Probing PeV scale SUSY-breaking with Satellite Galaxies and Primordial Gravitational Waves

Abstract

We study an inevitable cosmological consequence in PeV scale SUSY-breaking scenarios. We focus on the SUSY-breaking scale corresponding to the gravitino mass $m_{3/2}=100\mathrm{eV}-1\mathrm{keV}$. We argue that the presence of an early matter-dominated era and the resulting entropy production are requisite for the Universe with this gravitino mass. We infer the model-independent minimum amount of the entropy production $\hat{I}”$ by requiring that the number of dwarf satellite galaxies $N_{\mathrm{sat}}$ in the Milky Way exceed the currently observed value, i.e. $N_{\mathrm{sat}}\gtrsim 63$. This entropy production is inevitably imprinted on the primordial gravitational waves (pGWs) produced during the inflationary era. We study how the information on the value of $\hat{I}”$ and the time of entropy production are encoded in the pGW spectrum $\hat{I}{\text{c◯}}_{\mathrm{GW}}$. If the future GW surveys observe a suppression feature in the pGW spectrum for the frequency range $\mathcal{O}(10^{-10})\mathrm{Hz}\lesssim f_{\mathrm{GW}}\lesssim \mathcal{O}(10^{-5})\mathrm{Hz}$, it works as a smoking gun for PeV SUSY-breaking scenarios. Even if they do not, our study can be used to rule out all such scenarios.

8 pages, 3 figures, published version, typos fixed