Imperial College London

Carlo R. Contaldi

Faculty of Natural SciencesDepartment of Physics

Professor of Theoretical Physics



+44 (0)20 7594 1527c.contaldi




505Huxley BuildingSouth Kensington Campus





Publication Type

135 results found

Rocha G, Contaldi CR, Colombo LPL, Bond JR, Gorski KM, Lawrence CRet al., Performance of XFaster likelihood in real CMB experiments

We assess the strengths and weaknesses of several likelihood formalisms,including the XFaster likelihood. We compare the performance of the XFasterlikelihood to that of the Offset Lognormal Bandpower likelihood on simulateddata for the Planck satellite. Parameters estimated with these two likelihoodsare in good agreement. The advantages of the XFaster likelihood can thereforebe realized without compromising performance.

Journal article

Contaldi CR, The OPERA neutrino velocity result and the synchronisation of clocks

The CERN-OPERA experiment claims to have measured a one-way speed ofneutrinos that is apparently faster than the speed of light c. One-way speedmeasurements such as these inevitably require a convention for thesynchronisation of clocks in non-inertial frames since the Earth is rotating.We argue that the effect of the synchronisation convention is not properlytaken into account in the OPERA analysis and may well invalidate theirinterpretation of superluminal neutrino velocity.

Journal article

Thomas DB, Contaldi CR, Viability of the cluster mass function formalism in parametrised modified gravity

Model-independent parametrisations for examining departures from GeneralRelativity have been increasingly studied over the past few years. Variousobservables have been used to constrain the parameters and forecasts for futuresurveys have been carried out. In one such forecast, galaxy cluster counts wereused to constrain the parameters. Here, we carry out a limited set of $N$-bodysimulations, with a modified Poisson equation, to examine the accuracy ofexisting mass functions for modified gravity cosmologies. As well as alteringthe gravitational calculation, we include the effect of a screening scale toensure consistency of the theory with solar system tests. Our results suggestthat if a screening scale exists its effect can be taken into account in thecluster count calculation through its effect on the linear matter powerspectrum. If this is done, the accuracy of the standard mass function formalismin modified gravity theories with reasonably small departures from GeneralRelativity, as tested in this work, is comparable to the standard case.

Journal article

Clark CN, Contaldi CR, MacTavish CJ, Modelling the Polarisation of Microwave Foreground Emission on Large Angular Scales

Templates for polarised emission from Galactic foregrounds at frequenciesrelevant to Cosmic Microwave Background (CMB) polarisation experiments areobtained by modelling the Galactic Magnetic Field (GMF) on large scales. Thiswork extends the results of O'Dea et al. by including polarised synchrotronradiation as a source of foreground emission. The polarisation direction andfraction in this calculation are based solely on the underlying choice of GMFmodel and therefore provide an independent prediction for the polarisationsignal on large scales. Templates of polarised foregrounds may be of use whenforecasting effective experimental sensitivity. In turn, as measurements of theCMB polarisation over large fractions of the sky become routine, this modelwill allow for the data to constrain parameters in the, as yet, not wellunderstood form of the GMF.

Journal article

Horner JS, Contaldi CR, BICEP's bispectrum

The simplest interpretation of the Bicep2 result is that the scalarprimordial power spectrum is slightly suppressed at large scales. These modelsresult in a large tensor-to-scalar ratio $r$. In this work we show that thetype of inflationary trajectory favoured by Bicep2 also leads to a largernon-Gaussian signal at large scales, roughly an order of magnitude larger thana standard slow-roll trajectory.

Journal article

Horner JS, Contaldi CR, The bispectrum of single-field inflationary trajectories with $c_{s} \neq 1$

The bispectrum of single-field inflationary trajectories in which the speedof sound of the inflationary trajectories $c_s$ is constant but not equal tothe speed of light $c=1$ is explored. The trajectories are generated as randomrealisations of the Hubble Slow-Roll (HSR) hierarchy and the bispectra arecalculated using numerical techniques that extends previous work. This methodallows for out-of-slow-roll models with non-trivial time dependence andarbitrarily low $c_s$. The ensembles obtained using this method yielddistributions for the shape and scale-dependence of the bispectrum and theirrelations with the standard inflationary parameters such as scalar spectraltilt $n_s$ and tensor-to-scalar ratio $r$. The distributions demonstrate thesqueezed-limit consistency relations for arbitrary single-field inflationarymodels.

