In pursuit of Love numbers: First templated search for compact objects with large tidal deformabilities in the LIGO-Virgo data

Abstract

\We report results on the first matched-filtering search for binaries with compact objects having large tidal deformabilities in the LIGO-Virgo gravitational wave (GW) data. The tidal deformability of a body is quantified by the ``Love number'' $\mathrm{\ensuremath{\Lambda}}\ensuremath{\propto}(r/m{)}^{5}$, where $r/m$ is the body's (inverse) compactness. Due to its strong dependence on compactness, the $\mathrm{\ensuremath{\Lambda}}$ of larger-sized compact objects can easily be many orders of magnitude greater than those of black holes and neutron stars, leaving phase shifts which are sufficiently large for these binaries to be missed by binary black hole (BBH) templated searches. In this paper, we conduct a search using inspiral-only waveforms with zero spins but finite tides, with the search space covering chirp masses $3{M}_{\ensuremath{\bigodot}}<\mathcal{M}<15{M}_{\ensuremath{\bigodot}}$ and effective tidal deformabilities ${10}^{2}\ensuremath{\lesssim}\stackrel{\texttildelow{}}{\mathrm{\ensuremath{\Lambda}}}\ensuremath{\lesssim}{10}^{6}$. We find no statistically significant GW candidates. This null detection implies an upper limit on the merger rate of such binaries in the range $[1\ensuremath{-}300]\text{ }\text{ }{\mathrm{Gpc}}^{\ensuremath{-}3}\text{ }{\mathrm{year}}^{\ensuremath{-}1}$, depending on $\mathcal{M}$ and $\stackrel{\texttildelow{}}{\mathrm{\ensuremath{\Lambda}}}$. While our constraints are model agnostic, we discuss the implications on beyond the Standard Model scenarios that give rise to boson stars and superradiant clouds. Using inspiral-only waveforms, we recover many of the BBH signals which were previously identified with full inspiral-merger-ringdown templates. We also empirically constrain the Love number of the compact objects in these binaries to $\mathrm{\ensuremath{\Lambda}}\ensuremath{\lesssim}{10}^{3}$ at the 90% credible level in the best cases, consistent with the expectation of vanishing Love number for black holes in general relativity. Our work is the first-ever dedicated template-based search for compact objects that are not black holes or neutron stars. Additionally, our work demonstrates a novel way of finding new physics in GW data, widening the scope of potential discovery to previously unexplored parameter space.