REVIEW
Cosmological-Parameter Determination with Microwave Background Maps
Astrophysics · Submitted 20 Dec 1995 · 52 references
Pith's verdict: The paper that turned CMB parameter forecasting into a quantitative business: eleven parameters, full correlations, and headline numbers that mostly survived contact with real data.
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Referee report
The paper
The paper claims
A full-sky microwave background map with half-degree resolution can, in principle, measure the Universe's total density, its expansion rate, and its cosmological constant to about ±0.1 each, with no prior information about any other cosmic-
The reading
What carries the argument
The machinery is a curvature-matrix (Fisher-matrix) forecast. Each parameter's partial derivative of the predicted multipole moments, $��C_��/��s_i$, is computed by evaluating the spectrum at the fiducial model and at one small step in each direction, so eleven parameters cost twelve spectrum evaluations. These derivatives are combined with the per-multipole error bars, which add cosmic variance to beam-diluted pixel noise, into $��_{ij} = ��_�� ��_��^{-2} (��C_��/��s_i)(��C_��/��s_j)$, and the inverse of that matrix is read as the covariance of the fitted parameters. Fixing some parameters is just inverting a submatrix; covering a fraction $f_{sky}$ of the sky scales the whole thing by $f_{sky}^{-1}$. The fast spectrum itself comes from extending a semi-analytic solution of the coupled Boltzmann, fluid, and Einstein equations to include an open Universe, a cosmological constant, tensor modes, and reionization, with fitting formulas for the integrated Sachs-Wolfe effect, the shift in conformal distance, curvature-scale suppression at low multipoles, and damping from reionization.
Extended reading notes
Core claim
The central claim is that a full-sky microwave background temperature map with $0.5^��$ angular resolution and a noise level of 15 $��$K per pixel can determine $��$, $h$, and $��$ with standard errors of $��0.1$ or better, even with no prior information on any of the other cosmological parameters. The physical carrier of this claim is the Doppler-peak structure of the angular power spectrum: the angular scale of the first peak tracks the geometry of the Universe, the peak heights and spacings respond to the baryon density and the redshift of matter-radiation equality, and the late-time integrated Sachs-Wolfe effect plus the shift in conformal distance break the near-degeneracy that otherwise lets a cosmological constant masquerade as a change in matter density. The authors also report that with sub-degree resolution a map can constrain the baryon density competitively with big-bang nucleosynthesis, restrict the optical depth to reionization to about 0.5 or less, and put limits on the effective number of light neutrino species. They are explicit that the inflationary observables fare badly unless other parameters are known: the tensor amplitude $r$ and tensor index $n_T$ get essentially no useful constraint from temperature maps alone, because the tensor contribution dies away on scales smaller than about a degree.
Load-bearing premise
The quoted error bars are the inverse of a curvature matrix, which is only a standard error if the likelihood is close to a parabola in all eleven parameters at once; the paper checks this only along one parameter at a time and says plainly that it has not surveyed the full eleven-dimensional contours.
Editorial extensions
If this is right
- If the first Doppler peak is found near $�� \simeq 200$, the geometry of the Universe is flat to within a few percent, independent of the values of the other cosmological parameters — a direct test of the inflationary prediction.
- A cosmological constant could be measured to better than $��0.1$, which separates a $��$-dominated Universe from either an open or a flat matter-dominated one, a distinction current lensing statistics cannot make.
- With resolution approaching $0.1^��$, the baryon-to-photon ratio could be pinned down competitively with big-bang nucleosynthesis, giving an independent check on the baryon content implied by primordial element abundances.
- The Hubble constant would be measured without any distance ladder, from the same map that measures the geometry.
- Because the errors scale as $f_{sky}^{-1/2}$, the same forecast can be applied to combinations of balloon, ground-based, and satellite maps rather than only to a single all-sky survey.
Reading between the lines
- The forecast is a statement about information content, not about data: the same machinery predicts that a poor map is worse than its noise level suggests, because the parameters trade against each other along directions in the eleven-dimensional space that a single-parameter error bar conceals.
- Because the cosmological-constant and curvature effects push the Doppler peak in opposite angular directions, the paper's logic implies that a measured peak position alone cannot settle the geometry; the peak height and the low-multipole Sachs-Wolfe plateau must be measured together, which is a concrete argument for wide frequency coverage and large sky area rather than deep small fields.
- The explicit finding that tensor modes are unconstrained without independent knowledge of the other parameters suggests that the natural next step is polarization: the same acoustic information carried in polarization spectra is sensitive to reionization and to gravity waves in a way the temperature spectrum is not.
- The paper's own machinery implies a design trade: below about $0.5^��$ beam size the gains come mostly from better determination of the classical parameters, while the tensor information saturates, so a smaller beam buys geometry and baryon density but not a probe of the inflaton potential.
