Gravitational wave searches for ultralight bosons with LIGO and LISA (1706.06311v2)

Abstract: Ultralight bosons can induce superradiant instabilities in spinning black holes, tapping their rotational energy to trigger the growth of a bosonic condensate. Possible observational imprints of these boson clouds include (i) direct detection of the nearly monochromatic (resolvable or stochastic) gravitational waves emitted by the condensate, and (ii) statistically significant evidence for the formation of "holes" at large spins in the spin versus mass plane (sometimes also referred to as "Regge plane") of astrophysical black holes. In this work, we focus on the prospects of LISA and LIGO detecting or constraining scalars with mass in the range $m_s\in [10^{-19},\,10^{-15}]$ eV and $m_s\in [10^{-14},\,10^{-11}]$ eV, respectively. Using astrophysical models of black-hole populations calibrated to observations and black-hole perturbation theory calculations of the gravitational emission, we find that, in optimistic scenarios, LIGO could observe a stochastic background of gravitational radiation in the range $m_s\in [2\times 10^{-13}, 10^{-12}]$ eV, and up to $10^4$ resolvable events in a $4$-year search if $m_s\sim 3\times 10^{-13}\,{\rm eV}$. LISA could observe a stochastic background for boson masses in the range $m_s\in [5\times 10^{-19}, 5\times 10^{-16}]$, and up to $\sim 10^3$ resolvable events in a $4$-year search if $m_s\sim 10^{-17}\,{\rm eV}$. LISA could further measure spins for black-hole binaries with component masses in the range $[10^3, 10^7]~M_\odot$, which is not probed by traditional spin-measurement techniques. A statistical analysis of the spin distribution of these binaries could either rule out scalar fields in the mass range $\sim [4 \times 10^{-18}, 10^{-14}]$ eV, or measure $m_s$ with ten percent accuracy if light scalars in the mass range $\sim [10^{-17}, 10^{-13}]$ eV exist.

• The paper demonstrates that gravitational wave detectors like LIGO and LISA can identify ultralight bosons via signals from superradiant instabilities around spinning black holes.
• It employs black hole perturbation theory to predict a stochastic background and resolves up to 10,000 events for specific boson mass ranges.
• The findings offer new constraints on dark matter properties and open avenues for probing physics beyond the Standard Model.

Gravitational Wave Searches for Ultralight Bosons with LIGO and LISA

The paper "Gravitational Wave Searches for Ultralight Bosons with LIGO and LISA" provides a comprehensive investigation into the potential of gravitational wave detectors to explore the existence of ultralight bosons, a candidate for dark matter, through their interaction with astrophysical black holes (BHs). Researchers explore the capacity of LIGO and LISA to detect or constrain the presence of scalar particles with masses between $10^{-19}$ eV and $10^{-11}$ eV. This mass range is significant due to the intriguing dynamics it introduces when interacting with spinning black holes.

The authors base their analysis on the superradiant instability mechanism, wherein spinning black holes transfer rotational energy to surrounding bosonic fields, forming a bosonic cloud. This cloud, in turn, emits nearly monochromatic gravitational waves, potentially detectable by LIGO and LISA. Two main observational signatures are proposed: direct detection of the emitted gravitational waves and the identification of "holes" in the black hole spin versus mass plane, known as the Regge plane. These holes would be an indication that spinning black holes have lost angular momentum due to superradiance, leaving behind less massive and slower spinning remnants.

Detection Potential with LIGO and LISA

The paper presents detailed calculations of the observable gravitational radiation from these boson clouds using black hole perturbation theory. For LIGO, it is suggested that the detector could observe a stochastic background of gravitational waves for boson masses in the range of $m_s \in [2 \times 10^{-13}, 10^{-12}]$ eV and resolve up to $10^4$ events over a four-year search period if $m_s \sim 3 \times 10^{-13}$ eV. For LISA, the paper indicates a potential detection of a stochastic background for boson masses $m_s \in [5 \times 10^{-19}, 5 \times 10^{-16}]$ eV, and resolving about 1000 events over a similar time span if $m_s \sim 10^{-17}$ eV.

Implications and Further Directions

This research has significant implications for understanding dark matter and fundamental physics beyond the Standard Model. The potential detection or exclusion of certain mass ranges of ultralight bosons via gravitational wave astronomy represents a novel approach to exploring these fundamental questions. The limitations of conventional particle physics approaches, particularly due to the feeble interaction of these hypothetical particles with Standard Model particles, are circumvented by utilizing the astrophysical laboratory provided by black holes and gravitational waves.

Future efforts could expand on this work by incorporating more sophisticated astrophysical models, accounting for possible interactions between the bosonic clouds and surrounding environments, and developing advanced data analysis techniques to enhance the sensitivity of gravitational wave detectors. Collaboration between theoretical insights and observational strategies will be crucial in refining mass constraints and improving the potential for a breakthrough in detecting ultralight bosons. Additionally, as gravitational wave observatories continue to improve in sensitivity, these methodologies could extend to place even more stringent constraints on the properties of ultralight bosons.