Cosmology with dropout selection: Straw-man surveys and CMB lensing

We seek to prove the means, motive and opportunity of 2 < z < 5 dropout galaxies for large-scale structure. Together with low-z tracers, these samples would map practically every linear mode and facilitate a tomographic decomposition of the CMB lensing kernel over an unprecedented volume, thereby yielding a proxy for (the time evolution of) matter density fluctuations that provides compelling tests of horizon-scale General Relativity, neutrino masses and Inflation-- viz., curvature, running of the spectral index and a scale-dependent halo bias induced by (local) primordial non-Gaussianity. Focusing on color-color selection, we estimate the completeness, contamination, and spectroscopic survey speed of tailored Lyman-break galaxy (LBG) samples. We forecast the potential of CMB lensing cross-correlation, clustering redshifts and Redshift-Space Distortions (RSD) analyses. In particular, we estimate: the depth dependence of interlopers based on CFHTLS data and propagate this to biases in cosmology; new inferences of (non-linear) halo bias at these redshifts and depths using legacy data; detailed forecasts of LBG spectra as would be observed by DESI, PFS, and their successors. We further assess the relative competitiveness of potential spectroscopic facilities based on an intuitive figure-of-merit and define a modernisation of traditional selections to the photometric system of LSST where necessary. We confirm these science cases to be compelling for achievable facilities in the next decade by defining a LBG sample of increasing Lyman-alpha equivalent width with redshift, which delivers both percent-level RSD constraints on the growth rate at high-z and measurements of CMB lensing cross-correlation at z=3 and 4 with a significance measured in the hundreds. Finally, we discuss the limitations and avenues for improvement beyond this initial exploration (abridged).Comment: 59 pages, comments welcom

X-ray variability of the quasar 3C273

Observations of the quasar 3C273 made during 1975-77 have shown that the X-ray flux varied on a time scale of several months. No similar variation was present in radio and optical data taken at similar times. If this variation results from luminosity variations of a central compact object, then an upper limit of ≤4 x 1017cm can be set on its dimensions

Using large galaxy surveys to distinguish z~0.5 quiescent galaxy models

One of the most striking properties of galaxies is the bimodality in their star-formation rates. A major puzzle is why any given galaxy is star-forming or quiescent, and a wide range of physical mechanisms have been proposed as solutions. We consider how observations, such as might be available in upcoming large galaxy surveys, might distinguish different galaxy quenching scenarios. To do this, we combine an N-body simulation and multiple prescriptions from the literature to create several quiescent galaxy mock catalogues. Each prescription uses a different set of galaxy properties (such as history, environment, centrality) to assign individual simulation galaxies as quiescent. We find how and how much the resulting quiescent galaxy distributions differ from each other, both intrinsically and observationally. In addition to tracing observational consequences of different quenching mechanisms, our results indicate which sorts of quenching models might be most readily disentangled by upcoming observations and which combinations of observational quantities might provide the most discriminatory power. Our observational measures are auto, cross, and marked correlation functions, pro- jected density distributions, and group multiplicity functions, which rely upon galaxy positions, stellar masses and of course quiescence. Although degeneracies between models are present for individual observations, using multiple observations in concert allows us to distinguish between all ten models we consider. In addition to identifying intrinsic and observational consequences of quiescence prescriptions and testing these quiescence models against each other and observations, these methods can also be used to validate colors (or other history and environment dependent properties) in simulated mock catalogues.Comment: 20 pages, 14 figures. Version to appear in MNRAS, incorporating helpful suggestions from referee and other

Stochastic superspace phenomenology at the Large Hadron Collider

We analyse restrictions on the stochastic superspace parameter space arising from 1 fb$^{-1}$ of LHC data, and bounds on sparticle masses, cold dark matter relic density and the branching ratio of the process $B_s \rightarrow \mu^+ \mu^-$. A region of parameter space consistent with these limits is found where the stochasticity parameter, \xi, takes values in the range -2200 GeV < \xi < -900 GeV, provided the cutoff scale is $\mathcal{O}(10^{18})$ GeV.Comment: 9 pages, 13 figure

