325 research outputs found
Cosmology beyond BAO from the 3D distribution of the Lyman-α forest
We propose a new method for fitting the full-shape of the Lyman-α (Lyâα) forest 3D correlation function in order to measure the Alcock-Paczynski (AP) effect. Our method preserves the robustness of baryon acoustic oscillations (BAO) analyses, while also providing extra cosmological information from a broader range of scales. We compute idealized forecasts for the Dark Energy Spectroscopic Instrument (DESI) using the Lyâα autocorrelation and its cross-correlation with quasars, and show how this type of analysis improves cosmological constraints. The DESI Lyâα BAO analysis is expected to measure H(zeff)rd and DM(zeff)/rd with a precision of âŒ0.9 per centâ , where H is the Hubble parameter, rd is the comoving BAO scale, DM is the comoving angular diameter distance, and the effective redshift of the measurement is zeff â 2.3. By fitting the AP parameter from the full shape of the two correlations, we show that we can obtain a precision of âŒ0.5â0.6 per cent on each of H(zeff)rd and DM(zeff)/rd. Furthermore, we show that a joint full-shape analysis of the Lyâα auto and cross-correlation with quasars can measure the linear growth rate times the amplitude of matter fluctuations in spheres of 8âhâ1Mpc, fÏ8(zeff). Such an analysis could provide the first ever measurement of fÏ8(zeff) at redshift zeff > 2. By combining this with the quasar autocorrelation in a joint analysis of the three high-redshift two-point correlation functions, we show that DESI could be able to measure fÏ8(zeff â 2.3) with a precision of 5â12 per centâ , depending on the smallest scale fitted
Nominal Logic Programming
Nominal logic is an extension of first-order logic which provides a simple
foundation for formalizing and reasoning about abstract syntax modulo
consistent renaming of bound names (that is, alpha-equivalence). This article
investigates logic programming based on nominal logic. We describe some typical
nominal logic programs, and develop the model-theoretic, proof-theoretic, and
operational semantics of such programs. Besides being of interest for ensuring
the correct behavior of implementations, these results provide a rigorous
foundation for techniques for analysis and reasoning about nominal logic
programs, as we illustrate via examples.Comment: 46 pages; 19 page appendix; 13 figures. Revised journal submission as
of July 23, 200
The Jubilee ISW Project - II. Observed and simulated imprints of voids and superclusters on the cosmic microwave background
We examine the integrated SachsâWolfe (ISW) imprint of voids and superclusters on the cosmic microwave background. We first study results from the Jubilee N-body simulation. From Jubilee, we obtain the full-sky ISW signal from structures out to redshift z = 1.4 and a mock luminous red galaxy catalogue. We confirm that the expected signal in the concordance cold dark matter (CDM) model is very small and likely to always be much smaller than the anisotropies arising at the last scattering surface. Any current detections of such an imprint must, therefore, predominantly arise from something other than an ISW effect in a CDM universe. Using the simulation as a guide, we then look for the signal using a catalogue of voids and superclusters from the Sloan Digital Sky Survey. We find a result that is consistent with the CDM model, i.e. a signal consistent with zero
Work Zone Simulator Analysis: Driver Performance and Acceptance of Missouri Alternate Lane Shift Configurations
The objective of this project is to evaluate MoDOTâs alternate lane shift sign configuration for work zones. The single signproposed by MoDOT provides the traveler with enough information to let them know that all lanes are available to shift around thework zone, whereas the MUTCD signs require drivers to see two signs. This research simulation project evaluates the driversâ laneshifting performance and acceptance of the alternate lane shift sign proposed by MoDOT to be used on work zones as compared tothe MUTCD lane shift signs. Based on the study results, no difference was observed between MUTCD lane shift sign andMoDOT lane shift sign lane shift patterns with respect to driving patterns. In summary, statistical data analysis clearlydemonstrated that there was not a noticeable, statistical difference between lane change patterns of drivers in the MoDOT alternatesigns with MUTCD signs in the work zone
Reconciling the local void with the CMB
In the standard cosmological model, the dimming of distant Type Ia supernovae
is explained by invoking the existence of repulsive `dark energy' which is
causing the Hubble expansion to accelerate. However this may be an artifact of
interpreting the data in an (oversimplified) homogeneous model universe. In the
simplest inhomogeneous model which fits the SNe Ia Hubble diagram without dark
energy, we are located close to the centre of a void modelled by a
Lema\'itre-Tolman-Bondi metric. It has been claimed that such models cannot fit
the CMB and other cosmological data. This is however based on the assumption of
a scale-free spectrum for the primordial density perturbation. An alternative
physically motivated form for the spectrum enables a good fit to both SNe Ia
(Constitution/Union2) and CMB (WMAP 7-yr) data, and to the locally measured
Hubble parameter. Constraints from baryon acoustic oscillations and primordial
nucleosynthesis are also satisfied.Comment: 13 pages, 4 figures. Typos corrected and missing references added.
Matches the published version in PR
Self-similarity and universality of void density profiles in simulation and SDSS data
The stacked density profile of cosmic voids in the galaxy distribution provides an important tool for the use of voids for precision cosmology. We study the density profiles of voids identified using the ZOBOV watershed transform algorithm in realistic mock luminous red galaxy (LRG) catalogues from the Jubilee simulation, as well as in void catalogues constructed from the SDSS LRG and Main Galaxy samples. We compare different methods for reconstructing density profiles scaled by the void radius and show that the most commonly used method based on counts in shells and simple averaging is statistically flawed as it underestimates the density in void interiors. We provide two alternative methods that do not suffer from this effect; one based on Voronoi tessellations is also easily able to account from artefacts due to finite survey boundaries and so is more suitable when comparing simulation data to observation. Using this method, we show that the most robust voids in simulation are exactly self-similar, meaning that their average rescaled profile does not depend on the void size. Within the range of our simulation, we also find no redshift dependence of the mean profile. Comparison of the profiles obtained from simulated and real voids shows an excellent match. The mean profiles of real voids also show a universal behaviour over a wide range of galaxy luminosities, number densities and redshifts. This points to a fundamental property of the voids found by the watershed algorithm, which can be exploited in future studies of voids
Cosmological measurements from void-galaxy and galaxy-galaxy clustering in the Sloan Digital Sky Survey
We present the cosmological implications of measurements of void-galaxy and
galaxy-galaxy clustering from the Sloan Digital Sky Survey (SDSS) Main Galaxy
Sample (MGS), Baryon Oscillation Spectroscopic Survey (BOSS), and extended BOSS
(eBOSS) luminous red galaxy catalogues from SDSS Data Release 7, 12, and 16,
covering the redshift range . We fit a standard CDM
cosmological model as well as various extensions including a constant dark
energy equation of state not equal to , a time-varying dark energy equation
of state, and these same models allowing for spatial curvature. Results on key
parameters of these models are reported for void-galaxy and galaxy-galaxy
clustering alone, both of these combined, and all these combined with
measurements from the cosmic microwave background (CMB) and supernovae (SN).
For the combination of void-galaxy and galaxy-galaxy clustering plus CMB and
SN, we find tight constraints of for a
base CDM cosmology, additionally allowing the dark energy equation of state to
vary, and further extending to
non-flat models.Comment: 11 pages, 9 figures. Submitted to MNRA
- âŠ