Probing the sign-changeable interaction between dark energy and dark
  matter with current observations
  We consider the models of vacuum energy interacting with cold dark matter in
this study, in which the coupling can change sigh during the cosmological
evolution. We parameterize the running coupling $b$ by the form
$b(a)=b_0a+b_e(1-a)$, where at the early-time the coupling is given by a
constant $b_{e}$ and today the coupling is described by another constant
$b_{0}$. We explore six specific models with (i) $Q(a)=b(a)H_0\rho_0$, (ii)
$Q(a)=b(a)H_0\rho_{\rm de}$, (iii) $Q(a)=b(a)H_0\rho_{\rm c}$, (iv)
$Q(a)=b(a)H\rho_0$, (v) $Q(a)=b(a)H\rho_{\rm de}$, and (vi)
$Q(a)=b(a)H\rho_{\rm c}$. The current observational data sets we use to
constrain the models include the JLA compilation of type Ia supernova data, the
Planck 2015 distance priors data of cosmic microwave background observation,
the baryon acoustic oscillations measurements, and the Hubble constant direct
measurement. We find that, for all the models, we have $b_0<0$ and $b_e>0$ at
around the 1$\sigma$ level, and $b_0$ and $b_e$ are in extremely strong
anti-correlation. Our results show that the coupling changes sign during the
evolution at about the 1$\sigma$ level, i.e., the energy transfer is from dark
matter to dark energy when dark matter dominates the universe and the energy
transfer is from dark energy to dark matter when dark energy dominates the
universe.
