arXiv subjects

Jie Liu

Publications and source records attributed to Jie Liu.

At least 721 records · Page 40Linked to original sources

arXiv2010

Cold Dark Matter Isocurvature Perturbations: Cosmological Constraints and Applications

In this paper we present the constraints on cold dark matter (CDM) isocurvature contributions to the cosmological perturbations. By employing Markov Chain Monte Carlo method (MCMC), we perform a global analysis for cosmological parameters using the latest astronomical data, such as 7-year Wilkinson Microwave Anisotropy Probe (WMAP7) observations, matter power spectrum from the Sloan Digital Sky Survey (SDSS) luminous red galaxies (LRG), and "Union2" type Ia Supernovae (SNIa) sample. We find that the correlated mixture of adiabatic and isocurvature modes are mildly better fitting to the current data than the pure adiabatic ones, with the minimal $χ^2$ given by the likelihood analysis being reduced by 3.5. We also obtain a tight limit on the fraction of the CDM isocurvature contributions, which should be less than 14.6% at 95% confidence level. With the presence of the isocurvature modes, the adiabatic spectral index becomes slightly bigger, n_s^{\rm adi}=0.972\pm0.014~(1\,σ), and the tilt for isocurvature spectrum could be large, namely, the best fit value is n_s^{\rm iso}=3.020. Finally, we discuss the effect on WMAP normalization priors, shift parameter R, acoustic scale l_A and z_{*}, from the CDM isocurvaure perturbation. By fitting the mixed initial condition to the combined data, we find the mean values of R, l_A and z_{*} can be changed about 2.9σ, 2.8σand 1.5σrespectively, comparing with those obtained in the pure adiabatic condition.

astro-ph.CO↗

arXiv2010

Evidences for bouncing evolution before inflation in cosmological surveys

Inflationary cosmology with a preceding nonsingular bounce can lead to changes on the primordial density fluctuations. One significant prediction is that the amplitude of the power spectrum may undergo a jump at a critical scale. In this Letter we propose a phenomenological parametrization of the primordial power spectrum in this scenario and confront the jump feature with latest cosmological data. Performing a global fitting, we utilize this possibility to derive a novel method for constraining bounce parameters via cosmological measurements. Combining the CMB, LSS and SNIa data, our result interestingly reveals that a nonsingular bounce, if exists, should be a fast bounce which happens at a very high energy scale, as we get an upper limit on the bounce parameters.

astro-ph.CO↗

arXiv2010

Aligned Graphene Nanoribbons and Crossbars from Unzipped Carbon Nanotubes

Aligned graphene nanoribbon (GNR) arrays were made by unzipping of aligned single-walled and few-walled carbon nanotube (CNT) arrays. Nanotube unzipping was achieved by a polymer-protected Ar plasma etching method, and the resulting nanoribbon array was transferred onto any substrates. Atomic force microscope (AFM) imaging and Raman mapping on the same CNTs before and after unzipping confirmed that ~80% of CNTs were opened up to form single layer sub-10 nm GNRs. Electrical devices made from the GNRs (after annealing in H2 at high temperature) showed on/off current (Ion/Ioff) ratios up to 103 at room temperature, suggesting semiconducting nature of the narrow GNRs. Novel GNR-GNR and GNR-CNT crossbars were fabricated by transferring GNR arrays across GNR and CNT arrays, respectively. The production of ordered graphene nanoribbon architectures may allow for large scale integration of GNRs into nanoelectronics or optoelectronics.

cond-mat.mtrl-sci↗

arXiv2010

The dynamical behavior of the Extended Holographic Dark Energy with Hubble Horizon

The extended holographic dark energy model with the Hubble horizon as the infrared cutoff avoids the problem of the circular reasoning of the holographic dark energy model. Unfortunately, it is hit with the no-go theorem. In this paper, we consider the extended holographic dark energy model with a potential, $V(ϕ)$, for the Brans-Dicke scalar field. With the addition of a potential for the Brans-Dicke scalar field, the extended holographic dark energy model using the Hubble horizon as the infrared cutoff is a viable dark energy model, and the model has the dark energy dominated attractor solution.

