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Cheng-Yi Sun

Publications and source records attributed to Cheng-Yi Sun.

At least 19 recordsLinked to original sources
arXiv2014

Probing Planckian physics in de Sitter space with quantum correlations

We study the quantum correlation and quantum communication channel of both free scalar and fermionic fields in de Sitter space, while the Planckian modification presented by the choice of a particular $α$-vacuum has been considered. We show that the occurrence of degradation of quantum entanglement between field modes for an inertial observer in curved space, due to the radiation associated with its cosmological horizon. Comparing with standard Bunch-Davies choice, the possible Planckian physics causes some extra decrement on the quantum correlation, which may provide the means to detect quantum gravitational effects via quantum information methodology in future. Beyond single-mode approximation, we construct proper Unruh modes admitting general $α-$vacua, and find a convergent feature of both bosonic and fermionic entanglements. In particular, we show that the convergent points of fermionic entanglement negativity are dependent on the choice of $α$. Moreover, an one-to-one correspondence between convergent points $H_c$ of negativity and zeros of quantum capacity of quantum channels in de Sitter space has been proved.

quant-ph↗
arXiv2013

Stable Large-Scale Perturbations in Interacting Dark-Energy Model

It is found that the evolutions of density perturbations on the super-Hubble scales are unstable in the model with dark-sector interaction $Q$ proportional to the energy density of cold dark matter (CDM) $ρ_m$ and constant equation of state parameter of dark energy $w_d$. In this paper, to avoid the instabilities, we suggest a new covariant model for the energy-momentum transfer between DE and CDM. Then we show that the the large-scale instabilities of curvature perturbations can be avoided in our model in the universe filled only by DE and CDM. Furthermore, by including the additional components of radiation and baryons, we calculate the dominant non-adiabatic modes in the radiation era and find that the modes grow in the power law with exponent at the order of unit.

astro-ph.CO↗
arXiv2012

Quantum correlations with vacuum ambiguity in de Sitter space

We study the quantum correlations of free scalar field with vacuum ambiguity of de Sitter space. We show the occurrence of degradation of quantum entanglement and quantum discord between field modes for inertial observer in curved space due to the radiation associated with cosmological horizon. In particular, we find that quantum correlations can be used to encode infinite de Sitter invariant vacua, which correspond to infinite set of possible physical worlds. This may provide a superselection rule of physical vacuum via quantum information tasks. We also discuss the simulation of such quantum effects of vacuum ambiguity in ion trap experiments.

quant-ph↗
arXiv2012

Another Two Dark Energy Models Motivated from Karolyhazy Uncertainty Relation

The K$\acute{\text{a}}$rolyh$\acute{\text{a}}$zy uncertainty relation indicates that there exists the minimal detectable cell $δt^{3}$ over the region $t^3$ in Minkowski spacetime. Due to the energy-time uncertainty relation, the energy of the cell $δt^3$ can not be less $δt^{-1}$. Then we get a new energy density of metric fluctuations of Minkowski spacetime as $δt^{-4}$. Motivated by the energy density, we propose two new dark energy models. One model is characterized by the age of the universe and the other is characterized by the conformal age of the universe. We find that in the two models, the dark energy mimics a cosmological constant in the late time.

hep-th↗
arXiv2012

New Interaction between Dark Energy and Dark Matter Changes Sign during Cosmological Evolution

It is found by Cai and Su that the interaction between dark energy and cold dark matter is likely to change the sign during the cosmological evolution. Motivated by this, we suggest a new form of interaction between dark energy and dark matter, which changes from negative to positive as the expansion of our universe changes from decelerated to accelerated. We find that the interacting model is consistent with the second law of thermodynamics and the observational constraints. And, we also discuss the unified adiabatic-squared sound speed of the model.

gr-qc↗
arXiv2011

Stability of curvature perturbation with new covariant form for energy-momentum transfer in dark sector

It was found that the model with interaction between cold dark matter (CDM) and dark energy (DE) proportional to the energy density of CDM $ρ_m$ and constant equation of state of DE $w_d$ suffered from instabilities of the density perturbations on the supper-Hubble scales. Here we suggest a new covariant model for the energy-momentum transfer between CDM and DE. Then using the covariant model, we analyze the evolution of density perturbations on the supper-Hubble scale. We find that the instabilities can be avoided in the model with constant $w_d$ and interaction proportional to $ρ_m$. Furthermore, we analyze the dominant non-adiabatic mode in the radiation era and find that the mode grows regularly.

gr-qc↗
arXiv2011

Domain wall partition function of the eight-vertex model with a non-diagonal reflecting end

