A general analytical expression for the Gaussian covariance of complex multi-tracer power spectra is derived, applied to multipoles and 2D spectra, and validated against Monte Carlo simulations.
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Measuring primordial non-gaussianity without cosmic variance
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abstract
Non-gaussianity in the initial conditions of the universe is one of the most powerful mechanisms to discriminate among the competing theories of the early universe. Measurements using bispectrum of cosmic microwave background anisotropies are limited by the cosmic variance, i.e. available number of modes. Recent work has emphasized the possibility to probe non-gaussianity of local type using the scale dependence of large scale bias from highly biased tracers of large scale structure. However, this power spectrum method is also limited by cosmic variance, finite number of structures on the largest scales, and by the partial degeneracy with other cosmological parameters that can mimic the same effect. Here we propose an alternative method that solves both of these problems. It is based on the idea that on large scales halos are biased, but not stochastic, tracers of dark matter: by correlating a highly biased tracer of large scale structure against an unbiased tracer one eliminates the cosmic variance error, which can lead to a high signal to noise even from the structures comparable to the size of the survey. The square of error improvement on non-gaussianity parameter f_nl relative to the power spectrum method scales as Pn/2, where P and n is the power spectrum and the number density of the biased tracer, respectively. For an ideal survey out to z=2 the error reduction can be as large as a factor of seven, which should guarantee a detection of non-gaussianity from an all sky survey of this type. The improvements could be even larger if high density tracers that are sensitive to non-gaussianity can be identified and measured over a large volume.
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representative citing papers
DESI DR2 and ACT DR6 data yield 17σ LRG-velocity, 8.3σ ELG-velocity, and 6.8σ QSO-velocity detections plus a 3.1σ velocity-velocity signal, producing f_NL^loc = 15.9_{-34.4}^{+34.6} from the velocity field.
Neglecting linear GR effects biases f_NL at 1–3σ for Euclid/SPHEREx in SFB forecasts; multi-tracer improves Doppler detection and weakly breaks b_ϕ f_NL degeneracy.
A joint multi-tracer Fisher analysis of DESI and PFS cross-spectra calibrates bias parameters from data, improving forecasted constraints on fσ8 by 33%, neutrino mass by 80%, and Ωm by 49% compared to single-tracer baselines.
Validates redshift-space power spectrum and bispectrum analysis on Abacus-PNG mocks to recover unbiased f_NL constraints for Euclid spectroscopic sample.
Cross-correlation of DESI DR1 quasars with Planck PR4 CMB lensing constrains local f_NL to 2^{+28}_{-34} (p=1.6) or 6^{+20}_{-24} (p=1.0), tightening previous limits by 35%.
Dust-cleaned CIB and CMB lensing cross-correlations yield f_NL^local = 43 ± 23, tightening constraints on local primordial non-Gaussianity.
DESI will target luminous red galaxies to z=1, emission-line galaxies to z=1.7, quasars for tracers and Ly-alpha forest at 2.1<z<3.5, plus a bright galaxy survey, to obtain more than 30 million redshifts for BAO and matter power spectrum measurements.
Updated SKAO-AA4 forecasts show multi-tracer HI+galaxy analyses can reach σ(f_local_NL)≲1 and improve αs bounds by tens of percent when combined with future CMB, while foregrounds and GR light-cone effects remain the main systematics.
Forecasts show SKA-Mid cross-correlations with ET/CE gravitational wave events can constrain GW source bias and time-delay distributions.
Presents the science case, reference design, and project plan for the CMB-S4 ground-based CMB experiment.
citing papers explorer
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Complex yet Hermitian: Gaussian covariance of cross-correlation and multi-tracer power spectra
A general analytical expression for the Gaussian covariance of complex multi-tracer power spectra is derived, applied to multipoles and 2D spectra, and validated against Monte Carlo simulations.
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Measurement of the galaxy-velocity power spectrum of DESI tracers with the kinematic Sunyaev-Zeldovich effect using DESI DR2 and ACT DR6
DESI DR2 and ACT DR6 data yield 17σ LRG-velocity, 8.3σ ELG-velocity, and 6.8σ QSO-velocity detections plus a 3.1σ velocity-velocity signal, producing f_NL^loc = 15.9_{-34.4}^{+34.6} from the velocity field.
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Impact and measurability of linear relativistic effects in galaxy surveys
Neglecting linear GR effects biases f_NL at 1–3σ for Euclid/SPHEREx in SFB forecasts; multi-tracer improves Doppler detection and weakly breaks b_ϕ f_NL degeneracy.
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Multi-tracers, multi-surveys: a joint Fisher analysis of DESI+PFS
A joint multi-tracer Fisher analysis of DESI and PFS cross-spectra calibrates bias parameters from data, improving forecasted constraints on fσ8 by 33%, neutrino mass by 80%, and Ωm by 49% compared to single-tracer baselines.
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Euclid preparation: Testing multi-field inflation with galaxy power spectrum and bispectrum
Validates redshift-space power spectrum and bispectrum analysis on Abacus-PNG mocks to recover unbiased f_NL constraints for Euclid spectroscopic sample.
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Constraining primordial non-Gaussianity from DESI DR1 quasars and Planck PR4 CMB Lensing
Cross-correlation of DESI DR1 quasars with Planck PR4 CMB lensing constrains local f_NL to 2^{+28}_{-34} (p=1.6) or 6^{+20}_{-24} (p=1.0), tightening previous limits by 35%.
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New constraints on primordial non-Gaussianity from large-scale cross-correlations of CMB lensing and the cosmic infrared background
Dust-cleaned CIB and CMB lensing cross-correlations yield f_NL^local = 43 ± 23, tightening constraints on local primordial non-Gaussianity.
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The DESI Experiment Part I: Science,Targeting, and Survey Design
DESI will target luminous red galaxies to z=1, emission-line galaxies to z=1.7, quasars for tracers and Ly-alpha forest at 2.1<z<3.5, plus a bright galaxy survey, to obtain more than 30 million redshifts for BAO and matter power spectrum measurements.
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Beyond {\Lambda}CDM with the SKA Observatory -- II: Unveiling the Secrets of the Early Universe
Updated SKAO-AA4 forecasts show multi-tracer HI+galaxy analyses can reach σ(f_local_NL)≲1 and improve αs bounds by tens of percent when combined with future CMB, while foregrounds and GR light-cone effects remain the main systematics.
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Using SKAO to Understand the Clustering of Gravitational Wave Sources
Forecasts show SKA-Mid cross-correlations with ET/CE gravitational wave events can constrain GW source bias and time-delay distributions.
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CMB-S4 Science Case, Reference Design, and Project Plan
Presents the science case, reference design, and project plan for the CMB-S4 ground-based CMB experiment.