The Shift of the Baryon Acoustic Oscillation Scale: A Simple Physical
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  A shift of the baryon acoustic oscillation (BAO) scale to smaller values than
predicted by linear theory was observed in simulations. In this paper, we try
to provide an intuitive physical understanding of why this shift occurs,
explaining in more pedagogical detail earlier perturbation theory calculations.
We find that the shift is mainly due to the following physical effect. A
measurement of the BAO scale is more sensitive to regions with long wavelength
overdensities than underdensities, because (due to non-linear growth and bias)
these overdense regions contain larger fluctuations and more tracers and hence
contribute more to the total correlation function. In overdense regions the BAO
scale shrinks because such regions locally behave as positively curved closed
universes, and hence a smaller scale than predicted by linear theory is
measured in the total correlation function. Other effects which also contribute
to the shift are briefly discussed. We provide approximate analytic expressions
for the non-linear shift including a brief discussion of biased tracers and
explain why reconstruction should entirely reverse the shift. Our expressions
and findings are in agreement with simulation results, and confirm that
non-linear shifts should not be problematic for next-generation BAO
measurements.
