Gravitational wave production by rotating primordial black holes

Question

Referee this paper: arXiv:1511.05642 by Ruifeng Dong, William H Kinney,

Dejan Stojkovic

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Please use comments to point to previous work in this direction, and reviews to referee the accuracy of the paper. Feel free to edit this submission to summarise the paper (just click on edit, your summary will then appear under the horizontal line)

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Comments

Just from reading the abstract: The gravitational detectors cannot detect a weak stochastic background and probably never will be able to. The signal is very noisy, and if there is any stochastic background, it is averaged out and what the GW detector really does is that it tries to find nice coherent wave-forms deviating from the background. The only possible way of detecting a stochastic background would be if it were unexpectedly large and in a frequency range where there is no other possible physical source.

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@Void I think the real problem is that GW signal with so high frequencies, i.e. higher than \(10^{17}Hz\), is not detectable with current technologies, which focus on low frequencies (not very higher than \(1 Hz\)). On the other hand, the signal from PBH's evaporation is not weak in magnitude (the GW's present energy fraction can be as high as \(10^{-5}\)). 

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@ruifeng14 The energy fraction might be a good measure for cosmology but not for local detection. The $\sim 10^{-5}$ CMB energy fraction is also a weak background noise which is possible to separate from the foreground sources thanks only to the relative tractability of noise in photon detection. I am just saying that the current measurement principles of gravitational waves are in principle noisy and, as long as they build on the same detection principle, will be only barely able to detect strong coherent signals.

Btw., by a simple order of magnitude estimate, a signal of $10^{17} Hz$ is even not measurable by classical mechanical devices because that would correspond to $\sim 100 eV$ binding energies, well above even the electron structure of usual materials. For these frequencies, a quantum detection is necessary, and we know that the rates of detection of gravitons even under ideal conditions are usually extremely small.

Simply stated, I think it would be more accurate to say that such a signal will not be directly detectable in the foreseeable future; if you want to make a link to observation, an indirect alternative of detection must be offered.

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@Void Yes, you are right. For now, the detection of gravity waves is still classical, because no quantum gravity effect has been confirmed yet. Thanks for your comment.