Constraints on dark matter from dynamical heating of stars in ultrafaint dwarfs. II. Substructure and the primordial power spectrum

Abstract

There is a large and growing interest in observations of small-scale structure in dark matter. We propose a new way to probe dark matter structures in the <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mrow> <a:mo>∼</a:mo> <a:mn>10</a:mn> <a:mi>–</a:mi> <a:msup> <a:mrow> <a:mn>10</a:mn> </a:mrow> <a:mrow> <a:mn>8</a:mn> </a:mrow> </a:msup> <a:msub> <a:mrow> <a:mi>M</a:mi> </a:mrow> <a:mrow> <a:mo stretchy="false">⊙</a:mo> </a:mrow> </a:msub> </a:mrow> </a:math> range. This allows us to constrain the primordial power spectrum over shorter distances scales than possible with direct observations from the CMB. For <d:math xmlns:d="http://www.w3.org/1998/Math/MathML" display="inline"> <d:mi>k</d:mi> </d:math> in the range <f:math xmlns:f="http://www.w3.org/1998/Math/MathML" display="inline"> <f:mrow> <f:mo>∼</f:mo> <f:mn>10</f:mn> <f:mi>–</f:mi> <f:mn>1000</f:mn> <f:mtext> </f:mtext> <f:mtext> </f:mtext> <f:msup> <f:mrow> <f:mi>Mpc</f:mi> </f:mrow> <f:mrow> <f:mo>−</f:mo> <f:mn>1</f:mn> </f:mrow> </f:msup> </f:mrow> </f:math> our constraints on the power spectrum are orders of magnitude stronger than previous bounds. We also set some of the strongest constraints on dark matter isocurvature perturbations. Our method relies on the heating effect such dark matter substructures would have on the distribution of stars in an ultrafaint dwarf galaxy. Many models of inflation produce enhanced power at these short distance scales and can thus be constrained by our observation. Further, many dark matter models such as axion dark matter, self-interacting dark matter and dissipative dark matter, produce dense structures which could be constrained this way. Published by the American Physical Society 2024

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