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Are Ultracompact Minihalos Really Ultracompact? by Delos, M. Sten; Erickcek, Adrienne L.; Bailey, Avery P.; Alvarez, Marcelo A. is a scholarly article available to read on EtoBox.

What is Are Ultracompact Minihalos Really Ultracompact? about?

Ultracompact minihalos (UCMHs) have emerged as a valuable probe of the primordial power spectrum of density fluctuations at small scales. UCMHs are expected to form at early times in regions with ${\delta\rho/\rho \gtrsim 10^{-3}}$, and they are theorized to possess an extremely compact ${\rho\propto r^{-9/4}}$ radial density profile, which enhances their observable signatures. Nonobservation of UCMHs can thus constrain the primordial power spectrum. Using $N$-body simulations to study the collapse of extreme density peaks at ${z \simeq 1000}$, we show that UCMHs forming under realistic conditions do not develop the ${\rho\propto r^{-9/4}}$ profile and instead develop either ${\rho\propto r^{-3/2}}$ or ${\rho\propto r^{-1}}$ inner density profiles depending on the shape of the power spectrum. We also demonstrate via idealized simulations that self-similarity---the absence of a scale length---is necessary to produce a halo with the ${\rho\propto r^{-9/4}}$ profile, and we argue that this implies such halos cannot form from a Gaussian primordial density field. Prior constraints derived from UCMH nonobservation must be reworked in light of this discovery. Although the shallower densit

Author

Delos, M. Sten; Erickcek, Adrienne L.; Bailey, Avery P.; Alvarez, Marcelo A.

Published

2017

Language

EN