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Ding-fang Zeng

Publications and source records attributed to Ding-fang Zeng.

At least 37 records · Page 2Linked to original sources
arXiv2018

Phase Structure and QNMs of A Charged AdS Dilaton Black Hole

We investigate the phase structure of a charged AdS dilaton black hole in the extended phase space which takes the cosmological constant, i.e. the AdS-$Λ$ parameter as pressures. Through both thermal ensemble and quasinormal mode analysis, we find that stable phase of the black hole with non-trivial dilaton profiles always exists for both large and small couplings when the AdS-$Λ$ is considered dynamical degrees of freedom. This forms a somewhat contrast with previous works which does not do so. Our results provide new examples for the parallelism or equivalences between thermal ensemble methods and dynamic perturbation analysis for black hole phase structures.

hep-th↗
arXiv2017

Resolving the Schwarzschild singularity in both classic and quantum gravity

The Schwarzschild singularity's resolution has key values in cracking the key mysteries related with black holes, the origin of their horizon entropy and the information missing puzzle involved in their evaporations. We provide in this work the general dynamic inner metric of collapsing stars with horizons and with non-trivial radial mass distributions. We find that static central singularities are not the final state of the system. Instead, the final state of the system is a periodically zero-cross breathing ball. Through 3+1 decomposed general relativity and its quantum formulation, we establish a functional Schrödinger equation controlling the micro-state of this breathing ball and show that, the system configuration with all the matter concentrating on the central point is not the unique eigen-energy-density solution. Using a Bohr-Sommerfield like "orbital" quantisation assumption, we show that for each black hole of horizon radius $r_h$, there are about $e^{r_h^2/\ell^2_\mathrm{pl}}$ allowable eigen-energy-density profile. This naturally leads to physic interpretations for the micro-origin of horizon entropy, as well as solutions to the information missing puzzle involved in Hawking radiations.

hep-th↗
arXiv2017

$d_{\ell}(z)$ and BAO in the emergent gravity and the dark universe

We illustrate that $Λ$MOND cosmology following from E. Verlinde's emergent gravity idea which contains only constant dark energy and baryonic matters governed by linear inverse gravitation forces at and beyond galaxy scales fit with the luminosity distance v.s. redshift relationship, i.e. $d_\ell(z)$ of type Ia supernovae equally well as the standard $Λ$CDM cosmology does. But in a rather broad and reasonable parameter space, $Λ$MOND gives too strong baryon acoustic oscillation, i.e. BAO signals on the matter power spectrum contradicting with observations from various galaxy survey and counting experiments.

astro-ph.CO↗
arXiv2016

Schwinger pairs production in a soft-wall model

The Schwinger pairs production rate is calculated numerically in the soft-wall model with the help of a simpler method in determining the soft-wall's position beyond which probe strings connecting the Schwinger pairs do not fall into. Behaviours of the production rate in both the upper critical region and the middle linear part are studied carefully. The latter exhibits interesting new features un-noted previously. All results are presented in comparisons with hard-wall models.

hep-th↗
arXiv2016

Geodesic Motions in AdS Soliton Background Space-time

We study both massive and massless particle's geodesic motion in the background of general dimensional AdS-Sol space-time. We find that the massive particles oscillate along the radial direction, while massless particles experience one-time bouncing as they approach the "horizon" line of the soliton. Our results provide a direct way to understand the negative energy/masses leading to the AdS-Sol geometry. As a potential application, we extend the point particle to a 3-brane and fix the background as a 5+1 dimension AdS-Sol, thus obtain a very natural bouncing/cyclic cosmological model.

hep-th↗
arXiv2015

Scale-free power spectrums in the delayed cosmology

The delayed cosmology [JCAP 02(2012)046] assumes that the evolution of geometries is delayed relative to that of matter and/or energies. This idea allows inflation occur without inflaton fields or vacuum energies of any kind as drivings. We considered the production and evolution of primordial perturbations in this model. The results indicate that, with delaying, we could get a nearly scale-free power spectrum of perturbations starting from a radiation dominated early universe.

astro-ph.CO↗
arXiv2014

Screening of quark-monopole in N=4 plasma

We study a quark-monopole bound system moving in N=4 SYM plasma with a constant velocity by the AdS/CFT correspondence. The screening length of this system is calculated, and is smaller than that of the quark-antiquark bound state.

