C. R. Contaldi

Imperial College London, Londinium, England, United Kingdom

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Publications (118)428.09 Total impact

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    Jonathan S. Horner, Carlo R. Contaldi
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    ABSTRACT: The bispectrum of single-field inflationary trajectories in which the speed of sound of the inflationary trajectories $c_s$ is constant but not equal to the speed of light $c=1$ is explored. The trajectories are generated as random realisations of the Hubble Slow-Roll (HSR) hierarchy and the bispectra are calculated using numerical techniques that extends previous work. This method allows for out-of-slow-roll models with non-trivial time dependence and arbitrarily low $c_s$. The ensembles obtained using this method yield distributions for the shape and scale-dependence of the bispectrum and their relations with the standard inflationary parameters such as scalar spectral tilt $n_s$ and tensor-to-scalar ratio $r$. The distributions demonstrate the squeezed-limit consistency relations for arbitrary single-field inflationary models.
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    Jonathan S. Horner, Carlo R. Contaldi
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    ABSTRACT: The simplest interpretation of the Bicep2 result is that the scalar primordial power spectrum is slightly suppressed at large scales. These models result in a large tensor-to-scalar ratio $r$. In this work we show that the type of inflationary trajectory favoured by Bicep2 also leads to a larger non-Gaussian signal at large scales, roughly an order of magnitude larger than a standard slow-roll trajectory.
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    Carlo R. Contaldi
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    ABSTRACT: The recent BICEP2 detection of, what is claimed to be primordial $B$-modes, opens up the possibility of constraining not only the energy scale of inflation but also the detailed acceleration history that occurred during inflation. In turn this can be used to determine the shape of the inflaton potential $V(\phi)$ for the first time - if a single, scalar inflaton is assumed to be driving the acceleration. We carry out a Monte Carlo exploration of inflationary trajectories given the current data. Using this method we obtain a posterior distribution of possible acceleration profiles $\epsilon(N)$ as a function of $e$-fold $N$ and derived posterior distributions of the primordial power spectrum $P(k)$ and potential $V(\phi)$. We find that the BICEP2 result, in combination with Planck measurements of total intensity Cosmic Microwave Background (CMB) anisotropies, induces a significant feature in the scalar primordial spectrum at scales $k\sim 10^{-3}$ Mpc$^{-1}$. This is in agreement with a previous detection of a suppression in the scalar power.
    Journal of Cosmology and Astroparticle Physics 07/2014; 2014(10). DOI:10.1088/1475-7516/2014/10/072 · 5.88 Impact Factor
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    ABSTRACT: We present the results of integration and characterization of the SPIDER instrument after the 2013 pre-flight campaign. SPIDER is a balloon-borne polarimeter designed to probe the primordial gravitational wave signal in the degree-scale $B$-mode polarization of the cosmic microwave background. With six independent telescopes housing over 2000 detectors in the 94 GHz and 150 GHz frequency bands, SPIDER will map 7.5% of the sky with a depth of 11 to 14 $\mu$K$\cdot$arcmin at each frequency, which is a factor of $\sim$5 improvement over Planck. We discuss the integration of the pointing, cryogenic, electronics, and power sub-systems, as well as pre-flight characterization of the detectors and optical systems. SPIDER is well prepared for a December 2014 flight from Antarctica, and is expected to be limited by astrophysical foreground emission, and not instrumental sensitivity, over the survey region.
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    ABSTRACT: We present the second generation BLASTbus electronics. The primary purposes of this system are detector readout, attitude control, and cryogenic housekeeping, for balloon-borne telescopes. Readout of neutron transmutation doped germanium (NTD-Ge) bolometers requires low noise and parallel acquisition of hundreds of analog signals. Controlling a telescope's attitude requires the capability to interface to a wide variety of sensors and motors, and to use them together in a fast, closed loop. To achieve these different goals, the BLASTbus system employs a flexible motherboard-daughterboard architecture. The programmable motherboard features a digital signal processor (DSP) and field-programmable gate array (FPGA), as well as slots for three daughterboards. The daughterboards provide the interface to the outside world, with versions for analog to digital conversion, and optoisolated digital input/output. With the versatility afforded by this design, the BLASTbus also finds uses in cryogenic, thermometry, and power systems. For accurate timing control to tie everything together, the system operates in a fully synchronous manner. BLASTbus electronics have been successfully deployed to the South Pole, and flown on stratospheric balloons.
