[1011.2729] Have Baryonic Acoustic Oscillations in the gala
Posted: December 10 2010
There is a claim by Gazta\~naga et al in 0807.3551 to have detected the radial mode of the BAO signal, and in 0808.1921 the signal was used it to put constraints on cosmological parameters. This would be important, because the radial signal provides a measurement of [tex]H(z)[/tex] which is independent of distance measurements, making it possible to test the FRW metric (see 0712.3457).
This detection has been criticised on the grounds that the expected signal is much smaller, see http://cosmocoffee.info/viewtopic.php?t=1301&highlight=.
Kazin et al analysed the radial signal in 1004.2244. They found that although there is a clustering signal in the data, it is not possible to distinguish the model with BAO from a model without BAO with statistical significance. They concluded that therefore it cannot be concluded that the clustering feature would be due to the radial BAO.
Now Cabr\'e and Gazta\~naga return to the topic. They agree that the models with and without the radial BAO signal cannot be distinguished by the current data. However, they find that the same is true for the BAO monopole signal: there is no detection of the BAO. (See also 0903.0950, where it is also argued that the BAO have not been detected.) Nevertheless, they argue that if you assume that the features seen in the data are the BAO and not noise, you can still get good parameter constraints.
I would compare this to seeing a peak in particle physics experiments. If you assume that the peak corresponds to a real particle, then you may be able to determine the mass very accurately, if the peak is very sharp. However, this says nothing about the probability that the peak may be just noise. However, I would somehow think that the error bars should include the possibility that the feature is noise. As noted, this holds true also for the usual BAO analysis.
This detection has been criticised on the grounds that the expected signal is much smaller, see http://cosmocoffee.info/viewtopic.php?t=1301&highlight=.
Kazin et al analysed the radial signal in 1004.2244. They found that although there is a clustering signal in the data, it is not possible to distinguish the model with BAO from a model without BAO with statistical significance. They concluded that therefore it cannot be concluded that the clustering feature would be due to the radial BAO.
Now Cabr\'e and Gazta\~naga return to the topic. They agree that the models with and without the radial BAO signal cannot be distinguished by the current data. However, they find that the same is true for the BAO monopole signal: there is no detection of the BAO. (See also 0903.0950, where it is also argued that the BAO have not been detected.) Nevertheless, they argue that if you assume that the features seen in the data are the BAO and not noise, you can still get good parameter constraints.
I would compare this to seeing a peak in particle physics experiments. If you assume that the peak corresponds to a real particle, then you may be able to determine the mass very accurately, if the peak is very sharp. However, this says nothing about the probability that the peak may be just noise. However, I would somehow think that the error bars should include the possibility that the feature is noise. As noted, this holds true also for the usual BAO analysis.