Creation Of Scalar Particles Research Articles

Particle creation and destruction of quantum coherence by topological change

The possibility is considered that changes of spatial topology occur as tunneling events in quantum gravity. Creation of scalar and spinor particles during these tunneling transitions is studied. The relevant formalism based on the euclidean Schrödinger equation and coherent state representation is developed. This formalism is illustrated in a two-dimensional example. It is argued that the particle creation during the topological changes induces the loss of quantum coherence. The particle creation is calculated in the case of O(4)-invariant background euclidean four-dimensional metrics. This calculation is used for estimating the loss of quantum coherence. An upper limit on the rate of the topological changes, A⪅10 −17M Pl 4 , is derived from the observation of K 0− K 0 oscillations.

Particle creation by a self-coupled scalar field.

The creation of the quanta of a self-coupled scalar field due to the time dependence of the classical scalar field is investigated. In general, a time-dependent solution of the classical field equation leads, in quantum field theory, to the creation of scalar particles. This effect tends to dissipate the energy of the classical field. A formalism for calculating the rate of this particle creation is developed and applied to several model self-coupled scalar field theories. The application of the results to inflationary cosmology is discussed.

Particle and energy creation by moving mirrors.

We consider the creation of massless scalar particles by a moving mirror in two-dimensional space-time. The correct form for the Bogoliubov coefficients is given and their high-frequency behavior is investigated. We next consider the energy radiated by the mirror and show that this is related in the expected way to the number of particles produced only if a particular condition on the trajectory is fulfilled. The well-known moving-mirror formula of Fulling and Davies, which gives the radiated energy as a functional of the mirror trajectory, is here rederived from the Bogoliubov transformation, without recourse to regularization. Finally we analyze the response of a particle detector, and solve the paradox of how the detector can respond even when the mirror is radiating no energy.

Scalar Field Condensation in a Gravitational Field of a Massive Object

It is shown that scalar particle creation in the gravitational field of a massive object could occur even if the radius of the object is larger than the Schwarzschild radius. Scalar field condensation could change the metric drastically, and decrease the observable mass of the system.

Feynman propagators and particle creation in linearly expanding Bianchi type-I universes

Scalar particle creation in the linearly expanding Bianchi type-I universes is studied using the Feynman propagator technique. Explicit expressions for the propagators corresponding to an arbitrary "in" vacuum and the "out" vacuum defined by the WKB positive-frequency solutions are derived. The initial conditions are then singled out by requiring the square integrability of the analytically continued kernels of the propagators considered. It is shown that for each particular model there is only one Riemannian kernel which satisfies this condition. Furthermore, it is proved that all the kernels selected this way admit a well-defined path-integral representation defined on the Riemannian domains of physically allowed values of coordinates. This result confirms the assumption of Chitre and Hartle that the propagator they found in the isotropic model (which is precisely that singled out by the square-integrability condition) can be represented by a path integral defined on the domain to the future of the initial singularity. The initial conditions corresponding to the selected propagators are analyzed. It is shown that they give rise to the creation of pairs with spectrum, which at high energies resembles that of blackbody radiation in one, two, or three directions, depending on the background geometry. Finally, the conceptual and technical problems associated with the complexified spacetime path-integral method, as applied to cosmological models, are discussed.

On the Creation of Scalar Particles in an Early Stage of the Friedmann Closed-Universe

On the Creation of Scalar Particles in an Early Stage of the Friedmann Closed-Universe

Creation of particles by shell-focusing singularities

The creation of massless scalar particles in asymptotically flat spacetimes containing shell-focusing naked singularities which evolve from nonsingular initial data is studied. In the case where the singularity is marginally naked, i.e., its Cauchy horizon coincides with the event horizon, we are able to compute the spectrum of created particles by Hawking's method. The spectrum of particles is no longer thermal, but can be expressed as a quasithermal spectrum with a frequency-dependent temperature. In the high-frequency limit the effective temperature approaches a constant value greater than the Hawking temperature. In the more general case where the Cauchy horizon and event horizon do not coincide, we calculate the expectation value of the stress-energy tensor of the scalar field in the two-dimensional spacetimes obtained by suppressing the spherical coordinates. In all cases the energy flux along the Cauchy horizon diverges in a positive sense. This strongly suggests that the metric's back-reaction to the flux of created particles will prevent the formation of naked shell-focusing singularities.

Statistical Effect of Interactions on Particle Creation in Expanding Universe

The statistical effect of interactions which drives many-particle systems toward equilibrium is expected to change the qualitative and quantitative features of particle creation in expanding universe. To investigate this problem a simplified model called the finite-time reduction model is formulated and applied to the scalar particle creation in the radiation dominant Friedmann universe. The number density of created particles and the entropy production due to particle creation are estimated. The result for the number density is compared with that in the conventional free field theory. It is shown that the statistical effect increases the particle creation and lengthens the active creation period. As for the entropy production it is shown that it is negligible for scalar particles in the Friedmann universe.

