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Velocity-induced acoustic oscillations (VAOs) in the early Universe can serve as a standard ruler. This method allows precise measurement of the Hubble expansion rate during cosmic dawn using 21-cm data.

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Area of Science:

  • Cosmology
  • Astrophysics
  • Early Universe Physics

Background:

  • The Universe contains dark matter and baryonic matter, with only baryons interacting with photons.
  • Baryon acoustic oscillations (BAOs) arise from photon-baryon coupling, creating supersonic relative velocities between dark matter and baryons.
  • These velocities imprint the acoustic scale, hindering early star formation and modulating the 21-cm signal during cosmic dawn (z~20).

Purpose of the Study:

  • To propose using velocity-induced acoustic oscillations (VAOs) as a standard ruler to probe cosmic dawn.
  • To determine the precision of measuring the Hubble expansion rate H(z) at z=15-20 using VAOs.

Main Methods:

  • Utilizing numerical simulations and analytic models to understand VAO characteristics.
  • Analyzing the 21-cm power spectrum data from the upcoming HERA interferometer.
  • Combining simulation results with observational data to constrain cosmological parameters.

Main Results:

  • VAOs possess a well-defined shape, frozen at recombination and independent of star formation astrophysics.
  • Three years of HERA data can measure H(z) at z=15-20 with percent-level precision (0.3%-11%).
  • Measurement precision depends on astrophysical feedback strength and foreground contamination.

Conclusions:

  • VAOs offer a novel standard ruler for cosmic dawn studies.
  • This method provides a new way to measure the Universe's expansion rate during an unprobed epoch.
  • The findings open a new observational window into the mysterious cosmic-dawn era.