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

324 results found

Bond JR, Jaffe AH, 1999, Constraining large-scale structure theories with the cosmic background radiation, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, Vol: 357, Pages: 57-75, ISSN: 1364-503X

The case is strong that cosmic microwave background (CMB) and large-scale structure (LSS) observations can be combined to determine the theory of structure formation and the cosmological parameters that define it. We review: the relevant (10+) parameters associated with the inflation model of fluctuation generation and the matter content of the universe; the relation between LSS and primary and secondary CMB anisotropy probes as a function of wavenumber; how COBE constraints on energy injection rule out explosions as a dominant source of LSS; and how current anisotropy band-powers in multipole-space, at levels ca. (10-5)2, strongly support the gravitational instability theory and suggest the universe could not have reionized too early. We use Bayesian analysis methods to determine what current CMB and CMB+LSS data imply for inflation-based Gaussian fluctuations in tilted ΛCDM, ΛhCDM and oCDM model sequences with cosmological age 11-15 Gyr, consisting of mixtures of baryons, cold 'c' (and possibly hot 'h') dark matter, vacuum energy 'Λ', and curvature energy 'o' in open cosmologies. For example, we find the slope of the initial spectrum is within about 5% of the (preferred) scale-invariant form when just the CMB data are used, and for ΛCDM when LSS data are combined with CMB; with both, a non-zero value of ΩΛ is strongly preferred (ca. 2/3 for a 13 Gyr sequence, similar to the value from SNIa). The oCDM sequence prefers Ωtot < 1, but is overall much less likely than the flat ΩΛ ≠ 0 sequence with CMB + LSS. We also review the rosy forecasts of angular power spectra and parameter estimates from future balloon and satellite experiments when foreground and systematic effects are ignored to show where cosmic parameter determination can go with CMB information alone.


Kamionkowski M, Jaffe AH, 1998, New troubles for inflation?, Nature, Vol: 395, Pages: 639-641, ISSN: 0028-0836


, 1998, 100 and 50 years ago, Nature, Vol: 395, Pages: 640-640, ISSN: 0028-0836


Hanany S, Jaffe AH, Scannapieco E, 1998, The effect of the detector response time on bolometric cosmic microwave background anisotropy experiments, Monthly Notices of the Royal Astronomical Society, Vol: 299, Pages: 653-660, ISSN: 0035-8711

We analyse the effects of the detector response time on bolometric measurements of the anisotropy of the cosmic microwave background (CMB). We quantify the effect in terms of a single dimensionless parameter L defined as the ratio between the time the beam sweeps its own size and the bolometer response time. As L decreases below ∼2.5, the point-source response of the experiment becomes elongated. We introduce a window function matrix based on the timestream data to assess the effects of the elongated beam. We find that the values of the window function matrix elements decrease slowly as a function of L. Our analysis and results apply to other cases of beam asymmetry. For the High Frequency Instrument on board the Planck Surveyor satellite we show that, for a broad range of L, the ability of the experiment to extract the cosmological parameters is not degraded. Our analysis enhances the flexibility in tuning the design parameters of CMB anisotropy experiments.


Knox L, Bond JR, Jaffe AH, Segal M, Charbonneau Det al., 1998, Comparing cosmic microwave background datasets, Physical Review D, Vol: 58, ISSN: 0556-2821


Bond JR, Jaffe AH, Knox L, 1998, Estimating the power spectrum of the cosmic microwave background, Physical Review D, Vol: 57, Pages: 2117-2137, ISSN: 0556-2821


Jaffe AH, Kamionkowski M, 1998, Calculation of the Ostriker-Vishniac effect in cold dark matter models, Physical Review D - Particles, Fields, Gravitation and Cosmology, Vol: 58, Pages: 10-4300110, ISSN: 1550-7998

We present a new derivation of the cosmic microwave background anisotropy spectrum from the Ostriker-Vishniac effect for an open, flat, or closed universe, and calculate the anisotropy expected in cold dark matter (CDM) models. We provide simple semi-analytic fitting formulas for the Vishniac power spectrum that can be used to evaluate the expected anisotropy in CDM models for any arbitrary ionization history. In a flat universe, CDM models normalized to cluster abundances produce rms temperature anisotropies of 0.8–2.4 μK on arcminute angular scales for a constant ionization fraction of unity, whereas an ionization fraction of 0.2 yields rms anisotropies of 0.3–0.8 μK. In an open and/or high-baryon-density universe, the level of anisotropy is somewhat higher. The signal in some of these models may be detectable with planned interferometry experiments. The damping of the acoustic peaks in the primary-anisotropy spectrum at degree angular scales depends primarily on the optical depth and only secondarily on the epoch of reionization. On the other hand, the amplitude of Ostriker-Vishniac anisotropies depends sensitively on the epoch of reionization. Therefore, when combined with the estimate of the reionization optical depth provided by maps of degree-scale anisotropies, the Ostriker-Vishniac effect can provide a unique probe of the epoch of reionization. © 1998 The American Physical Society.


