Creation Of Scalar Particles Research Articles

Cosmological particle creation using an equal-time Wigner formalism

It is well known that the expansion of the universe can create particles. However, due to ambiguities when defining particles during the expansion, there are still debates about how to choose vacuum and particle states. To clarify how particles are produced in an expanding universe, we study the creation of real scalar particles in flat Friedmann-Lemaître-Robertson-Walker spacetimes by using a recently developed equal-time Wigner formalism. By comparing this quantum kinetic formalism with the standard Bogoliubov approach, we make a natural definition of a particle number in terms of kinetic phase-space functions, which we then compare with common adiabatic particle numbers. With inspiration from flat spacetime QED, we perform numerical calculations and discuss the interpretation of the particle numbers in terms of a hypothetical switch-off in the expansion rate. Finally, we consider how this interpretation is affected by regularization. Published by the American Physical Society 2024

Scalar particle creation in a quantum gravity perspective

In gravity’s rainbow perspective (GRP), we intend to analyze the particle production coming from electromagnetic and gravitational fields of the spin-0 (scalar) particles. In accordance with this purpose, a constant external electric field is taken into account together with a rainbow metric with non-isotropic expansion. We obtain the number density of the created Klein–Gordon particles in terms of particle mass, particle charge, external electric field parameter, rainbow functions and particle momentum by using the Bogoliubov transformation method. We display that the number density of the created scalar particles becomes thermal both in the absence of the external constant electric field and in the massless case. We also provide a graphical analysis to scrutinize the particle creation process in the GRP. In this context, it has been observed that rainbow functions drastically alter the number density of the created scalar particles.

Particle production in accelerated thin bubbles

We investigate the creation of scalar particles inside a region delimited by a bubble which is expanding with non-zero acceleration. The bubble is modelled as a thin shell and plays the role of a moving boundary, thus influencing the fluctuations of the test scalar field inside it. Bubbles expanding in Minkowski spacetime as well as those dividing two de Sitter spacetimes are explored in a unified way. Our results for the Bogoliubov coefficient βk when considering only the squeezing effects show that in all cases the creation of scalar particles decreases with the mass, and is much more significant in the case of nonzero curvature. They also show that the dynamics of the bubble and its size are relevant for particle creation, but in the dS-dS case the combination of both effects leads to a behaviour different from that of Minkowski space-time, due to the presence of a length scale (the Hubble radius of the internal geometry).

Noncommutative scalar field in de Sitter space–time and pair creation process

In this work, we address the process of pair creation of scalar particles in [Formula: see text] de Sitter space–time in presence of a constant electromagnetic field by applying the noncommutativity on the scalar field up to first-order in [Formula: see text]. We calculate the density of particles created in the vacuum by the mean of the Bogoliubov transformations. In contrast to a previous result, we show that noncommutativity contributes to the pair creation process. We find that the noncommutativity plays the same role of chemical potential and gives an important interest for studies at high energies.

Pair creation in curved Snyder space

We study the problem of pair creation of scalar particles by an electric field in curved Snyder space. We find exact solutions for the Klein–Gordon equation with a constant electric field in terms of hypergeometric functions. Then we calculate the pair creation probability and the number of created pairs of particles through Bogoliubov transformation technique.

Phenomenology of cosmological particle creation, Dirac sea and all that

We constructed the conformally invariant model for scalar particle creation induced by strong gravitational fields. Starting from the “usual” hydrodynamical description of the particle motion written in the Eulerian coordinates we substituted the particle number conservation law (which enters the formalism) by “the particle creation law”, proportional to the square of the Weyl tensor (following the famous result by Ya.B. Zel’dovich and A.A. Starobinsky). Then, demanding the conformal invariance of the whole dynamical system, we have got both the (Weyl)-conformal gravity and the Einstein-Hilbert gravity action integral with dilaton field. Thus, we obtained something like the induced gravity suggested first by A.D. Sakharov. It is shown that the resulting system is self-consistent. We considered also the vacuum equations. It is shown that, beside the “empty vacuum”, there may exist the “dynamical vacuum”, which is nothing more but the Dirac sea. The latter is described by the unexpectedly elegant equation which includes both the Bach and Einstein tensors and the cosmological terms. All the vacuum solutions violate the local conformal invariance.

Gravitational particle creation in a stiff matter dominated universe

A scenario for gravitational particle creation in a stiff matter dominated flat Friedmann-Robertson-Walker universe is presented. The primary creation of scalar particles is calculated using quantum field theory in curved spacetime and it is found to be strongly dependent on the scalar mass and the expansion parameter of the universe. The particle creation is most effective for a very massive scalar field and large expansion parameter. We demonstrate the phenomenon by applying it to cosmological toy model scenario, where secondary particles are created by the scalar field decay.

