Topological Quantum Field Theories (TQFT)

TQFT represents a significant domain in mathematical physics. These theories are distinguished by their lack of dependence on a background metric, which means they do not have local degrees of freedom. This absence of a metric implies that spatial and temporal measurements are not defined within these frameworks. Additionally, the Hamiltonian of such theories possesses only zero eigenstates. The non-trivial nature of these theories arises from phenomena like vacuum-to-vacuum tunneling, which will be discussed in more detail.

Their significance can be summarized by several key aspects:

1. They provide a foundational structure for other quantum field theories.
2. They often yield precise results.
3. They forge deep connections between the realms of physics and advanced mathematics.

In this article, I will expand on Edward Witten's insight that the Jones polynomial invariant has its roots in quantum field theory. Specifically, I will illustrate how the skein relation for Jones polynomials can be derived using 3-dimensional Chern-Simons theory.

Mathematical Insight: The WZNW Model

The WZNW (Wess–Zumino–Novikov–Witten) model is a nonlinear sigma model characterized by an action that is a functional of a bosonic field ( g(x): Sigma to G ) (where ( Sigma ) is a two-dimensional compact Riemann surface). This field resides in a group manifold ( G ) with an associated Lie algebra ( mathfrak{g} ). The constant ( a^2 ) is dimensionless and positive. Although the classical action is conformally invariant, this invariance is lost upon quantization, a problem that Witten addressed by introducing an additional term into the action.

Chern-Simons Theory

Utilizing the complex structure on the Riemann surface ( M ), we derive the commutation relations between gauge connections as discussed in my previous article. The Hilbert space ( mathcal{H} ) is defined such that the constraint ( F=0 ) transforms into an equation that delineates the wave functions of ( mathcal{H} ).

WZNW Model Dynamics

In our analysis, we will consider the current algebra of the WZNW model (details omitted for brevity) in the adjoint representation of ( SU(2) ). By coupling the currents to a gauge field with ( G=SU(2) ) on ( Sigma ), we can derive a Ward–Takahashi identity.

This relationship allows us to express the partition function ( Z(A) ) of the WZNW model on a Riemann surface ( Sigma ) as a sum of products of holomorphic and anti-holomorphic components. The wave functions ( Psi(A) ) are interpreted as the canonical quantization of the ( SU(2) ) WZW model on ( Sigma ) and are referred to as conformal blocks. This leads us to the conclusion that conformal blocks in the WZW model correspond to wave functions of Chern-Simons theory on ( mathbb{R} times Sigma ), and vice-versa.

The correspondence can be utilized to compute observables in Chern-Simons theory. For instance, consider a compact oriented 3-manifold ( M ) that can be divided into two handlebodies, a process known as Heegaard splitting. If the two handlebodies share the same boundary ( Sigma ), their union forms a closed 3-dimensional manifold ( M ).

Deriving the Skein Relation for Jones Polynomial through Chern-Simons Theory

We begin by examining an arbitrary 3-manifold ( M ) with a link ( L ) embedded in it, formed by Wilson loops in the fundamental representation ( R = square ) of ( SU(2) ). The components of the link are oriented, non-intersecting knots ( {K_i} ) for ( i=1,2,ldots ), each assigned a representation ( R_i ) of ( G ).

Upon identifying a crossing in ( L ), we enclose it within a sphere (illustrated in gray).

We analyze the crossing within the 3-ball, recognizing that it cannot be untangled. Following Witten's methodology, we cut the manifold ( M ) into a connected sum ( M = M_r # M_l ), where the boundary of ( M_r ) is the surface of the 3-ball, and the exterior is ( M_l = M setminus B_r ).

The objective is to evaluate the path-integral quantization across both ( M_l ) and ( M_r ), which assigns Hilbert spaces ( mathcal{H}_l ) and ( mathcal{H}_r ) to their respective boundaries. The dimensions of these spaces are contingent upon the number of marked points.

As we apply diffeomorphisms to ( M_r ), new manifolds with swapped marked points emerge. The transformations ( M_r to X_1 ) and ( M_r to X_2 ) correspond to the Conway triple.

Through this approach, we derive the skein relation, establishing that the Jones Polynomial invariants can indeed be extracted from Chern-Simons topological field theory.

Physics Insights: Understanding Particle Statistics

Quantum mechanics offers a framework for understanding the behavior of microscopic particles, with the quantum state of a system mathematically represented by its state vector in a Hilbert space. A notable feature of quantum particles is their indistinguishability, leading to two classifications: bosons and fermions.

Bosons, which include particles such as photons and gluons, are force carriers in the Standard Model, while fermions (e.g., quarks and electrons) are typically associated with matter. The exchange symmetry principle defines the behavior of these particles, with bosons exhibiting symmetric wave functions and fermions demonstrating antisymmetric wave functions, as dictated by the spin-statistics theorem.

Anyons: A New Class of Particles

In (2+1)-dimensional spacetimes, another category of particles known as anyons emerges, which do not conform to traditional bosonic or fermionic statistics. The exchange of anyons leads to fractional statistics, adding a layer of complexity to particle interactions.

Through Chern-Simons theory, we can derive the statistical behavior of anyons, revealing that their interactions yield phase contributions that are not necessarily integers, demonstrating the rich tapestry of particle physics.

Thank you for engaging with this exploration, and I welcome any feedback or insights you may have! For further content on physics and other topics like mathematics and machine learning, please visit my personal website at www.marcotavora.me and my GitHub.