Non-Gaussianity and Excursion Set Theory: Halo Bias

We study the impact of primordial non-Gaussianity generated during inflation on the bias of halos using excursion set theory. We recapture the familiar result that the bias scales as $k^{-2}$ on large scales for local type non-Gaussianity but explicitly identify the approximations that go into this conclusion and the corrections to it. We solve the more complicated problem of non-spherical halos, for which the collapse threshold is scale dependent.Comment: 13 pages, 3 figures. v2 references added. Matches published versio

School Dropouts and Conditional Cash Transfers: Evidence from a Randomized Controlled Trial in Rural China’s Junior High Schools.

Recent anecdotal reports suggest that dropout rates may be higher and actually increasing over time in poor rural areas. There are many reasons not to be surprised that there is a dropout problem, given the fact that China has a high level of poverty among the rural population, a highly competitive education system and rapidly increasing wages for unskilled workers. The overall goal of this study is to examine if there is a dropout problem in rural China and to explore the effectiveness that a Conditional Cash Transfer (CCT) program could have on dropouts (and mechanism by which the CCT might affect drop outs). To meet this objective, we conducted a randomized controlled trial (RCT) of a CCT using a sample of 300 junior high school students in a nationally-designated poor county in Northwest China. Using our data, we found that the annual dropout rate in the study county was high, about 7%. We find, however, that a CCT program reduces drop outs by 60%; the dropout rate is 13.3% in the control group and 5.3 % in the treatment group. The program is most effective in the case of girls, younger students and the poorest performing students.

School dropouts and conditional cash transfers: evidence from a randomized controlled trial in rural China's junior high schools.

Recent anecdotal reports suggest that dropout rates may be higher and actually increasing over time in poor rural areas. There are many reasons not to be surprised that there is a dropout problem, given the fact that China has a high level of poverty among the rural population, a highly competitive education system and rapidly increasing wages for unskilled workers. The overall goal of this study is to examine if there is a dropout problem in rural China and to explore the effectiveness that a Conditional Cash Transfer (CCT) program could have on dropouts (and mechanism by which the CCT might affect drop outs). To meet this objective, we conducted a randomized controlled trial (RCT) of a CCT using a sample of 300 junior high school students in a nationally-designated poor county in Northwest China. Using our data, we found that the annual dropout rate in the study county was high, about 7.0%. We find, however, that a CCT program reduces drop outs by 60%; the dropout rate is 13.3% in the control group and 5.3 % in the treatment group. The program is most effective in the case of girls, younger students and the poorest performing students.

Do Poor Students Benefit from China’s Merger Program? Transfer Path and Educational Performance.

Aiming to provide better education facilities and improve the educational attainment of poor rural students, China’s government has been merging remote rural primary schools to centralized village, town, or county schools since the late 1990s. To accompany the policy, boarding facilities have been constructed that allow (mandate) primary school-aged children to live at school rather than at home. More generally, there also have been efforts to improve rural schools, especially those in counties and towns. Unfortunately, little empirical work has been available to evaluate the impact of the new merger and investment programs on the educational performance of students. Drawing on a unique dataset that records both the path by which students navigate their primary school years (i.e., which different types of schools did students attend) as well as math test scores in three poverty-stricken counties, we use descriptive statistics and multivariate analysis (both OLS and covariate matching) to analyze the relationship between different transfer paths and student educational performance. This allows us to examine the costs and benefits of the school merger and investment programs. The results of the analysis show that students who attend county schools perform systematically better than those attend village or town schools. However, completing primary school in town schools seems to have no effect on students’ academic performance. Surprisingly, starting primary education in a teaching point does not hurt rural students; on the contrary, it increases their test scores in some cases. Finally, in terms of the boarding effect, the neutral estimate in OLS and the negative estimate in covariate matching results confirm that boarding at school does not help the students; in some cases it may even reduce their academic performance.

Effects of biasing on the galaxy power spectrum at large scales

n this paper we study the effect of biasing on the power spectrum at large scales. We show that even though non-linear biasing does introduce a white noise contribution on large scales, the $P(k)\propto k^n$ behavior of the matter power spectrum on large scales may still be visible and above the white noise for about one decade. We show, that the Kaiser biasing scheme which leads to linear bias of the correlation function on {\em large} scales, also generates a linear bias of the {\rm power spectrum} on rather small scales. This is a consequence of the divergence on small scales of the pure Harrison-Zeldovich spectrum. However, biasing becomes k-dependent when we damp the underlying power spectrum on small scales. We also discuss the effect of biasing on the baryon acoustic oscillations.Comment: 9 pages, 4 figures. One figure and comments clarifying the linear biasing on small scales and references added. V3 version accepted in PR

Planar cell polarity signalling controls cell division orientation during zebrafish gastrulation

Oriented cell division is an integral part of pattern development in processes ranging from asymmetric segregation of cell-fate determinants to the shaping of tissues. Despite proposals that it has an important function in tissue elongation, the mechanisms regulating division orientation have been little studied outside of the invertebrates Caenorhabditis elegans and Drosophila melanogaster1. Here, we have analysed mitotic divisions during zebrafish gastrulation using in vivo confocal imaging and found that cells in dorsal tissues preferentially divide along the animal–vegetal axis of the embryo. Establishment of this animal–vegetal polarity requires the Wnt pathway components Silberblick/Wnt11, Dishevelled and Strabismus. Our findings demonstrate an important role for non-canonical Wnt signalling in oriented cell division during zebrafish gastrulation, and indicate that oriented cell division is a driving force for axis elongation. Furthermore, we propose that non-canonical Wnt signalling has a conserved role in vertebrate axis elongation, orienting both cell intercalation and mitotic division

Detecting the Earliest Galaxies Through Two New Sources of 21cm Fluctuations

The first galaxies that formed at a redshift ~20-30 emitted continuum photons with energies between the Lyman-alpha and Lyman limit wavelengths of hydrogen, to which the neutral universe was transparent except at the Lyman-series resonances. As these photons redshifted or scattered into the Lyman-alpha resonance they coupled the spin temperature of the 21cm transition of hydrogen to the gas temperature, allowing it to deviate from the microwave background temperature. We show that the fluctuations in the radiation emitted by the first galaxies produced strong fluctuations in the 21cm flux before the Lyman-alpha coupling became saturated. The fluctuations were caused by biased inhomogeneities in the density of galaxies, along with Poisson fluctuations in the number of galaxies. Observing the power-spectra of these two sources would probe the number density of the earliest galaxies and the typical mass of their host dark matter halos. The enhanced amplitude of the 21cm fluctuations from the era of Lyman-alpha coupling improves considerably the practical prospects for their detection.Comment: 11 pages, 7 figures, ApJ, published. Normalization fixed in top panels of Figures 4-

The Far-Infrared Background Correlation with CMB Lensing

The intervening large--scale structure distorts cosmic microwave background (CMB) anisotropies via gravitational lensing. The same large--scale structure, traced by dusty star--forming galaxies, also induces anisotropies in the far--infrared background (FIRB). We investigate the resulting inter--dependence of the FIRB and CMB with a halo model for the FIRB. In particular, we calculate the cross--correlation between the lensing potential and the FIRB. The lensing potential can be quadratically estimated from CMB temperature and/or polarization maps. We show that the cross--correlation can be measured with high signal--to--noise with data from the Planck Surveyor. We discuss how such a measurement can be used to understand the nature of FIRB sources and their relation to the distribution of dark matter.Comment: 9 pages, 5 figures, submitted to Ap