## Publications

141 results found

Gambrel AE, Rahlin AS, Song X,
et al., 2021, The XFaster Power Spectrum and Likelihood Estimator for the Analysis of Cosmic Microwave Background Maps, *ASTROPHYSICAL JOURNAL*, Vol: 922, ISSN: 0004-637X

Golat S, Contaldi CR, 2021, Geodesic noise and gravitational wave observations by pulsar timing arrays, *PHYSICS LETTERS B*, Vol: 818, ISSN: 0370-2693

Shaw EC, Ade PAR, Akers S, et al., 2020, Design and pre-flight performance of SPIDER 280 GHz receivers, SPIE ASTRONOMICAL TELESCOPES + INSTRUMENTATION, Publisher: SPIE, Pages: 1-1

In this work we describe upgrades to the Spider balloon-borne telescope in preparation for its second flight, currently planned for December 2021. The Spider instrument is optimized to search for a primordial B-mode polarization signature in the cosmic microwave background at degree angular scales. During its first flight in 2015, Spider mapped ~10% of the sky at 95 and 150 GHz. The payload for the second Antarctic flight will incorporate three new 280 GHz receivers alongside three refurbished 95- and 150 GHz receivers from Spider's first flight. In this work we discuss the design and characterization of these new receivers, which employ over 1500 feedhorn-coupled transition-edge sensors. We describe pre-flight laboratory measurements of detector properties, and the optical performance of completed receivers. These receivers will map a wide area of the sky at 280 GHz, providing new information on polarized Galactic dust emission that will help to separate it from the cosmological signal.

Margalit A, Contaldi CR, Pieroni M, 2020, Phase decoherence of gravitational wave backgrounds, *Physical Reveiw D*

Metric perturbations affect the phase of gravitational waves as theypropagate through the inhomogeneous universe. This effect causes StochasticGravitational Wave Backgrounds (SGWBs) to lose any phase coherence that mayhave been present at emission or horizon entry. We show that, for a standardcosmological model, this implies complete loss of coherence above frequencies$f \sim 10^{-12}$ Hz. The result is that any attempts to map SGWBs usingphase-coherent methods have no foreseeable applications. Incoherent methodsthat solve directly for the intensity of the SGWBs are the only methods thatcan reconstruct the angular dependence of any SGWB.

Contaldi CR, Pieroni M, Renzini A,
et al., 2020, Maximum likelihood map making with the Laser Interferometer Space Antenna, *Physical Review D: Particles, Fields, Gravitation and Cosmology*, Vol: 102, Pages: 043502 – 1-043502 – 13, ISSN: 1550-2368

Given the recent advances in gravitational-wave detection technologies, the detection and characterization of gravitational-wave backgrounds (GWBs) with the Laser Interferometer Space Antenna (LISA) is a real possibility. To assess the abilities of the LISA satellite network to reconstruct anisotropies of different angular scales and in different directions on the sky, we develop a map-maker based on an optimal quadratic estimator. The resulting maps are maximum likelihood representations of the GWB intensity on the sky integrated over a broad range of frequencies. We test the algorithm by reconstructing known input maps with different input distributions and over different frequency ranges. We find that, in an optimal scenario of well understood noise and high frequency, high SNR signals, the maximum scales LISA may probe are ℓmax≲15. The map-maker also allows to test the directional dependence of LISA noise, providing insight on the directional sky sensitivity we may expect.

Alonso D, Contaldi CR, Cusin G,
et al., 2020, Noise angular power spectrum of gravitational wave background experiments, *Physical Review D: Particles, Fields, Gravitation and Cosmology*, Vol: 101, Pages: 124048 – 1-124048 – 17, ISSN: 1550-2368

We construct a model for the angular power spectrum of the instrumental noise in interferometer networks mapping gravitational wave backgrounds (GWBs) as a function of detector noise properties, network configuration, and scan strategy. We use the model to calculate the noise power spectrum for current and future ground-based experiments, as well as for planned space missions. We present our results in a language similar to that used in cosmic microwave background and intensity mapping experiments, and connect the formalism with the sensitivity curves that are common lore in GWB analyses.

