Phase and stability of black strings in Einstein-Gauss-Bonnet theory at large D

The phase and stability of black strings in the Einstein-Gauss-Bonnet (EGB) theory are investigated by using the large D effective theory approach. The spacetime metric and thermodynamics are derived up to the next-to-leading order (NLO) in the 1/D expansion. We find that the entropy current defined by the Iyer-Wald formula follows the second law. As in the Einstein theory, the entropy difference from the total mass produces an entropy functional for the effective theory. Including the NLO correction, we find that for the large Gauss-Bonnet coupling constant $\alpha_{\rm GB}$, the Gregory-Laflamme instability of uniform black strings needs longer wavelength. Moreover, we show that the critical dimension, beyond which non-uiform black strings becomes more stable than uniform ones, increases as $\alpha_{\rm GB}$ becomes large, and approaches to a finite value for $\alpha_{\rm GB}\to \infty$.