Is the EMI model a QFT? An inquiry on the space of allowed entropy functions

The mutual information I(A, B) of pairs of spatially separated regions satisfies, for any d-dimensional CFT, a set of structural physical properties such as positivity, monotonicity, clustering, or Poincaré invariance, among others. If one imposes the extra requirement that I(A, B) is extensive as a function of its arguments (so that the tripartite information vanishes for any set of regions, I3(A, B, C ) ≡ 0), a closed geometric formula involving integrals over ∂A and ∂B can be obtained. We explore whether this “Extensive Mutual Information” model (EMI), which in fact describes a free fermion in d = 2, may similarly correspond to an actual CFT in general dimensions. Using the long-distance behavior of IEMI(A, B) we show that, if it did, it would necessarily include a free fermion, but also that additional operators would have to be present in the model. Remarkably, we find that IEMI(A, B) for two arbitrarily boosted spheres in general d exactly matches the result for the free fermion current conformal block $$ {G}_{\Delta =\left(d-1\right),J=1}^d $$ G ∆ = d − 1 , J = 1 d . On the other hand, a detailed analysis of the subleading contribution in the long-distance regime rules out the possibility that the EMI formula represents the mutual information of any actual CFT or even any limit of CFTs. These results make manifest the incompleteness of the set of known constraints required to describe the space of allowed entropy functions in QFT.

Fermion-current basis and correlation functions for the integrable spin-1 chain

We use the fermion-current basis in the space of local operators for the computation of the expectation values for the integrable spin chain of spins 1. Our main tool consists in expressing a given local operator in the fermion-current basis. For this, we use the same method as in the spin-1/2 case which is based on the arbitrariness of the Matsubara data.

REDUCED PHASE SPACE QUANTIZATION OF MASSIVE VECTOR THEORY

We quantize massive vector theory in such a way that it has a well-defined massless limit. In contrast to the approach by Stückelberg where ghost fields are introduced to maintain manifest Lorentz covariance, we use reduced phase space quantization with nonlocal dynamical variables which in the massless limit smoothly turn into the photons, and check explicitly that the Poincaré algebra is fulfilled. In contrast to conventional covariant quantization our approach leads to a propagator which has no singularity in the massless limit and is well behaved for large momenta. For massive QED, where the vector field is coupled to a conserved fermion current, the quantum theory of the nonlocal vector fields is shown to be equivalent to that of the standard local vector fields. An inequivalent theory, however, is obtained when the reduced nonlocal massive vector field is coupled to a nonconserved classical current.

Infrared dynamics in (2+1) dimensions

In this work we study the asymptotic behavior of (2+1)-dimensional quantum electrodynamics in the infrared region. We show that an appropriate redefinition of the fermion current operator leads to an asymptotic evolution operator that contains a divergent Coulomb phase factor and a contribution from the electromagnetic field at large distances, factored from the evolution operator for free fields, and we conclude that the modified scattering operator maps two spaces of coherent states of the electromagnetic field, as in the Kulish–Faddeev model for QED (quantum electrodynamics) in four space-time dimensions. PACS No. 11.10Kk, 11.55m

THE ζ FUNCTION ANSWER TO PARITY VIOLATION IN THREE-DIMENSIONAL GAUGE THEORIES

We study parity violation in (2+1)-dimensional gauge theories coupled to massive fermions. Using the ζ function regularization approach we evaluate the ground state fermion current in an arbitrary gauge field background, showing that it gets two different contributions which violate parity invariance and induce a Chern–Simons term in the gauge field effective action. One is related to the well-known classical parity breaking produced by a fermion mass term in three dimensions; the other, already present for massless fermions, is related to peculiarities of gauge-invariant regularization in odd-dimensional spaces.

BOSE-FERMI TRANSMUTATION 2+1 DIMENSIONS: EFFECT OF SELF-INTERACTIONS AND THE MAXWELL TERM

We show the partition function of self-interacting charged scalar fields coupled with Abelian gauge fields governed by Maxwell-Chern-Simons action is equivalent in the long-wavelength approximation to that of a massive four-Fermi theory. The coupling constants and mass of the fermionic theory is explicitly related to those of the bosonic theory. The gauge invariant charged scalar current is shown to be transmuted to fermion current. The physical mass of the fermion is computed at the mean field level and shown to be finite at large self-coupling.

INDUCED QUANTUM NUMBERS IN SOME 2 + 1 DIMENSIONAL MODELS

The fermion current induced by slow variations in background scalar and gauge fields are computed for a class of 2 + 1 dimensional σ-like models. Local current densities proportional to topological currents in the background fields are found. The coefficient depends discontinuously on certain field ratios. The induced fermion numbers we find, mesh nicely with recent results on induced angular momentum and induced statistics. In particular, the spin and statistics is intimately related to the global parity anomaly. Lattice realizations are suggested.