Imperial College London

Professor Andrew H Jaffe

Faculty of Natural SciencesDepartment of Physics

Professor of Astrophysics and Cosmology



+44 (0)20 7594 7526a.jaffe Website




Miss Louise Hayward +44 (0)20 7594 7679




1018BBlackett LaboratorySouth Kensington Campus





Publication Type

314 results found

Kaiser N, Jaffe A, 1997, Bending of light by gravity waves, Astrophysical Journal, Vol: 484, Pages: 545-554, ISSN: 0004-637X

We describe the statistical properties of light rays propagating though a random sea of gravity waves and compare with the case for scalar metric perturbations from density inhomogeneities. For scalar fluctuations, the deflection angle grows as the square root of the path length D in the manner of a random walk, and the rms displacement of a ray from the unperturbed trajectory grows as D3/2. For gravity waves the situation is very different. The mean square deflection angle remains finite and is dominated by the effect of the metric fluctuations at the ends of the ray, and the mean square displacement grows only as the logarithm of the path length. In terms of power spectra, the displacement for scalar perturbations has P(k) ∝ 1/k4while, for gravity waves, the trajectories of photons have P(k) ∝ 1/k, which is a scale-invariant or "flicker noise" process, and departures from rectilinear motion are suppressed relative to the scalar case by a factor of ∼(λ/D)3/2, where λ is the characteristic scale of the metric fluctuations and D is the path length. This result casts doubt on the viability of some recent proposals for detecting or constraining the gravity wave background by astronomical measurements. © 1997. The American Astronomical Society. All rights reserved.


Jaffe A, 1996, H<inf>0</inf>and odds on cosmology, Astrophysical Journal, Vol: 471, Pages: 24-29, ISSN: 0004-637X

Recent observations by the Hubble Space Telescope of Cepheids in the Virgo cluster imply a Hubble constant H0= 80 ± 17 km s-1Mpc-1; other recent observations find 70 ≲ H0≲ 90 km s-1Mpc-1, with several large excursions in either direction. We attempt to clarify some issues of interpretation of these results for determining the global cosmological parameters Ω and A. In this paper, we use these results as a case study in the formalism of Bayesian model comparison, allowing a rigorous comparison of the different cosmological possibilities. We concentrate our analysis on three recent determinations of the Hubble constant, but the results are generic so long as they prefer H0t0≳ 1, which would seem to require ∧ gt; 0 within the context of Friedmann-Robertson-Walker cosmologies. With our more rigorous methods, the data do indeed suggest a universe with a nonzero cosmological constant but vanishing curvature: Ω + ∧ = 1. © 1996. The American Astronomical Society. All rights reserved.


Jaffe AH, Kaiser N, 1995, Likelihood analysis of large-scale flows, Astrophysical Journal, Vol: 455, Pages: 26-31, ISSN: 0004-637X

We apply a likelihood analysis to the data of Lauer and Postman, with P(k) parameterized by (σ8, Γ), the likelihood function peaks at σ8≃ 0.3, Γ ≲ 0.025, indicating at face value very strong large-scale power, although at a level incompatible with COBE. There is, however, a ridge of likelihood such that more conventional power spectra do not seem strongly disfavored. The likelihood calculated using as data only the components of the bulk flow solution peaks at higher σ8, in agreement with other analyses, but it is rather broad. The likelihood incorporating both bulk flow and shear gives a different picture. The components of the shear are all low, and this pulls the peak to lower amplitudes as a compromise. The Lauer and Postman velocity data alone are therefore consistent with models with very strong large- scale power which generates a large bulk flow, but the small shear (which also probes fairly large scales) requires that the power would have to be at very large scales, which is strongly disfavored by COBE. The velocity data also seem compatible with more conventional P(k) with 0.2 ≲ Γ ≲ 0.5, and the likelihood is peaked around σ8∼ 1, in which case the bulk flow is a moderate, but not extreme, statistical fluctuation. If we apply the same techniques to the data of Riess, Press, & Kirshner, the results are quite different. The flow is not inconsistent with the microwave dipole, and we derive only an upper limit to the amplitude of the power spectrum: σ8≲ 1.5 at ∼99%.


