Low Reheating Temperature and the Visible Sterile Neutrino

We present here a scenario, based on a low reheating temperature $T_R\ll 100\mathrm{M}\mathrm{e}\mathrm{V}$ at the end of (the last episode of) inflation, in which the coupling of sterile neutrinos to active neutrinos can be as large as experimental bounds permit (thus making this neutrino “visible” in future experiments). In previous models this coupling was forced to be very small to prevent a cosmological overabundance of sterile neutrinos. Here the abundance depends on how low the reheating temperature is. For example, the sterile neutrino required by the Liquid Scintillator Neutrino Detector result may not have any cosmological problem within our scenario.

Figure 1

Bounds and sensitivity regions for ${\nu }_e\leftrightarrow {\nu }_s$ oscillations. See text.

Figure 2

Same as Fig. 1 for ${\nu }_{\mu ,\tau }\leftrightarrow {\nu }_s$. For ${\nu }_{\tau }\leftrightarrow {\nu }_s$, the darkest gray excluded region does not apply. See text.