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In this paper we considered the bosonic string action in the presence ofmetric $G_{\mu\nu}$, Kalb-Ramond field $B_{\mu\nu}$ and dilaton field $\Phi$.The quantum conformal invariance is achieved if all three one-loop$\beta$-functions are zero. But, $\beta^\Phi$, $\beta$-function related to thedilaton field, can also be equal to some nonzero constant $c$, which isactually the central charge of Virasoro algebra. The anomaly contained in theSchwinger term of Virasoro algebra is canceled by adding Liouville term to thesigma model action and quantum conformal invariance is restored. The space-timeaction, which Euler-Lagrange equations of motion are quantum conformalinvariance conditions with nonzero $\beta^{\Phi}$, is Einstein-Hilbert actionwith some matter and cosmological constant. The cosmological constant isobtained within landscape framework as linear function of the central charge ofVirasoro algebra.

String theory landscape and cosmological constant