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    ABSTRACT: We present the technology and control methods developed for the pointing system of the SPIDER experiment. SPIDER is a balloon-borne polarimeter designed to detect the imprint of primordial gravitational waves in the polarization of the Cosmic Microwave Background radiation. We describe the two main components of the telescope's azimuth drive: the reaction wheel and the motorized pivot. A 13 kHz PI control loop runs on a digital signal processor, with feedback from fibre optic rate gyroscopes. This system can control azimuthal speed with < 0.02 deg/s RMS error. To control elevation, SPIDER uses stepper-motor-driven linear actuators to rotate the cryostat, which houses the optical instruments, relative to the outer frame. With the velocity in each axis controlled in this way, higher-level control loops on the onboard flight computers can implement the pointing and scanning observation modes required for the experiment. We have accomplished the non-trivial task of scanning a 5000 lb payload sinusoidally in azimuth at a peak acceleration of 0.8 deg/s$^2$, and a peak speed of 6 deg/s. We can do so while reliably achieving sub-arcminute pointing control accuracy.
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    ABSTRACT: An attitude determination system for balloon-borne experiments is presented. The system provides pointing information in azimuth and elevation for instruments flying on stratospheric balloons over Antarctica. In-flight attitude is given by the real-time combination of readings from star cameras, a magnetometer, sun sensors, GPS, gyroscopes, tilt sensors and an elevation encoder. Post-flight attitude reconstruction is determined from star camera solutions, interpolated by the gyroscopes using an extended Kalman Filter. The multi-sensor system was employed by the Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry (BLASTPol), an experiment that measures polarized thermal emission from interstellar dust clouds. A similar system was designed for the upcoming flight of SPIDER, a Cosmic Microwave Background polarization experiment. The pointing requirements for these experiments are discussed, as well as the challenges in designing attitude reconstruction systems for high altitude balloon flights. In the 2010 and 2012 BLASTPol flights from McMurdo Station, Antarctica, the system demonstrated an accuracy of <5' rms in-flight, and <5" rms post-flight.
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    Carlo R. Contaldi, Marco Peloso, Lorenzo Sorbo
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    ABSTRACT: The BICEP2 collaboration has reported a strong B mode signal in the CMB polarization, which is well fit by a tensor-to-scalar ratio of r ~ 0.2. This is greater than the upper limit r < 0.11 obtained from the temperature anisotropies under the assumption of a constant scalar spectral index n_s. This discrepancy can be reduced once the statistical error and the contamination from polarized dust are accounted for. If however a large value for r will be confirmed, it will need to be reconciled with the temperature anisotropies data. The most advocated explanation involves a variation of n_s with scales that has a magnitude significantly greater than the generic slow roll predictions. We instead study the possibility that the large scale temperature anisotropies are not enhanced because (1) of a suppression of the scalar power at large scales, or (2) of an anti-correlation between tensor and scalar modes. The first possibility can be achieved for instance by a sudden change of the speed of the inflaton; the second possibility requires breaking of Lorentz invariance, and it also leads to violation of statistical isotropy in the temperature data, which is (i) of O (10%) or less, and (ii) present only at large scales. Interestingly, violation of statistical isotropy with these two properties appears to be present both in the WMAP and Planck data.
