Core-collapse supernovae stymie secret neutrino interactions

Beyond-the-Standard-Model interactions of neutrinos among themselves—secret interactions—in the supernova core may prevent the shock revival, halting the supernova explosion. Besides, if supernova neutrinos en route to Earth undergo secret interactions with relic neutrinos, the neutrino burst reaching Earth may be down-scattered in energy, falling below the detection threshold. We probe secret neutrino interactions through supernova neutrinos and apply our findings to the supernova SN 1987A. We place the most stringent bounds on flavor-universal secret interactions occurring through a new mediator with mass between 10 MeV and 1 GeV.

Figure 1

Constraints on secret neutrino interactions ($\nu \mathrm{SI}$), in terms of the coupling $g$ and mass $M$ of the new $\nu \mathrm{SI}$ mediator. Our new constraints come from considering $\nu \mathrm{SI}$ between SN neutrinos en route to Earth and $\mathrm{C}\nu \mathrm{B}$ neutrinos (“SN 1987A propagation”) and $\nu \mathrm{SI}$ between neutrinos in the SN core (“SN 1987A core”). We consider $\nu \mathrm{SIs}$ that are flavor-universal ($g_{ee}=g_{\mu \mu }=g_{\tau \tau }$). Because of this, for the SN1987A core bound, although electron-type neutrinos interact the most in the SN core, our bound applies to all neutrino flavors equally. An earlier SN constraint (“SN 1987A Kolb & Turner”) [13] comes from the strength of the $\nu \mathrm{SI}$ interaction rate of neutrinos from the SN 1987A en route to Earth, but our refined treatment supersedes it. Other constraints come from Big Bang nucleosynthesis (BBN for $g_{ee}=g_{\mu \mu }=g_{\tau \tau }$) [14], particle decays (we distinguish between flavors, “Lab $g_{ee}$”, “Lab $g_{\mu \mu }$”, “Lab $g_{\tau \tau }$” [15]) [16], double beta decay ($\varphi \beta \beta$, for $g_{ee}$) [17], and the cosmic microwave background (CMB for $g_{11}=g_{22}=g_{33}$, in the neutrino mass eigenstate basis) [18]. For cosmological bounds, see also Ref. [19].

Figure 2

Constraints on the mass and coupling of the $\nu \mathrm{SI}$ mediator based on $\nu \mathrm{SI}$ occurring in the SN core. The color coding represents the average number $N_{2\nu \to 4\nu }$ of $\nu \mathrm{SI}$ $\nu +\overline{\nu }\to 2\nu +2\overline{\nu }$ interactions that occur in the SN, see Eq. (7). The region above the black line is excluded for the default case with $R_{\min }=15\mathrm{km}$ and $⟨E⟩=30\mathrm{MeV}$. The region above the dashed line is the exclusion region for the conservative case with $R_{\min }=30\mathrm{km}⟨E⟩=15\mathrm{MeV}$. There, $N_{2\nu \to 4\nu }\ge 1$ and the neutrino energy deposition is insufficient to revive the stalled shock wave, thus halting the SN explosion.

Figure 3

Illustration of the energy down-scattering of SN neutrinos reaching Earth due to $\nu \mathrm{SI}$ scattering off the $\mathrm{C}\nu \mathrm{B}$. Left: neutrino energy distribution in arbitrary units before and after $\nu \mathrm{SI}$ as a function of the neutrino energy for ${\log }_{10}(g)=-1.75$ and ${\log }_{10}(M/\mathrm{MeV})=-3.50$. Supernova neutrinos are down-scattered as a result of $\nu \mathrm{SI}$. Right: the color scale represents the percentage of neutrinos that reach Earth for a SN located 50 kpc away. The $x$-axis is the arrival direction of the neutrinos at Earth, where $\cos \theta =1$ means straight-line propagation from the SN to Earth, while the $y$-axis is the SN neutrino energy after $\nu \mathrm{SI}$ on $\mathrm{C}\nu \mathrm{B}$ neutrinos. The initial energy spectrum is same one as in the left panel. The dashed horizontal line marks the detection energy threshold of 5 MeV.

Figure 4

Feynman diagrams for some of the illustrative $2\nu \to 4\nu$ $\nu \mathrm{SI}$ processes.

Figure 5

Energy dependence of the cross section ${\sigma }_{2\nu \to 4\nu }$ $\nu \mathrm{SI}$ process as a function of the center-of-mass energy, for our approximation, Eqs. (2) and (3), and for the precise cross section computed using a single representative contributing diagram.