15,236 research outputs found
Spontaneous breaking of conformal invariance in theories of conformally coupled matter and Weyl gravity
We study the theory of Weyl conformal gravity with matter degrees of freedom
in a conformally invariant interaction. Specifically, we consider a triplet of
scalar fields and SO(3) non-abelian gauge fields, i.e. the Georgi-Glashow model
conformally coupled to Weyl gravity. We show that the equations of motion admit
solutions spontaneously breaking the conformal symmetry and the gauge symmetry,
providing a mechanism for supplying a scale in the theory. The vacuum solution
corresponds to anti-de-Sitter space-time, while localized soliton solutions
correspond to magnetic monopoles in asymptotically anti-de-Sitter space-time.
The resulting effective action gives rise to Einstein gravity and the residual
U(1) gauge theory. This mechanism strengthens the reasons for considering
conformally invariant matter-gravity theory, which has shown promising
indications concerning the problem of missing matter in galactic rotation
curves.Comment: 20 pages, 1 figure, revised and added reference
Quantum effects in Acoustic Black Holes: the Backreaction
We investigate the backreaction equations for an acoustic black hole formed
in a Laval nozzle under the assumption that the motion of the fluid is
one-dimensional. The solution in the near-horizon region shows that as phonons
are (thermally) radiated the sonic horizon shrinks and the temperature
decreases. This contrasts with the behaviour of Schwarzschild black holes, and
is similar to what happens in the evaporation of (near-extremal)
Reissner-Nordstrom black holes (i.e. infinite evaporation time). Finally, by
appropriate boundary conditions the solution is extended in both the asymptotic
regions of the nozzle.Comment: 23 pages, latex, 1 figure; revised version, to appear in Phys. Rev.
Cutoffs, Stretched Horizons and Black Hole Radiators
We argue that if the UV cutoff of an effective field theory with many low
energy degrees if freedom is of the order, or below, the scale of the stretched
horizon in a black hole background, which in turn is significantly lower than
the Planck scale, the black hole radiance rate may not be enhanced by the
emission of all the light IR modes. Instead, there may be additional
suppressions hidden in the UV completion of the field theory, which really
control which light modes can be emitted by the black hole. It could turn out
that many degrees of freedom cannot be efficiently emitted by the black hole,
and so the radiance rate may be much smaller than its estimate based on the
counting of the light IR degrees of freedom. If we apply this argument to the
RS2 brane world, it implies that the emission rates of the low energy CFT modes
will be dramatically suppressed: its UV completion is given by the bulk gravity
on , and the only bulk modes that could be emitted by a black
hole are the 4D s-waves of bulk modes with small 5D momentum, or equivalently,
small 4D masses. Further, their emission is suppressed by bulk warping, which
lowers the radiation rate much below the IR estimate, yielding a radiation flux
, where is the Hawking radiation rate of a
single light species. This follows directly from low CFT cutoff , a large number of modes and the fact that 4D
gravity in RS2 is induced, .Comment: LaTeX, 25 pages, 5 .eps figures; v3: references added, presentation
improved, published in Physical Review
A Planck-like problem for quantum charged black holes
Motivated by the parallelism existing between the puzzles of classical
physics at the beginning of the XXth century and the current paradoxes in the
search of a quantum theory of gravity, we give, in analogy with Planck's black
body radiation problem, a solution for the exact Hawking flux of evaporating
Reissner-Nordstrom black holes. Our results show that when back-reaction
effects are fully taken into account the standard picture of black hole
evaporation is significantly altered, thus implying a possible resolution of
the information loss problem.Comment: 6 pages, LaTeX file, Awarded Fifth Prize in the Gravity Research
Foundation Essay Competition for 200
Possession is Nine-Tenths of the Law:Bourgeois behavior, property and inequality in an Hawk Dove experiment
Two-dimensional black holes in accelerated frames: quantum aspects
By considering charged black hole solutions of a one parameter family of two
dimensional dilaton gravity theories, one finds the existence of quantum
mechanically stable gravitational kinks with a simple mass to charge relation.
Unlike their Einsteinian counterpart (i.e. extreme Reissner-Nordstr\"om), these
have nonvanishing horizon surface gravity.Comment: 18 pages, harvmac, 2 figure
Back-reaction effects in acoustic black holes
Acoustic black holes are very interesting non-gravitational objects which can
be described by the geometrical formalism of General Relativity. These models
can be useful to experimentally test effects otherwise undetectable, as for
example the Hawking radiation. The back-reaction effects on the background
quantities induced by the analogue Hawking radiation could be the key to
indirectly observe it. We briefly show how this analogy works and derive the
backreaction equations for the linearized quantum fluctuations in the
background of an acoustic black hole. A first order in hbar solution is given
in the near horizon region. It indicates that acoustic black holes, unlike
Schwarzschild ones, get cooler as they radiate phonons. They show remarkable
analogies with near-extremal Reissner-Nordstrom black holes.Comment: 10 pages, 1 figure; Talk given at the conference ``Constrained
Dynamics and Quantum Gravity (QG05)", Cala Gonone (Italy), September 200
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