Narrow Results

We have examined a homogeneous massive scalar field minimally coupled to the spatially flat Friedmann–Robertson–Walker metric, in squeezed and coherent state formalisms, in semiclassical theory of gravity. In the oscillatory phase of inflaton, the approximate leading solution to the semiclassical Einstein equation has the same power-law expansion as that of the classical Einstein equation for both coherent and squeezed state formalisms. Quantum fluctuations of the inflaton in coherent and squeezed vacuum states are studied, by using dispersion relations. The uncertainty relation for coherent state does not depend on the coherent state parameter while the uncertainty relation for squeezed vacuum state depends on the associated squeezing parameter and squeezing angle.

We provide an explicit solution representing an anisotropic power-law inflation within the framework of rolling tachyon model. This is generated by allowing a non-minimal coupling between the tachyon and the world-volume gauge field on non-BPS D3 brane. We also show that this solution is perturbatively stable.

We study the semiclassical Einstein equation and inflaton in the oscillatory region of the FRW Universe. We study the relative deviation of particle production in coherent and squeezed vacuum states for a minimally coupled scalar field in the oscillatory region of flat FRW Universe. We also study the behavior of inflaton field in non-oscillatory region. We examine whether the solution obtained in slow-roll approximation satisfies Klein–Gordon equation and commutation relation as well.

A new scenario of baryogenesis via the ratchet mechanism is proposed based on an analogy with the forced pendulum. The oscillation of the inflaton field during the reheating epoch after inflation plays the role of the driving force, while the phase $𝜃$ of a scalar baryon field (a complex scalar field with baryon number) plays the role of the angle of the pendulum. When the inflaton is coupled to the scalar baryon, the behavior of the phase $𝜃$ can be analogous to that of the angle of the forced pendulum. If the oscillation of the driving force is adjusted to the pendulum’s motion, a directed rotation of the pendulum is obtained with a nonvanishing value of $\dot{𝜃}$, which models successful baryogenesis since $\dot{𝜃}$ is proportional to the baryon number density. Similar ratchet models which lead to directed motion have been used in the study of molecular motors in biology. There, the driving force is supplied by chemical reactions, while in our scenario this role is played by the inflaton during the reheating epoch.

In the present paper we develop a concept of parallel ordinary (O) and mirror (M) worlds. We have shown that in the case of a broken mirror parity (MP), the evolutions of fine structure constants in the O- and M-worlds are not identical. It is assumed that E₆-unification inspired by superstring theory restores the broken MP at the scale ~ 10¹⁸GeV, what unavoidably leads to the different E₆-breakdowns at this scale: E₆ → SO(10) × U(1)_Z — in the O-world, and E′₆ → SU(6)′ × SU(2)′_Z — in the M-world. Considering only asymptotically free theories, we have presented the running of all the inverse gauge constants in the one-loop approximation. Then a "quintessence" scenario suggested in Refs. 56–61 is discussed for our model of accelerating universe. Such a scenario is related with an axion ("acceleron") of a new gauge group SU(2)′_Z which has a coupling constant g_Z extremely growing at the scale Λ_Z ~ 10^-3eV.

In this paper, we study nonclassical inflaton, which is minimally coupled to the semi-classical gravity in FRW universe in Coherent Squeezed Vacuum State (CSVS). We have determined the Oscillatory phase of inflaton, power-law expansion, scale factor, density fluctuations, quantum fluctuations and particle production for CSVS. We have obtained an estimated leading solution of scale factor in CSVS and found it proportional to $t^{2/3}$ and showing similar diversification as demonstrated by Semi-classical Einstein Equation (SCEE) of gravity in matter dominated universe. We have also studied the validity of SCEE in CSVS. We have computed validity of uncertainty relation for FRW Universe by determining the quantum fluctuation for CSVS. Our results show that Quantum fluctuations don’t depend on coherent parameter $\mathbf{\Upsilon }$ as the uncertainty relation doesn’t effect by the displacement of $\mathbf{\Upsilon }$ in phase space. We have also studied the production of particles in CSVS for oscillating massive inflaton in flat FRW universe.

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.

A minimally coupled nonclassical homogeneous scalar field is examined in the flat FRW universe in the semiclassical theory of gravity. Particle production in thermal coherent and squeezed states is studied for the flat FRW universe, in the oscillatory phase of the inflaton. Solutions for the semiclassical Friedmann equations are obtained in the thermal nonclassical states. Validity of the semiclassical theory is examined in the thermal coherent and squeezed states in the oscillatory phase of inflaton. Particle creation can be enhanced due to thermal and quantum effects. Quantum fluctuations of the inflaton in thermal coherent and squeezed state formalisms are also studied. Classical gravity differ from semiclassical gravity in the thermal coherent state only by an amplitude factor.

In this paper, we study the effect of the quantum backreaction on Brans–Dicke cosmology in inflation era. We consider an inflaton field in the $D$-dimensional spacetime in the framework of Brans–Dicke model. We use a new notation for the Brans–Dicke field in terms of the dilaton field. Then we obtain the vacuum expectation value of the full energy–momentum tensor using WKB approximation of the mode functions which satisfy the equations of motion. The obtained vacuum expectation values of energy–momentum tensor are divergent. In order to renormalize it, we introduce a constant cut-off $\mathrm{\Omega }$. The vacuum expectation value of energy–momentum tensor is separated to the UV and IR parts by using $\mathrm{\Omega }$ cut-off. Then, we use the dimensional regularization method to eliminate divergences by introducing a counterterm action. Also, we calculate the IR contribution of the vacuum expectation value of energy–momentum tensor. Thus, we obtain a physically finite result for the quantum energy–momentum tensor. Finally, we find the effect of backreaction on scale factor.

In this paper, we study the semiclassical evolution of a “coherently oscillating massive scalar field”. This field is nominally linked to the spatially levelled Friedmann–Robertson–Walker (FRW) metric. By use of two-mode quantum optical states formalism, we evaluated the power-law cosmology with scale factor as a power function of cosmic time. In the oscillatory phase of scalar field, it was found that, in all the four different combinations of quantum states, quantum scalar field obeying the time-dependent Schrödinger equation leads to the power-law expansion, in good agreement with that of the matter-dominated era. However, in the semiclassical theory of gravity in contrary to the classical description of gravity, we obtained two behavioral solutions corresponding to two different pattern evolution of the scale factor. This behavioral pattern evolution of scale factor of the universe has an important quantum implication associated with it.

We compare two action integrals and identify the Lagrangian multiplier to set up a constraint equation on cosmological expansion. This is a direct result of the fourth equation of our manuscript which unconventionally compares the general-relativity action integral with the second derived action integral. This leads to Eq. (3)–(5), a bound on the cosmological constant. We replace the Hamber quantum-gravity reference-based action integral with a result from Klauder’s “Enhanced Quantization,” while showing its relevance to early-universe black-hole production and the volume of space producing 100 black holes of 10² Planck mass in a radius of 10³ Planck length for entropy of about 1000.

Primordial black holes (PBHs) can be produced when large density perturbations enter the horizon in the early universe. They can be dark matter (DM) and the black holes detected by the LIGO-Virgo collaborations. In this proceeding, we show that the large enhancement of the perturbations, required for the DM PBHs and LIGO/Virgo PBHs, can be realized in inflation models with a downward step. This enhancement mechanism is related to the particle production associated with the non-adiabatic evolution of the inflaton. This proceeding is based on our original paper.