The observed Higgs mass indicates that the Standard Model can be valid up to near the Planck scale M _ { \text { P } } .
Within this framework , it is important to examine how little modification is necessary to fit the recent experimental results in particle physics and cosmology .
As a minimal extension , we consider the possibility that the Higgs field plays the role of inflaton and that the dark matter is the Higgs-portal scalar field .
We assume that the extended Standard Model is valid up to the string scale 10 ^ { 17 } \text { GeV } .
( This translates to the assumption that all the non-minimal couplings are not particularly large , \xi \lesssim 10 ^ { 2 } , as in the critical Higgs inflation , since M _ { \text { P } } / \sqrt { 10 ^ { 2 } } \sim 10 ^ { 17 } \text { GeV } . )
We find a correlated theoretical bound on the tensor-to-scalar ratio r and the dark matter mass m _ { \text { DM } } .
As a result , the Planck bound r < 0.09 implies that the dark-matter mass must be smaller than 1.1 TeV , while the PandaX-II bound on the dark-matter mass m _ { \text { DM } } > 0.7 \pm 0.2 \text { TeV } leads to r \gtrsim 2 \times 10 ^ { -3 } .
Both are within the range of near-future detection .
When we include the right-handed neutrinos of mass M _ { \text { R } } \sim 10 ^ { 14 } GeV , the allowed region becomes wider , but we still predict r \gtrsim 10 ^ { -3 } in the most of the parameter space .
The most conservative bound becomes r > 10 ^ { -5 } if we allow three-parameter tuning of m _ { \text { DM } } , M _ { \text { R } } , and the top-quark mass .