Fundamental uncertainty in the BAO scale from isocurvature modes

Zunckel, Caroline; Okouma, Patrice; Kasanda, Simon Muya; Moodley, Kavilan; Bassett, Bruce A.

doi:10.1016/j.physletb.2011.01.012

Cited by 13 publications

(18 citation statements)

References 28 publications

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“…However, Mangilli et al (2010) show that a particular combination of isocurvature modes may exist that can change the sound horizon by a moderate amount before the CMB anisotropies are observably altered. This possibility bears more investigation, e.g., of other late-time observable consequences of such a model (Mangilli et al, 2010;Carbone et al, 2011;Zunckel et al, 2011).…”

Section: Cosmological Systematicsmentioning

confidence: 99%

Observational probes of cosmic acceleration

et al. 2013

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The accelerating expansion of the universe is the most surprising cosmological discovery in many decades, implying that the universe is dominated by some form of "dark energy" with exotic physical properties, or that Einstein's theory of gravity breaks down on cosmological scales. The profound implications of cosmic acceleration have inspired ambitious efforts to understand its origin, with experiments that aim to measure the history of expansion and growth of structure with percent-level precision or higher. We review in detail the four most well established methods for making such measurements: Type Ia supernovae, baryon acoustic oscillations (BAO), weak gravitational lensing, and the abundance of galaxy clusters. We pay particular attention to the systematic uncertainties in these techniques and to strategies for controlling them at the level needed to exploit "Stage IV" dark energy facilities such as BigBOSS, LSST, Euclid, and WFIRST. We briefly review a number of other approaches including redshift-space distortions, the Alcock-Paczynski effect, and direct measurements of the Hubble constant H 0 . We present extensive forecasts for constraints on the dark energy equation of state and parameterized deviations from General Relativity, achievable with Stage III and Stage IV experimental programs that incorporate supernovae, BAO, weak lensing, and cosmic microwave background data. We also show the level of precision required for clusters or other methods to provide constraints competitive with those of these fiducial programs. We emphasize the value of a balanced program that employs several of the most powerful methods in combination, both to cross-check systematic uncertainties and to take advantage of complementary information. Surveys to probe cosmic acceleration produce data sets that support a wide range of scientific investigations, and they continue the longstanding astronomical tradition of mapping the universe in ever greater detail over ever larger scales.

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Section: Cosmological Systematicsmentioning

confidence: 99%

Observational probes of cosmic acceleration

et al. 2013

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“…CMB temperature anisotropies limit the contribution of baryon isocurvature perturbations (fluctuations in the baryon-to-photon ratio) [15,16] and CDM isocurvature perturbations (fluctuations in the dark-matter-to-photon ratio) [14,[17][18][19] to the total perturbation amplitude [20][21][22][23][24][25][26][27][28][29][30][31][32]. The recent Planck CMB results limit the CDM isocurvature fraction to be & 0:039 of the total perturbation amplitude.…”

Section: Introductionmentioning

confidence: 99%

Baryons do trace dark matter 380,000 years after the big bang: Search for compensated isocurvature perturbations with WMAP 9-year data

et al. 2014

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Primordial isocurvature fluctuations between photons and either neutrinos or nonrelativistic species such as baryons or dark matter are known to be subdominant to adiabatic fluctuations. Perturbations in the relative densities of baryons and dark matter (known as compensated isocurvature perturbations or CIPs), however, are surprisingly poorly constrained. CIPs leave no imprint in the cosmic microwave background (CMB) on observable scales, at least at linear order in their amplitude and zeroth order in the amplitude of adiabatic perturbations. It is thus not yet empirically known if baryons trace dark matter at the surface of last scattering. If CIPs exist, they would spatially modulate the Silk damping scale and acoustic horizon, causing distinct fluctuations in the CMB temperature/polarization power spectra across the sky: this effect is first order in both the CIP and adiabatic mode amplitudes. Here, temperature data from the Wilkinson Microwave Anisotropy Probe (WMAP) are used to conduct the first CMB-based observational search for CIPs, using off-diagonal correlations and the CMB trispectrum. Reconstruction noise from weak lensing and point sources is shown to be negligible for this data set. No evidence for CIPs is observed, and a 95% confidence upper limit of 1:1 Â 10 À2 is imposed to the amplitude of a scale-invariant CIP power spectrum. This limit agrees with CIP sensitivity forecasts for WMAP and is competitive with smaller-scale constraints from measurements of the baryon fraction in galaxy clusters. It is shown that the rootmean-squared CIP amplitude on 5-100 scales is smaller than $0:07-0:17 (depending on the scale) at the 95% confidence level. Temperature data from the Planck satellite will provide an even more sensitive probe for the existence of CIPs, as will the upcoming ACTPol and SPTPol experiments on smaller angular scales.

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“…They are produced in topological-defect models for structure formation [10] and in more complicated models of inflation [11][12][13][14][15][16]. CMB temperature anisotropies limit the amplitude of baryon isocurvature perturbations (fluctuations in the baryon-to-photon ratio) [17,18] and cold dark-matter (CDM) isocurvature perturbations (fluctuations in the dark-matter-to-photon ratio) [19][20][21][22] to be & 13% of the total perturbation amplitude [7,[23][24][25][26][27][28][29][30][31][32][33].…”

Section: Introductionmentioning

confidence: 99%

Compensated isocurvature perturbations and the cosmic microwave background

2011

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Measurements of cosmic microwave background (CMB) anisotropies constrain isocurvature fluctuations between photons and nonrelativistic particles to be subdominant to adiabatic fluctuations. Perturbations in the relative number densities of baryons and dark matter, however, are surprisingly poorly constrained. In fact, baryon-density perturbations of fairly large amplitude may exist if they are compensated by darkmatter perturbations, so that the total density remains unchanged. These compensated isocurvature perturbations (CIPs) leave no imprint on the CMB at observable scales, at linear order. B modes in the CMB polarization are generated at reionization through the modulation of the optical depth by CIPs, but this induced polarization is small. The strongest known constraint & 10% to the CIP amplitude comes from galaxy-cluster baryon fractions. Here, it is shown that modulation of the baryon density by CIPs at and before the decoupling of Thomson scattering at z $ 1100 gives rise to CMB effects several orders of magnitude larger than those considered before. Polarization B modes are induced, as are correlations between temperature/polarization spherical-harmonic coefficients of different lm. It is shown that the CIP field at the surface of last scatter can be measured with these off-diagonal correlations. The sensitivity of ongoing and future experiments to these fluctuations is estimated. Data from the WMAP, ACT, SPT, and Spider experiments will be sensitive to fluctuations with amplitude $5-10%. The Planck satellite and Polarbear experiment will be sensitive to fluctuations with amplitude $3%. SPTPol, ACTPol, and future space-based polarization methods will probe amplitudes as low as $0:4%-0:6%. In the cosmic-variance limit, the smallest CIPs that could be detected with the CMB are of amplitude $0:05%.

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Fundamental uncertainty in the BAO scale from isocurvature modes

Cited by 13 publications

References 28 publications

Observational probes of cosmic acceleration

Observational probes of cosmic acceleration

Baryons do trace dark matter 380,000 years after the big bang: Search for compensated isocurvature perturbations with WMAP 9-year data

Compensated isocurvature perturbations and the cosmic microwave background

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