Carlo Contaldi

Research Summary

[ Computational Astrophysics, Cosmology, Early Universe and General Relativity ]

Carlo Contaldi works on the calculation of cosmological parameters from a number of Cosmic Microwave Background data sets. He is also working on the interpretation of interferometric data from Caltech's Cosmic Background Imager (CBI) which provides measurements of the CMB power spectrum at extremely high angular resolution. Finally, he is working on the use of weak lensing surveys to constrain the origin of the dark energy. Related to the latter is his study of the low power in the CMB power spectrum on large scales.

Research Projects:
(September 2002 - August 2003)

Analysis of Cosmic Background Interferometer CMB Data

CITA researchers Dick Bond, Carlo Contaldi, and Ue-Li Pen collaborated with former CITAzens Dmitry Pogosyan (University of Alberta), Steve Myers (NRAO), and Simon Prunet(IAP) and with Brian Mason (NRAO) and Tim Pearson, Tony Readhead and Jonathon Sievers of Caltech (now at CITA) to analyze new measurements of the polarization of the CMB from the Cosmic Background Imager experiment, a 13 element interferometer sited on the Atacama plateau in Chile. The work involved the extension of the analysis pipleline developed by the collaboration to include polarization of the CMB. The CBI aims to be the first instrument to return results on the polarization spectrum at arcminute scales. The first results covering the analysis of the first year of polarization measurements are expected to be released in early 2004. As part of the collaboration Dick Bond, Carlo Contaldi, and Ue-Li Pen have also been completing the analysis of the previously collected CBI total intensity measurements extending the analysis to two full years of data. This work follows on from the ground breaking results announced in May 2002 in a series of five papers by the CBI collaboration.

Analysis of Boomerang CMB Data

The Boomerang team members at CITA, Dick Bond, Carlo Contaldi and Barth Netterfield concluded the analysis of the 1998 flight data in a paper where the analyzed area was extended to cover roughly 3% of the sky. The work highlighted the robustness of the measurements and presented the definitive picture of the power spectrum at multipoles l<1000. The Boomerang effort has now shifted to the analysis of the latest flight (January 2003) which featured Polarization Sensitive Bolometers (PSB) for the measurement of polarization of the CMB. This work is ongoing and intense and is expected to produce a spectrum of the polarization in early 2004. The target is to map the first acoustic pea in the "E"-type (gradient) polarization, giving further confirmation of the basic paradigm of perturbation generation but also revealing the details of recombination and possible deviations from the standard picture of anisotropy formation.

Analysis of ACBAR data

Dick Bond and Carlo contaldi, together with Dmitry Pogosyan (University of Alberta) collaborated with the ACBAR experiment (PI Bill Holzapfel, UC Berkeley) in the analysis of the ACBAR data. The ACBAR team published a power spectrum with higly accurately determined band powers in the range of multipoles between 1000 and 2500. The work focused on extracting parameter constraints using the ACBAR spectrum and other measurements. The results were publihsed in a paper (Goldstein et al.) that defined the final snap-shot of the state of the field immediately previous to the realease of the first WMAP results. When compared to the WMAP results it highlights how successfully and accurately the CMB experiments leading upto the WMAP release had mapped out the basic features of the spectrum upto l=1000.

Joint analysis of WMAP and weak lensing data

A collaboration between Carlo Contaldi, Henk Hoekstra and Antony Lewis produced the first parameter estimates from a fully consistent joint analysis of CMB and the RCS weak lensing data. The results showed how these combinations already give constraints as good if not surpassing those from conventional combinations such as CMB with galaxy clustering data. As an extension of this line of research, Contaldi, Hoekstra and Lewis are now including the final release VIRMOS data into their pipeline in work that will be submitted shortly.

Study of low CMB power on large scales

Following the WMAP release and the confirmation of an observed quadrupole power that is lower than expected in standard $\Lambda$CDM models. Carlo Contaldi, Marco Peloso, Lev Kofman and Andrei Linde (Standord University) collaborated in a paper that showed how one could build highly tuned models of inflation to introduce a cutoff in the initial perturbation spectrum. The cutoff scale was fit to the WMAP data and a lower limit was obtained. Although the low quadrupole is only marginally inconsistent with the models it has generated a huge amount of interest in the field. Given the tuning involved in obtaining a cutoff in the spectrum arising from inflation it is possible that the quadrupole may be hinting at a late Universe effect. Indeed, much of the interest has been due to the possible connection with the late time domination by a Dark Energy component which is responsible for the accelerating expansion rate observed by the supernovae luminosity distance measurements, and the observed quadrupole of the CMB. Contaldi, Peloso and Kofman are continuing the research along these lines.

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