Notes on Spinoptics in a Stationary Spacetime

In arXiv:1105.5629, equations of the modified geometrical optics for circularly polarized photon trajectories in a stationary spacetime are derived by using a (1+3)-decomposed form of Maxwell's equations. We derive the same results by using a four-dimensional covariant description. In our procedure, the null nature of the modified photon trajectory naturally appears and the energy flux is apparently null. We find that, in contrast to the standard geometrical optics, the inner product of the stationary Killing vector and the tangent null vector to the modified photon trajectory is no longer a conserved quantity along light paths. This quantity is furthermore different for left and right handed photon. A similar analysis is performed for gravitational waves and an additional factor of 2 appears in the modification due to the spin-2 nature of gravitational waves.Comment: 15 pages, to appear in PR

Orbital-selective Mass Enhancements in Multi-band Ca2−x_{2-x}Srx_{x}RuO4_{4} Systems Analyzed by the Extended Drude Model

We investigated optical spectra of quasi-two-dimensional multi-band Ca$_{2-x}$Sr$_{x}$RuO$_{4}$ systems. The extended Drude model analysis on the ab-plane optical conductivity spectra indicates that the effective mass should be enhanced near $x=0.5$. Based on the sum rule argument, we showed that the orbital-selective Mott-gap opening for the $d_{yz/zx}$ bands, the widely investigated picture, could not be the origin of the mass enhancement. We exploited the multi-band effects in the extended Drude model analysis, and demonstrated that the intriguing heavy mass state near $x=0.5$ should come from the renormalization of the $d_{xy}$ band.Comment: 4 figure

A Low Order Theory of Arctic Sea Ice Stability

We analyze the stability of a low-order coupled sea ice and climate model and extract the essential physics governing the time scales of response as a function of greenhouse gas forcing. Under present climate conditions the stability is controlled by longwave radiation driven heat conduction. However, as greenhouse gas forcing increases and the ice cover decays, the destabilizing influence of ice-albedo feedback acts on equal footing with longwave stabilization. Both are seasonally out of phase and as the system warms towards a seasonal ice state these effects, which underlie the bifurcations between climate states, combine exhibiting a "slowing down" to extend the intrinsic relaxation time scale from ~ 2 yr to 5 yr.Comment: 5 pages, 2 figure

Epitaxial growth of (111)-oriented LaAlO3_3/LaNiO3_3 ultra-thin superlattices

The epitaxial stabilization of a single layer or superlattice structures composed of complex oxide materials on polar (111) surfaces is severely burdened by reconstructions at the interface, that commonly arise to neutralize the polarity. We report on the synthesis of high quality LaNiO$_3$/mLaAlO$_3$ pseudo cubic (111) superlattices on polar (111)-oriented LaAlO$_3$, the proposed complex oxide candidate for a topological insulating behavior. Comprehensive X-Ray diffraction measurements, RHEED, and element specific resonant X-ray absorption spectroscopy affirm their high structural and chemical quality. The study offers an opportunity to fabricate interesting interface and topology controlled (111) oriented superlattices based on ortho-nickelates

Efficient banking under interstate branching

Nationally chartered banks will be allowed to branch across state lines beginning June 1, 1997. Whether they will depends on their assessment of the profitability of such a delivery system for their services and on their preferences regarding risk and return. The authors investigate the probable effect of interstate branching on banks' risk-return tradeoff, accounting for the endogeneity of deposit volatility. If interstate branching improves the risk-return tradeoff banks face, banks that branch across state lines may choose a higher level of risk in return for higher profits. The authors find distinct efficiency gains due to geographic diversity.Branch banks ; Interstate banking

Safety in numbers? Geographic diversification and bank insolvency risk

The Riegle-Neal Interstate Banking and Branching Efficiency Act, passed in September 1994 and effective June 1, 1997, will allow nationally chartered banks to branch across state lines. This act will remove impediments to interstate expansion and permit the consolidation of existing interstate networks ; What will be the impact of this legislation on bank performance and bank safety? Removing impediments to geographic expansion should improve the risk-return tradeoff faced by most banks. However, this paper argues that economic theory does not tell us whether an improvement in the risk-return tradeoff will lead to a reduction in the volatility of bank returns or in the probability of insolvency. ; The authors investigate the role of geographic diversification on bank performance and safety using bank holding company data. The authors find that an increase in the number of branches lowers insolvency risk and increases efficiency for inefficient bank holding companies; an increase in the number of states in which a bank holding company operates increases insolvency risk but has an insignificant effect on efficiency. Branch expansion raises the risk of insolvency for efficient bank holding companies, while an increase in the number of states has an insignfiicant effect on insolvency riskBank failures ; Interstate banking

Recovering risky technologies using the almost ideal demand system: an application to U.S. banking

Using modern duality theory to recover technologies from data can be complicated by the risk characteristics of production. In many industries, risk influences cost and revenue and can create the potential for costly episodes of financial distress. When risk is an important consideration in production, the standard cost and profit functions may not adequately describe the firm's technology and choice of production plan. In general, standard models fail to account for risk and its endogeneity. The authors distinguish between exogenous risk, which varies over the firm's choice sets, and endogenous risk, which is chosen by the firm in conjunction with its production decision. They show that, when risk matters in production decisions, it is important to account for risk's endogeneity. ; For example, better risk diversification that results, for example, from an increase in scale, improves the reward to risk-taking and may under certain conditions induce the firm to take on more risk to increase the firm's value. A choice of higher risk at a larger scale could add to costs and mask scale economies that may result from better diversification. ; This paper introduces risk into the dual model of production by constructing a utility-maximizing model in which managers choose their most preferred production plan. The authors show that the utility function that ranks production plans is equivalent to a ranking of subjective probability distributions of profit that are conditional on the production plan. The most preferred production plan results from the firm's choice of an optimal profit distribution. The model is sufficiently general to incorporate risk aversion as well as risk neutrality. Hence, it can account for the case where the potential for costly financial distress makes trading profit for reduced risk a value-maximizing strategy. ; The authors implement the model using the Almost Ideal Demand System to derive utility-maximizing share equations for profit and inputs, given the output vector and given sources of risk to control for choices that would affect endogenous risk. The most preferred cost function is obtained from the profit share equation and we show that, if risk neutrality is imposed, this system is identical to the standard translog cost system except that it controls for sources of risk. ; The authors apply the model to the U.S. banking industry using 1989-90 data on banks with over $1 billion in assets. The authors find evidence that managers trade return for reduced risk, which is consistent with the significant regulatory and financial costs of bank distress. In addition, the authors find evidence of significant scale economies that help explain the recent wave of large bank mergers. Using these same data, the authors also estimate the standard cost function, which does not explicitly account for risk, and they obtain the usual results of esentially constant returns to scale, which contradicts the often-stated rationale for bank mergers.Banks and banking ; Economies of scale