gr-qc↗

arXiv2010

Entropic cosmology: a unified model of inflation and late-time acceleration

Holography is expected as one of the promising descriptions of quantum general relativity. We present a model for a cosmological system involving two holographic screens and find that their equilibrium exactly yields a standard Friedmann-Robertson-Walker universe. We discuss its cosmological implications by taking into account higher order quantum corrections and quantum nature of horizon evaporation. We will show that this model could give rise to a holographic inflation at high energy scales and realize a late-time acceleration in a unified approach. We test our model from the SN Ia observations and find it can give a nice fit to the data.

astro-ph.CO↗

arXiv2010

A Markov Chain Monte Carlo Study on Dark Matter Property Related to the Cosmic e$^{\pm}$ Excesses

In this paper we develop a Markov Chain Monte Carlo code to study the dark matter properties in interpreting the recent observations of cosmic ray electron/positron excesses. We assume that the dark matter particles couple dominantly to leptons and consider two cases separately with annihilating or decaying into lepton pairs. The constraint on the central density profile from diffuse $γ$-rays around the Galactic center is also included in the Markov Chain Monte Carlo code self-consistently. In the numerical study, 7 parameters are introduced. We fit two data sets independently and find that for the Data set I (PAMELA+ATIC), dark matter with $m_χ\approx0.7$ TeV for annihilation (or 1.4 TeV for decay) and pure $e^+e^-$ channel is favored, while for the Data set II (PAMELA+Fermi-LAT+H.E.S.S.) $m_χ\approx 2$ TeV for annihilation (or 4 TeV for decay) and the combination of $μ^+μ^-$ and $τ^+τ^-$ final states can best fit the data. The H.E.S.S. observation of the Galactic center $γ$-rays puts a strong constraint on the central density profile of the dark matter halo for the annihilation dark matter scenario. In this case the NFW profile which is regarded as the typical predication from the cold dark matter scenario, is excluded with a high significance ($>5σ$). For the decaying dark matter scenario, the constraint is much weaker.

astro-ph.CO↗

arXiv2009

Nonlinear Ramsey interferometry with the Rosen-Zener pulses on a two-component Bose-Einstein condensate

We propose a feasible scheme to realize nonlinear Ramsey interferometry with a two-component Bose-Einstein condensate, where the nonlinearity arises from the interaction between coherent atoms. In our scheme, two Rosen-Zener pulses are separated by an intermediate holding period of variable duration and through varying the holding period we have observed nice Ramsey interference patterns in time domain. In contrast to the standard Ramsey fringes our nonlinear Ramsey patterns display diversiform structures ascribed to the interplay of the nonlinearity and asymmetry. In particular, we find that the frequency of the nonlinear Ramsey fringes exactly reflects the strength of nonlinearity as well as the asymmetry of system. Our finding suggests a potential application of the nonlinear Ramsey interferometry in calibrating the atomic parameters such as scattering length and energy spectrum.

cond-mat.other↗

arXiv2009

Berry Phase in Atom-Molecule Conversion Systems and Fractional Monopole

We investigate the geometric phase or Berry phase of adiabatic quantum evolution in an atom-molecule conversion system, and find that the Berry phase in such system consists of two parts: the usual Berry connection term and a novel term from the nonlinearity brought forth by the atom-molecule conversion. The geometric phase can be viewed as the flux of the magnetic field of a monopole through the surface enclosed by a closed path in parameter space. The charge of the monopole, however, is found to be one third of the elementary charge of the usual quantized monopole.

cond-mat.quant-gas↗

arXiv2009

The electric current induced heat generation in a strongly interacting quantum dot in the Coulomb blockade regime

The heat generation by an electric current flowing through a quantum dot with the dot containing both electron-electron interaction and electron-phonon interaction, is studied. Using the non-equilibrium Keldysh Green's function method, the current-induced heat generation is obtained. We find that for a small phonon frequency, heat generation is proportional to the current. However, for a large phonon frequency, heat generation is in general qualitatively different from the current. It is non-monotonic with current and many unique and interesting behaviors emerge. The heat generation could be very large in the Coulomb blockade region, in which the current is very small due to the Coulomb blockade effect. On the other hand, in the resonant tunneling region, the heat generation is very small despite a large current, an ideal condition for device operation. In the curve of heat generation versus the bias, a negative differential of the heat generation is exhibited, although the current is always monotonously increasing with the bias voltage.

