259 research outputs found
Classification of static and homogeneous solutions in exactly solvable models of two-dimensional dilaton gravity
We give the full list of types of static (homogeneous)solutions within a wide
family of exactly solvable 2D dilaton gravities with backreaction of conformal
fields. It includes previously known solutions as particular cases. Several
concrete examples are considered for illustration. They contain a black hole
and cosmological horizon in thermal equilibrium, extremal and ultraextremal
horizons, etc. In particular, we demonstrate that adS and dS geometries can be
\QTR{it}{exact} solutions of semiclassical field equations for a
\QTR{it}{nonconstant} dilaton field.Comment: 19 pages. To appear in Int. J. Mod. Phys.
Ultra-high energy collisions in static space-times: single versus multi-black hole cases
We consider collision of two particles near static electrically charged
extremal black holes and elucidate the conditions under which the energy in the
centre of mass frame E_{c.m.} grows unbounded. For a single black hole, we
generalize the results obtained earlier for the Reissner-Nordstr\"om metric, to
distorted black holes. In the multi-black hole space-time, qualitatively new
features appear. If the point of collision is close to at least two horizons
simultaneously, unbounded E_{c.m.} are possible (i) without fine-tuning of
particles' parameters, (ii) for an arbitrary mutual orientation of two
velocities. Such a combination of properties (i) and (ii) has no analogues in
the single black hole case and facilitates the condition of getting unbounded
E_{c.m.}. Collisions in the electro-vacuum Majumdar-Papapetrou metric (several
extremal black holes in equilibrium) is analyzed explicitly.Comment: 18 pages. Essentially expanded, presentation improved. To appear in
GR
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