arXiv subjects

Qing Gao

Publications and source records attributed to Qing Gao.

At least 73 records · Page 4Linked to original sources

arXiv2018

Reconstruction of extended inflationary potentials for attractors

We give the procedure to reconstruct the extended inflationary potentials for attractors and use the $α$ attractor and the constant-roll model as examples to show how to reconstruct the class of extended inflationary potentials in the strong coupling limit. We also derive the strong coupling condition which the coupling constant $ξ$ satisfies. The class of extended inflationary potentials has the same attractor, and the reconstructed extended inflationary potentials are consistent with the observational constraints. The existence of the attractors from extended inflationary models further challenges the model discrimination just by the observables $n_s$ and $r$.

gr-qc↗

arXiv2018

Constant-roll tachyon inflation and observational constraints

For the constant-roll tachyon inflation, we derive the analytical expressions for the scalar and tensor power spectra, the scalar and tensor spectral tilts and the tensor to scalar ratio up to the first order by using the method of Bessel function approximation. The derived $n_s-r$ results for the constant-roll inflation are also compared with the observations, we find that only one constant-roll inflation is consistent with the observations and observations constrain the constant-roll inflation to be slow-roll inflation. The tachyon potential is also reconstructed for the constant-roll inflation which is consistent with the observations.

gr-qc↗

arXiv2018

An Exponential Quantum Projection Filter for Open Quantum Systems

An approximate exponential quantum projection filtering scheme is developed for a class of open quantum systems described by Hudson- Parthasarathy quantum stochastic differential equations, aiming to reduce the computational burden associated with online calculation of the quantum filter. By using a differential geometric approach, the quantum trajectory is constrained in a finite-dimensional differentiable manifold consisting of an unnormalized exponential family of quantum density operators, and an exponential quantum projection filter is then formulated as a number of stochastic differential equations satisfied by the finite-dimensional coordinate system of this manifold. A convenient design of the differentiable manifold is also presented through reduction of the local approximation errors, which yields a simplification of the quantum projection filter equations. It is shown that the computational cost can be significantly reduced by using the quantum projection filter instead of the quantum filter. It is also shown that when the quantum projection filtering approach is applied to a class of open quantum systems that asymptotically converge to a pure state, the input-to-state stability of the corresponding exponential quantum projection filter can be established. Simulation results from an atomic ensemble system example are provided to illustrate the performance of the projection filtering scheme. It is expected that the proposed approach can be used in developing more efficient quantum control methods.

math-ph↗

arXiv2018

Do long-cadence data of {\it Kepler} satellite capture the basic properties of flares ?

Flare research is becoming a burgeoning realm in the study of stellar activity due to the launch of {\it Kepler} in 2009. {\it Kepler} provides data with two time resolutions, i.e., the long-cadence (LC) data with a time resolution of 30 minutes and the short-cadence(SC) data with a time resolution of 1 minute, both of which can be used to study stellar flares. In this paper, we search flares in light curves with both LC data and SC data, and compare them in aspects of the true-flare rate, the flare energy, the flare amplitude, and the flare duration. It is found that LC data systematically underestimated the energies of flares by 25\%, and underestimated the amplitudes of flares by 60\% compared with SC flares. The duration are systematically overestimated by 50\% compared with SC flares. However, the above percentages are poorly constrained and there is a lot of scatter. About 60\% SC flares have not been detected by LC data. We investigate the limitation of LC data, and suggest that although LC data cannot reflect the detailed profiles of flares, they also can capture the basic properties of stellar flares.

astro-ph.SR↗

arXiv2018

The observational constraint on constant-roll inflation

We discuss the constant-roll inflation with constant $ε_2$ and constant $\barη$. By using the method of Bessel function approximation, the analytical expressions for the scalar and tensor power spectra, the scalar and tensor spectral tilts, and the tensor to scalar ratio are derived up to the first order of $ε_1$. The model with constant $ε_2$ is ruled out by the observations at the $3σ$ confidence level, and the model with constant $\barη$ is consistent with the observations at the $1σ$ confidence level. The potential for the model with constant $\barη$ is also obtained from the Hamilton-Jacobi equation. Although the observations constrain the constant-roll inflation to be slow-roll inflation, the $n_s-r$ results from the constant-roll inflation are not the same as those from the slow-roll inflation even when $\barη\sim 0.01$.

gr-qc↗

arXiv2017

Self-to-self transitions in open quantum systems: the origin and solutions

The information of quantum pathways can be extracted in the framework of the Hamiltonian-encoding and Observable-decoding method. For closed quantum systems, only off-diagonal elements of the Hamiltonian in the Hilbert space is required to be encoded to obtain the desired transitions. For open quantum systems, environment-related terms will appear in the diagonal elements of the Hamiltonian in the Liouville space. Therefore, diagonal encodings have to be performed to differentiate different pathways, which will lead to self-to-self transitions and inconsistency of pathway amplitudes with Dyson expansion. In this work, a well-designed transformation is proposed to avoid the counter-intuitive transitions and the inconsistency, with or without control fields. A three-level open quantum system is employed for illustration, and numerical simulations show that the method are consistent with Dyson expansion.

quant-ph↗

arXiv2017

Reconstruction of constant slow-roll inflation

By using the relations between the slow-roll parameters and the power spectrum for the single field slow-roll inflation, we derive the scalar spectral tilt $n_s$ and the tensor to scalar ratio $r$ for the constant slow-roll inflation and obtain the constraint on the slow-roll parameter $η$ from the Planck 2015 results. The inflationary potential for the constant slow-roll inflation is then reconstructed in the framework of both general relativity and scalar-tensor theory of gravity, and compared with the recently reconstructed E model potential. In the strong coupling limit, we show that the $η$ attractor is reached.

