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Xin-He Meng

Publications and source records attributed to Xin-He Meng.

67 records · Page 4Linked to original sources
arXiv2004

Can vacuum decay in our Universe?

We take a phenomenological approach to study the cosmological evolution of decaying vacuum cosmology ($Λ(t)$CDM) based on a simple assumption about the form of the modified matter expansion rate. In this framework, almost all the current vacuum decaying models can be unified in a simple manner. We argue that the idea of letting vacuum decay to resolve the fine-tuning problem is inconsistent with cosmological observations. We also discuss some issues in confronting $Λ(t)$CDM with observation. Using the effective equation of state formalism, we indicate that $Λ(t)$CDM is a possible candidate for phantom cosmology. Moreover, confronted with a possible trouble of effective equation of state formalism, we construct the effect dark energy density. Finally, we discuss the evolution of linear perturbation.

astro-ph↗
arXiv2004

Note on the Radion Effective Potential in the Presence of Branes

In String Theory compactification, branes are often invoked to get the desired form of the radion effective potential. Current popular way of doing this assumes that the introduction of branes will not modify the background geometry in an important way. In this paper, we show by an explicit example that at least in the codimension 2 case, the gravitational backreaction of the brane cannot be neglected in deriving the radion effective potential. Actually, in this case, the presence of branes will have no effect on the dynamics of radion.

hep-th↗
arXiv2004

Cosmological dynamics of D-cceleration

We study the cosmological dynamics of an effective theory for a strongly coupled scalar field in the moduli space of $\mathcal{N}=4$ supersymmetric Yang-Mills theory recently proposed by Silverstein and Tong, called "D-cceleration". We discuss various Energy Conditions in this theory. Then we prove the inflationary attractor property using the Hamilton-Jacobi method and study the phase portrait as well as the cosmological evolution of the scalar field.

astro-ph↗
arXiv2004

Improved Gell-Mann--Okubo Relations and SU(3) Rotation Excitations of Baryon States

The corrections to the Gell-Mann--Okubo relations of baryon masses are presented in the SU(3) Skyrme model. These corrections are calculated up to the second order in flavor breaking at the skyrmion quantum mechanics. The results are compatible with the experimental data. They could be regarded as a signal of existence of the SU(3) rotation excitation states of baryons: 27-let (with spin 1/2 or 3/2), 10*-let (with spin 1/2) and 35-let (with spin 3/2).

hep-ph↗
arXiv2004

$R^2$ corrections to the cosmological dynamics of inflation in the Palatini formulation

We investigate the corrections to the inflationary cosmological dynamics due to a $R^2$ term in the Palatini formulation which may arise as quantum corrections to the effective Lagrangian in early universe. We found that the standard Friedmann equation will not be changed when the scalar field is in the potential energy dominated era. However, in the kinetic energy dominated era, the standard Friedmann equation will be modified and in the case of closed and flat universe, the Modified Friedmann equation will automatically require that the initial kinetic energy density of the scalar field must be in sub-Planckian scale.

gr-qc↗
arXiv2004

Palatini Formulation of Modified Gravity with $\ln R$ Terms

Recently, corrections to the standard Einstein-Hilbert action are proposed to explain the current cosmic acceleration in stead of introducing dark energy. We discuss the Palatini formulation of the modified gravity with a $\ln R$ term suggested by Nojiri and Odintsov. We show that in the Palatini formulation, the $\ln R$ gravity can drive a current exponential accelerated expansion and it reduces to the standard Friedmann evolution for high redshift region. We also discuss the equivalent scalar-tensor formulation of the theory. We indicate that the $\ln R$ gravity may still have a conflict with electron-electron scattering experiment which stimulates us to pursue a more fundamental theory which can give the $\ln R$ gravity as an effective theory. Finally, we discuss a problem faced with the extension of the $\ln R$ gravity by adding $R^m$ terms.

hep-th↗
arXiv2004

Inflationary attractor in Gauss-Bonnet brane cosmology

The inflationary attractor properties of the canonical scalar field and Born-Infeld field are investigated in the Randall-Sundrum II scenario with a Gauss-Bonnet term in the bulk action. We find that the inflationary attractor property will always hold for both the canonical and Born-Infeld fields for any allowed non-negative Gauss-Bonnet coupling. We also briefly discuss the possibility of explaining the suppressed lower multiples and running scalar spectral index simultaneously in the scenario of Gauss-Bonnet brane inflation.

hep-ph↗
arXiv2003

Inflationary attractor property of phantoms

There are some motivations to consider inflation driven by a phantom field. Before entering into some specific models and perform data fitting, it is important first investigating some general features that any viable inflation model should hold. The inflationary attractor property is an important one of those features. In this paper we will show that the inflationary attractor property still holds for canonical and Born-Infeld phantom fields in the standard Friedmann-Robertson-Walker cosmology, however, it does not hold for canonical and Born-Infeld phantom fields in the Randall -Sundrum II cosmology.

hep-ph↗
arXiv2003

Gravitational potential in Palatini formulation of modified gravity

General Relativity has so far passed almost all the ground-based and solar-system experiments. Any reasonable extended gravity models should consistently reduce to it at least in the weak field approximation. In this work we derive the gravitational potential for the Palatini formulation of the modified gravity of the L(R) type which admits a de Sitter vacuum solution. We conclude that the Newtonian limit is always obtained in those class of models and the deviations from General Relativity is very small for a slowly moving source.

gr-qc↗
arXiv2003

Matter loops corrected modified gravity in Palatini formulation

Recently, corrections to the standard Einstein-Hilbert action are proposed to explain the current cosmic acceleration in stead of introducing dark energy. In the Palatini formulation of those modified gravity models, there is an important observation due to Arkani-Hamed: matter loops will give rise to a correction to the modified gravity action proportional to the Ricci scalar of the metric. In the presence of such term, we show that the current forms of modified gravity models in Palatini formulation, specifically, the 1/R gravity and $\ln R$ gravity, will have phantoms. Then we study the possible instabilities due to the presence of phantom fields. We show that the strong instability in the metric formulation of 1/R gravity indicated by Dolgov and Kawasaki will not appear and the decay timescales for the phantom fields may be long enough for the theories to make sense as effective field theory . On the other hand, if we change the sign of the modification terms to eliminate the phantoms, some other inconsistencies will arise for the various versions of the modified gravity models. Finally, we comment on the universal property of the Palatini formulation of the matter loops corrected modified gravity models and its implications.

hep-th↗
arXiv1999

Conservative Currents of Boundary Charges in $AdS_{2+1}$ Gravity

The boundary charges which constitute the Virasoro algebra in 2+1 dimensional anti-de Sitter gravity are derived by way of Noether theorem and diffeomorphic invariance. It shows that the boundary charges under discussion recently exhaust all the independent nontrivial charges available. Therefore, the state counting via the Virasoro algebra is complete.

hep-th↗