The Instability of Vacua in Gauss-Bonnet Gravity

Understand

Owing to the quadratic nature of the theory, Einstein-Gauss-Bonnet gravity generically permits two distinct vacuum solutions.

• One solution (the "Einstein" vacuum) has a well defined limit as the Gauss-Bonnet coupling goes to zero, whereas the other solution (the "stringy" vacuum) does not.
• There has been some debate regarding the stability of these vacua, most recently from Deser and Tekin who have argued that the corresponding black hole solutions have positive mass and as such both vacua are stable.
• Whilst the statement about the mass is correct, we argue that the stringy vacuum is still perturbatively unstable.