Journal article

Golat S, Contaldi CR, Geodesic Noise and Gravitational Wave Observations by Pulsar Timing Arrays

Signals from millisecond pulsars travel to us along geodesics that areaffected by the space--time metric along the line-of-sight. The exact lengthand redshifting along the geodesics determine the Time-of-Arrival (ToA) of thepulses. The metric is determined by the distribution of dark matter, gas, andstars in the galaxy and, in the final stages of travel, by the distribution ofsolar system bodies. The inhomogeneous distribution of stellar masses can havea small but significant statistical effect on the ToAs through the perturbationof geodesics. This will result in additional noise in ToA observations that mayaffect Pulsar Timing Array (PTA) constraints on gravitational waves at very lowfrequencies. We employ a simple model for the stellar distribution in ourgalaxy to estimate the scale of both static and dynamic sources of what we termgenerically ``geodesic noise''. We find that geodesic noise is ${\cal O}(10)$ns for typical lines-of-sight. This indicates that it is relevant for estimatesof PTA sensitivity and may limit future efforts for detection of gravitationalwaves by PTAs.

Journal article

Aguirre J, Amblard A, Ashoorioon A, Baccigalupi C, Balbi A, Bartlett J, Bartolo N, Benford D, Birkinshaw M, Bock J, Bond D, Borrill J, Bouchet F, Bridges M, Bunn E, Calabrese E, Cantalupo C, Caramete A, Carbone C, Chatterjee S, Church S, Chuss D, Contaldi C, Cooray A, Das S, Bernardis FD, Bernardis PD, Zotti GD, Delabrouille J, Dsert F-X, Devlin M, Dickinson C, Dicker S, Dobbs M, Dodelson S, Dore O, Dotson J, Dunkley J, Falvella MC, Fixsen D, Fosalba P, Fowler J, Gates E, Gear W, Golwala S, Gorski K, Gruppuso A, Gundersen J, Halpern M, Hanany S, Hazumi M, Hernandez-Monteagudo C, Hertzberg M, Hinshaw G, Hirata C, Hivon E, Holmes W, Holzapfel W, Hu W, Hubmayr J, Huffenberger K, Irwin K, Jackson M, Jaffe A, Johnson B, Jones W, Kaplinghat M, Keating B, Keskitalo R, Khoury J, Kinney W, Kisner T, Knox L, Kogut A, Komatsu E, Kosowsky A, Kovac J, Krauss L, Kurki-Suonio H, Landau S, Lawrence C, Leach S, Lee A, Leitch E, Leonardi R, Lesgourgues J, Liddle A, Lim E, Limon M, Loverde M, Lubin P, Magalhaes A, Maino D, Marriage T, Martin V, Matarrese S, Mather J, Mathur H, Matsumura T, Meerburg P, Melchiorri A, Meyer S, Miller A, Milligan M, Moodley K, Neimack M, Nguyen H, O'Dwyer I, Orlando A, Pagano L, Page L, Partridge B, Pearson T, Peiris H, Piacentini F, Piccirillo L, Pierpaoli E, Pietrobon D, Pisano G, Pogosian L, Pogosyan D, Ponthieu N, Popa L, Pryke C, Raeth C, Ray S, Reichardt C, Ricciardi S, Richards P, Rocha G, Rudnick L, Ruhl J, Rusholme B, Scoccola C, Scott D, Sealfon C, Sehgal N, Seiffert M, Senatore L, Serra P, Shandera S, Shimon M, Shirron P, Sievers J, Sigurdson K, Silk J, Silverberg R, Silverstein E, Staggs S, Stebbins A, Stivoli F, Stompor R, Sugiyama N, Swetz D, Tartari A, Tegmark M, Timbie P, Tristram M, Tucker G, Urrestilla J, Vaillancourt J, Veneziani M, Verde L, Vieira J, Watson S, Wandelt B, Wilson G, Wollack E, Wyman M, Yadav A, Yannick G-H, Zahn O, Zaldarriaga M, Zemcov M, Zwart Jet al., Observing the Evolution of the Universe

