A commutative generalization of the   1 U gauge symmetry group is proposed. The twoparametric family of two-connected abelian Lie groups is obtained. The necessity of existence of so-called imaginary charges and electromagnetic fields with negative energy density (dark photons) is derived. The possibilities when the overall Lagrangian represents a sum or difference of two identical Lagrangians for the visible and hidden sectors (i.e. copies of unbroken   1 U ) are ruled out by the extended symmetry. The distinction between the two types of fields resides in the fact that for one of them current and electromagnetic kinetic terms in Lagrangians are identical in sign, whereas for another type these terms are opposite in sign. As a consequence, and in contrast to the common case, like imaginary charges attract and unlike charges repel. Some cosmological issues of the proposed hypothesis are discussed. Particles carrying imaginary charges ("allotons") are proposed as dark matter candidates. Such a matter would be imaginary charged on a large scale for the reason that dark atoms would carry non-compensated charges. Consequently, there exist (dark) electromagnetic fields with negative energy density on cosmological scales (the reviving of the idea of Faradayan cosmology). This leads to the hypothesis that the modern state of the Universe is radiation-dominated by dark photons with negative energy density that is the source of the observed late-time cosmological acceleration. This provides an explanation for the small value of the cosmological constant as a renormalized vacuum energy.PACS numbers: 11.15.-q, 14.70.-e, 95.35.+d, 95.36.+x INTRODUCTIONThe idea of interactions (even long-range   1 U interactions) in the dark sector is not new [1].A new kind of photon, which couples to dark matter but not to ordinary matter, has been recently proposed by L. Ackerman et al. [2]. As mentioned in [3], an attractive non-gravitational force between DM concentrations is not only well-motivated theoretically, it may resolve some discomforts with conventional ΛCDM. DM could be weakly coupled to long-range forces, which might be related to dark energy. One difficulty with the latter is that such forces are typically mediated by scalar fields, and it is hard to construct natural models in which the scalar field remains massless (to provide a long-range force) while interacting with the DM at an interesting strength [2]. The authors of [2] point out that the dark photon comes from gauge symmetry, just

The idea of a new model explaining the coherent nature of dark matter and dark energy is proposed. Recent works by Farnes (2018) and Socas-Navarro (2019) proposed a cosmological model and its critical analysis in which both dark matter and dark energy are replaced with a single fluid of negative mass. This paper presents a modification of this idea using the hypothesis about the existence of so-called imaginary charges and electromagnetic fields with negative energy density (‘minus-fields’) proposed by Ya.Terletsky (1991) and derived by us from a commutative generalization of the U(1) gauge symmetry group. It is shown that dark photons could be a partial source of the observed late-time cosmological acceleration, saying that dark energy, or part of it could be not cosmological constant or scalar field (quintessence), but photons with negative energy instead. The unusual properties of imaginary charges ensure the existence of dark matter structures. The Friedmann equation, in case when minus-photons give considerable contribution to the energy balance of the Universe, gives the following condition for the accelerated expansion: . It is found that even a relatively small density of dark negative radiation can lead to a significant change in the expansion dynamics of the Universe and new effects are predicted. Last, we assert the need to develop a new type of detectors that can detect particles and waves with negative energy.