The effects of the gravitational back reaction of cosmological perturbations are investigated in a cosmological model where the universe is dominated by phantom energy. We assume a COBE normalized spectrum of cosmological fluctuations at the present time and calculate the effective energy–momentum tensor of the gravitational back-reactions of cosmological perturbations whose wavelengths at the time when the back-reactions are evaluated are larger than the Hubble radius. Our results reveal that the effects of gravitational back-reactions will counteract that of phantom energy sooner or later and can become large enough to terminate the phantom dominated phase before the big rip as the universe evolves. This arises because the phase space of infrared modes grows very rapidly as we come close to the big rip.
We study kinetic master equations for chemical reactions involving the formation and the natural decay of unstable particles in a thermal bath. We consider the decay channel of one into two particles and the inverse process, fusion of two thermal particles into one. We present the master equations for the evolution of the density of the unstable particles in the early Universe. We obtain the thermal invariant reaction rate using as an input the free space (vacuum) decay time and show the medium quantum effects on pi + pi rho reaction relaxation time. As another laboratory example we describe the K + K phi process in thermal hadronic gas in heavy-ion collisions. A particularly interesting application of our formalism is the pi(0) gamma + gamma process in the early Universe. We also explore the physics of pi(+/-) and mu(+/-) freeze-out in the Universe.
I study a model which describes the birth of the universe using a global topological phase transition with a complex manifold where the time, τ, is considered as a complex variable. Before the big bang τ is a purely imaginary variable so that the space can be considered as Euclidean. The phase transition from a pre-inflation to inflation is examined by studying the dynamical rotation of the time on the complex plane. Back-reaction effects are exactly calculated using Relativistic Quantum Geometry.
We present a family of algorithms for the fast determination of reaction paths and barriers in phase space and the computation of the corresponding rates. The method requires that reaction times be large compared to the microscopic time, irrespective of the origin-energetic, entropic, cooperative-of the time scale separation. It lends itself to temperature cycling as in simulated annealing and to activation-relaxation routines. The dynamics is ultimately based on supersymmetry methods used years ago to derive Morse theory. Thus, the formalism automatically incorporates all relevant topological information.
One-dimensional reaction–diffusion systems are mapped through a similarity transformation onto integrable (anda priorinonstochastic) quantum chains. Time-dependent properties of these chemical models can then be found exactly. The reaction–diffusion processes related to free fermion systems with site-independent interactions are classified. The time-dependence of the mean particle density is calculated. Furthermore, new integrable stochastic processes related to the Heisenberg XXZ chain are identified and the relaxation times for the particle density and density correlation for these systems are found.
The leading order correction to the metric of a Schwarzschild black hole, due to the back reaction of infalling fermionic matter fields, is shown to produce a shift of the event horizon such that particles that would constitute Hawking radiation at late retarded times are now trapped. Fermionic field operators associated with infalling and outgoing modes at the horizon behave canonically in the semiclassical approximation. They are, however, shown to satisfy a nontrivial exchange algebra given in terms of the back reaction, when the shift is ''quantized'' by means of correspondence. The consequent exchange algebra for bilinear fermionic densities is also obtained. [S0556-2821(97)01720-7]. PACS number(s): 04.70.Dy, 04.62.+v.
We discuss modifications of the thermal dark matter (DM) relic abundances in stringy cosmologies with D-particle space–time foamy backgrounds. As a result of back-reaction of massive DM on the background space–time, owing to its interaction with D-particle defects in the foam, quantum fluctuations are induced in the space–time metric. We demonstrate that these lead to the presence of extra source terms in the Boltzmann equation used to determine the thermal dark matter relic abundances. The source terms are determined by the specific form of the induced metric deformations; the latter depend on the momentum transfer of the DM particle during its interactions with the D-particle defects and so are akin to Finsler metrics. In the case of low string scales, arising from large extra dimensions, our results may have phenomenological implications for the search of viable supersymmetric models.
We analyze the effects of the back reaction due to a conformal field theory (CFT) on a black hole spacetime with negative cosmological constant. We study the geometry numerically obtained by taking into account the energy momentum tensor of CFT approximated by a radiation fluid. We find a sequence of configurations without a horizon in thermal equilibrium (CFT stars), followed by a sequence of configurations with a horizon. We discuss the thermodynamic properties of the system and how back reaction effects alter the space-time structure. We also provide an interpretation of the above sequence of solutions in terms of the AdS/CFT correspondence. The dual five-dimensional description is given by the Karch-Randall model, in which a sequence of five-dimensional floating black holes followed by a sequence of brane localized black holes correspond to the above solutions.
In the context of the semiclassical treatment of the Hawking radiation, we prove the universality of the reduced canonical momentum for the system of a massive shell self-gravitating in a spherical gravitational field within the Painleve family of gauges. We show that one can construct modes which are regular on the horizon both by considering as a Hamiltonian the exterior boundary term and by using as a Hamiltonian the interior boundary term. The late-time expansion is given in both approaches and their time Fourier expansion is computed to reproduce the self-reaction correction to the Hawking spectrum.