cond-mat.mes-hall↗

arXiv2009

Shapiro-like Resonance in Ultracold Molecule Production via an Oscillating Magnetic Field

We study the process of production of ultracold molecules from ultracold atoms using a sinusoidally oscillating magnetic field modulation. When the magnetic field is resonant roughly with the molecular binding energy, Shapiro-like resonances are observed. Their resonance profiles are well fitted by the Lorentzian functions. The line widths depend on both the amplitude and the duration of the applied modulations, and are found to be dramatically broadened by thermal dephasing effect. The resonance centers shift due to both many-body effect and finite temperature effect. Our theory is consistent with recent experiment (S. T. Thompson, E. Hodby, and C. E. Wieman, Phys. Rev. Lett. 95, 190404 (2005)). Our model predicts a 1/3 ceiling for the molecular production yield in uncondensed ultracold atomic clouds for a long coupling time, while for the condensed atoms the optimal conversion yield could be beyond the limit.

cond-mat.mes-hall↗

arXiv2009

Laser-assisted collision effect on nonsequential double ionization of helium in a few-cycle laser pulse

Nonsequential double ionization (NSDI) of helium in an intense few-cycle laser pulse is investigated by applying the three-dimensional semi-classical re-scattering method. It is found that the momentum distribution of He$^{2+}$ shows a single-double-single peak structure as the pulse intensity increases. According to the different mechanisms dominating the NSDI process, the laser intensity can be classified into three regimes where the momentum distribution of He$^{2+}$ exhibits different characteristics. In the relatively high intensity regime, an NSDI mechanism named the "laser-assisted collision ionization" is found to be dominating the NSDI process and causing the single peak structure. This result can shed light on the study of non-sequential ionization of a highly charged ion in a relatively intense laser pulse.

physics.atom-ph↗

arXiv2009

Testing Oscillating Primordial Spectrum and Oscillating Dark Energy with Astronomical Observations

In this paper we revisit the issue of determining the oscillating primordial scalar power spectrum and oscillating equation of state of dark energy from the astronomical observations. By performing a global analysis with the Markov Chain Monte Carlo method, we find that the current observations from five-year WMAP and SDSS-LRG matter power spectrum, as well as the "union" supernovae sample, constrain the oscillating index of primordial spectrum and oscillating equation of state of dark energy with the amplitude less than $|n_{\rm amp}|<0.116$ and $|w_{\rm amp}|<0.232$ at 95% confidence level, respectively. This result shows that the oscillatory structures on the primordial scalar spectrum and the equation of state of dark energy are still allowed by the current data. Furthermore, we point out that these kinds of modulation effects will be detectable (or gotten a stronger constraint) in the near future astronomical observations, such as the PLANCK satellite, LAMOST telescope and the currently ongoing supernovae projects SNLS.

astro-ph.CO↗

arXiv2008

Constraining Cosmological Parameters with Observational Data Including Weak Lensing Effects

In this paper, we study the cosmological implications of the 100 square degree Weak Lensing survey (the CFHTLS-Wide, RCS, VIRMOS-DESCART and GaBoDS surveys). We combine these weak lensing data with the cosmic microwave background (CMB) measurements from the WMAP5, BOOMERanG, CBI, VSA, ACBAR, the SDSS LRG matter power spectrum and the Type Ia Supernoave (SNIa) data with the "Union" compilation (307 sample), using the Markov Chain Monte Carlo method to determine the cosmological parameters. Our results show that the ΛCDM model remains a good fit to all of these data. For the dynamical dark energy model with time evolving EoS parameterized as w_{\DE}(a) = w_0 + w_a (1-a), we find that the best-fit model implying the mildly preference of Quintom model whose EoS gets across the cosmological constant boundary during evolution. Regarding the total neutrino mass limit, we obtain the upper limit, \sum m_ν< 0.471 eV (95% C.L.) within the framework of the flat ΛCDM model. Due to the obvious degeneracies between the neutrino mass and the EoS of dark energy model, this upper limit will be relaxed by a factor of 2 in the framework of dynamical dark energy models. For the constraints on the inflation parameters, we find that the upper limit on the ratio of the tensor to scalar is r<0.35 (95% C.L.) and the inflationary models with the slope n_s\geq1 are excluded at more than 2 σconfidence level. In this paper we pay particular attention to the contribution from the weak lensing data and find that the current weak lensing data do improve the constraints on matter density Ω_m, σ_8, \sum{m_ν}, and the EoS of dark energy.

