Cosmological backreaction in higher-derivative gravity expansions

We calculate a general effective stress-energy tensor induced by cosmological inhomogeneity in effective theories of gravity where the action is Taylor-expandable in the Riemann tensor and covariant derivatives of the Riemann tensor. This is of interest as an effective fluid that might provide an alternative to the cosmological constant, but it also applies to gravitational waves. We use an adaptation of Green and Wald's weak-averaging framework, which averages over perturbations in the field equation where the perturbation length scales are small compared to the averaging scale. In this adaptation, the length scale of the effective theory, $1/M$, is also taken to be small compared with the averaging scale. This ensures that the perturbation length scales remain in fixed proportion to the length scale of the effective theory as the cosmological averaging scale is taken to be large. We find that backreaction from higher-derivative terms in the effective action can continue to be important in the late universe, given a source of sufficiently high-frequency metric perturbations. This backreaction might also provide a window on exotic particle physics in the far ultraviolet.Comment: 27 pages, 2 references added, minor clarifications made, comments added to introduction and discussion, some details moved to appendice

An Empirical Investigation of the Performance of Japanese Mutual Funds: Skill or Luck?

This paper assesses the performance of 355 actively managed Japanese Equity Mutual Funds between April 2011 and April 2016. The equal weight portfolio and Jensen’s alpha measures of active management provide strong evidence that Japanese Mutual Funds fail to outperform the benchmark four-factor capital asset pricing model. When it comes to market timing, the Treynor and Mazuy measure shows that 33 funds have significant positive market timing ability which is largely offset by 31 funds with significant negative timing ability. To ensure the statistical inference is robust to the non-normality found in 33 funds we employ Fama and French’s cross-sectional bootstrap. The results show that a large proportion of funds fail to outperform a hypothetical world with no skill. On the persistence of skill we find that there is stronger persistence for poor performing funds than for strong performing funds

An Empirical Investigation of the Performance of Japanese Mutual Funds: Skill or Luck?

This paper assesses the performance of 355 actively managed Japanese Equity Mutual Funds between April 2011 and April 2016. The equal weight portfolio and Jensen’s alpha measures of active management provide strong evidence that Japanese Mutual Funds fail to outperform the benchmark four-factor capital asset pricing model. When it comes to market timing, the Treynor and Mazuy measure shows that 33 funds have significant positive market timing ability which is largely offset by 31 funds with significant negative timing ability. To ensure the statistical inference is robust to the non-normality found in 33 funds we employ Fama and French’s cross-sectional bootstrap. The results show that a large proportion of funds fail to outperform a hypothetical world with no skill. On the persistence of skill we find that there is stronger persistence for poor performing funds than for strong performing funds

American Longevity: Past, Present, and Future

How long we live, and how long members of our families and social groups live, is extraordinarily important to us. It's not a subject of daily discussion, but it would be if we were threatened with a return to earlier conditions. Unfortunately, the subject of longevity falls between the cracks of academe and has received far less attention than it warrants. We are all aware, at least dimly, that peole are living longer than they used to. The numbers are impressive: at the turn of the century, life expectancy at birth in the United States was 48 years; it's now 76 years. Since life expectancy during the Stone Age was in the range of 20 to 30 years, it is clear that a majority of the cumulative advances have taken place in the short span of the 20th century. Without the improvements during this century, half of us would not e here: a quarter of the present U.S. population would have been born and died, and another quarter would never have been born because of the pre-reproductive death of a mother, grandmother, or great grandmother. In developing countries, nearly all of the improvements in longevity have occurred in this century. How these gains were achieved has important implications for public policy; how large future gains will be is the single most important area of uncertainty affecting the fiscal viability of our "old age welfare state." These are the two related issues that I focus on in this policy brief.

Decomposing changes in income risk using consumption data

This paper concerns the decomposition of income risk into permanent and transitory components using repeated cross-section data on income and consumption. Our focus is on the detection of changes in the magnitudes of variances of permanent and transitory risks. A new approximation to the optimal consumption growth rule is developed. Evidence from a dynamic stochastic simulation is used to show that this approximation can provide a robust method for decomposing income risk in a nonstationary environment. We examine robustness to unobserved heterogeneity in consumption growth and to unobserved heterogeneity in income growth. We use this approach to investigate the growth in income inequality in the UK in the 1980s

Income risk and consumption inequality: a simulation study

This paper assesses the accuracy of decomposing income risk into permanent and transitory components using income and consumption data. We develop a specific approximation to the optimal consumption growth rule and use Monte Carlo evidence to show that this approximation can provide a robust method for decomposing income risk. The availability of asset data enables the use of a more accurate approximation allowing for partial self-insurance against permanent shocks. We show that the use of data on median asset holdings corrects much of the error in the simple approximation which assumes no self-insurance against permanent shocks

An application of design knowledge captured from multiple sources

The Hubble Space Telescope Operational Readiness Expert Safemode Investigation System (HSTORESIS) is a reusable knowledge base shell used to demonstrate the integration and application of design knowledge captured from multiple technical domains. The design of HSTORESIS is based on a partitioning of knowledge to maximize the potential for reuse of certain types of knowledge