Toward Understanding the Conformal Gravity

We constructed the conformally invariant model for scalar particle creation induced by strong gravitational fields. Starting from the usual hydrodynamic description of the particle motion written in the Eulerian coordinates, we substituted the particle number conservation law (which enters the formalism) by the particle creation law, proportional to the square of the Weyl tensor, following the famous result by Ya. B. Zel’dovich and A. A. Starobinsky. Then, demanding the conformal invariance of the whole dynamical system, we have got both the Weyl-conformal gravity and the Einstein–Hilbert dilaton gravity action integral. Thus, we obtained something like the induced gravity suggested first by A. D. Sakharov. It is shown that the resulting system is self-consistent.

Particle creation in bouncing cosmologies

We investigate scalar particle creation in a set of bouncing models where the bounce occurs due to quantum cosmological effects described by the Wheeler-DeWitt equation. The scalar field can be either conformally or minimally coupled to gravity, and it can be massive or massless, without self interaction. The analysis is made for models containing a single radiation fluid, and for the more realistic case of models containing the usual observed radiation and dust fluids, which can fit most of the observed features of our Universe, including an almost scale invariant power spectrum of scalar cosmological perturbations. In the conformal coupling case, the particle production is negligible. In the minimal coupling case, for massive particles, the results point to the same physical conclusion within observational constraints: particle production is most important at the bounce energy scale, and it is not sensitive neither to its mass nor whether there is dust in the background model. The only caveat is the case where the particle mass is larger than the bounce energy scale. On the other hand, the energy density of produced massive particles depend on their masses and the energy scale of the bounce. For very large masses and deep bounces, this energy density may overcome that of the background. In the case of massless particles, the energy density of produced particles can become comparable to the background energy density only for bounces occurring at energy scales comparable to the Planck scale or above, which lies beyond the scope of this paper: we expect that the simple Wheeler-DeWitt approach we are using should be valid only at scales some few orders of magnitude below the Planck energy. Nevertheless, in the case in which dust is present, there is an infrared divergence, which becomes important only for scales much larger than today's Hubble radius.

Particle creation phenomenology, Dirac sea and the induced Weyl and Einstein-dilaton gravity

We constructed the conformally invariant model for scalar particle creation induced by strong gravitational fields. Starting from the “usual” hydrodynamical description of the particle motion written in the Eulerian coordinates we substituted the particle number conservation law (which enters the formalism) by “the particle creation law”, proportional to the square of the Weyl tensor (following the famous result by Ya.B. Zel'dovich and A.A. Starobinsky). Then, demanding the conformal invariance of the whole dynamical system, we have got both the (Weyl)-conformal gravity and the Einstein-Hilbert gravity action integral with dilaton field. Thus, we obtained something like the induced gravity suggested first by A.D. Sakharov. It is shown that the resulting system is self-consistent. We considered also the vacuum equations. It is shown that, beside the “empty vacuum”, there may exist the “dynamical vacuum”, which is nothing more but the Dirac sea. The latter is described by the unexpectedly elegant equation which includes both the Bach and Einstein tensors and the cosmological terms.

Cosmological particle creation in conformal gravity

We constructed conformally invariant model for scalar particle creation induced by strong gravitational fields. Starting from usual hydrodynamical de- scription of particle motion written in Eulerian coordinates we substituted particle number conservation law (which enters formalism) by the particle creation law, proportional to square of Weyl tensor (following famous result by Ya. B. Zel'dovich and A. A. Starobinsky). Then, demanding conformal invariance of whole dynamical system, we have got both (Weyl)-conformal gravity and Einstein-Hilbert-dilaton gravity action integral. Thus, we obtained something like induced gravity suggested first by A. D. Sakharov. It is shown that resulting system is self-consistent. Some future developments of theory are discussed in concluding Chapter.

On the scalar particle creation by electromagnetic fields in Robertson–Walker spacetime

In the present paper, we obtained the scalar particle creation number density by using the Klein–Gordon equation coupled to the electromagnetic fields in the Robertson–Walker spacetime with the help of the Bogoliubov transformation method. We analyzed the resulting expression for the effect of a time-dependent electric field and a constant magnetic field on the particle production rate and found that the strong time-dependent electric field amplifies the particle creation and the magnetic field reduces the rate, in accordance with the previous findings.

