arXiv subjects

Yi-Fu Cai

Publications and source records attributed to Yi-Fu Cai.

187 records · Page 11Linked to original sources

arXiv2007

Hawking-Moss Tunneling in Noncommutative Eternal Inflation

The quantum behavior of noncommutative eternal inflation is quite different from the usual knowledge. Unlike the usual eternal inflation, the quantum fluctuation of noncommutative eternal inflation is suppressed by the Hubble parameter. Due to this, we need to reconsider many conceptions of eternal inflation. In this paper we study the Hawking-Moss tunneling in noncommutative eternal inflation using the stochastic approach. We obtain a brand-new form of the tunneling probability for this process and find that the Hawking-Moss tunneling is more unlikely to take place in the noncommutative case than in the usual one. We also conclude that the lifetime of a metastable de-Sitter (dS) vacuum in the noncommutative spacetime is longer than that in the commutative case.

gr-qc↗

arXiv2007

Cyclic Universe with Quintom matter in Loop Quantum Cosmology

In this paper, we study the possibility of model building of cyclic universe with Quintom matter in the framework of Loop Quantum Cosmology. After a general demonstration, we provide two examples, one with double-fluid and another double-scalar field, to show how such a scenario is obtained. Analytical and numerical calculations are both presented in the paper.

hep-th↗

arXiv2007

Null Energy Condition and Dark Energy Models

Null Energy Condition (NEC) requires the equation of state (EoS) of the universe $w_u$ satisfy $w_u\geq-1$, which implies, for instance in a universe with matter and dark energy dominating $w_u=w_mΩ_m+w_{de}Ω_{de}=w_{de}Ω_{de}\geq-1$. In this paper we study constraints on the dark energy models from the requirement of the NEC. We will show that with $Ω_{de}\sim0.7$, $w_{de}<-1$ at present epoch is possible. However, NEC excludes the possibility of $w_{de}<-1$ forever as happened in the Phantom model, but if $w_{de}<-1$ stays for a short period of time as predicted in the Quintom theory NEC can be satisfied. We take three examples of Quintom models of dark energy, namely the phenomenological EoS, the two-scalar-field model and the single scalar model with a modified Dirac-Born-Infeld (DBI) lagrangian to show how this happens.

gr-qc↗

arXiv2007

Probing Noncommutativity with Inflationary Gravitational Waves

In this paper we study the behaviour of gravitational wave background (GWB) generated during inflation in the environment of the noncommutative field approach. From this approach we derive out one additive term, and then we find that the dispersion relation of the gravitational wave would be modified and the primordial gravitational wave would obtain an effective mass. Therefore it breaks lorentz symmetry in local. Moreover, this additive term would a little raise up the energy spectrum of GWB in low frequency and then greatly suppress the spectrum at even lower energy scale of which the wave length may be near the current horizon. Therefore, a sharp peak is formed on the energy spectrum in the range of low frequencies. This peak should be a key criterion to detect the possible existence of noncommutativity of space-time in the background of our universe and a critical test for breaking lorentz symmetry in local field theory. Adding all possible effects on the evolution of GWB, we give some new information of the tensor power spectrum and its energy spectrum which may be probed in the future cosmological observations.

gr-qc↗

arXiv2007

Is Noncommutative Eternal Inflation Possible?

We investigate the condition for eternal inflation to take place in the noncommutative spacetime. We find that the possibility for eternal inflation's happening is greatly suppressed in this case. If eternal inflation cannot happen in the low energy region where the noncommutativity is very weak (the UV region), it will never happen during the whole inflationary history. Based on these conclusions, we argue that an initial condition for eternal inflation is available from the property of spacetime noncommutativity.

hep-th↗

arXiv2007

Bouncing Universe with Quintom Matter

The bouncing universe provides a possible solution to the Big Bang singularity problem. In this paper we study the bouncing solution in the universe dominated by the Quintom matter with an equation of state (EoS) crossing the cosmological constant boundary. We will show explicitly the analytical and numerical bouncing solutions in three types of models for the Quintom matter with an phenomenological EoS, the two scalar fields and a scalar field with a modified Born-Infeld action.

gr-qc↗

arXiv2007

Cosmic Duality in Quintom Universe

In this paper we study the duality in two-field Quintom models of Dark Energy. We find that an expanding universe dominated by Quintom-A field is dual to a contracting universe with Quintom-B field.

gr-qc↗