Publications
141 results found
Contaldi CR, 2017, Imaging parity-violating modes in the CMB, Astronomical Journal, Vol: 153, ISSN: 0004-6256
Correlations of polarization components in the coordinate frame are a natural basis for searches of parity-violating modes in the cosmic microwave background. This fact can be exploited to build estimators of parity-violating modes that are local and robust with respect to partial-sky coverage or inhomogeneous weighting. As an example application of a method based on these ideas, we develop a peak stacking tool that isolates the signature of parity-violating modes. We apply the tool to Planck maps and obtain a constraint on the monopole of the polarization rotation angle $\alpha \lt 0\buildrel{\circ}\over{.} 72$ at 95% We also demonstrate how the tool can be used as a local method for reconstructing maps of direction dependent rotation $\alpha (\hat{{\boldsymbol{n}}})$.
Contaldi CR, 2016, Imaging cosmic polarization rotation, International Journal of Modern Physics D, Vol: 25, ISSN: 0218-2718
We introduce a method to isolate the contribution of parity-violating modes to the peak constrained correlation function. This method can be used as a local estimate of polarization rotation. We test this method using simulations and by applying it to Planck maps [P. A. R. Ade et al., arXiv:1502.01589 astro.ph.co]. We obtain a constraint on the monopole of the polarization rotation angle α=0.31±0.23α=0.31±0.23.
Bryan S, Ade P, Amiri M, et al., 2016, A cryogenic rotation stage with a large clear aperture for the half-wave plates in the Spider instrument, Review of Scientific Instruments, Vol: 87, Pages: 014501-014501, ISSN: 1089-7623
We describe the cryogenic half-wave plate rotation mechanisms built for andused in Spider, a polarization-sensitive balloon-borne telescope array thatobserved the Cosmic Microwave Background at 95 GHz and 150 GHz during astratospheric balloon flight from Antarctica in January 2015. The mechanismsoperate at liquid helium temperature in flight. A three-point contact designkeeps the mechanical bearings relatively small but allows for a large (305 mm)diameter clear aperture. A worm gear driven by a cryogenic stepper motor allowsfor precise positioning and prevents undesired rotation when the motors aredepowered. A custom-built optical encoder system monitors the bearing angle toan absolute accuracy of +/- 0.1 degrees. The system performed well in Spiderduring its successful 16 day flight.
Gudmundsson JE, Ade PAR, Amiri M, et al., 2015, The thermal design, characterization, and performance of the Spider long-duration balloon cryostat, Cryogenics, Vol: 72, Pages: 65-76, ISSN: 1879-2235
We describe the SPIDER flight cryostat, which is designed to cool sixmillimeter-wavelength telescopes during an Antarctic long-duration balloonflight. The cryostat, one of the largest to have flown on a stratosphericpayload, uses liquid helium-4 to deliver cooling power to stages at 4.2 and 1.6K. Stainless steel capillaries facilitate a high flow impedance connectionbetween the main liquid helium tank and a smaller superfluid tank, allowing thelatter to operate at 1.6 K as long as there is liquid in the 4.2 K main tank.Each telescope houses a closed cycle helium-3 adsorption refrigerator thatfurther cools the focal planes down to 300 mK. Liquid helium vapor from themain tank is routed through heat exchangers that cool radiation shields,providing negative thermal feedback. The system performed successfully during a17 day flight in the 2014-2015 Antarctic summer. The cryostat had a total holdtime of 16.8 days, with 15.9 days occurring during flight.
Contaldi CR, 2014, BICEP's acceleration, JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS, ISSN: 1475-7516
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- Citations: 3
Horner JS, Contaldi CR, 2014, Non-gaussian signatures of general inflationary trajectories, JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS, ISSN: 1475-7516
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- Citations: 7
Contaldi CR, Horner JS, 2014, PLANCK and WMAP constraints on generalised Hubble flow inflationary trajectories, Journal of Cosmology and Astroparticle Physics, Vol: 2014, ISSN: 1475-7516
We use the Hamilton-Jacobi formalism to constrain the space of possible single field, inflationary Hubble flow trajectories when compared to the WMAP and PLANK 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(phgr) and also yields a prediction for, ℬ, the dimensionless amplitude of the non-Gaussian bispectrum.
