Limits on the time variation of the Fermi constant $G_F$ based on type Ia supernova observations

The light curve of a type Ia supernova decays at a rate set by the $\beta$-decay lifetimes of the ${}^{56}\mathrm{Ni}$ and ${}^{56}\mathrm{Co}$ produced in the explosion. This makes such a light curve sensitive to the value of the Fermi constant $G_F$ at the time of the supernova. Using data from the CfA Supernova Archive, we measure the dependence of the light curve decay rate on redshift and place a bound on the time variation of $G_F$ of $|\frac{{\dot{G}}_F}{G_F}|<{10}^{-9}{\mathrm{yr}}^{-1}$.

Figure 1

Light curves for SN1998aq. The magnitudes for the different bands are $m_U$, $m_B-2$, $m_V-4$, $m_R-6$, and $m_I-8$. The black lines represent linear fits between 50 and 130 days after the peak.

Figure 2

Plots of ${\dot{m}}_0$ versus $z$ for the U, B, V, R, and I bands. In each plot, the dashed horizontal line marks the mean $⟨{\dot{m}}_0⟩$; the substantial difference in this mean for different wavelength regions indicates a nonzero $\frac{d⟨{\dot{m}}_0⟩}{dk}$.

Figure 3

V-band light curves of SN1995ak and SN1998aq, showing linear fits in the ${}^{56}\mathrm{Co}$ decay region. The maximum intensity occurs at $t=0$, where $m_{\mathrm{V}}$ is normalized to $-12.5$ and $-12$, respectively.