A Study of the LEP and SLD Measurements of AbA_b

A systematic study is made of the data dependence of the parameter $A_{\rm{b}}$, that, since 1995, has shown a deviation from the Standard Model prediction of between 2.4 and 3.1 standard deviations. Issues addressed include: the effect of particular measurements, values found by individual experiments, LEP/SLD comparison, and the treatment of systematic errors. The effect, currently at the 2.4$\sigma$ level, is found to vary in the range from 1.7$\sigma$ to 2.9$\sigma$ by excluding marginal or particularly sensitive data. Since essentially the full LEP and SLD Z decay data sets are now analysed the meaning of the deviation, (new physics, or marginal statistical fluctuation) is unlikely to be given by the present generation of colliders.Comment: 15 pages 7 figures 7 table

Fitting Precision Electroweak Data with Exotic Heavy Quarks

The 1999 precision electroweak data from LEP and SLC persist in showing some slight discrepancies from the assumed standard model, mostly regarding $b$ and $c$ quarks. We show how their mixing with exotic heavy quarks could result in a more consistent fit of all the data, including two unconventional interpretations of the top quark.Comment: 7 pages, no figure, 2 typos corrected, 1 reference update

Origin of spin reorientation transitions in antiferromagnetic MnPt-based alloys

Antiferromagnetic MnPt exhibits a spin reorientation transition (SRT) as a function of temperature, and off-stoichiometric Mn-Pt alloys also display SRTs as a function of concentration. The magnetocrystalline anisotropy in these alloys is studied using first-principles calculations based on the coherent potential approximation and the disordered local moment method. The anisotropy is fairly small and sensitive to the variations in composition and temperature due to the cancellation of large contributions from different parts of the Brillouin zone. Concentration and temperature-driven SRTs are found in reasonable agreement with experimental data. Contributions from specific band-structure features are identified and used to explain the origin of the SRTs.Comment: 6 pages, 8 figure

Moral hazard under commercial and universal banking

Many claims have been made about the potential benefits, and the potential costs, of adopting a system of universal banking in the United States. We evaluate these claims using a model where there is a moral hazard problem between banks and “borrowers,” a moral hazard problem between banks and a deposit insurer, and a costly state verification problem. Under conditions we describe, allowing banks to take equity positions in firms strengthens their ability to extract surplus, and exacerbates problems of moral hazard. The incentives of universal banks to take equity positions will often be strongest when these problems are most severe.Universal banks

Deposit insurance: a reconsideration

This paper undertakes a simple general equilibrium analysis of the consequences of deposit insurance programs, the way in which they are priced and the way in which they fund revenue shortfalls. We show that the central issue is how the government will make up any FDIC losses. Under one scheme for making up the losses, we show that FDIC policy is irrelevant: it does not matter what premium is charged, nor does it matter how big FDIC losses are. Under another scheme, all that matters is the magnitude of the losses. And there is no presumption that small losses are “good.” We also show that multiple equilibria can be observed and Pareto ranked. Some economies may be “trapped” in equilibria with inefficient financial systems. Our analysis provides counterexamples to the following propositions. (1) Actuarially fair pricing of deposit insurance is always desirable. (2) Implicit FDIC subsidization of banks through deposit insurance is always undesirable. (3) “Large” FDIC losses are necessarily symptomatic of a poorly designed deposit insurance system.Deposit insurance

Trapping atoms using nanoscale quantum vacuum forces

Quantum vacuum forces dictate the interaction between individual atoms and dielectric surfaces at nanoscale distances. For example, their large strengths typically overwhelm externally applied forces, which makes it challenging to controllably interface cold atoms with nearby nanophotonic systems. Here, we show that it is possible to tailor the vacuum forces themselves to provide strong trapping potentials. The trapping scheme takes advantage of the attractive ground state potential and adiabatic dressing with an excited state whose potential is engineered to be resonantly enhanced and repulsive. This procedure yields a strong metastable trap, with the fraction of excited state population scaling inversely with the quality factor of the resonance of the dielectric structure. We analyze realistic limitations to the trap lifetime and discuss possible applications that might emerge from the large trap depths and nanoscale confinement.Comment: 13 pages, 4 figure