question on BAO
Posted: January 12 2010
In the many nice toy examples of the formation of BAO -- e.g.,
http://cmb.as.arizona.edu/~eisenste/aco ... ysics.html
http://astro.berkeley.edu/~mwhite/bao/
we have an expanding shell of baryons that begins to turn around after decoupling and fall back in to the dark matter well.
At the end of the analysis, one peak is at the origin (somewhat displaced because what's plotted is mass in a spherical shell, not the density), and the other is at the BAO scale.
Why does the BAO peak "stall", instead of ballistically falling back inwards? If I released a spherical shell of non-interacting dark matter particles around a central density, I would expect them to fall back onto the center.
What's the most important physical mechanism preventing that infall? It seems like it can't be the baryon sound speed, because we are (?) looking on scales much larger than the Jeans length. Meanwhile, the spherical symmetry of the problem suggests that any uniform collapse of shell into itself not affect the overall collapse onto the central mass.
http://cmb.as.arizona.edu/~eisenste/aco ... ysics.html
http://astro.berkeley.edu/~mwhite/bao/
we have an expanding shell of baryons that begins to turn around after decoupling and fall back in to the dark matter well.
At the end of the analysis, one peak is at the origin (somewhat displaced because what's plotted is mass in a spherical shell, not the density), and the other is at the BAO scale.
Why does the BAO peak "stall", instead of ballistically falling back inwards? If I released a spherical shell of non-interacting dark matter particles around a central density, I would expect them to fall back onto the center.
What's the most important physical mechanism preventing that infall? It seems like it can't be the baryon sound speed, because we are (?) looking on scales much larger than the Jeans length. Meanwhile, the spherical symmetry of the problem suggests that any uniform collapse of shell into itself not affect the overall collapse onto the central mass.