Gandilo NN, Ade PAR, Amiri M, et al., 2014, Attitude determination for balloon-borne experiments, GROUND-BASED AND AIRBORNE TELESCOPES V, Vol: 9145, ISSN: 0277-786X
Benton SJ, Ade PA, Amiri M, et al., 2014, BLASTbus electronics: general-purpose readout and control for balloon-borne experiments, GROUND-BASED AND AIRBORNE TELESCOPES V, Vol: 9145, ISSN: 0277-786X
Contaldi CR, Peloso M, Sorbo L, 2014, Suppressing the impact of a high tensor-to-scalar ratio on the temperature anisotropies, Journal of Cosmology and Astroparticle Physics, Vol: 2014, Pages: 1-14, ISSN: 1475-7516
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 sime 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 ns. 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 ns with scales (denoted as running) 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 of a suppression of the scalar power at large scales. Such a situation can be achieved for instance by a sudden change of the speed of the inflaton (by about 14%), and we show that it fits the temperature anisotropies and polarization data considerably better than a constant running (its χ2 improves by ~ 7.5 over that of the constant running, at the cost of one more parameter). We also consider the possibility that the large scale temperature fluctuations are suppressed by an anti-correlation between tensor and scalar modes. Unfortunately, while such effect does affect the temperature fluctuations at large scales, it does not affect the temperature power spectrum and cannot, therefore, help in reconciling a large value of r with the limits from temperature fluctuations.
Soler JD, Ade PAR, Amiri M, et al., 2014, Design and construction of a carbon fiber gondola for the SPIDER balloon-borne telescope, GROUND-BASED AND AIRBORNE TELESCOPES V, Vol: 9145, ISSN: 0277-786X
Rahlin AS, Ade PAR, Amiri M, et al., 2014, Pre-flight integration and characterization of the SPIDER balloon-borne telescope, MILLIMETER, SUBMILLIMETER, AND FAR-INFRARED DETECTORS AND INSTRUMENTATION FOR ASTRONOMY VII, Vol: 9153, ISSN: 0277-786X
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- Citations: 31
Shariff JA, Ade PAR, Amiri M, et al., 2014, Pointing control for the SPIDER balloon-borne telescope, GROUND-BASED AND AIRBORNE TELESCOPES V, Vol: 9145, ISSN: 0277-786X
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- Citations: 9
O'Dea DT, Clark CN, Contaldi CR, et al., 2012, A model for polarized microwave foreground emission from interstellar dust, Monthly Notices of the Royal Astronomical Society, Vol: 419, Pages: 1795-1803, ISSN: 0035-8711
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 (http://www.imperial.ac.uk/people/c.contaldi/fgpol) for these and additional maps at frequencies that will be targeted by upcoming experiments such as EBEX, Spider and SPTpol.
O'Dea DT, Ade PAR, Amiri M, et al., 2011, Spider Optimization II: Optical, Magnetic and Foreground Effects, The Astrophysical Journal: an international review of astronomy and astronomical physics, Vol: 738
Spider is a balloon-borne instrument designed to map the polarization of thecosmic microwave background (CMB) with degree-scale resolution over a largefraction of the sky. Spider's main goal is to measure the amplitude ofprimordial gravitational waves through their imprint on the polarization of theCMB if the tensor-to-scalar ratio, r, is greater than 0.03. To achieve thisgoal, instrumental systematic errors must be controlled with unprecedentedaccuracy. Here, we build on previous work to use simulations of Spiderobservations to examine the impact of several systematic effects that have beencharacterized through testing and modeling of various instrument components. Inparticular, we investigate the impact of the non-ideal spectral response of thehalf-wave plates, coupling between focal plane components and the Earth'smagnetic field, and beam mismatches and asymmetries. We also present a model ofdiffuse polarized foreground emission based on a three-dimensional model of theGalactic magnetic field and dust, and study the interaction of this foregroundemission with our observation strategy and instrumental effects. We find thatthe expected level of foreground and systematic contamination is sufficientlylow for Spider to achieve its science goals.
