Networks of Relations

We model networks of relational (or implicit) contracts, exploring how sanctioning power and equilibrium conditions change under different network configurations and information transmission technologies. In our model, relations are the links, and the value of the network lies in its ability to enforce cooperative agreements that could not be sustained if agents had no access to other network members’ sanctioning power and information. We identify conditions for network stability and in-network information transmission as well as conditions under which stable subnetworks inhibit more valuable larger networks

Gravity dual of spin and charge density waves

At high enough charge density, the homogeneous state of the D3-D7' model is unstable to fluctuations at nonzero momentum. We investigate the end point of this instability, finding a spatially modulated ground state, which is a charge and spin density wave. We analyze the phase structure of the model as a function of chemical potential and magnetic field and find the phase transition from the homogeneous state to be first order, with a second-order critical point at zero magnetic field.Comment: 26 pages, 16 figures; v2: refs. fixed and added; v3: refs. and discussion added, published versio

Finite-Size Effects in Lattice QCD with Dynamical Wilson Fermions

As computing resources are limited, choosing the parameters for a full Lattice QCD simulation always amounts to a compromise between the competing objectives of a lattice spacing as small, quarks as light, and a volume as large as possible. Aiming to push unquenched simulations with the Wilson action towards the computationally expensive regime of small quark masses we address the question whether one can possibly save computing time by extrapolating results from small lattices to the infinite volume, prior to the usual chiral and continuum extrapolations. In the present work the systematic volume dependence of simulated pion and nucleon masses is investigated and compared with a long-standing analytic formula by Luescher and with results from Chiral Perturbation Theory. We analyze data from Hybrid Monte Carlo simulations with the standard (unimproved) two-flavor Wilson action at two different lattice spacings of a=0.08fm and 0.13fm. The quark masses considered correspond to approximately 85 and 50% (at the smaller a) and 36% (at the larger a) of the strange quark mass. At each quark mass we study at least three different lattices with L/a=10 to 24 sites in the spatial directions (L=0.85-2.08fm).Comment: 21 pages, 20 figures, REVTeX 4; v2: caption of Fig.7 corrected, one reference adde

Networks of Relations

We model networks of relational (or implicit) contracts, exploring how sanctioning power and equilibrium conditions change under different network configurations and information transmission technologies. In our model, relations are the links, and the value of the network lies in its ability to enforce cooperative agreements that could not be sustained if agents had no access to other network members’ sanctioning power and information. We identify conditions for network stability and in-network information transmission as well as conditions under which stable subnetworks inhibit more valuable larger networks.Networks; Relational Contracts; Indirect Multimarket Contact; Social Capital.

The Key Authority - Secure Key Management in Hierarchical Public Key Infrastructures

We model a private key`s life cycle as a finite state machine. The states are the key`s phases of life and the transition functions describe tasks to be done with the key. Based on this we define and describe the key authority, a trust center module, which potentiates the easy enforcement of secure management of private keys in hierarchical public key infrastructures. This is done by assembling all trust center tasks concerning the crucial handling of private keys within one centralized module. As this module resides under full control of the trust center`s carrier it can easily be protected by well-known organizational and technical measures.Comment: 5 pages, 2 figure

How much efficiency gains and price reductions for an efficiency defense? 'Quanto Basta'

Potential efficiency gains due to a merger can be used by competition authorities to judge upon proposed mergers. In a world where agents’ efforts, observable or unobservable, affect the success of a production cost reducing project that may be conducted as a stand-alone firm or in a merger, we characterize the merger decision and the type of errors a competition authority may make when it relies on an efficiency defense. In addition, we show that the occurrence of either type of errors is always smaller under the unobservable efforts assumption, than under the observable efforts one.mergers, efficiency defense, moral hazard

Networks of Relations

In this paper, we model networks of relational contracts. We explore sanctioning power within these networks under different information technologies depending on the shape of the network. The value of the relational network lies in the enforcement of cooperative agreements which would not be enforceable for the agents without access to the punishment power of other network members. We identify conditions for stability of such networks, conditions for transmission of information about past actions, and conditions under which self-sustainable subnetworks may actually inhibit a stable networkNetworks, Relational Contracts, Collusion, Social Capital

Improving the dynamical overlap algorithm

We present algorithmic improvements to the overlap Hybrid Monte Carlo algorithm, including preconditioning techniques and improvements to the correction step, used when one of the eigenvalues of the Kernel operator changes sign, which is now O(\Delta t^2) exact.Comment: 6 pages, 3 figures; poster contribution at Lattice 2005(Algorithms and machines