With the help of the Drinfeld twist or factorizing F-matrix for the eight-vertex SOS model, we obtain the explicit determinant expression of the partition function of the eight-vertex model with a generic non-diagonal reflecting end and domain wall boundary condition. Our result shows that, contrary to the eight-vertex model without a reflection end, the partition function can be expressed as a single determinant.

math-ph↗
arXiv2011

Inflation and New Agegraphic Dark Energy

In the note, we extend the discussion of the new agegraphic dark energy (NADE) model to include the inflation stage. Usually, in the inflation models, for convenience the conformal time $η$ is set to be zero at the end of inflation. This is incompatible with the NADE model since $η=0$ indicates the divergence of NADE. To avoid the difficulty, we can redefine the conformal time as $η+δ$. However, we find that the positive constant $δ$ must be so large that NADE can not become dominated at present time.

hep-th↗
arXiv2011

Weak Gravity Conjecture and Holographic/Agegraphic Dark Energy

A criterion that should be satisfied in the inflation and quintessence models is motivated from the weak gravity conjecture (WGC) by Huang. However, it is found that the criterion is inconsistent with the Holographic dark energy (HDE) and new agegraphic dark energy (NADE) models. In the note, we firstly show that in the HDE and NADE models the criterion should be be replaced respectively by two new criterions. Secondly, we apply the new criterions indicated by WGC to survey the two models. We find that the contradiction between WGC and the NADE model is removed when the new criterion is used. In the HDE model, we find the effects of the spatial curvature and the interaction should be considered in order to match the new criterion.

gr-qc↗
arXiv2010

Weak Gravity Conjecture and Holographic Dark Energy Model with Interaction and Spatial Curvature

In the paper, we apply the weak gravity conjecture to the holographic quintessence model of dark energy. Three different holographic dark energy models are considered: without the interaction in the non-flat universe; with interaction in the flat universe; with interaction in the non-flat universe. We find that only in the models with the spatial curvature and interaction term proportional to the energy density of matter, it is possible for the weak gravity conjecture to be satisfied.

gr-qc↗
arXiv2010

Trapping Horizons in the Sultana-Dyer Space-Time

The Sultana-Dyer space-time is suggested as a model describing a black hole embedded in an expanding universe. Recently, in \cite{0705.4012}, its global structure is analyzed and the trapping horizons are shown. In the paper, by directly calculating the expansions of the radial null vector fields normal to the space-like two-spheres foliating the trapping horizons, we find that the trapping horizon outside the event horizon in the Sultana-Dyer space-time is a past trapping horizon. Further, we find that the past trapping horizon is an outer, instantaneously degenerate or inner trapping horizon accordingly when the radial coordinate is less than, equal to or greater than some value.

gr-qc↗
arXiv2010

Naked Singularity in the Sultana-Dyer Space-Time

How to describe a black hole embedded in an expanding universe is an important topic. Some models about this issue are suggested by assuming that the metric is a conformal transformation of the Schwarzschild metric or of the isotropic black hole metric. However, there exists naked singularities in the two metrics. Recently, it is argued that the singularity in the Sultana-Dyer space-time is covered by an apparent horizon surface. But we find that such an apparent horizon does not exist if the null energy condition holds.

gr-qc↗
arXiv2009

Dark Energy Accretion onto a Black Hole in an Expanding Universe

By using the solution describing a black hole embedded in the FLRW universe, we obtain the evolving equation of the black hole mass expressed in terms of the cosmological parameters. The evolving equation indicates that in the phantom dark energy universe the black hole mass becomes zero before the Big Rip is reached.

hep-th↗
arXiv2008

Phantom Energy Accretion onto Black Holes in Cyclic Universe

Black holes pose a serious problem in the cyclic or oscillating cosmology. It is speculated that, in the cyclic universe with phantom turnarounds, black holes will be torn apart by the phantom energy before turnaround before they can create any problems. In this paper, using the mechanism of the phantom accretion onto black holes, we find that black holes do not disappear before the phantom turnaround. But the remanent black holes will not cause any problems due to the Hawking evaporation.

hep-th↗
arXiv2006

A Cyclic Cosmological Model in the Landscape Scenario

In [1], KKLT give a mechanism to generate de Sitter vacua in string theory. And the scenario, \emph{Landscape}, is suggested to explain the problem of the cosmological constant. In this paper, adopting a simple potential describing the \emph{landscape}, we investigate the decay of the vacuum and the evolution of the universe after the decay. We find that the big crunch of the universe is inevitable. But, according to the modified Friedmann equation in [11], the singularity of the big crunch is avoided. Furthermore, we find that this gives a cyclic cosmological model.

hep-th↗