39,063 research outputs found
Gravitational collapse in anti-de Sitter space-time
No full textWe study the semiclassical evolution of a self-gravitating thick shell in anti-de Sitter space-time. We treat the matter on the shell as made of quantized bosons and evaluate the back-reaction of the loss of gravitational energy which is radiated away as a non-adiabatic effect. A peculiar feature of anti-de Sitter is that such an emission also occurs for large shell radius, contrary to the asymptotically flat case. © 2003 Published by Elsevier B.V
Effective action and thermodynamics of radiating shells in general relativity
No full textAn effective action is obtained for the area and mass aspect of a thin shell of radiating self-gravitating matter. On following a mini-superspace approach, the geometry of the embedding space-time is not dynamical but fixed to be either Minkowski or Schwarzschild inside the shell and Vaidya in the external space filled with radiation. The Euler-Lagrange equations of motion are discussed and shown to entail the expected invariance of the effective Lagrangian under time reparametrization. They are equivalent to the usual junction equations and suggest a macroscopic quasi-static thermodynamic description. © 1999 The American Physical Society
Thermodynamics for radiating shells in anti-de Sitter space-time
No full textA thermodynamical description for the quasi-static collapse of radiating, self-gravitating spherical shells of matter in anti-de Sitter space-time is obtained. It is shown that the specific heat at constant area and other thermodynamical quantities may diverge before a black hole has eventually formed. This suggests the possibility of a phase transition occurring along the collapse process. The differences with respect to the asymptotically flat case are also highlighted. © 2003 Published by Elsevier Science B.V
Nonminimally coupled scalar fields in homogeneous universes
No full textThe equations governing the evolution of non-minimally coupled scalar matter and the scale factor of a Robertson-Walker universe are derived from a minisuperspace action. As for the minimally coupled case, it is shown that the entire semiclassical dynamics can be retrieved from the Wheeler-DeWitt equation via the Born-Oppenheimer reduction, which properly yields the (time-time component of the) covariantly conserved energy-momentum tensor of the scalar field as the source term for gravity. However, for a generic coupling, the expectation value of the operator which evolves the matter state in time is not equal to the source term in the semiclassical Einstein equation for the scale factor of the universe and the difference between these two quantities is related to the squeezing and quantum fluctuations of the matter state. We also argue that matter quantum fluctuations become relevant in an intermediate regime between quantum gravity and semiclassical gravity and study several cases in detail. © 2000 The American Physical Society
Gravitational collapse of a shell of quantized matter
No full textThe semiclassical collapse, including lowest-order back-reaction, of a thin shell of self-gravitating quantized matter is illustrated. The conditions for which self-gravitating matter forms a thin shell are first discussed and an effective Lagrangian for such matter is obtained. The matter-gravity system is then quantized, the semiclassical limit for gravitation is taken and the method of adiabatic invariants is applied to the resulting time-dependent matter Hamiltonian. The governing equations are integrated numerically, for suitable initial conditions, in order to illustrate the effect of back-reaction, due to the creation of matter, in slowing down the collapse near the horizon
Gravitational collapse of a radiating shell
No full textWe study the collapse of a self-gravitating and radiating shell of bosonic matter. The matter constituting the shell is quantized and the construction is viewed as a semiclassical model of possible black hole formation. It is shown that the shell internal degrees of freedom are excited by the quantum nonadiabaticity of the collapse and, consequently, on coupling them to a massless scalar field, the collapsing matter emits a burst of coherent (thermal) radiation. The back reaction on the trajectory is also estimated. ©2001 The American Physical Society
Quantum Gravity Effects in Black Holes at the LHC
No full textWe study possible back-reaction and quantum gravity effects in the evaporation of black holes which could be produced at the LHC through a modification of the Hawking emission. The corrections are phenomenologically taken into account by employing a modified relation between the black hole mass and temperature. The usual assumption that black holes explode around TeV is also released, and the evaporation process is extended to (possibly much) smaller final masses. We show that these effects could be observable for black holes produced with a relatively large mass and should therefore be taken into account when simulating micro-black hole events for the experiments planned at the LHC
Classical dynamics and stability of collapsing thick shells of matter
No full textWe study the collapse towards the gravitational radius of a macroscopic spherical thick shell surrounding an inner massive core. This overall electrically neutral macroshell is composed by many nested delta-like massive microshells which can bear non-zero electric charge, and a possibly non-zero cosmological constant is also included. The dynamics of the shells is described by means of Israel's (Lanczos) junction conditions for singular hypersurfaces and, adopting a Hartree (mean field) approach, an effective Hamiltonian for the motion of each microshell is derived which allows to check the stability of the matter composing the macroshell. We end by briefly commenting on the quantum effects which may arise from the extension of our classical treatment to the semiclassical level
Radion Induced Spontaenous Baryogenesis
No full textWe describe a possible scenario for the baryogenesis arising when matter is added on the branes of a Randall-Sundrum model with a radion stabilizing potential. We show that the radion field can naturally induce spontaneous baryogenesis when the cosmological evolution for the matter on the branes is taken into account
Charged black hole remnants at the LHC
No full textWe investigate possible signatures of long-lived (or stable) charged black holes at the Large Hadron Collider. In particular, we find that black hole remnants are charac- terised by quite low speed. Due to this fact, the charged remnants could, in some cases, be very clearly distinguished from the background events, exploiting d E /d X measure- ments. We also compare the estimate energy released by such remnants with that of typical Standard Model particles, using the Bethe–Bloch formula
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