Searching for Supersymmetry with the ATLAS detector

This thesis presents a new method by which one may use data from the ATLAS detector of the Large Hadron Collider at CERN to measure the parameters of the theory of supersymmetry (SUSY). The technique uses a Markov Chain Monte Carlo sampling algorithm to combine measurements of exclusive variables, in the form of kinematic endpoints that arise in the invariant mass distributions of leptons and jets given out in sparticle decay chains, with inclusive data, in the form of the cross-section of events passing a missing transverse energy cut. This improves the precision of sparticle mass measurements (beyond that obtained using exclusive data alone), whilst also enabling experimental uncertainties to be handled in an intuitive fashion. The method is demonstrated on an mSUGRA benchmark model, and is also used to constrain a model with a greater number of parameters. Throughout, an attempt is made to break some of the unrealistic assumptions that characterise current SUSY search techniques, and to this end it is successfully demonstrated that one can use the Markov Chain method to obtain precise results even if it is not possible to precisely determine which sparticles produced the endpoints in the invariant mass distributions. This decay chain ambiguity is extended by looking at a sample SUSY model with non-universal Higgs masses, in which cascade decays featuring three body decays become more prominent. The positions of the associat ed endpoints are calculated for a squark cascade decay, and are subsequently studied with the aid of a benchmark model. In addition, this thesis presents work relating to the development of an online monitoring package for the ATLAS Semi-Conductor Tracker (SCT). A tool for the calculation of noise occupancies is developed and tested against existing calibration data, prior to its application to various data sets obtained during the SR1 cosmic commissioning tests at CERN in the summer of 2006. It is found that the modules of the SCT included in the test have an average noise occupancy of less than $5 \times 10^{-4}$ per strip per event, and thus meet the design specification

Redshift Weights for Baryon Acoustic Oscillations : Application to Mock Galaxy Catalogs

Large redshift surveys capable of measuring the Baryon Acoustic Oscillation (BAO) signal have proven to be an effective way of measuring the distance-redshift relation in cosmology. Building off the work in Zhu et al. (2015), we develop a technique to directly constrain the distance-redshift relation from BAO measurements without splitting the sample into redshift bins. We parametrize the distance-redshift relation, relative to a fiducial model, as a quadratic expansion. We measure its coefficients and reconstruct the distance-redshift relation from the expansion. We apply the redshift weighting technique in Zhu et al. (2015) to the clustering of galaxies from 1000 QuickPM (QPM) mock simulations after reconstruction and achieve a 0.75% measurement of the angular diameter distance $D_A$ at $z=0.64$ and the same precision for Hubble parameter H at $z=0.29$. These QPM mock catalogs are designed to mimic the clustering and noise level of the Baryon Oscillation Spectroscopic Survey (BOSS) Data Release 12 (DR12). We compress the correlation functions in the redshift direction onto a set of weighted correlation functions. These estimators give unbiased $D_A$ and $H$ measurements at all redshifts within the range of the combined sample. We demonstrate the effectiveness of redshift weighting in improving the distance and Hubble parameter estimates. Instead of measuring at a single 'effective' redshift as in traditional analyses, we report our $D_A$ and $H$ measurements at all redshifts. The measured fractional error of $D_A$ ranges from 1.53% at $z=0.2$ to 0.75% at $z=0.64$. The fractional error of $H$ ranges from 0.75% at $z=0.29$ to 2.45% at $z = 0.7$. Our measurements are consistent with a Fisher forecast to within 10% to 20% depending on the pivot redshift. We further show the results are robust against the choice of fiducial cosmologies, galaxy bias models, and RSD streaming parameters.Comment: 13 pages, 8 figures, submitted to MNRA