arXiv subjects

Dao-Jun Liu

Publications and source records attributed to Dao-Jun Liu.

30 records · Page 2Linked to original sources

arXiv2014

Black holes and gravitational waves in three-dimensional f(R) gravity

In the three-dimensional pure Einstein gravity, the geometries of the vacuum space-times are always trivial, and gravitational waves (gravitons) are strictly forbidden. For the first time, we find a vacuum circularly symmetric black hole with nontrivial geometries in $f(R)$ gravity theory, in which a true singularity appears. In this frame with nontrivial geometry, a perturbative gravitational wave does exist. Beyond the perturbative level, we make a constructive proof of the existence of a gravitational wave in $f(R)$ gravity, where the Birkhoff-like theorem becomes invalid. We find two classes of exact solutions of circularly symmetric pure gravitational wave radiation and absorption.

physics.gen-ph↗

arXiv2014

K-Inflation in Noncommutative Space-Time

The power spectra of the scalar and tensor perturbations in the noncommutative k-inflation model are calculated in this paper. In this model, all the modes created when the stringy space-time uncertainty relation is satisfied are generated inside the sound/Hubble horizon during inflation for the scalar/tensor perturbations. It turns out that a linear term describing the noncommutative space-time effect contributes to the power spectra of the scalar and tensor perturbations. Confronting the general noncommutative k-inflation model with latest results from \textit{Planck} and BICEP2, and taking $c_S$ and $λ$ as free parameters, we find that it is well consistent with observations. However, for the two specific models, i.e. the tachyon and DBI inflation models, it is found that the DBI model is not favored, while the tachyon model lies inside the $1σ$ contour, if the e-folds number is assumed to be around $50\sim60$.

astro-ph.CO↗

arXiv2014

Note on Power-Law Inflation in Noncommutative Space-Time

In this paper, we propose a new method to calculate the mode functions in the noncommutative power-law inflation model. In this model, all the modes created when the stringy space-time uncertainty relation is satisfied are generated inside the Hubble horizon during inflation. It turns out that a linear term describing the noncommutative space-time effect contributes to the power spectra of the scalar and tensor perturbations. Confronting this model with latest results from \textit{Planck} and BICEP2, we constrain the parameters in this model and we find it is well consistent with observations.

astro-ph.CO↗

arXiv2012

Quasinormal modes for asymptotic safe black holes

Under the hypothesis of asymptotic safety of gravity, the static, spherically symmetric black hole solutions in the infrared limit are corrected by non-perturbative effects. Specifically, the metric is modified by the running of gravitational couplings. In this work, we investigate the effects of this correction to the quasinormal modes (QNMs) of a test scalar field propagating in this kind of black hole background analytically and numerically. It is found that although the quasi-period frequencies and the damping of oscillations are respectively enhanced and weakened by the quantum correction term, the stability of the black hole remains.

gr-qc↗

arXiv2011

Can be OPERA neutrino as tachyonic chameleon?

Whether there is a superluminal object existing in the real world is a mystery in modern physics. Recently, OPERA collaboration claims that they have observed superluminal neutrinos in their experiments. This leads to a rest mass paradox by combining the observational results from SN1987A, if one considers the neutrino as a tachyon. In this paper, we identify the neutrino as a tachyonic chameleon, whose mass depends not only on coordinate frame but also on the environment, in which the neutrino propagates without the need of violation of the Lorentz-invariance at a fundamental level. We have compared our results with these observations and made some predictions that can be tested in the near future. Also, we have clarified the concept of rest mass for subluminal and superluminal object.

physics.gen-ph↗

arXiv2011

A modified model of non-locally corrected gravity: Cosmology and the Newtonian limit

A modified form of non-locally corrected theory of gravity is investigated in the context of cosmology and the Newtonian limit. This form of non-local correction to classic Einstein-Hilbert action can be locally represented by a triple-scalar-tensor theory in which one of the scalar degree of freedom is phantom-like and the other two are quintessence-like. We show that there exists a stable de Sitter solution for the cosmological dynamics if a suitable form of potential function $V(ϕ)$ (or equivalently, $f(R)$) is selected. However, no matter what a potential function is selected, there is always an early time repeller solution corresponding to a radiation dominated universe. Besides, the equations for linear scalar perturbations are presented and it is shown that the form of potential function $V(ϕ)$ is stringently constrained by the Solar system test, although the post-Newtonian parameter $γ$ is not directly affected by this function.