astro-ph↗

arXiv2008

Reading molecular messages from the intersections of high-order harmonic spectra at different orientations

We investigate the orientation dependence of high-order harmonic generation (HHG) from H$_2^+$ with different internuclear distances irradiated by intense laser fields both numerically and analytically. The calculated molecular HHG spectra are found to be sensitive to molecular axis orientation relative to incident laser field polarization and internuclear separation. In particular, the spectra calculated for different orientation angles demonstrate a kind of intersection, which is identified as arising due to intramolecular two-center interference in the HHG. The striking "intersection" phenomenon can be used to probe the molecular instantaneous structure.

physics.atom-ph↗

arXiv2008

Non-existence of Extended Holographic Dark Energy with Hubble Horizon

The extended holographic dark energy model with the Hubble horizon as the infrared cutoff avoids the problem of the circular reasoning of the holographic dark energy model. We show that the infrared cutoff of the extended holographic dark energy model cannot be the Hubble horizon provided that the Brans-Dicke parameter $ω$ satisfies the experimental constraint $ω> 10^4$, and this is proved as a no-go theorem. The no-go theorem also applies to the case in which the dark matter interacts with the dark energy.

gr-qc↗

arXiv2008

Many-Body Effects on Nonadiabatic Feshbach Conversion in Bosonic Systems

We investigate the dynamics of converting cold bosonic atoms to molecules when an external magnetic field is swept across a Feshbach resonance. Our analysis relies on a zero temperature quantum microscopic model that accounts for many-body effects, triggering the association process. We show that the picture of two-body molecular production depicted by Landau-Zener model is significantly altered due to many-body effects. In nonadiabatic regime, we derive an analytic expression for molecular conversion efficiency that explains the discrepancy between the prediction of Landau-Zener formula and experimental data[Hodby et al., Phys. Rev. Lett. {\bf 94}, 120402 (2005)]. Our theory is further extended to the formation of heteronuclear diatomic molecules and gives some interesting predictions.

cond-mat.mes-hall↗

arXiv2008

The role of particle interactions in a many-body model of Feshbach molecular formation in bosonic systems

In this paper, we investigate the atom-molecule conversion dynamics of a generalized many-body model that includes the atom-atom, atom-molecule, and molecule-molecule interactions, emphasizing the efficiency of the Feshbach molecular formation. We show that the picture of two-body molecular production depicted by the Landau-Zener model is significantly altered: The energy levels are dramatically distorted and the conversion efficiency is suppressed by the particle interactions. According to the rule of constant action and with the help of phase-space analysis, we derive an analytical expression for the conversion efficiency in the adiabatic limit. It shows a ceiling for the conversion efficiency when the interaction strength is larger than a critical value. We further derive a closed equation for the conversion efficiency with the stationary phase approximation. In the sudden limit, the conversion efficiency is twice that predicted by the two-body Landau-Zener formula. Our analytical formula has been confirmed by numerical calculations.

cond-mat.mes-hall↗

arXiv2008

Constraints on Dark Energy Models from Weak Gravity Conjecture

We study the constraints on the dark energy model with constant equation of state parameter $w=p/ρ$ and the holographic dark energy model by using the weak gravity conjecture. The combination of weak gravity conjecture and the observational data gives $w<-0.7$ at the $3σ$ confidence level. The holographic dark energy model realized by a scalar field is in swampland.

gr-qc↗