*Article* **Search for Manifestations of Spin–Torsion Coupling**

**Mariya Iv. Trukhanova 1,2 , Pavel Andreev <sup>1</sup> and Yuri N. Obukhov 2, \***


**Abstract:** We investigate the axial vector spin–torsion coupling effects in the framework of the Poincaré gauge theory of gravity with the general Yang–Mills type Lagrangian. The dynamical equations for the "electric" and "magnetic" components of the torsion field variable are obtained in the general form and it is shown that the helicity density and the spin density of the electromagnetic field appear as the physical sources. The modified Maxwell's equations for the electromagnetic field are derived, and the electromagnetic wave propagation under the action of the uniform homogeneous torsion field is considered. We demonstrate the Faraday effect of rotation of the polarization for such a wave and establish the strong bound on the possible cosmic axial torsion field from the astrophysical data.

**Keywords:** spin; gauge gravity; torsion; electromagnetic wave; Faraday effect
