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 ΛCDM 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 H₀=(66.6±1.5)~km/s/Mpc and H₀=(69.6±0.4)~km/s/Mpc, respectively, for the current-time Hubble parameter, and t₀=(8.35±0.68)~Gyr and t₀=(8.15±0.36)~Gyr, respectively, for the comoving-time age of the Universe. Tests of the model against other observations will be undertaken in subsequent works.