224 research outputs found
Measuring the growth of structure with multi-wavelength surveys of galaxy clusters
No full textCurrent and near-future galaxy cluster surveys at a variety of wavelengths are expected to provide a promising way to obtain precision measurements of the growth of structure over cosmic time. This in turn would serve as an important precision probe of cosmology. However, to realize the full potential of these surveys, systematic uncertainties arising from, for example, cluster mass estimates and sample selection must be well understood. This work follows several different approaches towards alleviating these uncertainties.
Cluster sample selection is investigated in the context of arcminute-resolution millimeter-wavelength surveys such as the Atacama Cosmology Telescope (ACT) and the South Pole Telescope (SPT). Large-area, realistic simulations of the microwave sky are constructed and cluster detection is simulated using a multi-frequency Wiener filter to separate the galaxy clusters, via their Sunyaev-Zel'dovich signal, from other contaminating microwave signals. Using this technique, an ACT-like survey can expect to obtain a cluster sample that is 90% complete and 85% pure above a mass of 3 x 10^14 Msun.
Cluster mass uncertainties are explored by comparing X-ray and weak-lensing mass estimates for shear-selected galaxy clusters in the Deep Lens Survey (DLS) to study possible biases in using cluster baryons or weak-lensing shear as tracers of the cluster total mass. Results are presented for four galaxy clusters that comprise the top-ranked shear-selected system in the DLS, and for three of these clusters there is agreement between X-ray and weak-lensing mass estimates. For the fourth cluster, the X-ray mass estimate is higher than that from weak-lensing by 2-sigma, and X-ray images suggest this cluster may be undergoing a merger with a smaller cluster, which may be biasing the X-ray mass estimate high.
The feasibility of measuring galaxy cluster peculiar velocities using an ACT-like instrument is also investigated. Such a possibility would allow one to measure structure growth via large-scale velocity fields and circumvent the uncertainties associated with measuring cluster masses. We show that such measurements are possible and yield statistical uncertainties of roughly 100 km/sec given either a temperature prior with 1-sigma errors of less than 2 keV or additional lower frequency millimeter-band observations.Ph.D.Includes bibliographical references
Mass-varying Dark Matter from a Phase Transition
Get PDFWe propose a mass-varying dark matter (MVDM) model consisting of a scalar
field and a fermionic field interacting via a simple Yukawa coupling, and
containing an exponential self-interaction potential for the scalar field.
Analyzing the evolution of this coupled scalar-fermion system in an expanding
Universe, we find that it initially behaves like radiation but then undergoes a
phase transition after which it behaves like pressureless dark matter. The one
free parameter of this model is the temperature at which the phase transition
occurs; the mass of the dark matter particle, given by the mass of the fermion,
is derived from this. For a phase transition temperature between 10 MeV and
GeV, the current dark matter relic density is achieved for a fermion
mass in the range of 1 GeV to GeV. In this dark matter model, the scalar
becomes a sub-dominant unclustered component of dark matter that can lower the
amplitude of structure formation by up to a few percent. Another feature is
that the mass-varying fermion component can lead to discrepant measurements of
the current dark matter density of about ten percent inferred from early and
late-time probes assuming LCDM.Comment: 12 pages, 7 figures; version matches that accepted by PRD, changes
are elaboration of some details; Mathematica code and notes for
numerical/analytic calculations are provided at
https://github.com/alphacephei/MVD
Mitigating Foreground Bias to the CMB Lensing Power Spectrum for a CMB-HD Survey
Get PDFA promising way to measure the distribution of matter on small scales (k ~ 10
hMpc^-1) is to use gravitational lensing of the Cosmic Microwave Background
(CMB). CMB-HD, a proposed high-resolution, low-noise millimeter survey over
half the sky, can measure the CMB lensing auto spectrum on such small scales
enabling measurements that can distinguish between a cold dark matter (CDM)
model and alternative models designed to solve problems with CDM on small
scales. However, extragalactic foregrounds can bias the CMB lensing auto
spectrum if left untreated. We present a foreground mitigation strategy that
provides a path to reduce the bias from two of the most dominant foregrounds,
the thermal Sunyaev-Zel'dovich effect (tSZ) and the Cosmic Infrared Background
(CIB). Given the level of realism included in our analysis, we find that the
tSZ alone and the CIB alone bias the lensing auto spectrum by 0.6 sigma and 1.1
sigma respectively, in the lensing multipole range of L in [5000,20000] for a
CMB-HD survey; combined these foregrounds yield a bias of only 1.3 sigma.
