Neglected solutions in quadratic gravity

Abstract: We report on several previously overlooked families of static spherically symmetric solutions in quadratic gravity. Our main result concerns the existence of solutions whose leading exponents depend on the ratio ${\omega=\alpha/(3\beta)}$ of the four-derivative couplings. We demonstrate that the space of models with ${\omega >1}$ contains a dense set that admits non-Frobenius solutions ${(s_, 2 - 3 s_)0}$ (in standard Schwarzschild coordinates), with certain rational numbers $s(\omega)$. These solutions correspond to a singular core at ${\bar{r}=0}$. Another related non-Frobenius family, $(s_, 2 - 3 s_*)\infty$, exists for a dense set of models with ${1/4 < \omega < 1}$, describing a singular boundary at ${\bar{r}\to\infty}$. Both families are uncovered by recasting the metric into special coordinates in which the solutions become Frobenius. Additionally, for models with any real ratios ${\omega\neq 1}$ we identify two novel families of non-Frobenius solutions around generic points ${\bar{r}=\bar{r}_0}$, $(3/2, 0){\bar{r}0, 1/4}$ and $(3/2, 0){\bar{r}_0, 1/2}$ describing a wormhole throat. Finally, we re-derive and summarize all known families of solutions in the standard as well as in modified Schwarzschild coordinates.