Kavli Affiliate: George Efstathiou
| First 5 Authors: Rajesh Mondal, Rennan Barkana, Anastasia Fialkov, ,
| Summary:
The 21-cm signal from the dark ages is a powerful tool for fundamental
cosmology and for probing new physics. While it can be used for precision
measurements within standard cosmology, here we study two non-standard models:
an excess radio background (ERB) model (possibly generated by dark matter
decay) and the millicharged dark matter (mDM) model. These models were inspired
by the possible EDGES detection of a strong global 21-cm absorption during
cosmic dawn, but more generally they provide a way to anticipate the potential
discovery space. We find that during the dark ages the 21-cm global signal in
the ERB model reaches a saturated form for an amplitude $A_{rm r}=0.4$, where
$A_{rm r}$ is the radio background intensity at cosmic dawn relative to the
cosmic microwave background. This amplitude is one fifth of the minimum
required to explain the EDGES signal, and corresponds to just 0.1% of the
observed extragalactic background; it would give a signal that can be detected
at 5.9$sigma$ significance (compared to 4.1$sigma$ for the standard signal)
and distinguished from the standard (no ERB) signal at 8.5$sigma$, all with a
1,000 hour global signal measurement. A lower $A_{rm r}=0.039$ could be
distinguished at 5$sigma$. The 21-cm power spectrum has potentially much more
information, but far greater resources would be required for comparable
constraints on the ERB signal. For the mDM model, over a range of viable
parameters, the global signal detection significance would be
$4.7-7.2,sigma$, and it could be distinguished from standard at
$2.2-9.3,sigma$. With an array of global signal antennas achieving an
effective 100,000 hr integration, the significance would be 10$times$ better.
Our analysis helps motivate the development of lunar and space-based dark ages
experiments.
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