Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Light-front gauge invariant formulation and electromagnetic duality   The gauge invariant formulation of Maxwell's equations and the
electromagnetic duality transformations are given in the light-front (LF)
variables. The novel formulation of the LF canonical quantization, which is
based on the kinematic translation generator $P^{+}$ rather then on the
Hamiltonian $P^{-}$, is proposed. This canonical quantization is applied for
the free electromagnetic fields and for the fields generated by electric and
magnetic external currents. The covariant form of photon propagators, which
agrees with Schwinger's source theory, is achieved when the direct interaction
of external currents is properly chosen. Applying the path integral formalism,
the equivalent LF Lagrangian density, which depends on two Abelian gauge
potentials, is proposed. Some remarks on the Dirac strings and LF non local
structures are presented in the Appendix.

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The categories of this paper are: gr-qc
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The categories of this paper are: solv-int
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The categories of this paper are: cs
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The categories of this paper are: econ
35
The categories of this paper are: mtrl-th
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The categories of this paper are: alg-geom
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The categories of this paper are: nucl-ex
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The categories of this paper are: ao-sci
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The categories of this paper are: comp-gas
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The categories of this paper are: cond-mat
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The categories of this paper are: chem-ph
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The categories of this paper are: astro-ph
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The categories of this paper are: quant-ph
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The categories of this paper are: math
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The categories of this paper are: hep-ph
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The categories of this paper are: hep-lat