Observations on spontaneous chiral symmetry breaking and mass gap of QCD in finite volume

We present the lattice QCD simulation with the 2+1+1 flavor full QCD ensembles using near-physical quark masses and different spatial sizes $L$, at $a\sim$ 0.055 \;fm. The results show that the scalar and pesudoscalar 2-point correlator with the valence pion mass of approximately 230 MeV become degenerated at $L\le 1.0$ \;fm, and such an observation suggests that the spontaneous chiral symmetry breaking disappears effectively there. At the same time, the mass gap between the nucleon and pion masses remains larger then $\Lambda_{\rm QCD}$ at the entire $L\in[0.2,0.7]$ fm range.