Contaldi CR, 2020, COVID-19: nowcasting reproduction factors using biased case testing data, Publisher: arXiv

Timely estimation of the current value for COVID-19 reproduction factor $R$has become a key aim of efforts to inform management strategies. $R$ is animportant metric used by policy-makers in setting mitigation levels and is alsoimportant for accurate modelling of epidemic progression. This brief paperintroduces a method for estimating $R$ from biased case testing data. Usingtesting data, rather than hospitalisation or death data, provides a muchearlier metric along the symptomatic progression scale. This can be hugelyimportant when fighting the exponential nature of an epidemic. We develop apractical estimator and apply it to Scottish case testing data to infer acurrent (20 May 2020) $R$ value of $0.74$ with $95\%$ confidence interval$[0.48 - 0.86]$.

Osherson B, Filippini JP, Fu J,
et al., 2020, Particle response of antenna-coupled TES arrays: results from SPIDER and the laboratory, *Journal of Low Temperature Physics*, Vol: 199, Pages: 1127-1136, ISSN: 0022-2291

Future mm-wave and sub-mm space missions will employ large arrays of multiplexed transition-edge-sensor (TES) bolometers. Such instruments must contend with the high flux of cosmic rays beyond our atmosphere that induce ‘glitches’ in bolometer data, which posed a challenge to data analysis from the Planck bolometers. Future instruments will face the additional challenges of shared substrate wafers and multiplexed readout wiring. In this work, we explore the susceptibility of modern TES arrays to the cosmic ray environment of space using two data sets: the 2015 long-duration balloon flight of the SPIDER cosmic microwave background polarimeter, and a laboratory exposure of SPIDER flight hardware to radioactive sources. We find manageable glitch rates and short glitch durations, leading to minimal effect on SPIDER analysis. We constrain energy propagation within the substrate through a study of multi-detector coincidences and give a preliminary look at pulse shapes in laboratory data.

Renzini A, Contaldi CR, 2019, Improved limits on a stochastic gravitational-wave background and its anisotropies from Advanced LIGO O1 and O2 runs, *Physical Review D: Particles, Fields, Gravitation and Cosmology*, Vol: 100, Pages: 063527-1-063527-9, ISSN: 1550-2368

We integrate the entire, publicly available, Advanced LIGO dataset to obtain maximum-likelihood constraint maps of the stochastic gravitational-wave background (SGWB). From these, we derive limits on the energy density of the stochastic background ΩGW and its anisotropy. We find 95% confident limits ΩGW<5.2×10−8 at 50 Hz for a spectral index α=2/3 consistent with a stochastic background due to inspiral events and ΩGW<3.2×10−7 for a scale (frequency) invariant spectrum. We also report upper limits on the angular power spectra Cℓ for three broadband integrations of the data. Finally, we present an estimate in which we integrate the data into ten separate spectral bins as a first attempt to carry out a model-independent estimate of the SGWB and its anisotropies.

Baker J, Baker T, Carbone C, et al., 2019, High angular resolution gravitational wave astronomy, Publisher: arXiv

Since the very beginning of astronomy the location of objects on the sky hasbeen a fundamental observational quantity that has been taken for granted.While precise two dimensional positional information is easy to obtain forobservations in the electromagnetic spectrum, the positional accuracy ofcurrent and near future gravitational wave detectors is limited to between tensand hundreds of square degrees, which makes it extremely challenging toidentify the host galaxies of gravitational wave events or to confidentlydetect any electromagnetic counterparts. Gravitational wave observationsprovide information on source properties and distances that is complementary tothe information in any associated electromagnetic emission and that is veryhard to obtain in any other way. Observing systems with multiple messengersthus has scientific potential much greater than the sum of its parts. Agravitational wave detector with higher angular resolution would significantlyincrease the prospects for finding the hosts of gravitational wave sources andtriggering a multi-messenger follow-up campaign. An observatory with arcminuteprecision or better could be realised within the Voyage 2050 programme bycreating a large baseline interferometer array in space and would havetransformative scientific potential. Precise positional information of standardsirens would enable precision measurements of cosmological parameters and offernew insights on structure formation; a high angular resolution gravitationalwave observatory would allow the detection of a stochastic background andresolution of the anisotropies within it; it would also allow the study ofaccretion processes around black holes; and it would have tremendous potentialfor tests of modified gravity and the discovery of physics beyond the StandardModel.