Jaffe AH, 1994, Quasilinear evolution of compensated cosmological perturbations: The nonlinear σ model, Physical Review D, Vol: 49, Pages: 3893-3909, ISSN: 0556-2821

We consider the evolution of perturbations to a flat FRW universe that arise from a ''stiff source,'' such as a self-ordering cosmic field that forms in a global symmetry-breaking phase transition and evolves via the Kibble mechanism. Although the linear respone of the normal matter to the source depends on the details of the source dynamics, we show that the higher-order nonlinear perturbative equations reduce to a form identical to those of source-free Newtonian gravity in the small wavelength limit. Consequently, the resulting n-point correlation functions and their spectral counterparts will have a hierarchical contribution arising from this gravitational evolution (as in the source-free case) in addition to that possibly coming from non-Gaussian initial conditions. We apply this formalism to the O(N) nonlinear σ model at large N and find that observable differences from the case of initially Gaussian perturbations and Newtonian gravity in the bispectrum and higher-order correlations are not expected on scales smaller than about 100h-1 Mpc. © 1994 The American Physical Society.


Jaffe AH, Stebbins A, Frieman JA, 1994, Minimal microwave anisotropy from perturbations induced at late times, Astrophysical Journal, Vol: 420, Pages: 9-25, ISSN: 0004-637X

Aside from primordial gravitational instability of the cosmological fluid, various mechanisms have been proposed to generate large-scale structure at relatively late times, including, e.g., "late-time" cosmological phase transitions. In these scenarios, it is envisioned that the universe is nearly homogeneous at the time of last scattering and that perturbations grow rapidly sometimes after the primordial plasma recombines. On this basis, it was suggested that large inhomogeneities could be generated while leaving relatively little imprint on the cosmic microwave background (MBR) anisotropy. In this paper, we calculate the minimal anisotropies possible in any "late-time" scenario for structure formation, given the level of inhomogeneity observed at present. Since the growth of the inhomogeneity involves time-varying gravitational fields, these scenarios inevitably generate significant MBR anisotropy via the Sachs-Wolfe effect. Moreover, we show that the large-angle MBR anisotropy produced by the rapid post-recombination growth of inhomogeneity is generally greater than that produced by the same inhomogeneity grown via gravitational instability. In "realistic" scenarios one can decrease the anisotropy compared to models with primordial adiabatic fluctuations, but only on very small angular scales. The value of any particular measure of the anisotropy can be made small in late-time models, but only by making the time-dependence of the gravitational field sufficiently "pathological".


Frieman JA, Jaffe AH, 1992, Cosmological constraints on pseudo Nambu-Goldstone bosons, Physical Review D, Vol: 45, Pages: 2674-2684, ISSN: 0556-2821

Particle-physics models with pseudo Nambu-Goldstone bosons (PNGB's) are characterized by two mass scales: a global spontaneous-symmetry-breaking scale f and a soft (explicit) symmetry-breaking scale . We investigate general model-insensitive constraints on this two-dimensional parameter space arising from the cosmological and astrophysical effects of PNGB's. In particular, we study constraints arising from vacuum misalignment and thermal production of PNGB's, topological defects, and the cosmological effects of PNGB decay products, as well as astrophysical constraints from stellar PNGB emission. Bounds on the Peccei-Quinn axion scale, 1010GeVfPQ 1010-1012GeV, emerge as a special case, where the soft breaking scale is fixed at QCD 100 MeV. © 1992 The American Physical Society.


Prather M, Jaffe AH, 1990, Global impact of the Antarctic ozone hole: Chemical propagation, Journal of Geophysical Research, Vol: 95, Pages: 3473-3473, ISSN: 0148-0227


Guenther DB, Jaffe A, Demarque P, 1989, The standard solar model - Composition, opacities, and seismology, The Astrophysical Journal, Vol: 345, Pages: 1022-1022, ISSN: 0004-637X


Collaboration TEBEX, Abitbol M, Aboobaker AM, Ade P, Araujo D, Aubin F, Baccigalupi C, Bao C, Chapman D, Didier J, Dobbs M, Feeney SM, Geach C, Grainger W, Hanany S, Helson K, Hillbrand S, Hilton G, Hubmayr J, Irwin K, Jaffe A, Johnson B, Jones T, Klein J, Korotkov A, Lee A, Levinson L, Limon M, MacDermid K, Miller AD, Milligan M, Raach K, Reichborn-Kjennerud B, Reintsema C, Sagiv I, Smecher G, Tucker GS, Westbrook B, Young K, Zilic Ket al., The EBEX Balloon Borne Experiment - Detectors and Readout

