Supernovae and Light Neutralinos: SN1987A Bounds on Supersymmetry Revisited

TL;DR

This work reexamines SN1987A bounds on light neutralinos within the MSSM when M1 and M2 are not tied by GUT relations, showing that a predominantly bino-like neutralino with $M_{\tilde{\chi}}\lesssim \mathcal{O}(1\ \text{GeV})$ is compatible with collider data. The authors compute neutralino production in the SN core from $e^+e^-$ annihilation and NN binostrahlung, applying both integrated-energy and Raffelt criteria, and relate emissivities to core temperature and degeneracy profiles. They derive the bino–nucleon effective couplings, evaluate the axial hadronic response using NN phase shifts, and provide a soft-radiation formalism to estimate neutralino emissivity in a neutron gas, yielding explicit bounds on squark and selectron masses as functions of $M_{\tilde{\chi}}$. The results show strong selectron-mass exclusions for very light neutralinos (e.g., $M_{\tilde{e}} \sim 300$–$900$ GeV for $M_{\tilde{\chi}} \sim 100$ MeV) but only a narrow squark-mass window near a few hundred GeV, with almost no bound on squarks for larger $M_{\tilde{\chi}}$; gravitational trapping does not affect the bounds in the studied mass range.

Abstract

For non-universal gaugino masses, collider experiments do not provide any lower bound on the mass of the lightest neutralino. We review the supersymmetric parameter space which leads to light neutralinos, $M_\lsp \lsim {\cal O}(1\gev)$, and find that such neutralinos are almost pure bino. In light of this, we examine the neutralino lower mass bound obtained from supernova 1987A (SN1987A). We consider the production of binos in both electron-positron annihilation and nucleon-nucleon binostrahlung. For electron-positron annihilation, we take into account the radial and temporal dependence of the temperature and degeneracy of the supernova core. We also separately consider the Raffelt criterion and show that the two lead to consistent results. For the case of bino production in $NN$ collisions, we use the Raffelt criterion and incorporate recent advances in the understanding of the strong-interaction part of the calculation in order to estimate the impact of bino radiation on the SN1987A neutrino signal. Considering these two bino production channels allows us to determine separate and combined limits on the neutralino mass as a function of the selectron and squark masses. For $M_\lsp \sim 100 \mev$ values of the selectron mass between 300 and 900 GeV are inconsistent with the supernova neutrino signal. On the other hand, in contrast to previous works, we find that SN1987A provides almost no bound on the squark masses: only a small window of values around 300 GeV can be excluded, and even then this window closes once $M_\lsp \gsim 20 \mev$.

Figures (11)

• Figure 1: The neutralino mass as a function of $M_2$ for various values of $M_1$ and with $\tan\beta=10$, $\mu=300\,{\rm GeV}$. The downward spikes correspond to true zeros of the neutralino mass. The bold horizontal line indicates the value $M_{{\tilde{\chi}}}= 200\,{\rm MeV}$, below which we consider in this paper. To the right of the bold vertical line at about $M_2=120\,{\rm GeV}$ the chargino mass satisfies the lower mass bound from LEP2.
• Figure 2: Neutralino power $P_{{\tilde{\chi}}}(M_{{\tilde{\chi}}},t)$ for $t=0.5$ seconds as a function of the neutralino mass, $M_{{\tilde{\chi}}}$, with the selectron mass $M_{{\tilde{e}}} =200\,{\rm GeV}$. The solid curve shows our numerical computation while the dashed curve represents the fit Eq. (\ref{['fit-e']}). The two curves are almost indistinguishable.
• Figure 3: The dependence of the neutralino lower mass bound on the selectron mass. Here we chose $E_{{\tilde{\chi}}}^{\rm max}=10^{52}\,$erg and $t_0=1\,$s. The green-dashed line indicates the lower bound on the selectron mass from LEP2. Beyond $M_{\tilde{e}}=1$ TeV the exclusion curve drops rapidly.
• Figure 4: The minimum allowed value of $M_{{\tilde{\chi}}}$, $M_{{\tilde{\chi}}}^{\rm min}$, as a function of the time over which we integrate, $t_0$. The curves correspond to three different values of the selectron mass: $M_{\tilde{e}}=300,\, 500,\,1000\,{\rm GeV}$. Here $E_{{\tilde{\chi}}}^{\rm max}=10^{52}\,$erg and the neutralino is pure bino. Our choice of $t_0=1$ second is indicated by the grey vertical line.
• Figure 5: The neutralino mass bound as a function of $E_{{\tilde{\chi}}}^{\rm max}$ for three different values of the selectron mass: $M_{\tilde{e}}=300,\, 500,\,1000\,{\rm GeV}$. Here $t_0=1\,$s and the neutralino is again pure bino. Our choice of Eq. (\ref{['energy']}) is represented by the black vertical line.