Probing primordial–black-hole dark matter with scalar induced gravitational waves

Abstract

The possibility that primordial black holes (PBHs) represent all of the dark matter (DM) in the Universe and explain the coalescences of binary black holes detected by LIGO/Virgo has attracted a lot of attention. PBHs are generated by the enhancement of scalar perturbations which inevitably produce the induced gravitational waves (GWs). We calculate the induced GWs up to the thirdorder correction which not only enhances the amplitude of induced GWs, but also extends the cutoff frequency from 2k * to 3k * . Such effects of the third-order correction lead to an around 10% increase of the signal-to-noise ratio (SNR) for both LISA and pulsar timing array (PTA) observations, and significantly widen the mass range of PBHs in the stellar mass window accompanying detectable induced GWs for PTA observations including IPTA, FAST and SKA. On the other hand, the null detections of the induced GWs by LISA and PTA experiments will exclude the possibility that all of the DM is comprised of PBHs and the GW events detected by LIGO/Virgo are generated by PBHs.

Gauge independence of induced gravitational waves

“…Gravitational waves (GWs) are a useful probe of small-scale curvature perturbations [3][4][5][6][7][8] since if the latter is enhanced, a sizable amount of GWs is produced at the second order of the cosmological perturbation. We call it the induced GWs 1 (see early works [9][10][11][12] and recent developments [13][14][15][16][17][18][19][20][21][22]). Such an enhancement of the curvature perturbations are often considered in the context of the primordial black hole (PBH) [23][24][25] (see also Refs.…”

From primordial black holes abundance to primordial curvature power spectrum (and back)

“…Several authors have proposed different ways to probe such scales, including CMB spectral distortions [98], analyses of Silk damping effects [99], exploiting WIMP properties [100,101] (in the last case assuming they are the main component of dark matter), reconstructing quasar light curves [102] or through the detection of gravitational waves generated by large scalar perturbations, see e.g., Refs. [103][104][105][106][107][108][109][110][111] and references therein for constraints coming from ongoing (PTA [112][113][114]) and future (SKA [115,116], LISA [115,117]) experiments.…”

Log-dependent slope of scalar induced gravitational waves in the infrared regions

“…Actually, the curvature perturbations couple to the tensor perturbations at second-order, thus inevitably generating the scalar induced GWs (SIGWs) in the radiation dominated era [28][29][30][31][32][33][34]. The enhancement of scalar curvature perturbation for significantly forming PBHs will generate relatively large SIGWs which provide a new way to probe PBHs [35]. See some other related works in .…”