Gluon Sivers Function in Transverse Single-Spin Asymmetries of Direct Photons at NICA

Transverse single-spin asymmetries in the production of direct photons at the Nuclotron-based Ion Collider fAcility (NICA) are studied within the generalized parton model and its color gauge-invariant extension. Predictions for the possible asymmetry values at various NICA energies are presented. A kinematical region where the contribution of the gluon Sivers function to the asymmetry in question is dominant over the quark Sivers function is found.