We elucidate the relationship between 2d integrable field theories and 2d integrable lattice models, in the framework of the 4d Chern-Simons theory. The 2d integrable field theory is realized by coupling the 4d theory to multiple 2d surface order defects, each of which is then discretized into 1d defects. We find that the resulting defects can be dualized into Wilson lines, so that the lattice of discretized defects realizes integrable lattice models. Our discretization procedure works systematically for a broad class of integrable models (including trigonometric and elliptic models), and uncovers a rich web of new dualities among integrable field theories. We also study the anomaly-inflow mechanism for the integrable models, which is required for the quantum integrability of field theories. By analyzing the anomalies of chiral defects, we derive a new set of bosonization dualities between generalizations of massless Thirring models and coupled Wess-Zumino-Witten (WZW) models. We study an embedding of our setup into string theory, where the thermodynamic limit of the lattice models is realized by polarizations of D-branes.

In this paper, we present a theory for gravity coupled with scalar, SU$(n)$ and spinor fields on manifolds with null-boundary. We perform the symplectic reduction of the space of boundary fields and give the constraints of the theory in terms of local functionals of boundary vielbein and connection. For the three different couplings, the analysis of the constraint algebra shows that the set of constraints does not form a first class system.

We show how one can define novel gauge-theoretic Floer homologies of four, three, and two-manifolds from the physics of a certain topologically-twisted 5d ${\cal N}=2$ gauge theory via its supersymmetric quantum mechanics interpretation. They are associated with Vafa-Witten, Hitchin, and $G_{\mathbb{C}}$-BF configurations on the four, three, and two-manifolds, respectively. We also show how one can define novel symplectic Floer homologies of Hitchin spaces, which in turn will allow us to derive novel Atiyah-Floer correspondences that relate our gauge-theoretic Floer homologies to symplectic intersection Floer homologies of Higgs bundles. Furthermore, topological invariance and 5d "S-duality" suggest a web of relations and a Langlands duality amongst these novel Floer homologies and their loop/toroidal group generalizations. Last but not least, via a 2d gauged Landau-Ginzburg model interpretation of the 5d theory, we derive, from the soliton string theory that it defines and the 5d partition function, a Fukaya-Seidel type $A_\infty$-category of Hitchin configurations on three-manifolds -- thereby categorifying the aforementioned Floer homology of three-manifolds -- and its novel Atiyah-Floer type correspondence. Our work therefore furnishes purely physical proofs and generalizations of the mathematical conjectures by Haydys [1], Abouzaid-Manolescu [2], and Bousseau [3], and more.