The Consistent Newtonian Limit of Einstein's Gravity with a Cosmological Constant

We derive the `exact' Newtonian limit of general relativity with a positive cosmological constant $\Lambda$. We point out that in contrast to the case with $\Lambda = 0$, the presence of a positive $\Lambda$ in Einsteins's equations enforces, via the condition $| \Phi | \ll 1$, on the potential $\Phi$, a range ${\cal R}_{max}(\Lambda) \gg r \gg {\cal R}_{min} (\Lambda)$, within which the Newtonian limit is valid. It also leads to the existence of a maximum mass, ${\cal M}_{max}(\Lambda)$. As a consequence we cannot put the boundary condition for the solution of the Poisson equation at infinity. A boundary condition suitably chosen now at a finite range will then get reflected in the solution of $\Phi$ provided the mass distribution is not spherically symmetric.Comment: Latex, 15 pages, no figures, errors correcte

Current at a distance and resonant transparency in Weyl semimetals

Surface Fermi arcs are the most prominent manifestation of the topological nature of Weyl semimetals. In the presence of a static magnetic field oriented perpendicular to the sample surface, their existence leads to unique inter-surface cyclotron orbits. We propose two experiments which directly probe the Fermi arcs: a magnetic field dependent non-local DC voltage and sharp resonances in the transmission of electromagnetic waves at frequencies controlled by the field. We show that these experiments do not rely on quantum mechanical phase coherence, which renders them far more robust and experimentally accessible than quantum effects. We also comment on the applicability of these ideas to Dirac semimetals.Comment: 10 pages, 8 figure

HST archive primer, version 4.1

This version of the HST Archive Primer provides the basic information a user needs to know to access the HST archive via StarView the new user interface to the archive. Using StarView, users can search for observations interest, find calibration reference files, and retrieve data from the archive. Both the terminal version of StarView and the X-windows version feature a name resolver which simplifies searches of the HST archive based on target name. In addition, the X-windows version of StarView allows preview of all public HST data; compressed versions of public images are displayed via SAOIMAGE, while spectra are plotted using the public plotting package, XMGR. Finally, the version of StarView described here features screens designed for observers preparing Cycle 5 HST proposals

Nonthermal Emission Associated with Strong AGN Outbursts at the Centers of Galaxy Clusters

Recently, strong AGN outbursts at the centers of galaxy clusters have been found. Using a simple model, we study particle acceleration around a shock excited by an outburst and estimate nonthermal emission from the accelerated particles. We show that emission from secondary electrons is consistent with the radio observations of the minihalo in the Perseus cluster, if there was a strong AGN outburst >~10^8 yrs ago with an energy of ~1.8x10^62 erg. The validity of our model depends on the frequency of the large outbursts. We also estimate gamma-ray emission from the accelerated particles and show that it could be detected with GLAST.Comment: Accepted for publication in ApJ

Optimal eigenvalues estimate for the Dirac operator on domains with boundary

We give a lower bound for the eigenvalues of the Dirac operator on a compact domain of a Riemannian spin manifold under the \MIT bag boundary condition. The limiting case is characterized by the existence of an imaginary Killing spinor.Comment: 10 page

Improved Constraints on the Acceleration History of the Universe and the Properties of the Dark Energy

We extend and apply a model-independent analysis method developed earlier by Daly & Djorgovski to new samples of supernova standard candles, radio galaxy and cluster standard rulers, and use it to constrain physical properties of the dark energy as functions of redshift. Similar results are obtained for the radio galaxy and supernova data sets. The first and second derivatives of the distance are compared directly with predictions in a standard model based on General Relativity. The good agreement indicates that General Relativity provides an accurate description of the data on look-back time scales of about ten billion years. The first and second derivatives are combined to obtain the acceleration parameter, assuming only the validity of the Robertson-Walker metric, independent of a theory of gravity and of the physical nature of the dark energy. The acceleration of the universe at the current epoch is indicated by the analysis. The effect of non-zero space curvature on q(z) is explored. We solve for the pressure, energy density, equation of state, and potential and kinetic energy of the dark energy as functions of redshift assuming that General Relativity is the correct theory of gravity, and the results indicate that a cosmological constant in a spatially flat universe provides a good description of each of these quantities over the redshift range from zero to about one. We define a new function, the dark energy indicator, in terms of the first and second derivatives of the coordinate distance and show how this can be used to measure deviations of w from -1 and to obtain a new and independent measure of Omega.Comment: 46 pages, submitted for publicatio