hep-th↗
arXiv2014

Baryon Asymmetries in the Natural Inflation Model

A variation of Affleck-Dine mechanism was proposed to generate the observed baryon asymmetry in [1], in which the inflaton was assumed to be a complex scalar field with a weakly broken $U(1)$ symmetry, and the baryon asymmetry generation was easily unified with the stage of inflation and reheating. We adapt this mechanism to natural inflation scenarios and compare the results with those in chaotic inflation models. We compute the net particle number obtained at the end of inflation and transform it into net baryon number after reheatings. We observed that in natural inflation models, the desired baryon-to-photon ratio can be achieved equally well as in chaotic models.

astro-ph.CO↗
arXiv2013

A Semi-analytical Solution to Classic Yang-Mills Equations with Both Asymptotical Freedom and Confining Features

It is well known that confinings and asymptotic freedom are properties of quantum chromo-dynamics (QCD). But hints of these features can also be observed at purely classic levels. For this purpose we need to find solutions to the colorly-sourceful Yang-Mills equations with both confining and asymptotic freedom features. We provide such a solution in this paper which at the near-source region is of serial form, while at the far-away region is approximately expressed through simple elementary functions. From the solution, we derive out a classically non-perturbative beta function describing the running of effective coupling constant, which is linear in the couplings both in the infrared and ultraviolet region.

hep-th↗
arXiv2013

n+1 Dimensional Gravity duals to quantum criticalities with spontaneous symmetry breaking

We reexamine the charged AdS domain wall solution to the Einstein-Abelian-Higgs model proposed by Gubser et al as holographic superconductors at quantum critical points and comment on their statement about the uniqueness of gravity solutions. We generalize their explorations from 3+1 dimensions to arbitrary $n+1$Ds and find that the $n+1\geqslant5$D charged AdS domain walls are unstable against electric perturbations.

hep-th↗
arXiv2009

An Exact Hairy Black Hole Solution for AdS/CFT Superconductors

We provide an exact hairy black hole solution to an $n+1$ dimensional complex scalar field model coupled with gravity. The model is characterized by a potential with one parameter. Depending on the magnitude of this parameter, the effective mass square of the scalar field can be both positive and negative. No matter what case it is, there are temperature ranges in which the hairy black hole is thermodynamically stable against decaying into its no-hair counterpart. We use this solution as an AdS/CFT superconductor model and study its conductivity-frequency relation and find typical features observed in other AdS/CFT superconductor models.

hep-th↗
arXiv2008

Heavy Quark Potentials in Some Renormalization Group Revised AdS/QCD Models

We construct some AdS/QCD models by the systematic procedure of GKN. These models reflect three rather different asymptotics the gauge theory beta functions approach at the infrared region, $β\propto-λ^2, -λ^3$ and $β\propto-λ$, where $λ$ is the 't Hooft coupling constant. We then calculate the heavy quark potentials in these models by holographic methods and find that they can more consistently fit the lattice data relative to the usual models which do not include the renormalization group improving effects. But only use the lattice QCD heavy quark potentials as constrains, we cannot distinguish which kind of infrared asymptotics is the better one.

hep-th↗
arXiv2007

Viscosity and jet quenching from holographic model

We consider the backreaction of the fundamental flavor degrees of freedom on the AdS$_5$-Schwarz background, and calculate their contributions to the shear viscosity and jet-quenching parameter of the thermal quark-gluon plasma.

hep-ph↗
arXiv2007

Extending BCCNR flavored geometry to the negative coupling constant region

We extend BCCNR's flavored KW and KS geometries into the negative coupling constant region and try giving physical explanations from the dual gauge theory side. We show that, in the extended region, except the coupling constant being negative, all other fields of the super-gravity theory having good properties which can be described by the dual gauge theory.

hep-th↗
arXiv2007

Jet quenching parameters of Sakai-Sugimoto Model

Using gauge theory/string duality, we calculated the jet quenching parameter $\hat{q}$ of the Sakai-Sugimoto model in various phases. Being different from the $\mathcal{N}=4$ SYM theory where $\hat{q}\propto T^3$, we find that $\hat{q}\propto T^4/T_d$, where $T_d$ is the critical temperature of the confined/deconfined phase transition. By analyzing the $\hat{q}$ in different phases of this theory, we get better understanding about some statements in previous works, such as the non-universality and the explanation of discrepancies between the theory predictions and experiments.

hep-th↗
arXiv2007

Membrane in M5-branes Background

In this paper, we investigate the properties of a membrane in the M5-brane background. Through solving the classical equations of motion of the membrane, we can understand the classical dynamics of the membrane in this background.

hep-th↗