Cooperation and non-halting strategies

This note is a response to an unpublished paper by Evans and Thomas (1998) of which we have recently become aware. Evans and Thomas (1998) take issue with a paper that we published some years back on 'Cooperation and Effective Computability' in repeated games (Anderlini and Sabourian 1995). In that paper we showed that it is only the cooperative equilibria of an infinitely repeated two-player common-interest game with no discounting that survive both the restriction that players' strategies must be computable, and appropriately computable trembles. Evans and Thomas (1998) assert that our results are seemingly not robust to changes in the set of computable strategies at the disposal of each player. In particular, they claim that our equilibrium selection result does not extend to the case in which players are allowed to choose strategies that halt on certain histories but do not halt on others. The purpose of this note is to show that the claim in Evans and Thomas (1998) is misleading. We present a modification of the set-up of our earlier paper in which the cooperative equilibria are selected when strategies that halt on certain histories and do not halt on others are allowed. Although extensive modifications are required, the proof of this extension of our earlier result runs along the same general line of argument as the original proof

Efficient provision of public goods with endogenous redistribution

We study a continuous and balanced mechanism that is capable of implementing in Nash equilibrium all the Pareto-efficient individually rational allocations for an economy with public goods. The Government chooses a set of weights directly related to the Lindahl prices corresponding to the Pareto-efficient allocation it wants to implement. The mechanism then guarantees that initial endowments are re-allocated so that the chosen vector of Lindahl prices is indeed a Lindahl equilibrium, and implements the corresponding Lindahl allocation. Previously known mechanisms that implement the Lindahl correspondence do not allow the Government to choose which point on the Pareto frontier should be implemented, unless it can also redistribute initial endowments in the appropriate way. By contrast, in our case the Government directly controls the distribution of welfare in the economy. Finally, besides being balanced and continuous, our mechanism is `simple'. Each agent has to declare a desired increase in the amount of public good, and a vector of redistributive transfers of initial endowments (across other agents).

Bc physics at LHCb

The B+c meson is unique in the standard model as it is the ground state of a family of mesons containing two different heavy flavour quarks. Recent results on the B+c state are discussed and prospects of Bc studies at LHCb are described. Using the large data sample collected in 2011 at √s = 7TeV, the LHCb Collaboration achieved precise mass and production measurement of the B+c meson and reported the first observation of the B+c → J/ψ π+π−π+ and B+c → ψ(2S) π+ decay modes. Their branching fractions relative to B+c → J/ψπ+ are measured. Future studies on Bc excited states will provide a relevant input to the theoretical models of QCD-bound states involving two heavy quarks

Legal efficiency and consistency

© 2019 Elsevier B.V. We analyze the efficiency and consistency of court decisions under common and civil law. As a leading example, we study the enforcement of property rights. Judges are of two types: some are conservative and follow the precedent or the statute, while others maximize social welfare. When courts intervene ex-post, after the relevant economic choices have been made, welfare-maximizing courts face a “commitment problem.” Such an ex-post bias has implications on the relative “consistency” and efficiency of each legal system. Surprisingly, we find that court decisions are more consistent under common law than under civil law. The welfare comparison between the two systems is, instead, ambiguous. However, in changing economic environments, common law is more likely to dominate civil law because of its greater adaptability

Creep and locking of a low-angle normal fault: Insights from the Altotiberina fault in the Northern Apennines (Italy)

While low-angle normal faults have been recognized worldwide from geological studies, whether these structures are active or capable of generating big earthquakes is still debated. We provide new constraints on the role and modes of the Altotiberina fault (ATF) in accommodating extension in the Northern Apennines. We model GPS velocities to study block kinematics, faults slip rates and interseismic coupling of the ATF, which is active and accounts, with its antithetic fault, for a large part of the observed chain normal 3 mm/yr tectonic extension. A wide portion of the ATF creeps at the long-term slip rate (1.7 \ub1 0.3 mm/yr), but the shallow locked portions are compatible with M > 6.5 earthquakes. We suggest that positive stress accumulation due to ATF creep is most likely released by more favorable oriented splay faults, whose rupture may propagate downdip along low-angle normal fault surface and reduce the probability of occurrence of a seismic rupture of the shallower locked portion

Hydrodynamic Modelling for a Transportation System of Two Unmanned Underwater Vehicles: Semi-Empirical, Numerical and Experimental Analyses

Underwater transportation is an essential approach for scientific exploration, maritime construction and military operations. Determining the hydrodynamic coefficients for a complex underwater transportation system comprising multiple vehicles is challenging. Here, the suitability of a quick and less costly semi-empirical approach to obtain the hydrodynamic coefficients for a complex transportation system comprising two Unmanned Underwater Vehicles (UUVs) is investigated, where the interaction effects between UUVs are assumed to be negligible. The drag results were verified by Computational Fluid Dynamics (CFD) analysis at the steady state. The semi-empirical results agree with CFD in heave and sway; however, they were overpredicted in surge due to ignoring the wake effects. Furthermore, experiments were performed for the validation of the time-domain motion simulations with semi-empirical and CFD results. The simulations which were performed with the CFD drags were close to the experiments. The semi-empirical approach could be relied on once a correction parameter is included to account for the interactive effect between multiple UUVs. Overall, this work makes a contribution by deriving a semi-empirical approach for the dynamic and controlling system of dual UUVs, with CFD and experiments applied to ascertain its accuracy and potential improvement

Preparing and probing atomic number states with an atom interferometer

We describe the controlled loading and measurement of number-squeezed states and Poisson states of atoms in individual sites of a double well optical lattice. These states are input to an atom interferometer that is realized by symmetrically splitting individual lattice sites into double wells, allowing atoms in individual sites to evolve independently. The two paths then interfere, creating a matter-wave double-slit diffraction pattern. The time evolution of the double-slit diffraction pattern is used to measure the number statistics of the input state. The flexibility of our double well lattice provides a means to detect the presence of empty lattice sites, an important and so far unmeasured factor in determining the purity of a Mott state

Sublattice addressing and spin-dependent motion of atoms in a double-well lattice

We load atoms into every site of an optical lattice and selectively spin flip atoms in a sublattice consisting of every other site. These selected atoms are separated from their unselected neighbors by less than an optical wavelength. We also show spin-dependent transport, where atomic wave packets are coherently separated into adjacent sites according to their internal state. These tools should be useful for quantum information processing and quantum simulation of lattice models with neutral atoms