Separating the Universe into real and fake energy densities

Hu, Wayne; Chiang, Chi-Ting; Yin, Li; Loverde, Marilena

doi:10.1103/physrevd.94.023002

Cited by 30 publications

(48 citation statements)

References 34 publications

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“…For optimal extraction of information it is critical to accurately calibrate the response functions into the nonlinear regime using simulations. Separate universe simulations [4,[54][55][56][57][58][59][60][61][62][63][64][65] provide an efficient method to measure the response of various observables to the long density mode, such as power spectrum and halo mass function, without sample variance or shot noise. In a similar fashion, the mean tidal mode can be absorbed in the local simulation background at the Newtonian level.…”

Section: Resultsmentioning

confidence: 99%

Galaxy power-spectrum responses and redshift-space super-sample effect

Schmittfull

Seljak

2018

J. Cosmol. Astropart. Phys.

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As a major source of cosmological information, galaxy clustering is susceptible to long-wavelength density and tidal fluctuations. These long modes modulate the growth and expansion rate of local structures, shifting them in both amplitude and scale. These effects are often named the growth and dilation effects, respectively. In particular the dilation shifts the baryon acoustic oscillation (BAO) peak and breaks the assumption of the Alcock-Paczynski (AP) test. This cannot be removed with reconstruction techniques because the effect originates from long modes outside the survey. In redshift space, the long modes generate a large-scale radial peculiar velocity that affects the redshift-space distortion (RSD) signal. We compute the redshift-space response functions of the galaxy power spectrum to long density and tidal modes at leading order in perturbation theory, including both the growth and dilation terms. We validate these response functions against measurements from simulated galaxy mock catalogs. As one application, long density and tidal modes beyond the scale of a survey correlate various observables leading to an excess error known as the super-sample covariance, and thus weaken their constraining power. We quantify the supersample effect on BAO, AP, and RSD measurements, and study its impact on current and future surveys.

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Section: Resultsmentioning

confidence: 99%

Galaxy power-spectrum responses and redshift-space super-sample effect

Schmittfull

Seljak

2018

J. Cosmol. Astropart. Phys.

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“…The construction of the SU with components other than CDM that possess Jeans scales has been studied extensively in Ref. [59]. Here we briefly summarize the expansion history of the SU in Sec.…”

Section: Neutrino Separate Universementioning

confidence: 99%

Scale-dependent bias and bispectrum in neutrino separate universe simulations

Chiang

et al. 2018

Phys. Rev. D

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Cosmic background neutrinos have a large velocity dispersion, which causes the evolution of longwavelength density perturbations to depend on scale. This scale-dependent growth leads to the well-known suppression in the linear theory matter power spectrum that is used to probe neutrino mass. In this paper, we study the impact of long-wavelength density perturbations on small-scale structure formation. By performing separate universe simulations where the long-wavelength mode is absorbed into the local expansion, we measure the responses of the cold dark matter (CDM) power spectrum and halo mass function, which correspond to the squeezed-limit bispectrum and halo bias. We find that the scale-dependent evolution of the long-wavelength modes causes these quantities to depend on scale and provide simple expressions to model them in terms of scale and the amount of massive neutrinos. Importantly, this scale-dependent bias reduces the suppression in the linear halo power spectrum due to massive neutrinos by 13 and 26% for objects of biasb = 2 andb 1, respectively. We demonstrate with high statistical significance that the scale-dependent halo bias cannot be modeled by the CDM and neutrino density transfer functions at the time when the halos are identified. This reinforces the importance of the temporal nonlocality of structure formation, especially when the growth is scale dependent.

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“…(41) it is clear that the total growth response in Eq. (40) from a single realization of δ L is in general a random variable, dependent on the realization of I and R. This is in contrast to a cosmology in which a single degree of freedom determines δ L and each mode of δ L (k) has the same evolutionary history (e.g., for adiabatic perturbations in ΛCDM [6][7][8], quintessence [18], or neutrino-CDM cosmologies [19]). In what follows it will be helpful to define individual growth responses for the pieces of δ L generated by I and R,…”

Section: A Linear Perturbationsmentioning

confidence: 99%

Quintessential isocurvature in separate universe simulations

Jamieson

Loverde

2019

Phys. Rev. D

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In a universe with quintessence isocurvature, or perturbations in dark energy that are independent from the usual curvature perturbations, structure formation is changed qualitatively. The existence of two independent fields, curvature and isocurvature, causes the growth rate of matter perturbations to depend on their initial conditions. The quintessence perturbations cause their growth to depend on scale. We perform the first separate universe simulations for this cosmology. We demonstrate that the power spectrum response and the halo bias depend on scale and initial conditions and that the presence of the isocurvature mode changes the mapping from these quantities to the halo autoand cross-power spectra, and the squeezed-limit bispectrum. We compare the bias to several models, finding reasonable agreement with both a power-spectrum-response model with one free parameter and a model that fits two independent bias parameters for curvature and isocurvature sourced fluctuations. We also verify that simulation responses to pure isocurvature and pure curvature modes can be linearly combined to reproduce responses with different ratios of isocurvature and curvature. This allows our results to be used to predict the halo power spectrum and stochasticity with arbitrary large-scale curvature and isocurvature power spectra. In an appendix, we study the generation of quintessence isocurvature during inflation and show that a modified kinetic term is typically required to produce observable isocurvature modes in a field with wQ ≈ −1.

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Separating the Universe into real and fake energy densities

Cited by 30 publications

References 34 publications

Galaxy power-spectrum responses and redshift-space super-sample effect

Galaxy power-spectrum responses and redshift-space super-sample effect

Scale-dependent bias and bispectrum in neutrino separate universe simulations

Quintessential isocurvature in separate universe simulations

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