Quasars, their host galaxies, and their central black holes

We present the final results from our deep HST imaging study of the hosts of radio-quiet quasars (RQQs), radio-loud quasars (RLQs) and radio galaxies (RGs). We describe new WFPC2 R-band observations for 14 objects and model these images in conjunction with the data already reported in McLure et al (1999). We find that spheroidal hosts become more prevalent with increasing nuclear luminosity such that, for nuclear luminosities M_V < -23.5, the hosts of both radio-loud and radio-quiet AGN are virtually all massive ellipticals. Moreover we demonstrate that the basic properties of these hosts are indistinguishable from those of quiescent, evolved, low-redshift ellipticals of comparable mass. This result kills any lingering notion that radio-loudness is determined by host-galaxy morphology, and also sets severe constraints on evolutionary schemes which attempt to link low-z ULIRGs with RQQs. Instead, we show that our results are as expected given the relationship between black-hole and spheroid mass established for nearby galaxies, and apply this relation to estimate the mass of the black hole in each object. The results agree very well with completely-independent estimates based on nuclear emission-line widths; all the quasars in our sample have M(bh) > 5 x 10^8 solar masses, while the radio-loud objects are confined to M(bh) > 10^9 solar masses. This apparent mass-threshold difference, which provides a natural explanation for why RQQs outnumber RLQs by a factor of 10, appears to reflect the existence of a minimum and maximum level of black-hole radio output which is a strong function of black-hole mass. Finally, we use our results to estimate the fraction of massive spheroids/black-holes which produce quasar-level activity. This fraction is \~0.1% at the present day, rising to > 10% at z = 2-3.Comment: Revised version accepted for publication in Monthly Notices of the Royal Astronomical Society. 46 pages, the final 19 of which comprise an Appendix. 15 figures in main text. A further 14 4-panel greyscale plots and 14 line plots which appear in the Appendix have been reproduced here with reduced quality due to space limitations. A full resolution copy of the manuscript can be obtained via ftp://ftp.roe.ac.uk/pub/jsd/dunlop2002.ps.g

Two centuries of farmland prices in England

The dissemination of robust asset price data can help improve market efficiency, resource allocation and investment analysis. Land prices influence housing affordability, food security and the carbon infrastructure. Yet price and return histories for farmland in England are fragmented. To provide perspective, a long farmland price series is needed to improve transparency and bring the asset class into line with commercial and residential real estate. After reviewing the historical backdrop and considering methodology, this research uses a chain-linking approach to construct a long-term farmland price series for England. It then adjusts the series for inflation to examine real land prices. The resulting two-century English farmland prices series contributes to farmland market analysis. Notwithstanding some concerns with long-run chain component heterogeneity, the combined series helps us to understand English average farmland price dynamics. As measured by the geometric mean, English land price real capital returns have been positive over more than two centuries. Farmland real price growth was 0.33 per cent annually from 1781 to 2013 and 0.71 per cent from 1801 to 2013. The series contributes to an understanding of land price dynamics. Sir, – In these times, when the rental and marketable value of lan

Control of multiferroic domains by external electric fields in TbMnO3

The control of multiferroic domains through external electric fields has been studied by dielectric measurements and by polarized neutron diffraction on single-crystalline TbMnO$_3$. Full hysteresis cycles were recorded by varying an external field of the order of several kV/mm and by recording the chiral magnetic scattering as well as the charge in a sample capacitor. Both methods yield comparable coercive fields that increase upon cooling.Comment: 12 pages, 6 figure