Fifty years of the calculation of the density of particles created in the early Friedmann Universe

Particle creation in the early Universe: achievements and problems

Results on particle creation from vacuum by the gravitational field of the expanding Friedmann Universe are presented. Finite results for the density of particles and the energy density for created particles are given for different exact solutions for different regimes of the expansion of the Universe. The results are obtained as for conformal as for nonconformal particles. The hypothesis of the origination of visible matter from the decay of created from vacuum superheavy particles identified with the dark matter is discussed.

Stable Cosmic Time Crystals

Cosmological time crystals are created when a scalar field moves periodically through phase space in a spatially flat Friedmann-Robertson-Walker spacetime due to the presence of a limit cycle. All such cosmological time crystals in the literature suffer from gradient instabilities occurring at Null Energy Condition violating phases where the square sound speed for cosmological perturbations becomes negative. Here we present stable cosmological time crystals. Our analysis suggests this new form of scalar matter--cosmic time crystals--may be considered as a physically viable cosmological matter …

Particle creation in the oscillatory phase of inflaton

A thermal squeezed state representation of inflaton is constructed for a flat Friedmann-Robertson-Walker background metric and the phenomenon of particle creation is examined during the oscillatory phase of inflaton, in the semiclassical theory of gravity. An approximate solution to the semiclassical Einstein equation is obtained in thermal squeezed state formalism by perturbatively and is found obey the same power-law expansion as that of classical Einstein equation. In addition to that the solution shows oscillatory in nature except on a particular condition. It is also noted that, the coher…

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 apply the results to cosmology and calculate an upper bound for the equilibrium temperature of the secondary particles created by the scalar field decay.

物理宇宙学发展中几乎被遗忘的结果

Nearly forgotten results in development of physical cosmology

回顾物理宇宙学发展中被遗忘的关键成果，包括弗里德曼和勒梅特对宇宙膨胀及背景辐射的贡献。

Creation of particles in a cyclic universe driven by loop quantum cosmology

We consider an isotropic and homogeneous universe in loop quantum cosmology. We assume that the matter content of the universe is dominated by dust matter in early time and a phantom matter at late time which constitutes the dark energy component. The quantum gravity modifications to the Friedmann equation in this model indicate that the classical big bang singularity and the future big rip singularity are resolved and are replaced by quantum bounce. It turns out that the big bounce and recollapse in the herein model contribute to a cyclic scenario for the universe. We then study the quantum t…

A simple quantum cosmology

A simple and surprisingly realistic model of the origin of the universe can be developed using the Friedmann equation from general relativity, elementary quantum mechanics, and the experimental values of h, c, G and the proton mass. The model assumes there are N space dimensions (with N > 6) and the potential constraining the radius r of the invisible N -3 compact dimensions varies as r^4. In this model, the universe has zero total energy and is created from nothing. There is no initial singularity. If space-time is eleven dimensional, as required by M theory, the scalar field corresponding to…

绝热粒子创生机制下包含相互作用Umami Chaplygin流体的宇宙学模型的动力学系统分析：一些反弹特征

Dynamical systems analysis of a cosmological model with interacting Umami Chaplygin fluid in adiabatic particle creation mechanism: Some bouncing features

本文研究了在绝热粒子创生机制下包含相互作用Umami Chaplygin流体的空间平坦FLRW宇宙模型，通过动力学分析发现部分临界点能描述宇宙从早期暴胀到晚期暗能量主导的统一演化，并验证了其非奇异反弹行为。

Cosmological perturbations in the entangled inflationary universe

In this paper it is presented the model of a multiverse made up of universes which are created in entangled pairs that conserve the total momentum conjugated to the scale factor. For the background spacetime it is assumed a FRW metric with a scalar field with mass $m$ minimally coupled to gravity. For the fields that propagate in the entangled spacetimes it is considered the perturbations of the spacetime and the scalar field, whose quantum states become entangled too. They turn out to be in a quasi thermal state and the corresponding thermodynamical magnitudes are computed. Three observables …

具有Weyl边界的宇宙中的暖暴胀

Warm inflation in a Universe with a Weylian boundary

本研究将Weyl型几何边界引入Einstein-Hilbert作用量，推导含Weyl向量的广义Friedmann方程，构建三类暖暴胀模型，数值模拟证实边界效应在早期宇宙辐射产生及暴胀阶段转变中起重要作用。

具有热粒子产生的动态时空的热容与量子压缩性

Heat capacity and quantum compressibility of dynamical spacetimes with thermal particle creation

本文将动态时空量子热力学推广到具有热粒子产生的宇宙学时空，基于 Bernard-Duncan 模型计算有质量共形标量场的配分函数和自由能，进而推导出时空的热容与量子压缩性。

通过粒子产生缓解宇宙学常数问题

Alleviating the cosmological constant problem from particle production

本文提出一种几何抵消机制，通过原始时期真空能量在准de Sitter相中转化为几何准粒子来缓解宇宙学常数问题，并探讨其作为暗物质候选者的可能性及对ΛCDM范式的修正。