  We investigate the effect of coupled dark energy (cDE) on the spin alignments
in isolated pairs of galactic halos, using the publicly available data from the
hydrodynamical cDE simulations (H-CoDECs) which were run for various cDE models
such as EXP001, EXP002, EXP003 (with exponential potential and constant
coupling), EXP008e3 (with exponential potential and exponential coupling) and
SUGRA003 (with supergravity potential and negative constant coupling) as well
as for a standard LCDM cosmology (with the WMAP7 parameters). Measuring the
cosines of the angles between the spin axes in isolated pairs of galactic halos
for each model and determining its probability density distribution, we show
that for the SUGRA003 model with bouncing cDE the null hypothesis of no spin
alignment in pairs of galactic halos is rejected at 99.999% confidence level.
In contrast, the LCDM cosmology yields no significant signal of spin alignment
and the other four cDE models also exhibit only weak signals of
spin-alignments. The strength of the spin alignment signal is found to be
almost independent of the total halo mass and separation distance in galaxy
pairs. Showing also that no signal is detected from the Sloan Digital Sky
Survey DR 7, we conclude that the spin alignments in galaxy pairs is in
principle a unique test of bouncing cDE models.
