Cosmological Standard Timers from Unstable Primordial Relics
  In this article we study a hypothetical possibility of tracking the evolution
of our Universe by introducing a series of the so-called standard timers. Any
unstable primordial relics generated in the very early Universe may serve as
the standard timers, as they can evolve through the whole cosmological
background until their end while their certain time-varying properties could be
a possible timer by recording the amount of physical time elapsed since the
very early moments. Accordingly, if one could observe these quantities at
different redshifts, then a redshift-time relation of the cosmic history can be
attained. To illustrate such a hypothetical possibility, we consider the
primordial black hole bubbles as a concrete example and analyze the mass
function inside a redshifted bubble by investigating the inverse problem of
Hawking radiation. To complete the analyses theoretically, the mass
distribution can serve as a calibration of the standard timers.