Collaboration TSO, Abitbol MH, Adachi S, et al., 2019, The Simons observatory: Astro2020 decadal project whitepaper, Publisher: arXiv

The Simons Observatory (SO) is a ground-based cosmic microwave background(CMB) experiment sited on Cerro Toco in the Atacama Desert in Chile thatpromises to provide breakthrough discoveries in fundamental physics, cosmology,and astrophysics. Supported by the Simons Foundation, the Heising-SimonsFoundation, and with contributions from collaborating institutions, SO will seefirst light in 2021 and start a five year survey in 2022. SO has 287collaborators from 12 countries and 53 institutions, including 85 students and90 postdocs. The SO experiment in its currently funded form ('SO-Nominal') consists ofthree 0.4 m Small Aperture Telescopes (SATs) and one 6 m Large ApertureTelescope (LAT). Optimized for minimizing systematic errors in polarizationmeasurements at large angular scales, the SATs will perform a deep,degree-scale survey of 10% of the sky to search for the signature of primordialgravitational waves. The LAT will survey 40% of the sky with arc-minuteresolution. These observations will measure (or limit) the sum of neutrinomasses, search for light relics, measure the early behavior of Dark Energy, andrefine our understanding of the intergalactic medium, clusters and the role offeedback in galaxy formation. With up to ten times the sensitivity and five times the angular resolution ofthe Planck satellite, and roughly an order of magnitude increase in mappingspeed over currently operating ("Stage 3") experiments, SO will measure the CMBtemperature and polarization fluctuations to exquisite precision in sixfrequency bands from 27 to 280 GHz. SO will rapidly advance CMB science whileinforming the design of future observatories such as CMB-S4.

Renzini AI, Contaldi CR, 2019, Gravitational wave background sky maps from advanced LIGO O1 data, *PHYSICAL REVIEW LETTERS*

We integrate the publicly available O1 LIGO time-domain data to obtain maximum-likelihood constraints on the Gravitational Wave Background (GWB) arising from stochastic, persistent signals. Our method produces sky-maps of the strain intensity I as a function of direction on the sky at a reference frequency f0. The data is integrated assuming a set of fixed power-law spectra for the signal. The maps provide upper limits on the amplitude of the GWB density ΩGW(f0) and any anisotropy around the background. We find 95\% confidence upper limits of ΩGW<4.8×10−7 at f0=50 Hz with similar constraints on a dipole modulation for the inspiral-dominated stochastic background case.

Bergman AS, Ade PAR, Akers S,
et al., 2018, 280 GHz Focal Plane Unit Design and Characterization for the SPIDER-2 Suborbital Polarimeter, *JOURNAL OF LOW TEMPERATURE PHYSICS*, Vol: 193, Pages: 1075-1084, ISSN: 0022-2291

Renzini AI, Contaldi CR, 2018, Mapping incoherent gravitational wave backgrounds, *Monthly Notices of the Royal Astronomical Society*, Vol: 481, Pages: 4650-4661, ISSN: 0035-8711

Given the recent detection of gravitational waves from individual sources, it is almost a certainty that some form of background of gravitational waves will be detected in future. The most promising candidate for such a detection is backgrounds made up of incoherent superposition of the signal of unresolved astrophysical, or backgrounds sourced by earlier cosmological events. Such backgrounds will also contain anisotropies about an average value. The information contained in the background level and any anisotropies will be extremely valuable as an astrophysical and cosmological probe. As such, the ability to reconstruct sky maps of the signal will become important as the sensitivity increases. We build and test a pixel-based, maximum-likelihood gravitational wave background (GWB) map-maker that uses the cross-correlation of sets of generalized baselines as input. The resulting maps are a representation of the GWB power, or strain ‘intensity’ on the sky. We test the algorithm by reconstructing known input maps with different baseline configurations. We also apply the map-maker to a subset of the Advanced Laser Interferometer Gravitational Wave observatory data.

Gualtieri R, Filippini JP, Ade PAR,
et al., 2018, SPIDER: CMB polarimetry from the edge of space, *Journal of Low Temperature Physics*, Vol: 193, Pages: 1112-1121, ISSN: 0022-2291

Spider is a balloon-borne instrument designed to map the polarization of the millimeter-wave sky at large angular scales. Spider targets the B-mode signature of primordial gravitational waves in the cosmic microwave background (CMB), with a focus on mapping a large sky area with high fidelity at multiple frequencies. Spider ’s first long-duration balloon (LDB) flight in January 2015 deployed a total of 2400 antenna-coupled transition-edge sensors (TESs) at 90 GHz and 150 GHz. In this work we review the design and in-flight performance of the Spider instrument, with a particular focus on the measured performance of the detectors and instrument in a space-like loading and radiation environment. Spider ’s second flight in December 2018 will incorporate payload upgrades and new receivers to map the sky at 285 GHz, providing valuable information for cleaning polarized dust emission from CMB maps.

