surpasses the $1\sigma$ confidence band.[]{data-label="f3"}](3.jpg)

![Profile curve of a traversable wormhole.[]{data-label="f4"}](4.pdf)

![Embedding diagram generated by rotating the profile curve about the vertical axis.[]{data-label="f5"}](5.jpg)

The minimum values of the derived $\chi^2$ for two different combined constraints, the best fitting values of the model parameter pair ($\Omega_{m0}$, $\Omega_{r_c}$), and the corresponding $1\sigma$ and $2\sigma$ confidence intervals are listed in Table \[tab1\]. Furthermore, the likelihood distributions of two different constraints for the DGP scenario are depicted in Figs. \[f1\] and \[f2\]. It is not difficult to find that, in our situation, the results of two different constraints share a high degeneracy; we cannot produce a tighter constraint apparently when adding Planck-2015 data to the joint constraints SNe Ia+OHD+GW.

Specific traversable wormholes
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We explore the related properties of traversable wormholes of the DGP scenario in this section. Through some simple calculations, we find that the EoS parameter $\omega_{eff}(z)<-1$ in terms of the $2\sigma$ confidence level when $z<0.2874$ (the value at which wormholes appear); i.e., the NEC is violated by the effects of the gravity leakage of the extra dimensions in the DGP braneworld scenario. It is worth noting that, in our previous works, we just considered the EoS when the model parameters take 