Gravitational-Wave Signatures of Nonstandard Neutrino Properties in Collapsing Stellar Cores

Abstract

We present a novel multi-messenger approach for probing nonstandard neutrino properties through the detection of gravitational waves (GWs) from collapsing stellar cores and associated supernova explosions. We show that neutrino flavor conversion inside the proto-neutron star (PNS), motivated by physics Beyond the Standard Model (BSM), can significantly boost PNS convection. This effect leads to large-amplitude GW emission over a wide frequency range during an otherwise relatively quiescent GW phase shortly after core bounce. Such a signal provides a promising new avenue for exploring nonstandard neutrino phenomena and other BSM physics impacting PNS convection.

Figures (9)

• Figure 1: FC of high-energy $\nu_x$ and $\bar{\nu}_x$ create $\nu_e$ and $\bar{\nu}_e$ in the PNS interior, an effect assumed to occur at the black dashed circle. If this happens well inside the average electron-type neutrinosphere, the newly created $\nu_e$ and $\bar{\nu}_e$ are quickly absorbed by free nucleons. This strong local heating (bright orange layer) enhances PNS convection (orange layer). The convective shell as well as g-mode activity (so-called gravity waves, not to be confused with gravitational waves) instigated in the convectively stable near-surface layer emit GWs.
• Figure 2: Convective mass motions inside the PNS for our 2D SN model M11.2 of an 11.2 M$_\odot$ progenitor with different neutrino FC scenarios. The four quadrants display the color-coded magnitude of the stellar gas velocity 40 ms after core bounce for the model without FCs (labeled by noFC) and values of $\rho_c=10^{12}$, $10^{13}$, and $10^{14}$ g cm$^{-3}$ for the threshold density below which FC is assumed to occur (clockwise from top left). The black dashed circular lines indicate these inner boundaries of the FC regions. Convection is almost nonexistent within the PNS at this early time after bounce in model noFC, whereas in all cases with FCs, significantly stronger convective activity has already developed. The red dashed circular lines indicate the average energy spheres of $\nu_e$, and the solid black circular lines mark the locations where the matter density is $10^{11}$ g cm$^{-3}$, which effectively coincide with the average energy spheres of $\bar{\nu}_e$.
• Figure 3: GW strains and their spectrograms for a SN distance of 10 kpc vs. time after bounce and an observer at the equator. The different panels correspond to our 2D SN simulations of 9 M$_\odot$ ( top row), 11.2 M$_\odot$ ( middle row), and 20 M$_\odot$ progenitors ( bottom row), considering different FC scenarios: noFC ( left panels), FC at $\rho < \rho_\mathrm{c}= 10^{13}$ g cm$^{-3}$ ( middle column), and at $\rho < \rho_\mathrm{c}= 10^{14}$ g cm$^{-3}$ ( right panels). Our noFC models possess extended periods (lasting 70--100 ms) of relative quiescence after a short post-bounce phase of GW activity due to prompt postshock convection, whereas the models with FCs exhibit strong GW emission over a wide frequency range during this time interval. Analogous results for $\rho_\mathrm{c}= 10^{9}, 10^{10}, 10^{11}$, and $10^{12}$ g cm$^{-3}$ are provided in SM SupplementalMaterial.
• Figure S1: Time-step and radial resolution dependence of the evolution of PNS convection in our 20 M$_\odot$ models with FC at $\rho < 10^{13}$${\mathrm{g} \mathrm{cm}^{-3}}$. The different panels display the color-coded root of the (mass weighted) angular average of the squared lateral velocity (i.e., the standard deviation of the lateral velocity) as a function of post-bounce time in a radial domain up to 35 km. The top panel shows the noFC case with our standard resolution and the second panel the run with FFC and standard resolution for comparison. The third and following panels from the top show our results with half the time step size, a quarter of the time step size, twice the number of radial grid zones, and four times the number of radial zones. The dashed lines mark, from deeper inside outward, the iso-density radii for $10^{14}$, $10^{13}$, and $10^{12}$${\mathrm{g} \mathrm{cm}^{-3}}$ for orientation. Increasing the time or radial resolution does not have any significant impact on the time when the PNS convection starts nor on the amplitude of the non-radial velocities beyond the expected stochastic variations and secondary resolution-dependent fine-scale flow structures.
• Figure S2: Analogue to Fig. 3. GW strains and their spectrograms for a SN distance of 10 kpc as functions of time after bounce, shown for an observer at the equator. The different panels display these results for our 2D SN simulations of a 9 M$_\odot$ progenitor ( top row), 11.2 M$_\odot$ star ( middle row), and a 20 M$_\odot$ case ( bottom row), considering different FC scenarios: noFC ( left panels) and FC at densities lower than $\rho_\mathrm{c}= 10^{9}$ g cm$^{-3}$ ( panels in middle column), and at $\rho < \rho_\mathrm{c}= 10^{10}$ g cm$^{-3}$ ( right panels).