Cosmological perturbation theory in 1+1 dimensions

Many recent studies have highlighted certain failures of the standard Eulerian-space cosmological perturbation theory (SPT). Its problems include (1) not capturing large-scale bulk flows [leading to an O(1) error in the 1-loop SPT prediction for the baryon acoustic peak in the correlation function], (2) assuming that the Universe behaves as a pressureless, inviscid fluid, and (3) treating fluctuations on scales that are non-perturbative as if they were. Recent studies have highlighted the successes of perturbation theory in Lagrangian space or theories that solve equations for the effective dynamics of smoothed fields. Both approaches mitigate some or all of the aforementioned issues with SPT. We discuss these physical developments by specializing to the simplified 1D case of gravitationally interacting sheets, which allows us to substantially reduces the analytic overhead and still (as we show) maintain many of the same behaviors as in 3D. In 1D, linear-order Lagrangian perturbation theory ("the Zeldovich approximation") is exact up to shell crossing, and we prove that n^{th}-order Eulerian perturbation theory converges to the Zeldovich approximation as n goes to infinity. In no 1D cosmology that we consider (including a CDM-like case and power-law models) do these theories describe accurately the matter power spectrum on any mildly nonlinear scale. We find that theories based on effective equations are much more successful at describing the dynamics. Finally, we discuss many topics that have recently appeared in the perturbation theory literature such as beat coupling, the shift and smearing of the baryon acoustic oscillation feature, and the advantages of Fourier versus configuration space. Our simplified 1D case serves as an intuitive review of these perturbation theory results.Comment: 28 pages + appendices; 10 figures; matches version accepted to JCA

Implications of the large OVI columns around low-redshift L∗L_* galaxies

Observations reveal massive amounts of OVI around star-forming $L_*$ galaxies, with covering fractions of near unity extending to the host halo's virial radius. This OVI absorption is typically kinematically centered upon photoionized gas, with line widths that are suprathermal and kinematically offset from the galaxy. We discuss various scenarios and whether they could result in the observed phenomenology (cooling gas flows, boundary layers, shocks, virialized gas, photoionized clouds in thermal equilibrium). If predominantly collisionally ionized, as we argue is most probable, the OVI observations require that the circumgalactic medium (CGM) of $L_*$ galaxies holds nearly all the associated baryons within a virial radius ($\sim 10^{11}M_\odot$) and hosts massive flows of cooling gas with $\approx30[nT/30{\rm~cm^{-3}K}]~M_\odot~$yr$^{-1}$, which must be largely prevented from accreting onto the host galaxy. Cooling and feedback energetics considerations require $10 <\langle nT\rangle<100{\rm~cm^{-3}K}$ for the warm and hot halo gases. We argue that virialized gas, boundary layers, hot winds, and shocks are unlikely to directly account for the bulk of the OVI. Furthermore, we show that there is a robust constraint on the number density of many of the photoionized $\sim10^4$K absorption systems that yields upper bounds in the range $n<(0.1-3)\times10^{-3}(Z/0.3)$cm$^{-3}$, where $Z$ is the metallicity, suggestive that the dominant pressure in some photoionized clouds is nonthermal. This constraint, which requires minimal ionization modeling, is in accord with the low densities inferred from more complex photoionization modeling. The large amount of cooling gas that is inferred could re-form these clouds in a fraction of the halo dynamical time, as some arguments require, and it requires much of the feedback energy available from supernovae and stellar winds to be dissipated in the CGM.Comment: 16 pages, matches version accepted to Ap

Prospects for Growth in the Euro Area

We review the recent performance of the Euro area economy, focusing in detail on the separate roles played by labour input, capital input, and total factor productivity (TFP). After a long period of catching up with US levels of labour productivity, Euro area productivity growth has, since the mid-1990s, fallen significantly behind. We show that this recent divergence has accelerated since 2000, and that this is mainly due to the poor rate of Euro area TFP growth. Based on prevailing trends, we estimate that potential output growth in the Euro area currently may be running as low as 1.5 percent per year. In addition, if TFP growth stays at recent levels, the output growth rate will decline further due to weaker capital deepening. To consider future Euro area prospects for growth, we examine a set of alternative scenarios, each of which posits a potential increase in a determinant of output growth. One of these scenarios focuses on the potential effects of greater labour market deregulation.

Assessing the Role of Income and Interest Rates in Determining House Prices

Property prices across many OECD countries have witnessed remarkable increases over the past 10 years. Two factors frequently posited for this boom are higher income levels and the benign interest rate environment experienced in many of these countries. However, empirical models of house prices struggle to achieve credible results concerning the impact of interest rates with coefficients that are frequently insignificant or of the wrong sign. In this paper we propose an intuitive theoretical model of house prices where the demand for housing is driven by how much individuals can borrow from financial institutions. This level of borrowing depends on disposable income levels and current interest rates. We empirically test this model by applying it to the Irish property market. Our results support the existence of a long-run relationship between actual house prices and the amount individuals can borrow with plausible and statistically significant adjustment to this long run equilibrium.

How are Irish households coping with their mortgage repayments? Information from the SILC Survey

This paper uses information contained within the Survey on Income and Living Conditions (SILC) to examine the ability of Irish households to sustain their mortgage repayments. We calculate mortgage repayment to income (MRTI) ratios for a representative sample of Irish households and examine the distribution of this ratio. In particular, we stratify information on marital, work and educational status along with household composition according to this MRTI. We also examine the distribution of information on household mortgages such as the source, the interest rate paid, the age and tenure, and the monthly repayment of the mortgage according to the same ratio. Finally, the distributional implications for the MRTI of a significant unemployment and interest rate shock are also examined.