Source: Same source for the Dark Matter definition below.

Topics: Astronomy, Astrophysics, Cosmology, Dark Matter, Einstein, General Relativity

Note: Your "secret decoder ring" for reading the Abstract.

Dark matter: It makes up about 85% of the universe, is invisible, and doesn't interact with matter except for gravitational effects. See: Center for Astrophysics, Harvard

"Tachyonic": Of, or referring to tachyons, (Greek for swift) theoretical particles that already travel faster-than-light and backward in time. Their rest mass, m_{0}^{i}, is assumed to be imaginary. As it loses energy, it's assumed to become infinitely fast, so you can see why it's a favorite science fiction trope, along with dark matter, literally tableau rasas.

ΛCDM assumes that the universe is composed of photons, neutrinos, ordinary matter (baryons, electrons), and cold (non-relativistic) dark matter, which only interacts gravitationally, plus "dark energy," which is responsible for the observed acceleration in the Hubble expansion. Source: Goddard Spaceflight Center: Lambda

H_{0} defines the Hubble constant, or, the rate at which the universe is expanding, determined by Hubble in the way back year of 1929 to be 500 km/s/Mpc. I'm going to defer to Wikipedia for this one.

km/s/Mpc = kilometers/second/megaparsec. Megaparsec is 1 million parsecs = 3,260,000 light years, or 3.26 x 10^{6} light years.

t_{0} = the present age of the universe, t_{0} = 2tH/3, where "tH" is the Hubble time. t_{0} is roughly 13.7 × 10^{9} years, or 4.32 × 10^{17} seconds.

Gyr = giga years, or 1 billion years = 1 x 10^{9} years (a lot).

**Abstract**

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 H_{0} = (66.6±1.5) km/s/Mpc and H_{0} = (69.6±0.4) km/s/Mpc, respectively, for the current-time Hubble parameter, and t_{0} = (8.35 ± 0.68) Gyr and t_{0} = (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.

Subject headings: cosmology, dark matter, tachyons, distance-redshift relation, supernovae

Testing Tachyon-Dominated Cosmology with Type Ia Supernovae, Samuel H. Kramer, Ian H. Redmount, Physics arXiv