Link in $\mathbb{R}\mathbb{P}^3$ and the Topological Vertex
John Chae
TL;DR
The paper addresses the problem of computing and understanding link invariants for links in $\mathbb{R} \mathbb{P}^3$ via open/closed string duality. It leverages large $N$ duality and a geometric transition to a toric Calabi-Yau geometry, enabling the use of (refined) topological vertex techniques to calculate colored unknot and Hopf link invariants. The key contributions are explicit computations yielding power-series invariants in Kahler parameters with positive $q$-expansions, the proposal that these are graded Poincaré polynomials of a link homology theory for $\mathbb{R} \mathbb{P}^3$, and a comparative analysis with the $S^3$ case that reveals novel mixed-term structure and $t$-dependence in the RP$^3$ setting. The work advances the categorification program for RP$^3$ links and supports a physical interpretation in terms of BPS state counting within open/closed string duality.
Abstract
We provide the first computations of colored unknots and Hopf link in $\mathbb{R}\mathbb{P}^3$ using both the topological vertex and its refinement. Our approach utilizes the toric Calabi-Yau threefold arising from the geometric transition of the cotangent bundle of $\mathbb{R}\mathbb{P}^3$ under the large $N$ duality. We find that the link invariants are series in the Kahler parameters of the toric Calabi-Yau manifold and the $q$-expansions of the rational functions of the series have positivity property. We conjecture that they are Poincare series of an infinite dimensional link homology theory for links in $\mathbb{R}\mathbb{P}^3$. We compare our results with that of the $S^3$ and speculate the consequences of the series nature of the invariants.
