Spherically Symmetric Black Holes and Physical Vacuum

Using the example of an action for an ideal fluid with a variable number of particles, a phenomenological description of the particle production processes against the background of strong external fields is explored. The conformal invariance of the part of the action associated with the particle creation law is shown. For spherically symmetric geometries, it is demonstrated that the physical vacuum for this model cannot be described by vacuum solutions of the black hole type both for general relativity and for some cases of quadratic gravity.