Tapomoy Guha Sarkar, Dhiraj Kumar Hazra
We explore possibility of using the three dimensional bispectra of the Ly-alpha forest and the redshifted 21-cm signal from the post-reionization epoch to constrain primordial non-Gaussianity. Both these fields map out the large scale distribution of neutral hydrogen and maybe treated as tracers of the underlying dark matter field. We first present the general formalism for the auto and cross bispectrum of two arbitrary three dimensional biased tracers and then apply it to the specific case. We have modeled the 3D Ly-alpha transmitted flux field as a continuous tracer sampled along 1D skewers which corresponds to quasars sight lines. For the post reionization 21-cm signal we have used a linear bias model. We use a Fisher matrix analysis to present the first prediction for bounds on f_NL and the other bias parameters using the three dimensional 21-cm bispectrum and other cross bispectra. The bounds on f_NL depend on the survey volume, and the various observational noises. We have considered a BOSS like Ly-alpha survey where the average number density of quasars \bar{n} = 10^{-3} Mpc^{-2} and the spectra are measured at a 2-sigma level. For the 21-cm signal we have considered a 4000 hrs observation with a futuristic SKA like radio array. We find that bounds on f_NL obtained in our analysis (6 <\Delta f_NL < 65) is competitive with CMBR and galaxy surveys and may prove to be an important alternative approach towards constraining primordial physics using future data sets. Further, we have presented a hierarchy of power of the bispectrum-estimators towards detecting the f_NL. Given the quality of the data sets, one may use this method to optimally choose the right estimator and thereby provide better constraints on f_NL. This shall be important in the quest towards understanding the mechanism behind the generation of primordial perturbations.
View original:
http://arxiv.org/abs/1211.4756
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