# How to determine if an emergent gauge theory is deconfined or not?

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2+1D lattice gauge theory can emerge in a spin system through fractionalization. Usually if the gauge structure is broken down to $\mathbb{Z}_N$, it is believed that the fractionalized spinons are deconfined. However in general, $\mathbb{Z}_N$ gauge theory also have a confined phase. The question is how to determine if the discrete emergent gauge theory is really deconfined or not?

For example, I am considering a $\mathbb{Z}_3$ gauge-Higgs model defined on the Kagome lattice with the Hamiltonian $H=J\sum_{\langle i j\rangle}\cos(\theta_i-\theta_j-A_{ij})$, where $\theta_i=0,\pm2\pi/3$ is the matter field and $A_{ij}=0,\pm2\pi/3$ is the gauge field. If the matter field is in a ferromagnetic phase, then I can understand that the gauge field will be Higgs out. But the matter field here is a Kagome antiferromagnet, which is strongly frustrated and may not order at low temperature. So in this case, I would suspect that the effective $\mathbb{Z}_3$ gauge theory will be driven into a confined phase. Is my conjecture right? How to prove or disprove that?

This post imported from StackExchange Physics at 2014-04-05 03:24 (UCT), posted by SE-user Everett You
asked Jun 2, 2012
Hope I'm not raising the dead here: but naively thinking, couldn't you try and compute the $\beta$-function and find out its sign? Like you do in QFTs normally?

This post imported from StackExchange Physics at 2014-04-05 03:24 (UCT), posted by SE-user A friendly helper
@Afriendlyhelper Thanks, but I am not sure what is the RG scheme for a lattice gauge theory. The lattice geometry is very important. Like the Kagome lattice I considered here is highly frustrated. Shouldn't that make a difference with the usual QFT RG?

This post imported from StackExchange Physics at 2014-04-05 03:24 (UCT), posted by SE-user Everett You
The only way I know to "prove" or "disprove" confinement is simulating the system on a computer. Some other techniques do exist, but every time I attend some confinement-related conference, there's some people fighting each other about the validity of these methods. BTW, computing the $\beta$-function won't work, as (if I'm not mistaken) a Higgs-phase gauge theory may still have negative $\beta$-function while being completely and utterly deconfined.

This post imported from StackExchange Physics at 2014-04-05 03:24 (UCT), posted by SE-user David Vercauteren

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I have to admit that I have no idea about the model you are working on, but the standard way to determine whether a gauge theory is confining or not is to calculate the vacuum expectation value of Wilson loops. The latter are gauge invariant operators that describe parallel transport around a closed loop in spacetime. If the vacuum expectation of a Wilson loop decreases exponentially with the area it encloses, the theory is confining. It is also possible to formulate such loops within the framework of lattice gauge theory, which seems to be of interest for your application. For a nice and accessible introduction see chapter 82 of Srednicki's book on QFT.

This post imported from StackExchange Physics at 2014-04-05 03:24 (UCT), posted by SE-user Frederic Brünner
answered Mar 6, 2014 by (1,130 points)

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