Long-Lived Inverse Chirp Signals from Core-Collapse in Massive Scalar-Tensor Gravity

This Letter considers stellar core collapse in massive scalar-tensor theories of gravity. The presence of a mass term for the scalar field allows for dramatic increases in the radiated gravitational wave signal. There are several potential smoking gun signatures of a departure from general relativity associated with this process. These signatures could show up within existing LIGO-Virgo searches.

Figure 1

Waveforms extracted at $5\times {10}^4\mathrm{km}$. The legend lists deviations from the fiducial parameters $\mu ={10}^{-14}\mathrm{eV}$, ${\alpha }_0={10}^{-2}$, ${\beta }_0=-20$, ${\mathrm{\Gamma }}_1=1.3$, ${\mathrm{\Gamma }}_2=2.5$, and ${\mathrm{\Gamma }}_{\mathrm{th}}=1.35$.

Figure 2

Left panel: The frequency-domain power spectrum of the scalar field $\sigma \equiv r\phi$ at the extraction sphere and 1 light second further out; the exponential decay of frequencies $f<{\omega }_{*}/(2\pi )$ can be clearly seen. This simulation was performed for a $12M_{\odot }$ star with $\mu ={10}^{-14}\mathrm{eV}$, ${\alpha }_0={10}^{-4}$, and ${\beta }_0=-20$. Center panel: The time-domain scalar field profiles for the two curves shown in the left panel; during the 1s of propagation, the signal becomes increasingly oscillatory, and the long-lived memory effect is exponentially suppressed. Right panels: The amplitude (top) and frequency (bottom) as functions of time for the scalar field $\phi$ from the same simulation as the other panels but at a distance of 10 kpc (it is not practical to plot the long, highly oscillatory time-domain signals at large distances). Also shown by the dotted and dashed curves are the amplitude profiles from other simulations using ${\alpha }_0={10}^{-2}$ and ${\alpha }_0={10}^0$; the amplitude of the scalar field depends relatively weakly on ${\alpha }_0$. For the simulations shown here, the energy radiated in scalar GWs is $\sim {10}^{-3}{M}_{\odot }$.