilibrium assumed, either sequential or simultaneous. In the framework of the endogenous timing model of Hamilton and Slutsky (1990), we show that simultaneous play never emerges as the equilibrium of mixed duopoly games. We provide sufficient conditions for the emergence of public and/or private leadership equilibria. These results are in sharp contrast with those obtained in private duopoly games in which simultaneous play is the general result. We show that the key difference lies in the fact that the objective of a welfare maximizing firm is generally increasing in the rival's output, while the contrary holds for private firms. We develop a comprehensive analysis of a mixed duopoly considering both the cases of domestic and international competition, and the possible strategic complementarity and substitutability. From a methodological viewpoint we make large use of the basic results of the theory of supermodular games in order to avoid extraneous assumptions such as concavity, existence and uniqueness of the equilibria

Efficiency gains and mergres

In the theoretical literature, strong arguments have been provided in support of the efficiency defense in antitrust merger policy. One of the most often cited results is due to Williamson (1968) that shows how relatively small reduction in cost could offset the deadweight loss of a large price increase. Furthermore, Salant et al. (1983) demonstrate that (not for monopoly) mergers are unprofitable absent efficiency gains. The general result, drawn in a Cournot framework by Farrel and Shapiro (1990), is that (not too large) mergers that are profitable are always welfare improving. In the present work we challenge the conclusions of this literature in two aspects. First, we show that Williamson’s results underestimate the welfare loss due to a price increase and overestimate the effect of efficiency gains. Then, we prove that the conditions for welfare improving mergers defined by Farrel and Shapiro (1990) hold true only when consumers are adversely affected. This seems an argument to disregard their policy prescriptions when antitrust authorities are more “consumers-priented”. In this respect, we provide a necessary and sufficient condition for a consumer surplus improving merger : in a two firm merger, efficiency gains must be larger than the pre-merger average markup.mergers, efficiency gains, Cournot oligopoly