Type-II Weyl semimetal vs gravastar

G. E. Volovik

*Low Temperature Laboratory, Aalto University, P.O. Box 15100, FI-00076 Aalto, Finland*

L. D. Landau Institute for Theoretical Physics, 142432 Chernogolovka, Russia

**Abstract**

The boundary between the type I and type II Weyl semimetals serves as the
event horizon for the "relativistic" fermions.
The interior of the black hole is represented by the type II Weyl
semimetal, where the Fermi surface is formed.
The process of the filling of the Fermi surface by electrons results in
the relaxation inside the horizon. This leads to the Hawking radiation
and to the reconstruction of the interior vacuum state. After the Fermi
surface is fully occupied, the interior region reaches the equilibrium
state, for which the Hawking radiation is absent.
If this scenario is applicable to the real black hole, then the final
state of the black hole will be the dark energy star with the event
horizon.
Inside the event horizon one would have de Sitter spacetime, which is
separated from the event horizon by the shell of the Planck length width.
Both the de Sitter part and the shell are made of the vacuum fields
without matter. This is distinct from the gravastar, in which the matter
shell is outside the "horizon", and which we call the type I gravastar.
But this is similar to the other type of the vacuum black hole, where the
shell is inside the event horizon, and which we call the type II
gravastar.
We suggest to study the vacuum structure of the type II gravastar using
the q-theory, where the vacuum variable is the 4-form field introduced
for the phenomenological description of the quantum vacuum.