Cosmological scalar-particle creation rate

We consider the scalar-particle creation rate and its energy distribution in a spatially flat expanding universe, using the quantum equivalence principle, to make the field decomposition into its positive- and negative-frequency parts over each Cauchy surface, up to the second order of an expansion in powers of the Hubble coefficient. The particle flux is evaluated in the hot big-bang model and compared with the experimental data.

Application of the propagator method to pair production in the Robertson-Walker metric

The method suggested earlier is applied to the problem of pair production in the Robertson-Walker universes with scale factorstλ, λ⩽1. The method is based on the postulate that the positive-frequency wave functions must be propagated forward in time by the causal propagator. The causal propagator is defined as the Green's function with minimal divergences on the “Euclidean section” of the space-time. The results for the casea(t)=t coincide with those of Chitre and Hartle. In the casea(t)=ttλ, λ<1, it is shown that the present approach predicts creation of conformal invariant massless scalar particles. It is demonstrated that the conformal transformation method gives the same predictions provided that the global properties of the space-time are taken into consideration.

Problems of classical and quantum-gravitational collapse X. Creation of massless scalar particles by the torsion field

The effect of the creation of massless scalar particles by a cosmological torsion field is considered. It is shown that the particles produced make an initially isotropic universe anisotropic.

On the Creation of Scalar Particles in Some Anisotropic Universe

Because of an importance of the particle creation (especially, its possible fulfilment of the black-body law with a definite temperature) in an early universe to various other cosmological problems, we study how the creation of scalar particles occurs in the Bianchi­ type I anisotropic universe adopted in our previous works on the quantized scalar field. It is shown that, as in a special isotropic case dealt with in recent papers, the creation may occur at the sacrifice of the requirement that the quantization procedure should reproduce the usual theory for a free field in the limit when the anisotropic universe changes into the Minkowski space-time. It is further shown that the creation occurs in accordance with the black-body law only in a 2-dimensional hyper-surface relating to the anisotropic cosmic expansion, provided that we fix two arbitrary constants appearing in a general expression for the Feynman propagator in terms of a procedure similar to that in the isotropic case. A speculation on the isotropization of our model-universe is also made from the standpoint of seeking the attainment of the thermal equilibrium in the whole universe.

Creation of particles by singularities in asymptotically flat spacetimes

The creation of massless scalar particles by naked singularities in asymptotically flat spacetimes is investigated within the geometrical-optics approximation. To avoid the need to impose boundary conditions on the singularity, we consider models in which a curvature singularity arises at a finite time in the past. We consider two particular types of models. One is a shell-crossing singularity formed in the gravitational collapse of a dust cloud. The energy flux of the created particles remains finite up to the time of formation of the singularity. In the particular case when the singularity forms on the event horizon, geometrical optics yields the exact flux, in spite of the high curvature of spacetime. The radiation obtained is identical to the thermal Hawking radiation emitted by black holes. The other models considered are those of charged shells for which the charge exceeds the mass. If these shells collapse to form naked singularities (which is possible if the proper mass is negative or if Einstein's equations are not imposed), an infinite flux of created particles results. In the cases examined here, the flux is negative for two-dimensional models and for the minimally coupled scalar field in four-dimensional models, whereas it is positive for the conformally coupled scalar field in four-dimensional models. In either case, the back reaction from particle creation will be large and may prevent formation of a naked singularity.

On the Creation of Scalar Particles in an Isotropic Universe

On the Creation of Scalar Particles in an Isotropic Universe

Scalar particle creation in an anisotropic universe

The problem of quantized scalar field creation in an anisotropic spatially homogeneous background universe is reexamined from a Schr\"odinger-picture point of view. For each mode a complete set of orthonormal wave functions, ${\ensuremath{\psi}}_{N}$, is obtained using the method of Salusti and Zirilli. These wave functions are valid at all times even if there is an initial cosmological singularity and depend only on the solution of the classical equation of motion. The wave functions are fixed completely by requiring the classical solution to have positive-frequency WKB form when the universe reaches the stage of adiabatic expansion. These wave functions are eigenfunctions of a conserved number operator which has the usual particle interpretation in the adiabatic regime. An intitial state near the singularity is chosen as a superposition of the wave functions, ${\ensuremath{\psi}}_{N}$, and the particle number in the adiabatic regime is calculated. For plane-wave initial states, which follow the classical behavior near the singularity, the final particle number depends only on the parameters of the initial wave packet. For an initial state which instantaneously diagonalizes the Hamiltonian, an (arbitrary) initial time must be chosen. If the mode in question is in the adiabatic regime at that time almost no particle creation occurs. If it is not adiabatic, creation occurs and becomes infinite if the initial time is taken to be that of the singularity. This creation is a consequence of the failure of particle number to be well defined in this regime. Comparisons with other particle-creation studies are made.