How did the universe evolve? The fine angular scale (l>1000) temperature andpolarization anisotropies in the CMB are a Rosetta stone for understanding theevolution of the universe. Through detailed measurements one may addresseverything from the physics of the birth of the universe to the history of starformation and the process by which galaxies formed. One may in addition trackthe evolution of the dark energy and discover the net neutrino mass. We are at the dawn of a new era in which hundreds of square degrees of skycan be mapped with arcminute resolution and sensitivities measured inmicroKelvin. Acquiring these data requires the use of special purposetelescopes such as the Atacama Cosmology Telescope (ACT), located in Chile, andthe South Pole Telescope (SPT). These new telescopes are outfitted with a newgeneration of custom mm-wave kilo-pixel arrays. Additional instruments are inthe planning stages.

Journal article

Contaldi CR, COVID-19: Nowcasting Reproduction Factors Using Biased Case Testing Data

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$[0.48 - 0.86]$.

Journal article

Contaldi CR, Bond JR, Pogosyan D, Mason BS, Myers ST, Pearson TJ, Pen UL, Prunet S, Readhead AC, Ruetalo MI, Sievers JL, Wadsley JW, Zhang PJet al., Cosmological Parameters from CMB measurements with the CBI

We derive cosmological parameters from the CBI measurements of the CosmicMicrowave Background (CMB) angular power spectrum. Our results provide anindependent confirmation of the standard $\Omega_{\rm tot}=1$ $\Lambda$CDMmodel within the adiabatic, inflationary paradigm. Above $\ell=2000$ theobservations show evidence of power in excess of that expected in the standardmodels. We use hydrodynamical simulations to show how Sunyaev-Zeldovich Effect(SZE) may account for the excess power for models with fluctuation amplitude$\sigma_8\sim 1$ which is in the high end of the range allowed by the primaryCMB observations.

Journal article

Contaldi CR, Nicholson G, Stoica H, Small cosmological signatures from multi-brane models

We analyse the signatures of brane inflation models with modulistabilisation. These are hybrid inflation models with a non-trivial field-spacemetric which can induce complex trajectories for the fields during inflation.This in turn could lead to observable features on the power spectrum of the CMBfluctuations through departures from near scale invariance or the presence ofisocurvature modes. We look specifically at multi-brane models in which thevolume modulus also evolves. We find that the signatures are highly sensitiveto the actual trajectories in field space, but their amplitudes are too smallto be observable even for future high precision CMB experiments.

Journal article

Contaldi CR, Bond JR, Pogosyan D, Mason BS, Myers ST, Pearson TJ, Pen UL, Prunet S, Readhead AC, Ruetalo MI, Sievers JL, Wadsley JW, Zhang PJet al., CMB observations with the Cosmic Background Imager (CBI) Interferometer

We review the recently published results from the CBI's first season ofobservations. Angular power spectra of the CMB were obtained from deepintegrations of 3 single fields covering a total of 3 deg^2 and 3 shallowersurveys of overlapping (mosaiced) fields covering a total of 40 deg^2. Theobservations show a damping of the anisotropies at high-l as expected from thestandard scenarios of recombination. We present parameter estimates obtainedfrom the data and discuss the significance of an excess at l>2000 observed inthe deep fields.

Journal article

Dodelson S, Easther R, Hanany S, McAllister L, Meyer S, Page L, Ade P, Amblard A, Ashoorioon A, Baccigalupi C, Balbi A, Bartlett J, Bartolo N, Baumann D, Beltran M, Benford D, Birkinshaw M, Bock J, Bond D, Borrill J, Bouchet F, Bridges M, Bunn E, Calabrese E, Cantalupo C, Caramete A, Carbone C, Carroll S, Chatterjee S, Chen X, Church S, Chuss D, Contaldi C, Cooray A, Creminelli P, Das S, Bernardis FD, Bernardis PD, Delabrouille J, Desert F-X, Devlin M, Dickinson C, Dicker S, DiPirro M, Dobbs M, Dore O, Dotson J, Dunkley J, Dvorkin C, Eriksen HK, Falvella MC, Finley D, Finkbeiner D, Fixsen D, Flauger R, Fosalba P, Fowler J, Galli S, Gates E, Gear W, Giraud-Heraud Y, Gorski K, Greene B, Gruppuso Aet al., The Origin of the Universe as Revealed Through the Polarization of the Cosmic Microwave Background