Including these foregrounds, we also find that a CMB-HD survey can distinguish
between a CDM model and a 10^-22 eV FDM model at the 5 sigma level. These
results provide an important step in demonstrating that foreground
contamination can be sufficiently reduced to enable a robust measurement of the
small-scale matter power spectrum with CMB-HD.Comment: 14 pages, 6 figures; power spectra and lensing covariance matrix from
this analysis are public at https://github.com/dwhan89/hdlensin
Cosmological Parameter Forecasts for a CMB-HD Survey
Get PDFWe present forecasts on cosmological parameters for a CMB-HD survey. For a
CDM + + model, we find
and using CMB and CMB lensing multipoles in the range
of , after adding anticipated residual foregrounds,
delensing the acoustic peaks, and adding DESI BAO data. This is about a factor
of two improvement in ability to probe inflation via compared to
precursor CMB surveys. The constraint can rule out light thermal
particles back to the end of inflation with 95% CL; for example, it can rule
out the QCD axion in a model-independent way assuming the Universe's reheating
temperature was high enough that the axion thermalized. We find that delensing
the acoustic peaks and adding DESI BAO tightens parameter constraints. We also
find that baryonic effects can bias parameters if not marginalized over, and
that uncertainties in baryonic effects can increase parameter error bars;
however, the latter can be mitigated by including information about baryonic
effects from kinetic and thermal Sunyaev-Zel'dovich measurements by CMB-HD. The
CMB-HD likelihood and Fisher estimation codes used here are publicly available;
the likelihood is integrated with Cobaya to facilitate parameter forecasting.Comment: 29 pages, 18 figures, 10 tables. The mock CMB-HD likelihood and
Fisher estimation codes are public at https://github.com/CMB-HD/hdlike and
https://github.com/CMB-HD/hdfisher ; v3: a few clarifying sentences added;
version matches that accepted by PR
Reforming institutions for service delivery : a framework for development assistance with an application to the health, nutrition, and population portfolio
Get PDFWorld Development Report 1997: The State in a Changing World (report no. 17300) argued that institutions-the rules of the game that govern production and exchange-shape a country's prospects for sustained market-led growth. The author provides an institutional framework for service delivery, an essential component of state capability. He applies this framework to an evaluation of Bank support for service delivery in the health, nutrition, and population sector. He argues for greater institutional pluralism in the ways the World Bank does business in infrastructure, rural, and social sectors, but cautions against making efficient service delivery an issue of"state versus market."The Bank and its clients face the challenge of fitting menus of"better practice"delivery options to maps of institutional reality. In the health, nutrition, and population sector, the Bank should (1) unbundle and categorize essential health and clinical services according to goods characteristics and (2) integrate country knowledge into operations through upstream assessments of state, political, and social institutions. Overall, the Bank has made progress toward a"goods characteristics"approach, particularly in infrastructure and some rural services-but it has lagged in the social sectors, where support remains largely technocratic. Cross-sector comparisons reveal four generations of support for service delivery. First-generation support focused mainly on physical implementation of projects. Second-generation interventions, which characterized most social service interventions, focused on improving the financial and organizational viability of implementing agencies through technical assistance. Third-generation support was marked by significant unbundling of service delivery activities and clearer links to goods characteristics. In irrigation (1982-94), telecommunications (1980s-present), and transport (1990s), the one-size-fits-all monopoly model gave way to a range of options based on greater private sector and citizen participation in delivery. These included leases, concessions, outsourcing, and contracting as well as building, operating, transfer, and turnover schemes. Fourth-generation interventions are works-in-progress and represent efforts to develop new governance arrangements that systematically combine competition, voice, and hierarchy in the design, delivery, and monitoring of Bank projects. The Bank has a poor track record building country knowledge of institutional endowments that affect service delivery. The author identifies concepts and tools valuable for sector specialists'operations.Enterprise Development&Reform,Public Health Promotion,Health Economics&Finance,Decentralization,Health Monitoring&Evaluation,Governance Indicators,Poverty Assessment,Environmental Economics&Policies,Health Monitoring&Evaluation,Health Economics&Finance
Current dark matter annihilation constraints from CMB and low-redshift data
Get PDFUpdated constraints on the dark matter cross section and mass are presented combining cosmic microwave background (CMB) power spectrum measurements from Planck, WMAP9, ACT, and SPT as well as several low-redshift data sets (BAO, HST, and supernovae). For the CMB data sets, we combine WMAP9 temperature and polarization data for l ≤ 431 with Planck temperature data for 432 ≤ l ≤ 2500, ACT and SPT data for l > 2500, and Planck CMB four-point lensing measurements. We allow for redshift-dependent energy deposition from dark matter annihilation by using a “universal" energy absorption curve. We also include an updated treatment of the excitation, heating, and ionization energy fractions and provide an updated deposition efficiency factors (f[subscript eff]) for 41 different dark matter models. Assuming perfect energy deposition (f[subscript eff] = 1) and a thermal cross section, dark matter masses below 26 GeV are excluded at the 2σ level. Assuming a more generic efficiency of f[subscript eff] = 0.2, thermal dark matter masses below 5 GeV are disfavored at the 2σ level. These limits are a factor of ∼2 improvement over those from WMAP9 data alone. These current constraints probe, but do not exclude, dark matter as an explanation for reported anomalous indirect detection observations from AMS-02/PAMELA and the Fermi gamma-ray inner-Galaxy data. They also probe relevant models that would explain anomalous direct detection events from CDMS, CRESST, CoGeNT, and DAMA, as originating from a generic thermal weakly interacting massive particle. Projected constraints from the full Planck release should improve the current limits by another factor of ∼2 but will not definitely probe these signals. The proposed CMB Stage IV experiment will more decisively explore the relevant regions and improve upon the Planck constraints by another factor of ∼2.Stony Brook University-Brookhaven National Laboratory (Research Initiatives Seed Grant 37298, Project 1111593)United States. Dept. of Energy (Cooperative Research Agreement Contract DE-FG02-05ER41360
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