Original abstract
The angular power spectrum of the cosmic microwave background (CMB) contains information on virtually all cosmological parameters of interest, including the geometry of the Universe ($\Omega$), the baryon density, the Hubble constant ($h$), the cosmological constant ($\Lambda$), the number of light neutrinos, the ionization history, and the amplitudes and spectral indices of the primordial scalar and tensor perturbation spectra. We review the imprint of each parameter on the CMB. Assuming only that the primordial perturbations were adiabatic, we use a covariance-matrix approach to estimate the precision with which these parameters can be determined by a CMB temperature map as a function of the fraction of sky mapped, the level of pixel noise, and the angular resolution. For example, with no prior information about any of the cosmological parameters, a full-sky CMB map with $0.5^\circ$ angular resolution and a noise level of 15 $\mu$K per pixel can determine $\Omega$, $h$, and $\Lambda$ with standard errors of $\pm0.1$ or better, and provide determinations of other parameters which are inaccessible with traditional observations. Smaller beam sizes or prior information on some of the other parameters from other observations improves the sensitivity. The dependence on the the underlying cosmological model is discussed.
The compiled record
The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.
The abstract, sentence by sentence
The angular power spectrum of the cosmic microwave background (CMB) contains information on virtually all cosmological parameters of interest, including the geometry of the Universe ($\Omega$), the baryon density, the Hubble constant ($h$), the cosmological constant ($\Lambda$), the number of light neutrinos, the ionization history, and the amplitudes and spectral indices of the primordial scalar and tensor perturbation spectra. We review the imprint of each parameter on the CMB. Assuming only that the primordial perturbations were adiabatic, we use a covariance-matrix approach to estimate the precision with which these parameters can be determined by a CMB temperature map as a function of the fraction of sky mapped, the level of pixel noise, and the angular resolution. For example, with no prior information about any of the cosmological parameters, a full-sky CMB map with $0.5^\circ$ angular resolution and a noise level of 15 $\mu$K per pixel can determine $\Omega$, $h$, and $\Lambda$ with standard errors of $\pm0.1$ or better, and provide determinations of other parameters which are inaccessible with traditional observations. Smaller beam sizes or prior information on some of the other parameters from other observations improves the sensitivity. The dependence on the the underlying cosmological model is discussed.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | The angular power spectrum of the cosmic microwave background (CMB) contains information on virtually all cosmological parameters of interest, including the geometry of the Universe ($\Omega$), the baryon density, the Hubble constant ($h$), the cosmological constant ($\Lambda$), the number of light neutrinos, the ionization history, and the amplitudes and spectral indices of the primordial scalar and tensor perturbation spectra. | background 1.00 | 0.06 | 0.07 | asserted 0.98 |
| s1 | We review the imprint of each parameter on the CMB. | contribution 0.93 | 0.66 | 0.03 | asserted 0.61 |
| s2 | Assuming only that the primordial perturbations were adiabatic, we use a covariance-matrix approach to estimate the precision with which these parameters can be determined by a CMB temperature map as a function of the fraction of sky mapped, the level of pixel noise, and the angular resolution. | method 0.94 | 0.89 | 0.12 | asserted 0.93 |
| s3 | For example, with no prior information about any of the cosmological parameters, a full-sky CMB map with $0.5^\circ$ angular resolution and a noise level of 15 $\mu$K per pixel can determine $\Omega$, $h$, and $\Lambda$ with standard errors of $\pm0.1$ or better, and provide determinations of other parameters which are inaccessible with traditional observations. | result 1.00 | 0.78 | 0.61 | asserted 0.80 |
| s4 | Smaller beam sizes or prior information on some of the other parameters from other observations improves the sensitivity. | result 0.69 | 0.43 | 0.06 | asserted 0.96 |
| s5 | The dependence on the the underlying cosmological model is discussed. | contribution 0.77 | 0.59 | 0.03 | unclear 0.62 |
What was examined, and what was not
- arXiv listing abstract v2
- full text
- figures and tables
- references and citing sentences
- relations to other papers
- P abstract
- S sections
- T body sentences
- C citations
- R cross-paper relations
Figures
Figures reproduced from arXiv:astro-ph/9512139 by the authors.
References
How later papers used it
70 later papers cite it
2 later papers by other authors are listed below: 2 used its method or tool. 3 more papers by the same authors are listed: 3 used its method or tool.
Uses its method or tool 5 of 27 papers with this label · 3 by the same authors
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Performed a Fisher matrix analysis using this paper's method.
Anisotropies in the Cosmic Neutrino Background after WMAP 5-year Data (2008) · 0.99 · paraphrased: the licence does not allow quoting
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Used a Fisher-matrix formalism as introduced in this paper.
Breaking degeneracies in the first galaxies with clustering (2023) · 0.96 · paraphrased: the licence does not allow quoting
By the same authors
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Evaluated the corresponding Fisher Matrix for a given future experiment and set of inflationary parameters using this paper's approach.
Red Density Perturbations and Inflationary Gravitational Waves (2007) (same authors) · 0.99 · paraphrased: the licence does not allow quoting
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Estimated the error on alpha using this paper's method.
