Geometry, Topology & Group Theory for Physics
A physics-first route through manifolds, Lie groups, representations, topology, fiber bundles, gauge connections, and Berry phase. Expanded with original in-page technical chapters, mathematical proofs, independently checked calculation baselines and directly embedded credited original instructor videos where relevant.
Published syllabus
Course Units
Manifolds as configuration spaces
A manifold is a space that is locally coordinated like Euclidean space but need not have one global coordinate chart. The sphere requires overlapping charts; failure of a global smooth chart is not a physical singularity. Coordinates label points, while transition functions define how local descriptions agree on overlaps.
Tangent spaces, cotangent spaces, and metrics
A tangent vector acts on smooth functions as a derivation, and a cotangent vector is a linear functional on tangent vectors. A metric is a nondegenerate symmetric bilinear form mapping two tangent vectors to a scalar. Covectors and vectors acquire different coordinate transformation laws; the metric connects them only after it is specified.
Curvature, geodesics, and parallel transport
Parallel transport uses a connection to compare tangent vectors at neighboring points without choosing arbitrary ambient embeddings. Geodesics have zero covariant acceleration under an affine parameter. Curvature detects path dependence of infinitesimal parallel transport; the Riemann tensor is built from the connection and its derivatives.
Groups, actions, and symmetry
A group captures composition, identity and inverse of symmetry transformations. A group action associates group elements with transformations of a physical state space. Continuous groups such as rotations possess infinitesimal generators, while discrete symmetries such as lattice translations may have qualitatively different invariants.
Lie algebras and infinitesimal generators
A Lie algebra is the tangent space at the identity of a Lie group equipped with the commutator bracket. For matrix groups, exponentiating generators constructs one-parameter subgroups. Structure constants encode the generator algebra, and the Jacobi identity ensures compatibility of nested commutators.
Representations of SU(2) and spin
SU(2) acts on complex spinors; its Lie algebra is generated by Pauli matrices. Irreducible spin-j representations have dimension 2j+1, with j integer or half-integer. The group double-covers SO(3), explaining the minus sign acquired by a spin-half state under a 2π rotation.
SU(3), Lorentz, and Poincare symmetry
SU(3) has eight independent generators and appears as the local color symmetry of QCD; its fundamental representation has dimension three. The Lorentz group preserves the Minkowski metric and admits spinor representations not captured by ordinary spatial vectors. The Poincaré group adds spacetime translations, with mass and spin labeling key irreducible representations.
Homotopy, homology, and invariants
Homotopy studies continuous deformation of maps; homology assigns algebraic invariants to cycles. The fundamental group detects classes of closed loops, while homology can count holes in different dimensions. These invariants are robust under continuous deformation but require a well-defined underlying topological space.
Fiber bundles and gauge connections
A fiber bundle assigns an auxiliary space to each base point while allowing globally nontrivial gluing. In gauge theory the local gauge potential A is a connection; a gauge transformation changes its components while preserving appropriately constructed observables. Parallel transport gives a path-ordered holonomy, the natural home of Wilson loops.
Gauge curvature and holonomy
Gauge curvature is the field strength of a connection. For a non-Abelian gauge field, the commutator term A∧A is essential and produces self-interaction absent in Abelian U(1) electromagnetism. Holonomy around infinitesimal loops is controlled by curvature; finite Wilson loops remain path-ordered and depend on the representation.
Berry phase and Chern numbers
For a smoothly parameterized nondegenerate eigenstate, the Berry connection is A=i⟨u|∇u⟩; its curvature measures geometric phase accumulation over parameter-space surfaces. Integrating curvature over a closed compact two-dimensional base can produce an integer Chern number when the associated bundle and gap assumptions hold.
Topological defects, anomalies, and research links
Defects are classified by order-parameter topology and dimensionality: line defects in a complex phase can carry integer winding, while monopoles use maps surrounding an isolated core. Quantum anomalies arise when a classical symmetry fails in the quantum measure or regulator, with concrete observable consequences. Defects and anomalies are related to topology but are not interchangeable concepts.