Narrow Results

Motivated by the work of Mersini, the particle production related to the tunneling in false vacuum decay is carefully investigated in the thin-wall approximation. It is shown that in this case the particle production is exponentially suppressed even when the momentum is comparable to the curvature scale of the bubble. The number of created particles is ultraviolet finite.

It is shown that, to the lowest order in ℏ, the particle production related to the tunneling that leads to the false vacuum decay is described by the orthogonal part of fluctuation field with respect to the bounce solution. As a simple example the spatially homogeneous tunneling is considered in order to illustrate the consequences coming from such a restriction of the fluctuation field.

The spectrum of created particles during the tunneling process, leading to the decay of a false vacuum state, is studied numerically in the thick-wall approximation. It is shown that in this case the particle production is very intensive for small momenta. The number of created particles is nearly constant n(p)≈1 for 4≤p≤500.

Neglecting the effect of particle production at the moment of bubble nucleation, the spectrum of created particles during the bubble expansion is evaluated in the thin-wall approximation. It is shown that the expanding thin-walled bubble makes the dominant contribution to the particle production.

The probability that a neutral meson π⁰ is produced from vacuum in the presence of a strong and time-varying magnetic field is calculated. Since the π⁰ has zero electric charge, the interaction with the external magnetic field occurs through the magnetic moment of the constituent quark–antiquark pairs. The phenomenological SU(6) quark model is used to build up perturbatively the one-particle neutral meson states in the presence of a static magnetic field. Then, the presence probability is obtained by means of the adiabatic perturbation theory. The mechanism proposed implies that the pion is produced together with another neutral meson. The final result is compared with the π^-–π⁺ pair presence probability in the same time-varying magnetic field. The π^± have almost the same mass of π⁰ but, unlike π⁰, are charged particle so the ratio of the two probabilities gives an order of magnitude of the relative strength of the two effective interactions with the external time depending magnetic field.

In this paper, we study the problem of scalar particle production in external electric field in de Sitter geometry. The total probability is calculated using the previously obtained result in [M. A. Băloi, Mod. Phys. Lett. A29, 1450138 (2014)] for transition amplitude in external electric field on de Sitter space. Then we make a graphical study of the total probability in terms of the ratio mass of the particle/expansion factor. Our results show that the probability depend on the direction in which the particles are emitted and that the probability becomes maximum when particles are emitted on the direction of the electric field. In the Minkowski limit, we obtain that the probability is vanishing.

We consider preheating in models in which the potential for the inflaton is given by a fractional power, as is the case in axion monodromy inflation. We assume a standard coupling between the inflaton field and a scalar matter field. We find that in spite of the fact that the oscillation of the inflaton about the field value which minimizes the potential is anharmonic, there is nevertheless a parametric resonance instability, and we determine the Floquet exponent which describes this instability as a function of the parameters of the inflaton potential.

The centrality dependence of the charged-particle multiplicity densities $(d{N}_{\mathrm{\text{ch}}}/d\eta )$ and transverse energy densities $(d{E}_T/d\eta )$ are investigated using the two-component Glauber approach for broad range of energies in heavy ion collisions at Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC). A comprehensive study shows that the data is well-described within the framework of two-component model which includes the contribution of “soft processes” and “hard processes” for different centrality classes and energies. The data at two different energies are compared by means of the ratio of $d{N}_{\mathrm{\text{ch}}}/d\eta$ (and $d{E}_T/d\eta$) to see the interplay of energy scaling and relative contribution of hard processes.

We consider a homogeneous and isotropic Universe, described by the minisuperspace Lagrangian with the scale factor as a generalized coordinate. We show that the energy of a closed Universe is zero. We apply the uncertainty principle to this Lagrangian and propose that the quantum uncertainty of the scale factor causes the primordial fluctuations of the matter density. We use the dynamics of the early Universe in the Einstein–Cartan theory of gravity with spin and torsion, which eliminates the big-bang singularity and replaces it with a nonsingular bounce. Quantum particle production in highly curved spacetime generates a finite period of cosmic inflation that is consistent with the Planck satellite data. From the inflated primordial fluctuations we determine the magnitude of the temperature fluctuations in the cosmic microwave background, as a function of the numbers of the thermal degrees of freedom of elementary particles and the particle production coefficient which is the only unknown parameter.

The definition of vacuum in curved space–time is a delicate object. With Minkowski-like vacuum definition, the current has a characteristic behavior in Robertson–Walker space–time. In this work we study the behavior of Dirac current in a de Sitter space–time. The rapid oscillations of current is observed with respect to time and indicate vigorous instability in initial vacuum and is interpreted as vigorous particle production.

