LIGO as a probe of dark sectors

We show how current LIGO data is able to probe interesting theories beyond the Standard Model, particularly dark sectors where a dark Higgs boson triggers symmetry breaking via a first-order phase transition. We use publicly available LIGO O2 data to illustrate how these sectors, even if disconnected from the Standard Model, can be probed by gravitational wave detectors. We link the LIGO measurements with the model content and mass scale of the dark sector, finding that current O2 data are testing a broad set of scenarios that can be mapped into many different types of dark-sector models where the breaking of $SU(N)$ theories with $N_f$ fermions is triggered by a dark Higgs boson at scales $\mathrm{\Lambda }\simeq {10}^8–{10}^9\mathrm{GeV}$ with reasonable parameters for the scalar potential.

Figure 1

The spectral shape of $S_{\mathrm{sw}}(f)$ by varying the peak frequency. The dashed and dotted black lines indicate the asymptotic behavior. The two solid vertical lines at 20 and 1726 Hz show the minimum and maximum frequency considered when deriving the constraints—only the part of the spectrum between the two boundaries are taken into account in our data analysis.

Figure 2

The 95% confidence level upper limit of ${\mathrm{\Omega }}_{\mathrm{GW}}(f_{\mathrm{ref}})$ for different peak frequencies $f_{\mathrm{pk}}$. The triangles and circles correspond to the upper limit at 25 Hz and at $f_{\mathrm{pk}}$, respectively. Note that each $f_{\mathrm{pk}}$ represents a specific ${\mathrm{\Omega }}_{\mathrm{GW}}$ considered in the analysis (see Fig. 1), and the upper limit depends on the choice of $f_{\mathrm{ref}}$. The relation between upper limits at different $f_{\mathrm{ref}}$ is given by Eq. (14). The dashed horizontal line corresponds to the BBN bound at $f_{\mathrm{pk}}$.

Figure 3

The 95% confidence level exclusion region from LIGO (curved contours) and the constraint from BBN (vertical contours) projected on the $\beta /H-T_N$ plane. The values of $\alpha$ are represented by the color variation, and $f_{\mathrm{pk}}$ is indicated by the white dashed contours. The markers in the top and bottom panels correspond to models with renormalizable and nonrenormalizable operators, respectively. If any marker contained within a contour has a larger $\alpha$ value than the corresponding contour then the corresponding combination of thermal parameters is excluded. Such excluded markers are also circled in red. Note that the range of the color bar is different in the top and bottom panels.