Testing Tachyon-Dominated Cosmology with Type Ia Supernovae

An open or hyperbolic Friedmann-Robertson-Walker spacetime dominated by tachyonic dark matter can exhibit an ``inflected’’ expansion – initially decelerating, later accelerating – similar but not identical to that of now-standard $\mathrm{\Lambda }$CDM models dominated by dark energy. The features of the tachyonic model can be extracted by fitting the redshift-distance relation of the model to data obtained by treating Type Ia supernovae as standard candles. Here such a model is fitted to samples of 186 and 1048 Type Ia supernovae from the literature. The fits yield values of $H_0=(66.6\pm 1.5)\text{km/s/Mpc}$ and $H_0=(69.6\pm 0.4)\text{km/s/Mpc}$, respectively, for the current-time Hubble parameter, and $t_0=(8.35\pm 0.68)\text{Gyr}$ and $t_0=(8.15\pm 0.36)\text{Gyr}$, respectively, for the comoving-time age of the Universe. Tests of the model against other observations will be undertaken in subsequent works.