Imprint of primordial gravitational wave with extremely low frequency on
  gravitational lens system
  Primordial gravitational waves with extremely low frequency are expected to
origin from inflation in the early Universe. The detection of such kind of
gravitational waves is of great significance to verify the inflationary theory
and determine the energy scale of inflation. Due to the foreground
contamination from dust in our Milky Way galaxy, the traditional method using
B-mode polarization faces challenges. In this work, we propose an alternative
way of detection by investigating the effect of primordial gravitational wave
with extremely low frequency on a gravitational lens system with a non-aligned
source-deflector-observer configuration. The results show that, with a series
of chosen parameters, gravitational lens system with perturbation from
extremely low frequency primordial gravitational wave could induce time delay
which could deviate from the time delay deduced from theoretical model as much
as about sixty percent, meaning that gravitational lens system with a
non-aligned configuration could serve as a potential long-base-line detector of
extremely low frequency primordial gravitational wave.
