Hunting for Dark Particles with Gravitational Waves

Abstract

The LIGO observation of gravitational waves from a binary black hole merger has begun a new era in fundamental physics. If new dark sector particles, be they bosons or fermions, can coalesce into exotic compact objects (ECOs) of astronomical size, then the first evidence for such objects, and their underlying microphysical description, may arise in gravitational wave observations. In this work we study how the macroscopic properties of ECOs are related to their microscopic properties, such as dark particle mass and couplings. We then demonstrate the smoking gun exotic signatures that would provide observational evidence for ECOs, and hence new particles, in terrestrial gravitational wave observatories. Finally, we discuss how gravitational waves can test a core concept in general relativity: Hawking's area theorem.

Figures (14)

• Figure 1: LIGO noise power spectral density, taken from LIGOREF. For a given characteristic GW frequency for a binary merger, on the upper axes we show the corresponding combination of ECO compactness $C = M/R$ and total mass $M_{\rm tot}$.
• Figure 2: The LIGO best sensitivity range in ECO mass $M$ and compactness $C$, for equal mass binary GW events. The yellow band corresponds to the GW frequency range $f=[50-1000]$ Hz, the green regions to a signal-to-noise ratio for an inspiral event occurring within the luminosity distance $D_L$, taking $\rho \geqslant 8$ as a criterion for detection.
• Figure 3: Left panel. Mass-compactness relation in the case of boson stars with repulsive self-interactions. The dimensionless mass $M_*$ is defined in eq. (\ref{['eq:DimensionlessMass']}). The region shaded in red exceeds the compactness of a Schwarzschild BH, $C_{BH} = 1/2$. The region shaded in green represents the typical NS compactness. The magenta circle and blue square represent boson stars with pressure plotted in the right panel. Right panel. Pressure (solid magenta and blue lines, normalised w.r.t. the value at the origin) as a function of the dimensionless radius $x_*$, defined as $x_* \equiv m_B^2 r/(M_{PL}\sqrt{\lambda/4\pi})$ (see Eby:2015hsqColpi:1986ye). The blue and purple regions span the polytropic relation $P \propto \rho^{\Gamma}$ with $\Gamma = [1-3]$ (respectively, on the right- and left-most part of the band). The dashed blue (magenta) line corresponds to $\Gamma = 1.8$ ($\Gamma = 1.55$).
• Figure 4: LIGO best sensitivity (region shaded in green, defined according to fig. \ref{['fig:SNR']} with $D_L = 450$ Mpc (dashed contour) and $D_L = 100$ Mpc (solid contour)) in terms of boson star mass $M$ and dark matter mass $m_B$. We restrict the analysis to self-couplings in the range given by eq. (\ref{['eq:AllowedLambda']}) in order to make contact with the solution of the CCDM problems. The red region is excluded by the condition $M_* > (M_{*})_{\rm max} \approx 0.22$.
• Figure 5: Left panel. Mass-compactness relation in the case of boson stars without self-interactions. Right panel. LIGO best sensitivity (defined as in fig. \ref{['fig:SNR']}) in terms of the boson star mass $M$ and dark matter mass $m_B$.