EBEX was a long-duration balloon-borne experiment to measure the polarizationof the cosmic microwave background. The experiment had three frequency bandscentered at 150, 250, and 410 GHz and was the first to use a kilo-pixel arrayof transition edge sensor (TES) bolometers aboard a balloon platform; shortlyafter reaching float we operated 504, 342, and 109 TESs at each of the bands,respectively. We describe the design and characterization of the array and thereadout system. We give the distributions of measured thermal conductances,normal resistances, and transition temperatures. With the exception of thethermal conductance at 150 GHz. We measured median low-loop-gain time constants$\tau_{0}=$ 88, 46, and 57 ms and compare them to predictions. Two measurementsof bolometer absorption efficiency show high ($\sim$0.9) efficiency at 150 GHzand medium ($\sim$0.35, and $\sim$0.25) at the two higher bands, respectively.We measure a median total optical load of 3.6, 5.3 and 5.0 pW absorbed at thethree bands, respectively. EBEX pioneered the use of the digital version of thefrequency domain multiplexing (FDM) system which multiplexed the bias andreadout of 16 bolometers onto two wires. We present accounting of the measurednoise equivalent power. The median per-detector noise equivalent temperaturesreferred to a black body with a temperature of 2.725 K are 400, 920, and 14500$\mu$K$\sqrt{s}$ for the three bands, respectively. We compare these values toour pre-flight predictions and to a previous balloon payload, discuss thesources of excess noise, and the path for a future payload to make full use ofthe balloon environment.


Collaboration TEBEX, Aboobaker AM, Ade P, Araujo D, Aubin F, Baccigalupi C, Bao C, Chapman D, Didier J, Dobbs M, Geach C, Grainger W, Hanany S, Helson K, Hillbrand S, Hubmayr J, Jaffe A, Johnson B, Jones T, Klein J, Korotkov A, Lee A, Levinson L, Limon M, MacDermid K, Matsumura T, Miller AD, Milligan M, Raach K, Reichborn-Kjennerud B, Sagiv I, Savini G, Spencer L, Tucker C, Tucker GS, Westbrook B, Young K, Zilic Ket al., The EBEX Balloon Borne Experiment - Optics, Receiver, and Polarimetry

The E and B Experiment (EBEX) was a long-duration balloon-borne cosmicmicrowave background polarimeter that flew over Antarctica in 2013. We describethe experiment's optical system, receiver, and polarimetric approach, andreport on their in-flight performance. EBEX had three frequency bands centeredon 150, 250, and 410 GHz. To make efficient use of limited mass and space wedesigned a 115 cm$^{2}$sr high throughput optical system that had two ambienttemperature mirrors and four anti-reflection coated polyethylene lenses perfocal plane. All frequency bands shared the same optical train. Polarimetry wasachieved with a continuously rotating achromatic half-wave plate (AHWP) thatwas levitated with a superconducting magnetic bearing (SMB). Rotation stabilitywas 0.45 % over a period of 10 hours, and angular position accuracy was 0.01degrees. This is the first use of a SMB in astrophysics. The measuredmodulation efficiency was above 90 % for all bands. To our knowledge the 109 %fractional bandwidth of the AHWP was the broadest implemented to date. Thereceiver that contained one lens and the AHWP at a temperature of 4 K, thepolarizing grid and other lenses at 1 K, and the two focal planes at 0.25 Kperformed according to specifications giving focal plane temperature stabilitywith fluctuation power spectrum that had $1/f$ knee at 2 mHz. EBEX was thefirst balloon-borne instrument to implement technologies characteristic ofmodern CMB polarimeters including high throughput optical systems, and largearrays of transition edge sensor bolometric detectors with mutiplexed readouts.


Didier J, Miller AD, Araujo D, Aubin F, Geach C, Johnson B, Korotkov A, Raach K, Westbrook B, Young K, Aboobaker AM, Ade P, Baccigalupi C, Bao C, Chapman D, Dobbs M, Grainger W, Hanany S, Helson K, Hillbrand S, Hubmayr J, Jaffe A, Jones T, Klein J, Lee A, Limon M, MacDermid K, Milligan M, Pascale E, Reichborn-Kjennerud B, Sagiv I, Tucker C, Tucker GS, Zilic Ket al., Intensity-Coupled-Polarization in Instruments with a Continuously Rotating Half-Wave Plate

We discuss a systematic effect associated with measuring polarization with acontinuously rotating half-wave plate. The effect was identified with the datafrom the E and B Experiment (EBEX), which was a balloon-borne instrumentdesigned to measure the polarization of the CMB as well as that from Galacticdust. The data show polarization fraction larger than 10\% while less than 3\%were expected from instrumental polarization. We give evidence that the excesspolarization is due to detector non-linearity in the presence of a continuouslyrotating HWP. The non-linearity couples intensity signals into polarization. Wedevelop a map-based method to remove the excess polarization. Applying thismethod for the 150 (250) GHz bands data we find that 81\% (92\%) of the excesspolarization was removed. Characterization and mitigation of this effect isimportant for future experiments aiming to measure the CMB B-modes with acontinuously rotating HWP.


