Thermal Excitations of Warped Membranes

Abstract

We explore thermal fluctuations of thin planar membranes with a frozen spatially-varying background metric and a shear modulus. We focus on a special class of $D$-dimensional ``warped membranes'' embedded in a $d-$dimensional space with $d\ge D+1$ and a preferred height profile characterized by quenched random Gaussian variables $\{h_\alpha({\bf q})\}$, $\alpha=D+1,\ldots, d$, in Fourier space with zero mean and a power law variance $\overline{ h_\alpha({\bf q}_1) h_\beta({\bf q}_2) } \sim \delta_{\alpha, \beta} \, \delta_{{\bf q}_1, -{\bf q}_2} \, q_1^{-d_h}$. The case $D=2$, $d=3$ with $d_h = 4$ could be realized by flash polymerizing lyotropic smectic liquid crystals. For $D < \max\{4, d_h\}$ the elastic constants are non-trivially renormalized and become scale dependent. Via a self consistent screening approximation we find that the renormalized bending rigidity increases for small wavevectors ${{\bf q}}$ as $\kappa_R \sim q^{-\eta_f}$, while the in-hyperplane elastic constants decrease according to $\lambda_R,\ \mu_R \sim q^{+\eta_u}$. The quenched background metric is relevant (irelevant) for warped membranes characterized by exponent $d_h > 4 - \eta_f^{(F)}$ ($d_h < 4 - \eta_f^{(F)}$), where $\eta_f^{(F)}$ is the scaling exponent for tethered surfaces with a flat background metric, and the scaling exponents are related through $\eta_u + \eta_f = d_h - D$ ($\eta_u + 2 \eta_f=4-D$).