Contaldi CR, Magueijo J, 2018, Unsqueezing of standing waves due to inflationary domain structure, *Physical Review D*, Vol: 98, ISSN: 2470-0010

The so-called trans-Planckian problem of inflation may be evaded by positing that modes come into existence only when they became “cis-Planckian” by virtue of expansion. However, this would imply that for any mode a new random realization would have to be drawn every N wavelengths, with N typically of order 1000 (but it could be larger or smaller). Such a redrawing of realizations leads to a heteroskodastic distribution if the region under observation contains several such independent domains. This has no effect on the sampled power spectrum for a scale-invariant raw spectrum, but at very small scales, it leads to a spectral index bias toward scale invariance and smooths oscillations in the spectrum. The domain structure would also “unsqueeze” some of the propagating waves, i.e., dismantle their standing wave character. By describing standing waves as traveling waves of the same amplitude moving in opposite directions, we determine the observational effects of unsqueezing. We find that it would erase the Doppler peaks in the cosmic microwave background, but only on very small angular scales, in which the primordial signal may not be readily accessible. The standing waves in a primordial gravitational wave background would also be turned into traveling waves. This unsqueezing of the gravitational wave background may constitute a detectable phenomenon.

Nagy JM, Ade PAR, Amiri M,
et al., 2017, A New Limit on CMB Circular Polarization from SPIDER, *Astrophysical Journal*, Vol: 844, ISSN: 0004-637X

We present a new upper limit on cosmic microwave background (CMB) circular polarization from the 2015 flight of Spider, a balloon-borne telescope designed to search for B-mode linear polarization from cosmic inflation. Although the level of circular polarization in the CMB is predicted to be very small, experimental limits provide a valuable test of the underlying models. By exploiting the nonzero circular-to-linear polarization coupling of the half-wave plate polarization modulators, data from Spider's 2015 Antarctic flight provide a constraint on Stokes V at 95 and 150 GHz in the range $33\lt {\ell }\lt 307$. No other limits exist over this full range of angular scales, and Spider improves on the previous limit by several orders of magnitude, providing 95% C.L. constraints on ${\ell }({\ell }+1){C}_{{\ell }}^{{VV}}/(2\pi )$ ranging from 141 to 255 μK2 at 150 GHz for a thermal CMB spectrum. As linear CMB polarization experiments become increasingly sensitive, the techniques described in this paper can be applied to obtain even stronger constraints on circular polarization.

Renzini AI, Contaldi CR, Heavens A, 2017, Mapping weak lensing distortions in the Kerr metric, *Physical Review D*, Vol: 95, ISSN: 2470-0010

Einstein’s theory of General Relativity implies that energy, i.e., matter, curves space-time and thusdeforms lightlike geodesics, giving rise to gravitational lensing. This phenomenon is well understood in thecase of the Schwarzschild metric and has been accurately described in the past; however, lensing in the Kerrspace-time has received less attention in the literature despite potential practical observational applications.In particular, lensing in such space is not expressible as the gradient of a scalar potential and as such is asource of curl-like signatures and an asymmetric shear pattern. In this paper, we develop a differentiablelensing map in the Kerr metric, reworking and extending previous approaches. By using standard tools ofweak gravitational lensing, we isolate and quantify the distortion that is uniquely induced by the presenceof angular momentum in the metric. We apply this framework to the distortion induced by a Kerr-likeforeground object on a distribution of background of sources. We verify that the new unique lensingsignature is orders of magnitude below current observational bounds for a range of lens configurations.

Contaldi CR, 2017, Anisotropies of gravitational wave backgrounds: a line of sight approach, *Physics Letters B*, Vol: 771, Pages: 9-12, ISSN: 0370-2693

In the weak field regime, gravitational waves can be considered as being made up of collisionless, relativistic tensor modes that travel along null geodesics of the perturbed background metric. We work in this geometric optics picture to calculate the anisotropies in gravitational wave backgrounds resulting from astrophysical and cosmological sources. Our formalism yields expressions for the angular power spectrum of the anisotropies. We show how the anisotropies are sourced by intrinsic, Doppler, Sachs–Wolfe, and Integrated Sachs–Wolfe terms in analogy with Cosmic Microwave Background photons.

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: 1

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

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