    Journal of Cosmology and Astroparticle Physics 03/2014; 2014(07). DOI:10.1088/1475-7516/2014/07/014 · 5.88 Impact Factor
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    Carlo R. Contaldi, Jonathan S. Horner
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    ABSTRACT: We use the Hamilton--Jacobi formalism to constrain the space of possible single field, inflationary Hubble flow trajectories when compared to the WMAP and Planck satellites Cosmic Microwave Background (CMB) results. This method yields posteriors on the space of Hubble Slow Roll (HSR) parameters that uniquely determine the history of the Hubble parameter during the inflating epoch. The trajectories are used to numerically determine the observable primordial power spectrum and bispectra that can then be compared to observations. Our analysis is used to infer the most likely shape of the inflaton potential $V(\phi)$ and also yields a prediction for, $f_{\rm NL}$, the dimensionless amplitude of the non-Gaussian bispectrum.
    Journal of Cosmology and Astroparticle Physics 12/2013; 2014(08). DOI:10.1088/1475-7516/2014/08/050 · 5.88 Impact Factor
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    Jonathan S. Horner, Carlo R. Contaldi
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    ABSTRACT: We carry out a numerical calculation of the bispectrum in generalised trajectories of canonical, single--field inflation. The trajectories are generated in the Hamilton-Jacobi (HJ) formalism based on Hubble Slow Roll (HSR) parameters. The calculation allows generally shape and scale dependent bispectra, or dimensionless $f_{NL}$, in the out-of-slow-roll regime. The distributions of $f_{NL}$ for various shapes and HSR proposals are shown as an example of how this procedure can be used within the context of Monte Carlo exploration of inflationary trajectories. We also show how allowing out-of-slow-roll behaviour can lead to a bispectrum that is relatively large for equilateral shapes.
    Journal of Cosmology and Astroparticle Physics 11/2013; 2014(09). DOI:10.1088/1475-7516/2014/09/001 · 5.88 Impact Factor
  • Jonathan S. Horner, Carlo R. Contaldi
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    ABSTRACT: The Hamilton-Jacobi (HJ) approach for exploring inflationary trajectories is employed in the generation of generalised inflationary non-Gaussian signals arising from single field inflation. Scale dependent solutions for $f_{NL}$ are determined via the numerical integration of the three--point function in the curvature perturbation. This allows the full exploration of single field inflationary dynamics in the out-of-slow-roll regime and opens up the possibility of using future observations of non-Gaussianity to constraint the inflationary potential using model-independent methods. The distribution of `equilateral' $f_{NL}$ arising from single field inflation with both canonical and non-canonical kinetic terms are show as an example of the application of this procedure.
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    C. N. Clark, C. R. Contaldi, C. J. MacTavish
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    ABSTRACT: Templates for polarised emission from Galactic foregrounds at frequencies relevant to Cosmic Microwave Background (CMB) polarisation experiments are obtained by modelling the Galactic Magnetic Field (GMF) on large scales. This work extends the results of O'Dea et al. by including polarised synchrotron radiation as a source of foreground emission. The polarisation direction and fraction in this calculation are based solely on the underlying choice of GMF model and therefore provide an independent prediction for the polarisation signal on large scales. Templates of polarised foregrounds may be of use when forecasting effective experimental sensitivity. In turn, as measurements of the CMB polarisation over large fractions of the sky become routine, this model will allow for the data to constrain parameters in the, as yet, not well understood form of the GMF.
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    ABSTRACT: The upcoming generation of cosmic microwave background experiments face a major challenge in detecting the weak cosmic B-mode signature predicted as a product of primordial gravitational waves. To achieve the required sensitivity these experiments must have impressive control of systematic effects and detailed understanding of the foreground emission that will influence the signal. In this paper, we present templates of the intensity and polarization of emission from one of the main Galactic foregrounds, interstellar dust. These are produced using a model which includes a three-dimensional description of the Galactic magnetic field, examining both large and small scales. We also include in the model the details of the dust density, grain alignment and the intrinsic polarization of the emission from an individual grain. We present here Stokes parameter template maps at 150 GHz and provide an online repository () for these and additional maps at frequencies that will be targeted by upcoming experiments such as EBEX, Spider and SPTpol.