Sellentin E, Jaffe AH, Heavens AF, On the use of the Edgeworth expansion in cosmology I: how to foresee and evade its pitfalls

Non-linear gravitational collapse introduces non-Gaussian statistics into thematter fields of the late Universe. As the large-scale structure is the targetof current and future observational campaigns, one would ideally like to havethe full probability density function of these non-Gaussian fields. The onlyviable way we see to achieve this analytically, at least approximately and inthe near future, is via the Edgeworth expansion. We hence rederive thisexpansion for Fourier modes of non-Gaussian fields and then continue by puttingit into a wider statistical context than previously done. We show that in itsoriginal form, the Edgeworth expansion only works if the non-Gaussian signal isaveraged away. This is counterproductive, since we target theparameter-dependent non-Gaussianities as a signal of interest. We hence alterthe analysis at the decisive step and now provide a roadmap towards acontrolled and unadulterated analysis of non-Gaussianities in structureformation (with the Edgeworth expansion). Our central result is that, althoughthe Edgeworth expansion has pathological properties, these can be predicted andavoided in a careful manner. We also show that, despite the non-Gaussianitycoupling all modes, the Edgeworth series may be applied to any desired subsetof modes, since this is equivalent (to the level of the approximation) tomarginalising over the exlcuded modes. In this first paper of a series, werestrict ourselves to the sampling properties of the Edgeworth expansion,i.e.~how faithfully it reproduces the distribution of non-Gaussian data. Afollow-up paper will detail its Bayesian use, when parameters are to beinferred.


Suzuki A, Arnold K, Edwards J, Engargiola G, Ghribi A, Holzapfel W, Lee AT, Meng XF, Myers MJ, O'Brient R, Quealy E, Rebeiz G, Richards P, Rosen D, Siritanasak Pet al., Multi-chroic dual-polarization bolometric detectors for studies of the Cosmic Microwave Background

We are developing multi-chroic antenna-coupled TES detectors for CMBpolarimetry. Multi-chroic detectors increase the mapping speed per focal planearea and provide greater discrimination of polarized galactic foregrounds withno increase in weight or cryogenic cost. In each pixel, a silicon lens-coupleddual polarized sinuous antenna collects light over a two-octave frequency band.The antenna couples the broadband millimeter wave signal into microstriptransmission lines, and on-chip filter banks split the broadband signal intoseveral frequency bands. Separate TES bolometers detect the power in eachfrequency band and linear polarization. We will describe the design andperformance of these devices and present optical data taken with prototypepixels. Our measurements show beams with percent level ellipticity, percentlevel cross-polarization leakage, and partitioned bands using banks of 2, 3,and 7 filters. We will also describe the development of broadbandanti-reflection coatings for the high dielectric constant lens. The broadbandanti-reflection coating has approximately 100 percent bandwidth and nodetectable loss at cryogenic temperature. Finally, we will describe an upgradefor the POLARBEAR CMB experiment and installation for the LITEBird CMBsatellite experiment both of which have focal planes with kilo-pixel of thesedetectors to achieve unprecedented mapping speed.


Thompson MA, Serjeant S, Jenness T, Scott D, Ashdown M, Brunt C, Butner H, Chapin E, Chrysostomou AC, Clark JS, Clements D, Collett JL, Coppin K, Coulson IM, Dent WRF, Economou F, Evans A, Friberg P, Fuller GA, Gibb AG, Greaves J, Hatchell J, Holland WS, Hudson M, Ivison RJ, Jaffe A, Joncas G, Jones HRA, Knapen JH, Leech J, Mann R, Matthews HE, Moore TJT, Mortier A, Negrello M, Nutter D, Pestalozzi MP, Pope A, Richer J, Shipman R, Urquhart JS, Vaccari M, Waerbeke LV, Viti S, Weferling B, White GJ, Wouterloot J, Zhu Met al., The SCUBA-2 "All-Sky" Survey

The sub-millimetre wavelength regime is perhaps the most poorly explored overlarge areas of the sky, despite the considerable effort that has been expendedin making deep maps over small regions. As a consequence the properties of thesub-millimetre sky as a whole, and of rare bright objects in particular,remains largely unknown. Here we describe a forthcoming survey (the SCUBA-2``All-Sky'' Survey, or SASSy) designed to address this issue by making alarge-area map of approximately one-fifth of the sky visible from the JCMT(4800 square degrees) down to a 1 sigma noise level of 30 mJy/beam. This mapforms the pilot for a much larger survey, which will potentially map theremaining sky visible from the JCMT, with the region also visible to ALMA as apriority. SASSy has been awarded 500 hours for the 4800 square degree pilotphase and will commence after the commissioning of SCUBA-2, expected in early2008.


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