Photon Spheres near Dilatonic Dyon-Like Black Holes in a Model with Two Abelian Gauge Fields and Two Scalar Fields

Dilatonic dyon-like black hole solutions with two (color) charges Q(1) and Q(2) (electric and magnetic ones) are considered in a gravitational 4D model with two scalar fields and two 2-forms. Two-dimensional dilatonic coupling vectors lambda(i), i=1,2, determining the model, obey the relation lambda(1)lambda(2)=1/2. Circular null geodesics in the field of such black holes are explored. The master equation for the photon sphere radius R is derived. A conjecture is suggested on the existence and uniqueness of the solution to the master equation with R>R-g, where R(g )is the horizon radius. This conjecture is varified for certain special cases, e.g., for a charge symmetric configuration: Q(1)(2)=Q(2)(2). In this charge symmetric case, we present a relation for the spectrum of quasinormal modes of a test massless scalar field in the eikonal approximation, and an example of circular orbits of a massive particle.