Dilaton coupling to R2 gravity via a modified Kähler potential in supergravity

Abstract We explore a supergravity model based on the modified Kähler potential $$\hat{K} = -3 \ln \left( \Phi + \Phi ^\dagger - \beta \, \mathcal {R} \bar{\mathcal {R}} -\right. \left. \gamma \, (\mathcal {R}\bar{\mathcal {R}})^2 \right) $$ K ^ = - 3 ln Φ + Φ † - β R R ¯ - γ ( R R ¯ ) 2 ,where $$\Phi $$ Φ is a chiral superfield containing the dilaton and $$\mathcal {R}$$ R is the chiral curvature superfield. The quartic term $$-\gamma (\mathcal {R}\bar{\mathcal {R}})^2$$ - γ ( R R ¯ ) 2 ensures stabilization of the curvature sector, in line with recent proposals in modified supergravity, while the linear term $$-\beta \mathcal {R}\bar{\mathcal {R}}$$ - β R R ¯ yields a dilaton-modulated contribution to the effective $$R^2$$ R 2 coefficient. As clarified via the superfield Legendre transform, the model is equivalent to Einstein supergravity coupled to three chiral superfields ( $$\Phi $$ Φ , S , T ), yielding six physical scalars. Full stability requires both the curvature–sector stabilization (via $$\gamma $$ γ ) and a non-vanishing dilaton VEV. When the extra scalars are stabilized and $$\langle \phi \rangle = \mathcal {O}(M_P)$$ ⟨ ϕ ⟩ = O ( M P ) , the kinetic mixing is exponentially suppressed during inflation ( $$Z \propto e^{-\sigma /\sqrt{6}}$$ Z ∝