    Monthly Notices of the Royal Astronomical Society 01/2012; 419:1795-1803. DOI:10.1111/j.1365-2966.2011.19851.x · 5.23 Impact Factor
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    Daniel B. Thomas, Carlo R. Contaldi
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    ABSTRACT: Model-independent parametrisations for examining departures from General Relativity have been increasingly studied over the past few years. Various observables have been used to constrain the parameters and forecasts for future surveys have been carried out. In one such forecast, galaxy cluster counts were used to constrain the parameters. Here, we carry out a limited set of $N$-body simulations, with a modified Poisson equation, to examine the accuracy of existing mass functions for modified gravity cosmologies. As well as altering the gravitational calculation, we include the effect of a screening scale to ensure consistency of the theory with solar system tests. Our results suggest that if a screening scale exists its effect can be taken into account in the cluster count calculation through its effect on the linear matter power spectrum. If this is done, the accuracy of the standard mass function formalism in modified gravity theories with reasonably small departures from General Relativity, as tested in this work, is comparable to the standard case.
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    ABSTRACT: SPIDER is a balloon-borne instrument designed to map the polarization of the cosmic microwave background (CMB) with degree-scale resolution over a large fraction of the sky. SPIDER's main goal is to measure the amplitude of primordial gravitational waves through their imprint on the polarization of the CMB if the tensor-to-scalar ratio, r, is greater than 0.03. To achieve this goal, instrumental systematic errors must be controlled with unprecedented accuracy. Here, we build on previous work to use simulations of SPIDER observations to examine the impact of several systematic effects that have been characterized through testing and modeling of various instrument components. In particular, we investigate the impact of the non-ideal spectral response of the half-wave plates, coupling between focal-plane components and Earth's magnetic field, and beam mismatches and asymmetries. We also present a model of diffuse polarized foreground emission based on a three-dimensional model of the Galactic magnetic field and dust, and study the interaction of this foreground emission with our observation strategy and instrumental effects. We find that the expected level of foreground and systematic contamination is sufficiently low for SPIDER to achieve its science goals.
    The Astrophysical Journal 08/2011; 738(1):63. DOI:10.1088/0004-637X/738/1/63 · 6.28 Impact Factor
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    Daniel B. Thomas, Carlo R. Contaldi
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    ABSTRACT: Model-independent parametrisations of modified gravity have attracted a lot of attention over the past few years and numerous combinations of experiments and observables have been suggested to constrain the parameters used in these models. Galaxy clusters have been mentioned, but not looked at as extensively in the literature as some other probes. Here we look at adding galaxy clusters into the mix of observables and examine how they could improve the constraints on the modified gravity parameters. In particular, we forecast the constraints from combining Planck satellite Cosmic Microwave Background (CMB) measurements and Sunyaev-Zeldovich (SZ) cluster catalogue with a DES-like weak lensing survey. We find that cluster counts significantly improve the constraints over those derived using CMB and WL. We then look at surveys further into the future, to see how much better it may be feasible to make the constraints.
    Journal of Cosmology and Astroparticle Physics 07/2011; 12(12). DOI:10.1088/1475-7516/2011/12/013 · 5.88 Impact Factor
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    ABSTRACT: We evaluate the ability of SPIDER, a balloon-borne polarimeter, to detect a divergence-free polarization pattern ("B-modes") in the Cosmic Microwave Background (CMB). In the inflationary scenario, the amplitude of this signal is proportional to that of the primordial scalar perturbations through the tensor-to-scalar ratio r. We show that the expected level of systematic error in the SPIDER instrument is significantly below the amplitude of an interesting cosmological signal with r=0.03. We present a scanning strategy that enables us to minimize uncertainty in the reconstruction of the Stokes parameters used to characterize the CMB, while accessing a relatively wide range of angular scales. Evaluating the amplitude of the polarized Galactic emission in the SPIDER field, we conclude that the polarized emission from interstellar dust is as bright or brighter than the cosmological signal at all SPIDER frequencies (90 GHz, 150 GHz, and 280 GHz), a situation similar to that found in the "Southern Hole." We show that two ~20-day flights of the SPIDER instrument can constrain the amplitude of the B-mode signal to r<0.03 (99% CL) even when foreground contamination is taken into account. In the absence of foregrounds, the same limit can be reached after one 20-day flight.