gr-qc↗

arXiv2010

Modified holographic dark energy in DGP brane world

In this paper, the cosmological dynamics of a modified holographic dark energy which is derived from the UV/IR duality by considering the black hole mass in higher dimensions as UV cutoff, is investigated in Dvali-Gabadaze-Porrati (DGP) brane world model. We choose Hubble horizon and future event horizon as IR cutoff respectively. And the two branches of the DGP model are both taken into account. When Hubble horizon is considered as IR cutoff, the modified holographic dark energy (HDE) behaves like an effect dark energy that modification of gravity in pure DGP brane world model acts and it can drive the expansion of the universe speed up at late time in $ε=-1$ branch which in pure DGP model can not undergo an accelerating phase. When future event horizon acts as IR cutoff, the equation of state parameter of the modified HDE can cross the phantom divide.

astro-ph.CO↗

arXiv2010

Dynamics of Brans-Dicke cosmology with varying mass fermions

In this paper, the cosmological dynamics of Brans-Dicke theory in which there are fermions with a coupling to BD scalar field as well as a self-interaction potential is investigated. The conditions that there exists a solution which is stable and represents a late-time accelerated expansion of the universe are found. The variable mass of fermions can not vanish exactly during the evolution of the universe once it exists initially. It is shown that the late-time acceleration depends completely on the self-interaction of the fermionic field if our investigation is restricted to the theory with positive BD parameter $ω$. Provided a negative $ω$ is allowed, there will be another two class of stable solutions describing late-time accelerated expansion of the universe.

astro-ph.CO↗

arXiv2009

A Self-gravitating Dirac-Born-Infeld Global Monopole

We generalize the field theory of global monopole to Dirac-Born-Infeld(DBI) field and investigate the gravitational property of a DBI global monopole in four-dimensional spherically symmetric spacetime. The coupled equations for the metric and the DBI scalar field are solved asymptotically and numerically. It is found that, just as a canonical global monopole, the gravitational effect of DBI global monopole is equivalent to that of a deficit solid angle in the metric plus a negative mass at the origin. However, compared with a canonical global monopole, for the same false vacuum and symmetry breaking scale, a DBI global monopole has a relatively smaller core and a larger absolute value of effective mass. Thus, it can give out a larger deflect angle when the light passing by. Especially, when the scale of warp factor is small enough, the effective mass of a DBI global monopole does not depend apparently on the value of the false vacuum, which is qualitatively different from that of a canonical global monopole.

hep-th↗

arXiv2008

Revisiting the parametrization of Equation of State of Dark Energy via SNIa Data

In this paper, we revisit the parameterizations of the equation of state of dark energy and point out that comparing merely the $χ^2$ of different fittings may not be optimal for choosing the "best" parametrization. Another figure of merit for evaluating different parametrizations based on the area of the $w(z) - z$ band is proposed. In light of the analysis of some two-parameter parameterizations and models based on available SNIa data, the area of $w(z)-z$ band seems to be a good figure of merit, especially in the situation that the value of $χ^2_{\rm min}$ for different parametrizations are very close. Therefore, we argue that both the area of the $w(z)-z$ band and $χ^2_{\rm min}$ should be synthetically considered for choosing a better parametrization of dark energy in the future experiments.

astro-ph↗

arXiv2008

Statefinder Diagnostic for Quintessence with or without Thermal Interaction

The cosmological dynamics of minimally coupled scalar field that couples to the background matter with thermal interactions is investigated by using statefinder diagnostics. The time evolution of the statefinder pairs $\{r,s\}$ and $\{r,q\}$ are obtained under the circumstance that different values of model parameters are chosen. We show that the thermal coupling term does not affect the location of the late-time attractor, but exert an influence on the evolution of the statefinder parameters. The most notable feature of the $r-s$ plane for the thermal coupling model which is distinguished from the other dark energy models is that some part of the curve with thermal coupling can form a closed loop in the second quadrant ($r>1,s<0$).

astro-ph↗

arXiv2007

Statefinder diagnostic for cosmology with the abnormally weighting energy hypothesis

In this paper, we apply the statefinder diagnostic to the cosmology with the Abnormally Weighting Energy hypothesis (AWE cosmology), in which dark energy in the observational (ordinary matter) frame results from the violation of weak equivalence principle (WEP) by pressureless matter. It is found that there exist closed loops in the statefinder plane, which is an interesting characteristic of the evolution trajectories of statefinder parameters and can be used to distinguish AWE cosmology from the other cosmological models.

astro-ph↗