Rocha G, Contaldi CR, Bond JR, et al., 2011, Application of XFASTER power spectrum and likelihood estimator to <i>Planck</i>, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 414, Pages: 823-846, ISSN: 0035-8711
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- Citations: 13
Tamanini N, Contaldi CR, 2011, Inflationary perturbations in Palatini generalized gravity, Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 83, ISSN: 1550-2368
We examine the generation of primordial perturbations during an inflationary epoch in generalized theories of gravity when the equations of motion are derived using the Palatini variational principle. Both f(R) and scalar-tensor theories are considered, and we compare our results with those obtained under the conventional metric formalism. Nonlinear generalizations of the action lead to different theories under the two variational choices, and we obtain distinct results for scalar and tensor spectral indices and their ratio. We find the following general result: Inflation driven solely by f(R) modifications does not result in suitable curvature perturbations, while scalar-tensor theories generate nearly scalar invariant curvature perturbations but no tensor modes.
Thomas DB, Contaldi CR, 2011, Beyond einstein: Cosmological tests of model independent modified gravity, Pages: 309-312
Model-independent parametrisations of modified gravity have attracted a lot of attention over the past few years; numerous combinations of experiments and observables have been suggested to constrain these parameterisations, and future surveys look very promising. 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 whether they could improve the constraints on the modified gravity parameters. In particular, we forecast the constraints from combining the Planck CMB spectrum and SZ cluster catalogue and a DES-like Weak Lensing survey. We've found that adding cluster counts improves the constraints obtained from combining CMB and WL data.
Fraisse AA, Ade PAR, Amiri M, et al., 2011, SPIDER: Probing the Early Universe with a Suborbital Polarimeter
Runyan MC, Ade PAR, Amiri M, et al., 2011, Design and performance of the Spider instrument
Filippini JP, Ade PAR, Amiri M, et al., 2011, SPIDER: a balloon-borne CMB polarimeter for large angular scales
Thomas DB, Contaldi CR, 2011, Testing model independent modified gravity with future large scale surveys
Natoli P, De Troia G, Hikage C, et al., 2010, BOOMERanG constraints on primordial non-Gaussianity from analytical Minkowski functionals, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 408, Pages: 1658-1665, ISSN: 0035-8711
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- Citations: 17
Contaldi C, Dowker F, Philpott L, 2010, Polarization Diffusion from Spacetime Uncertainty, Classical and Quantum Gravity, Vol: 27, ISSN: 0264-9381
A model of Lorentz invariant random fluctuations in photon polarization ispresented. The effects are frequency dependent and affect the polarization ofphotons as they propagate through space. We test for this effect by confrontingthe model with the latest measurements of polarization of Cosmic MicrowaveBackground (CMB) photons.
Nicholson G, Contaldi CR, Paykari P, 2010, Reconstruction of the primordial power spectrum by direct inversion, JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS, ISSN: 1475-7516
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- Citations: 39
Gudmundsson JE, Ade PAR, Amiri M, et al., 2010, Thermal architecture for the SPIDER flight cryostat, Pages: 77411M-77411M
Bryan SA, Ade PAR, Amiri M, et al., 2010, Modeling and characterization of the SPIDER half-wave plate, MILLIMETER, SUBMILLIMETER, AND FAR-INFRARED DETECTORS AND INSTRUMENTATION FOR ASTRONOMY V, Vol: 7741, ISSN: 0277-786X
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- Citations: 14
Himmetoglu B, Contaldi CR, Peloso M, 2009, Ghost instabilities of cosmological models with vector fields nonminimally coupled to the curvature, PHYSICAL REVIEW D, Vol: 80, ISSN: 1550-7998
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- Citations: 112
Thomas DB, Contaldi CR, Magueijo J, 2009, Rotation of Galaxies as a Signature of Cosmic Strings in Weak Lensing Surveys, PHYSICAL REVIEW LETTERS, Vol: 103, ISSN: 0031-9007
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- Citations: 20
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