consistency check of all transformation laws for our anyonization procedure. We also derive
the equation of state and expand it at high temperatures, where the analogy with the virial
expansion is most transparent. In the final section 4, we summarize the results and discuss
possible future directions and open problems. Appendix A provides more details on the
variation of the boundary action.
2 Holographic anyons
In this section we will outline a general method for anyonizing holographic matter. Firstly,
a few introductory comments are provided on previous work including a discussion of some
shortcomings related to ambiguities associated with gauge freedom. We then proceed to
propose a different prescription which will ultimately manage to circumvent such ambigu-
ities and describe how the two prescriptions are connected. To demonstrate the versatility
of this novel method, the transformed Green’s functions are obtained and computed, along
with further thermodynamic quantities and transport properties.
2.1 Alternative quantization
The procedure of alternative quantization
1
transforms a (2+1)-dimensional conformal field
theory (CFT) into another by changing the boundary conditions on the bulk gauge field. In
modern language, this procedure is an SL(2, Z) electromagnetic transformation. Therefore,
as the name suggests, the manner in which boundary degrees of freedom are separated into
source and response is changed, while the bulk description and equations of motion remain
untouched. It is important to note that the bulk action does not need to be invariant under
SL(2, Z), we only demand the bulk gauge equations of motion reduce to free ones close to
the boundary where Robin, i.e., combined Dirichlet/Neumann, boundary conditions are
imposed.
2
In fact, one could allow for a larger group of transformations, but keeping
in mind a possible, and desirable, embedding into string theory, where both the electric
charges and magnetic fields are integer-quantized, one restricts to SL(2, Z).
To be more specific, an anyon can be viewed as a quasiparticle consisting of a boson
or fermion with some additional fixed amount of magnetic flux attached per fundamental
unit of charge. In a conformal field theory with a global U(1) one can perform the pro-
cess of adding magnetic fluxes using an SL(2, Z) electromagnetic transformation [12, 13].
Under this transformation, the original CFT maps into another one with mixed charges
and magnetic fields and thus the charge carriers have been transformed into anyonic de-
grees of freedom. From the bulk gravitational point of view, one is choosing an alternative
quantization scheme for the gauge fields, i.e., the boundary values on the gauge fields
have combined Dirichlet/Neumann conditions. This was first implemented holographically
in [14] by showing that the SL(2, Z) transformation on a fractional quantum Hall state [19]
leads to a soft mode which is a prerequisite of an anyonic superfluid. Successful exten-
sions to flowing superfluids [20], to other D-brane models [21–23], and even extensions to
backgrounds not dual to CFTs [24, 25] have been constructed subsequently.
1
For a self-contained review in the present context, see [14].
2
This should be contrasted with [15–18], where the SL(2,
Z
)-symmetry was imposed in the bulk as well.
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