Black hole mergers and the QCD axion at Advanced LIGO

Asimina Arvanitaki, Masha Baryakhtar, Savas Dimopoulos, Sergei Dubovsky, and Robert Lasenby

Phys. Rev. D 95, 043001 – Published 8 February 2017

Abstract

In the next few years, Advanced LIGO (aLIGO) may see gravitational waves (GWs) from thousands of black hole (BH) mergers. This marks the beginning of a new precision tool for physics. Here we show how to search for new physics beyond the standard model using this tool, in particular the QCD axion in the mass range $μ_{a} \sim 10^{- 14}$ to $10^{- 10} eV$ . Axions (or any bosons) in this mass range cause rapidly rotating BHs to shed their spin into a large cloud of axions in atomic Bohr orbits around the BH, through the effect of superradiance (SR). This results in a gap in the mass vs spin distribution of BHs when the BH size is comparable to the axion’s Compton wavelength. By measuring the spin and mass of the merging objects observed at LIGO, we could verify the presence and shape of the gap in the BH distribution produced by the axion. The axion cloud can also be discovered through the GWs it radiates via axion annihilations or level transitions. A blind monochromatic GW search may reveal up to $1 0^{5}$ BHs radiating through axion annihilations, at distinct frequencies within $\sim 3 %$ of $2 μ_{a}$ . Axion transitions probe heavier axions and may be observable in future GW observatories. The merger events are perfect candidates for a targeted GW search. If the final BH has high spin, a SR cloud may grow and emit monochromatic GWs from axion annihilations. We may observe the SR evolution in real time.

Received 14 April 2016

DOI:https://doi.org/10.1103/PhysRevD.95.043001

Physics Subject Headings (PhySH)

Axions Gravitational wave detection Gravitational wave sources

Astronomical black holes

Particles & FieldsGravitation, Cosmology & Astrophysics

Authors & Affiliations

Asimina Arvanitaki^1,*, Masha Baryakhtar^1,†, Savas Dimopoulos^2,‡, Sergei Dubovsky^3,§, and Robert Lasenby^1,∥

¹Perimeter Institute for Theoretical Physics, Waterloo, Ontario N2L 2Y5, Canada
²Stanford Institute for Theoretical Physics, Stanford University, Stanford, California 94305, USA
³Center for Cosmology and Particle Physics, New York University New York, New York 10003, USA

^*aarvanitaki@perimeterinstitute.ca
^†mbaryakhtar@perimeterinstitute.ca
^‡savas@stanford.edu
^§dubovsky@nyu.edu
^∥rlasenby@perimeterinstitute.ca

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Vol. 95, Iss. 4 — 15 February 2017

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Images

Figure 1
Expected detectable sources in a blind monochromatic GW search, with sensitivity of current aLIGO (dashed), design aLIGO (solid), Voyager (wide-dashed) and Cosmic Explorer (dot-dashed) [26] for realistic mass and spin distributions, and BH formation rates ([11]). The shaded bands correspond to the range between pessimistic and optimistic BH distributions with design aLIGO (distributions as in [11], with the most narrow BH mass distribution removed as it is disfavored by the observation of GW150914). The coherent integration time is 2 days and total time 1 yr. The annihilation rate has been updated using the latest superradiance simulations [22]. Axion masses in the grayed-out region are disfavored by BH spin measurements [11]; the most optimistic distributions are disfavored by previous null LIGO searches [23, 24, 25].
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Figure 2
Expected distribution of intrinsic (top) and measured (bottom) spins and masses of merging BHs in the absence (left) and the presence (right) of an axion of mass $6 \times 10^{- 13} eV$ , normalized to 1000 events detected at aLIGO. We assume $σ_{M} / M \sim 10 %$ measurement error in the mass and $σ_{a_{*}} \sim 0.25$ error in the spin [30, 31]. We have assumed that all BBHs formed at a distance such that they take $1 0^{10} years$ to merge. The theoretical curves shown are boundaries of the regions where SR had at most $1 0^{10} years$ to spin down the BHs, and the effect of the companion BH does not significantly affect the SR rate.
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Figure 3
Number of observed events required to show that the BH spin distribution varies with BH mass, assuming the presence of an axion of mass $μ_{a}$ . Spin measurement errors of $σ_{a_{*}} = 0.25$ are assumed. Blue (red) curves correspond to BHs taking $1 0^{10} yrs$ ( $1 0^{7} yrs$ ) from formation to merger. The solid curves shows the median number of events required to reject the separable-distribution hypothesis at $2 σ$ . The upper/lower dashed curves show the upper/lower quartiles, respectively. The test statistic used is the Kolmogorov-Smirnov distance between the spin distributions outside and inside a given BH mass range, maximized over choice of mass range. Shaded region is as in Fig. 1.
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Figure 4
Expected annual annihilation events for aLIGO and future observatories from products of BH-NS mergers (magenta) or BBH mergers of equal mass (blue). We assume the binary formation mechanism does not allow for superradiance. We take $a_{*} = 0$ , $M = 1.4 M_{⊙}$ for the NS and a power-law mass distribution and flat spin distribution of the merging BHs. The bands represent the merger rate uncertainty given the observed BBHs [27, 29] and simulations for BH-NS (V4l and V2l in [36]). We assume a coherent integration time of 10 days for BBH and 1 year (or up to the duration of the signal) for BH-NS. Shaded region is as in Fig. 1.
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