Knox L, Bond JR, Jaffe AH, Segal M, Charbonneau Det al., 1998, Comparing cosmic microwave background datasets, Physical Review D - Particles, Fields, Gravitation and Cosmology, Vol: 58, ISSN: 1550-7998

To extract reliable cosmic parameters from cosmic microwave background datasets, it is essential to show that the data are not contaminated by residual non-cosmological signals. We describe general statistical approaches to this problem, with an emphasis on the case in which there are two datasets that can be checked for consistency. A first visual step is the Wiener filter mapping from one set of data onto the pixel basis of another. For more quantitative analyses, we develop and apply both Bayesian and frequentist techniques. We define the “contamination parameter” and advocate the calculation of its probability distribution as a means of examining the consistency of two datasets. The closely related “probability enhancement factor” is shown to be a useful statistic for comparison; it is significantly better than a number of (Formula presented) quantities we consider. Our methods can be used internally (between different subsets of a dataset) or externally (between different experiments), for observing regions that completely overlap, partially overlap or overlap not at all, and for observing strategies that differ greatly. We apply the methods to check the consistency (internal and external) of the MSAM92, MSAM94 and Saskatoon Ring datasets. From comparing the two MSAM datasets, we find that (given a particular model of the contaminant) the most probable level of contamination is 12%, with no contamination only 1.05 times less probable, 50% contamination about 8 times less probable and 100% contamination strongly ruled out at over (Formula presented) times less probable. From comparing the 1992 MSAM flight with the Saskatoon data, we find the most probable level of contamination to be 50%, with no contamination only 1.6 times less probable and 100% contamination 13 times less probable. Our methods can also be used to calibrate one experiment off of another. To achieve the best agreement between the Saskatoon and MSAM92 data, we find that t


Jaffe AH, Turner MS, 1997, Limits to radiative neutrino decay from SN 1987A, Physical Review D - Particles, Fields, Gravitation and Cosmology, Vol: 55, Pages: 7951-7959, ISSN: 1550-7998

We calculate limits to the properties of massive, unstable neutrinos using data from [Formula presented]-ray detectors on the Pioneer Venus Orbiter (PVO) Spacecraft. The absence of a [Formula presented]-ray signal in the PVO detector constrains the branching ratio to photons [Formula presented], mass [Formula presented], and radiative lifetime [Formula presented]. For low-mass [Formula presented] neutrinos decaying [Formula presented], [Formula presented] for [Formula presented], and [Formula presented] for [Formula presented]; limits for high-mass neutrinos are somewhat weaker due to Boltzmann suppression. We also calculate limits for decays that produce [Formula presented] rays through the bremsstrahlung channel, [Formula presented]. With one exception, the PVO limits are roughly comparable to those from an analysis of data from the Solar Max Mission (SMM) Satellite (which observed at higher [Formula presented]-ray energies but for a much shorter time). For neutrino mass states that are nearly degenerate, [Formula presented], our limits for the mode [Formula presented] become more stringent by a factor as large as [Formula presented], because more decay photons are shifted into the PVO energy window. For this same reason, SMM cannot constrain this case. © 1997 The American Physical Society.


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/k4 while, 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, 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".


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.


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


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.


Hotinli SC, Meyers J, Dalal N, Jaffe AH, Johnson MC, Mertens JB, Münchmeyer M, Smith KM, Engelen AVet al., Transverse Velocities with the Moving Lens Effect

Gravitational potentials which change in time induce fluctuations in theobserved cosmic microwave background (CMB) temperature. Cosmological structuremoving transverse to our line of sight provides a specific example known as themoving lens effect. Here we explore how the observed CMB temperaturefluctuations combined with the observed matter over-density can be used toinfer the transverse velocity of cosmological structure on large scales. Weshow that near-future CMB surveys and galaxy surveys will have the statisticalpower to make a first detection of the moving lens effect, and we discussapplications for the reconstructed transverse velocity.


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.


Conneely C, Jaffe AH, Mingarelli CMF, On the Amplitude and Stokes Parameters of a Stochastic Gravitational-Wave Background

The direct detection of gravitational waves has provided new opportunitiesfor studying the universe, but also new challenges, such as the detection andcharacterization of stochastic gravitational-wave backgrounds at differentgravitational-wave frequencies. In this paper we examine two different methodsfor their description, one based on the amplitude of a gravitational-wavesignal and one on its Stokes parameters. We find that the Stokes parameters areable to describe anisotropic and correlated backgrounds, whereas the usualpower spectra of the amplitudes cannot -- i.e. the Stokes spectra are sensitiveto properties such as the spatial distribution of the gravitational-wavesources in a realistic backgrounds.


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.


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