In this paper, we investigate the problem of fermion creation inside a three-dimensional cubic box. We present an appropriate wave function which satisfies the Dirac equation in this geometry with MIT bag model boundary condition. We consider the box with oscillating walls and introduce the time evolution of the quantized field by expanding it over the instantaneous basis. We explain how we can obtain the average number of particles created. In this regard, we find the Bogoliubov coefficients. We consider an oscillation and determine the coupling conditions between different modes that can be satisfied depending on the cavity's spectrum. Assuming the parametric resonance case we obtain an expression for the mean number of created fermions in each mode of an oscillation and their dynamical Casimir energy.

A gradual transition to the reflecting scattering mode developing already at the LHC energies is affecting multiparticle production dynamics, in particular, relation of the centrality with the impact parameter values of pp-collisions. We discuss the issues in the framework of the geometrical picture for the multiparticle production processes proposed by Chou and Yang. We consider effects of reflective scattering mode presence for the inclusive cross-sections.

We study the theory of interaction between charged scalar field and Maxwell field in de Sitter background. Solving the equation of interacting fields, we define the in–out fields as asymptotic free fields and construct the reduction formalism for scalar field. Then we derive the perturbation expansion of the scattering operator. The first-order transition amplitudes corresponding to particle production from de Sitter vacuum and pair production in an external field are analyzed. We show that all these effects are important only in strong gravitational fields and vanish in the flat limit.

We study particle production of coherently oscillating inflaton in semiclassical theory of gravity by representing inflaton in coherent and squeezed state formalisms. A comparative study of the inflaton in classical gravity with coherent state inflaton in semiclassical gravity is also presented.

In this work we investigate matter creation in the context of two types of varying speed of light (VSL) cosmologies. We write the energy conservation law arising from Einstein equations for a Friedmann–Robertson–Walker (FRW) line element in a flat universe, solve the field equations and study how particles are created as c changes with cosmic epoch. We calculate the "adiabatic" particle creation rate, the total number of particle as a function of time and find the constrains imposed by the second law of thermodynamics upon the models.

Here we study an anisotropic model of the universe with constant energy per particle. A decaying cosmological constant and particle production in an adiabatic process are considered as the sources for the entropy. The statefinder parameters {r, s} are defined and their behavior are analyzed graphically in some cases.

The complex time WKB approximation is an effective tool in studying particle production in curved space–time. We use it in this work to understand the formation of classical condensate in expanding de Sitter space–time. The CWKB leads to the emergence of thermal spectrum that depends crucially on horizons (as in de Sitter space–time) or observer dependent horizons (as in Rindler space–time). A connection is sought between the horizon and the formation of classical condensate. We concentrate on de Sitter space–time and study the cosmological perturbation of k = 0 mode with various values of m/H₀. We find that, for a minimally coupled free scalar field for , the one-mode occupation number grows more than unity soon after the physical wavelength of the mode crosses the Hubble radius and soon after that, diverges as , where . The results substantiate the previous works in this direction. We also find the correct oscillation and behavior of N(z) at small z from a single expression using CWKB approximation for various values of m/H₀. We also discuss decoherence in relation to the formation of classical condensate. We further find that the squeezed state formalism and CWKB method give identical results.

The thermodynamics of cosmological matter creation has been extensively investigated in the literature. In the context of general relativity, the particle production in the cosmological models is due to mechanisms such as an imperfect fluid with bulk viscosity or the decaying vacuum. Another interesting proposal is matter creation in cosmologies with variation of fundamental constants. In this work, we study the nonlinearity of the electrodynamics as a source of matter creation in cosmological models with flat Friedmann–Robertson–Walker (FRW) line geometry. We write the energy conservation law arising from Einstein field equations with cosmological term Λ, solve the field equations, and study how particles are created as the magnetic field B changes with cosmic epoch. We obtain solutions for the adiabatic particle creation rate, the total number of particles, and the scale factor as a function of time in three cases: Λ = 0, Λ = constant and Λ ∝ H² (cosmological term proportional to the Hubble parameter). We find the constraints imposed by the second law of thermodynamics upon the cosmological solutions.

We investigate the implications of a minimal top down model on cosmic ray particle production from super heavy vector boson annihilation with subsequent pseudo-scalar boson decay. Super heavy particles are assumed to exist according to a homogeneous distribution. Besides the particle production via decay, the thermal momentum distribution of the initial state as well as expansion effects and cosmic temperature corrections are considered in the context of a Friedmann–Robertson–Walker universe.

We investigate the particle production in a toroidally compactified space–time due to the expansion of a Friedmann cosmological model in ℝ³ × S¹ outside a U(1) local cosmic string. The case of a Friedmann space–time is also investigated where torsion is incorporated in the connection. We present a generalization to toroidal compactification of p extra dimensions, where the topology is given by ℝ³ × T^p. Some implications are presented and discussed. Besides the dynamics of space–time, we investigate in detail the physical consequences of the topological transformations.