    Journal of Cosmology and Astroparticle Physics 06/2011; DOI:10.1088/1475-7516/2013/04/047 · 5.88 Impact Factor
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    ABSTRACT: We describe the cryogenic system for SPIDER, a balloon-borne microwave polarimeter that will map 8% of the sky with degree-scale angular resolution. The system consists of a 1284 L liquid helium cryostat and a 16 L capillary-filled superfluid helium tank, which provide base operating temperatures of 4 K and 1.5 K, respectively. Closed-cycle helium-3 adsorption refrigerators supply sub-Kelvin cooling power to multiple focal planes, which are housed in monochromatic telescope inserts. The main helium tank is suspended inside the vacuum vessel with thermally insulating fiberglass flexures, and shielded from thermal radiation by a combination of two vapor cooled shields and multi-layer insulation. This system allows for an extremely low instrumental background and a hold time in excess of 25 days. The total mass of the cryogenic system, including cryogens, is approximately 1000 kg. This enables conventional long duration balloon flights. We will discuss the design, thermal analysis, and qualification of the cryogenic system.
    Proceedings of SPIE - The International Society for Optical Engineering 06/2011; DOI:10.1117/12.857925 · 0.20 Impact Factor
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    ABSTRACT: We describe SPIDER, a balloon-borne instrument to map the polarization of the millimeter-wave sky with degree angular resolution. Spider consists of six monochromatic refracting telescopes, each illuminating a focal plane of large-format antenna-coupled bolometer arrays. A total of 2,624 superconducting transition-edge sensors are distributed among three observing bands centered at 90, 150, and 280 GHz. A cold half-wave plate at the aperture of each telescope modulates the polarization of incoming light to control systematics. Spider's first flight will be a 20-30-day Antarctic balloon campaign in December 2011. This flight will map \sim8% of the sky to achieve unprecedented sensitivity to the polarization signature of the gravitational wave background predicted by inflationary cosmology. The Spider mission will also serve as a proving ground for these detector technologies in preparation for a future satellite mission.
    Proceedings of SPIE - The International Society for Optical Engineering 06/2011; DOI:10.1117/12.857720 · 0.20 Impact Factor
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    ABSTRACT: Here we describe the design and performance of the Spider instrument. Spider is a balloon-borne cosmic microwave background polarization imager that will map part of the sky at 90, 145, and 280 GHz with sub-degree resolution and high sensitivity. This paper discusses the general design principles of the instrument inserts, mechanical structures, optics, focal plane architecture, thermal architecture, and magnetic shielding of the TES sensors and SQUID multiplexer. We also describe the optical, noise, and magnetic shielding performance of the 145 GHz prototype instrument insert.
    Proceedings of SPIE - The International Society for Optical Engineering 06/2011; DOI:10.1117/12.857715 · 0.20 Impact Factor

Publication Stats

4k Citations
428.09 Total Impact Points

Institutions

  • 1999–2014
    • Imperial College London
      • Department of Physics
      Londinium, England, United Kingdom
  • 2009
    • University of London
      Londinium, England, United Kingdom
  • 2002–2008
    • University of Toronto
      • Canadian Institute for Theoretical Astrophysics
      Toronto, Ontario, Canada
  • 2006
    • Imperial Valley College
      Imperial, California, United States
  • 2003
    • University of Chicago
      • Department of Astronomy and Astrophysics
      Chicago, IL, United States