Oscillations in the inflaton potential? (2008) (same authors) · 0.94 · paraphrased: the licence does not allow quoting
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Calculated the Fisher matrix using this paper's method.
Cross-correlation between thermal Sunyaev-Zeldovich effect and the integrated Sachs-Wolfe effect (2016) (same authors) · 0.99 · paraphrased: the licence does not allow quoting
How the literature uses it
53 arXiv papers cite this in 57 sentences
Papers citing it · 22 sentences without a confident label
Uses its method or tool 19 papers
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To determine the degeneracies between $σ_B, n_B$, and other possible cosmological and astrophysical parameters, we perform an information matrix analysis without priors according to [ref] [equation] where $α$ and $β$ represent the varied parameters of our model deemed to have the highest impact on 21-cm observables [ref] [equation] Here, the varied cosmological parameters involve the Hubble constant $h ≡ H_0 / 100 km/s/Mpc$, the total matter and baryon densities $Ω_m$ and $Ω_b$, and the power spectral amplitude $A_s$.
21-cm fluctuations from primordial magnetic fields · Information Matrix Analysis · 1.00
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We begin by evaluating, for a given future experiment and for a given set of inflationary parameters, the corresponding Fisher Matrix [ref] [equation] where the $C_l^αβ$ are the power spectra for the temperature (TT), temperature-polarization (TE), E-mode polarization (EE), and B-mode polarization ($α$ and $β$ run over TT, EE, TE, BB), $θ_i$ is the set of parameters used in the Markov Chain, and $Cov_l$ is the “spectra covariance matrix” [ref] .
Red Density Perturbations and Inflationary Gravitational Waves · Introduction · 0.99
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We forecast HERA's sensitivity to EDE's fractional energy density, $$, by employing a Fisher analysis, following the formalism in Refs. [ref] to construct the Fisher matrix for the 21cm power spectrum, [equation] where $θ_i$ denotes the cosmological and astrophysical parameters we vary in our analysis[We ensure that parameters defined logarithmically are varied linearly.], [equation] Here $L_X^(II/III)$ are the X-ray luminosity of pop-II/III stars (normalized by the SFR in units of $erg s^-1 M_⊙^-1 yr$), $f_*^(II/III)$ are the pop-II/III star formation efficiency, $f_esc^(II/III)$ are the fraction of photons that were produced by pop-II/III stars and managed to escape the host galaxy and ionize the IGM, $α_*^(II/III)$ are the pop-II/III star formation efficiency power law index, whereas $A_LW$ and $A_v_cb$ are the amplitudes of the Lyman-Werner (LW) [ref] and CDM-baryon relative velocity
Early Dark Energy Effects on the 21cm Signal · Fisher analysis · 1.00
Uses its data or values 2 papers
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Taylor-expanding about the best-fit standard cosmological parameters $θ⃗_0$ given in Ref. [ref] (with $f_pbh, 0 = 0$), we rewrite this as χ^2(θ⃗) ≈ χ^2(θ⃗_0) + Δθ_i ∂C_ℓ^X/∂θ_i |_θ_0 (Σ^-1)^X X'_ℓℓ'(C_ℓ'^X'(θ⃗_0) - Ĉ^X'_ℓ') + 1/2 Δθ_i F_ij Δθ_j , where $Δθ_i ≡θ_i -θ_0, i$ and F_ij ≈∂C^X_ℓ/∂θ_i (Σ^-1)^X X'_ℓℓ'∂C^X'_ℓ'/∂θ_j + δ_i, i_τ δ_j, i_τ/σ_τ^2 is the Fisher-information or curvature matrix [ref] , for which we have neglected the smaller term linear in $(C^X_ℓ(θ⃗_0) - Ĉ^X_ℓ)$.
Cosmic microwave background limits on accreting primordial black holes · Analysis of Planck data · 0.84
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The current measurement of the baryon-to-entropy ratio of the Universe is given by [ref] Y_B≡n_B/s = (0.87 ±0.02) ×10^-10,
Electron EDM and soft leptogenesis in supersymmetric B-L extension of the standard model · Introduction · 0.93
Cites it as background 12 papers
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Dark matter is hypothesized to explain discrepancies in galactic rotation curves and other astronomical anomalies [ref] .
A possible explanation for NuTeV's anomalous dimuon events · Introduction · 0.92
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The Fisher matrix has been utilized in numerous, similar contexts in the cosmology literature [ref] , so we give only a brief review of important results and the caveats in our particular application.
Effects of Unstable Dark Matter on Large-Scale Structure and Constraints from Future Surveys · Forecasting Methods · 0.97
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The Fisher matrix has been utilized in numerous, similar contexts in the cosmology literature [ref] , so we give only a brief review of important results and the caveats in our particular application.
Weak Gravitational Lensing as a Method to Constrain Unstable Dark Matter · Forecasting Methods · 0.95
Discussion
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