Modern cosmology has sharpened questions posed for millennia about the originof our cosmic habitat. The age-old questions have been transformed into twopressing issues primed for attack in the coming decade: How did the Universebegin? and What physical laws govern the Universe at the highest energies? Theclearest window onto these questions is the pattern of polarization in theCosmic Microwave Background (CMB), which is uniquely sensitive to primordialgravity waves. A detection of the special pattern produced by gravity waveswould be not only an unprecedented discovery, but also a direct probe ofphysics at the earliest observable instants of our Universe. Experiments whichmap CMB polarization over the coming decade will lead us on our first stepstowards answering these age-old questions.

Journal article

Sievers JL, Mason BS, Weintraub L, Achermann C, Altamirano P, Bond JR, Bronfman L, Bustos R, Contaldi C, Dickinson C, Jones ME, May J, Myers ST, Oyarce N, Padin S, Pearson TJ, Pospieszalski M, Readhead ACS, Reeves R, Shepherd MC, Taylor AC, Torres Set al., Cosmological Results from Five Years of 30 GHz CMB Intensity Measurements with the Cosmic Background Imager

We present final results on the angular power spectrum of total intensityanisotropies in the CMB from the CBI. Our analysis includes all primordialanisotropy data collected between January 2000 and April 2005, and benefitssignificantly from an improved maximum likelihood analysis pipeline. It alsoincludes results from a 30 GHz foreground survey conducted with the Green BankTelescope (GBT) which places significant constraints on the possiblecontamination due to foreground point sources. We improve on previous CBIresults by about a factor of two in the damping tail. These data confirm, at~3-sigma, the existence of an excess of power over intrinsic CMB anisotropy onsmall angular scales (l > 1800). Using the GBT survey, we find currently knownradio source populations are not capable of generating the power; a newpopulation of faint sources with steeply rising spectral indices would berequired to explain the excess with sources... We also present a fullcosmological parameter analysis of the new CBI power spectrum... With CBIalone, the full parameter analysis finds the excess is 1.6-sigma above thelevel expected for a sigma_8=0.8 universe. We find the addition of high-l CMBdata substantially improves constraints on cosmic string contributions to theTT power spectrum as well as the running of the scalar spectral index... Wealso present forecasts for what other experiments should see at differentfrequencies and angular resolutions given the excess power observed by CBI. Wefind that the reported high-l bandpowers from current high resolution CMBbolometer experiments are consistent with each other and CBI if the excesspower is due to the SZE at the CBI-level of 2.5 +/- 1 times the sigma_8=0.8standard SZ template. <Abridged>

Journal article

Coble K, Ade PAR, Bock JJ, Bond JR, Borrill J, Boscaleri A, Contaldi CR, Crill BP, Bernardis PD, Farese P, Ganga K, Giacometti M, Hivon E, Hristov VV, Iacoangeli A, Jaffe AH, Jones WC, Lange AE, Martinis L, Masi S, Mason P, Mauskopf PD, Melchiorri A, Montroy T, Netterfield CB, Nyman L, Pascale E, Piacentini F, Pogosyan D, Polenta G, Pongetti F, Prunet S, Romeo G, Ruhl JE, Scaramuzzi Fet al., Observations of Galactic and Extra-galactic Sources From the BOOMERANG and SEST Telescopes

We present millimeter-wave observations of three extra-galactic and sixGalactic sources in the Southern sky. Observations were made at 90, 150, 240and 400 GHz with resolutions of 18, 10, 14 and 12 arcmin respectively duringthe 1998 Antarctic long duration balloon flight of BOOMERANG. Observations werealso made with the SEST telescope, at 90 and 150 GHz with resolutions of 57 and35 arcsec respectively. These observations can be used for calibrations ofCosmic Microwave Background (CMB) experiments as well as an understanding ofthe physical processes of the sources.

Journal article

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