Pair Creation of Scalar Particles in Intense Bichromatic Laser Fields

The creation of scalar particle pairs due to the decay of a highly energetic gamma quantum traveling in a laser field comprising two independent modes is considered. Employing the framework of strong-field scalar QED, detailed calculations aiming at two different aspects of the process are presented. We first investigate interference effects between reaction channels with absorption of different numbers of laser photons with commensurate frequency and demonstrate the possibility of coherent phase control. Then we study numerically a scheme of dynamical assistance, which offers prospects for an experimental realization of a Schwinger-like pair production process.

Influence of a minimal length on the creation of scalar particles

In this paper we have studied the problem of scalar particles pair creation by an electric field in the presence of a minimal length. Two sets of exact solutions for the Klein Gordon equation are given in momentum space. Then the canonical method based on Bogoliubov transformation connecting the "in" with the "out" states is applied to calculate the probability to create a pair of particles and the mean number of created particles. The number of created particles per unit of time per unit of length, which is related directly to the experimental measurements, is calculated. It is shown that, with an electric field less than the critical value, the minimal length minimizes the particle creation. It is shown, also, that the limit of zero minimal length reproduces the known results corresponding to the ordinary quantum fields.

Particle creation in a $$f(R)$$ f ( R ) theory with cosmological constraints

In this paper we study the creation of super-massive real scalar particles in the framework of a $f(R)=R-\beta/R^n$ modified gravity theory, with parameters constrained by observational data. The analysis is restrict to a homogeneous and isotropic flat and radiation dominated universe. We compare the results to the standard Einstein gravity with cosmological constant ($\Lambda CDM$ model), and we show that the total number density of created particles in the $f(R)$ model is very close to the standard case. Another interesting result is that the spectrum of created particles is $\beta$ independent at early times.

On creation of scalar particles with Gauss-Bonnet type coupling to curvature in Friedmann cosmological models

Calculations are presented for creation of massive and massless scalar particles coupled to Gauss-Bonnet type curvature in Friedmann cosmological models. It has been shown that, for fields of mass~$m$, the effect of the coupling parameter $\zeta$ with the Gauss-Bonnet invariant is insignificant if $\zeta m^2 \ll 1 $. In all cases under consideration, the created particle number is compatible by order of magnitude with the number of causally disconnected space-time regions by the Compton time, corresponding $1/m$ or $\sqrt{\zeta}$.

Effect of electromagnetic fields on the creation of scalar particles in a flat Robertson–Walker space-time

The influence of electromagnetic fields on the creation of scalar particles from vacuum in a flat Robertson–Walker space-time is studied. The Klein–Gordon equation with varying electric field and constant magnetic one is solved. The Bogoliubov transformation method is applied to calculate the pair creation probability and the number density of created particles. It is shown that the electric field amplifies the creation of scalar particles while the magnetic field minimizes it.

Pair creation in boost-invariantly expanding electric fields and two-particle correlations

Pair creation of scalar particles in a boost-invariant electric field which is confined in the forward light cone is studied. We present the proper-time evolution of momentum distributions of created particles, which preserve the boost invariance of the background field. The two-particle correlation of the created particles is also calculated. We find that long-range rapidity correlations may arise from the Schwinger mechanism in the boost-invariant electric field.

Non-commutative gauge gravity: second-order correction and scalar particle creation

We construct a non-commutative gauge theory for a charged scalar field and verify its invariance under local Poincaré and general coordinate transformations. We derive a general Klein–Gordon equation up to the second order of the non-commutativity parameter using the general modified field equation. As an application, we choose the Bianchi I universe and use the Seiberg–Witten maps to obtain the deformed non-commutative metric and study a particle production process. We show that non-commutativity plays the same role as an electric field, gravity and chemical potential.

Low-energy effective action in nonperturbative electrodynamics in curved space-time

We study the heat kernel for the Laplace-type partial differential operator acting on smooth sections of a complex spin-tensor bundle over a generic n-dimensional Riemannian manifold. Assuming that the curvature of the U(1) connection (that we call the electromagnetic field) is constant, we compute the first two coefficients of the nonperturbative asymptotic expansion of the heat kernel which are of zero and the first order in Riemannian curvature and of arbitrary order in the electromagnetic field. We apply these results to the study of the effective action in nonperturbative electrodynamics in four dimensions and derive a generalization of the Schwinger’s result for the creation of scalar and spinor particles in electromagnetic field induced by the gravitational field. We discover a new infrared divergence in the imaginary part of the effective action due to the gravitational corrections, which seems to be a new physical effect.