Dynamics of a test null string in the gravitational field of a null string domain that radially changes its size

The motion of a test null string “inside” an axially symmetric domain of null strings which has a layered structure and radially changes its size has been investigated. It is shown that the action of the gravitational field of such a domain on a test null string for any initial conditions leads to oscillations of a test null string inside a region limited in space. The motion (drift) of the region inside which the test null string oscillates depends on the ratio of the initial parameters characterizing the test null string and the null string domain. These regions can be considered as particles localized in space with an effective nonzero rest mass. For these particles, you can enter the concept of “life time”, which depends on the number of layers in the multi-string system. It is also possible to introduce the concept of particle “mass” (energy), which is determined by the size of the region in which the null string oscillates and depends on the trajectory of the null string in this region. Under the influence of changing external conditions one kind of particles can pass into another.