astro-ph.CO↗

arXiv2017

Hybrid Filtering for a Class of Quantum Systems with Classical Disturbances

A filtering problem for a class of quantum systems disturbed by a classical stochastic process is investigated in this paper. The classical disturbance process, which is assumed to be described by a linear stochastic differential equation, is modeled by a quantum cavity model. Then the hybrid quantum-classical system is described by a combined quantum system consisting of two quantum cavity subsystems. Quantum filtering theory and a quantum extended Kalman filter method are employed to estimate the states of the combined quantum system. An estimate of the classical stochastic process is derived from the estimate of the combined quantum system. The effectiveness and performance of the proposed methods are illustrated by numerical results.

quant-ph↗

arXiv2016

Alignment and measurement of the magnetic field for the BESIII muon counter

Based on cosmic ray events without a magnetic field taken with the BESIII detector during the summer shutdown of BEPCII in 2012 and di-muon events from a data sample taken at center-of-mass energy of 3.686 GeV in 2009, we compare the coordinates of hits registered in the BESIII muon counter with the expected interaction point extrapolated from reconstructed tracks from the inner tracking system in the absence of a magnetic field. By minimizing the difference, we align the muon counter with the inner tracking system. Moreover, the strength of the magnetic field in the muon counter is measured for the first time with di-muon events from data taken at a center-of-mass energy of 3.686~GeV. After the alignment and the magnetic field strength measurement, the offsets in the reconstructed hit positions for muon tracks are reduced, which improves the muon identification. The alignment and magnetic field strength measurement have been adopted in the latest version of the BESIII offline software system. This addition to the software reduces the systematic uncertainty for the physics analysis in cases where the muon counter information is used.

physics.ins-det↗

arXiv2016

Inflationary models with non-minimally derivative coupling

We derive the general formulae for the the scalar and tensor spectral tilts to the second order for the inflationary models with non-minimally derivative coupling without taking the high friction limit. The non-minimally kinetic coupling to Einstein tensor brings the energy scale in the inflationary models down to be sub-Planckian. In the high friction limit, the Lyth bound is modified with an extra suppression factor, so that the field excursion of the inflaton is sub-Planckian. The inflationary models with non-minimally derivative coupling are more consistent with observations in the high friction limit. In particular, with the help of the non-minimally derivative coupling, the quartic power law potential is consistent with the observational constraint at 95\% CL.

gr-qc↗

arXiv2016

Time-Variable Aluminum Absorption in the Polar AR Ursae Majoris, and an Updated Estimate for the Mass of the White Dwarf

We present spectra of the extreme polar AR Ursae Majoris (AR UMa) which display a clear Al I absorption doublet, alongside spectra taken less than a year earlier in which that feature is not present. Re-examination of earlier SDSS spectra indicates that the Al I absorption doublet was also present $\approx$8 years before our first non-detection. We conclude that this absorbing material is unlikely to be on the surface of either the white dwarf (WD) or the donor star. We suggest that this Al I absorption feature arises in circumstellar material, perhaps produced by the evaporation of asteroids as they approach the hot WD. The presence of any remaining reservoir of rocky material in AR UMa might help to constrain the prior evolution of this unusual binary system. We also apply spectral decomposition to find the stellar parameters of the M dwarf companion, and attempt to dynamically measure the mass of the WD in AR UMa by considering both the radial velocity curves of the H$_β$ emission line and the Na I absorption line. Thereby we infer a mass range for the WD in AR UMa of 0.91 $M_{\odot}$ $<$ $M_{\mathrm{WD}}$ $<$ 1.24 $M_{\odot}$.

astro-ph.HE↗

arXiv2016

The reconstruction of inflationary potentials

The observational data on the anisotropy of the cosmic microwave background constraints the scalar spectral tilt $n_s$ and the tensor to scalar ratio $r$ which depend on the first and second derivatives of the inflaton potential. The information can be used to reconstruct the inflaton potential in the polynomial form up to some orders. However, for some classes of potentials, $n_s$ and $r$ behave as $n_s(N)$ and $r(N)$ universally in terms of the number of e-folds $N$. The universal behaviour of $n_s(N)$ can be used to reconstruct a class of inflaton potentials. By parametrizing one of the parameters $n_s(N)$, $ε(N)$ and $ϕ(N)$, and fitting the parameters in the models to the observational data, we obtain the constraints on the parameters and reconstruct the classes of the inflationary models which include the chaotic inflation, T-model, hilltop inflation, s-dual inflation, natural inflation and $R^2$ inflation.

gr-qc↗

arXiv2016

The Distance Measurement of NGC 1313 With Cepheids

We present the detection of Cepheids in the barred spiral galaxy NGC 1313, using the Wide Field and Planetary Camera 2 on the Hubble Space Telescpoe. Twenty B (F450W) and V (F555W) epochs of observations spanning over three weeks were obtained, on which the profile-fitting photometry of all stars in the monitored field was performed using the package HSTphot. A sample of 26 variable stars have been identified to be Cepheids, with periods between 3 and 14 days. Based on the derived period-luminosity relations in B and V bands, we obtain an extinction-corrected distance modulus of mu = 28.32 +- 0.08 (random) +- 0.06 (systematic), employing the Large Magellanic Cloud as the distance zero point calibrator. The above moduli correspond to a distance of 4.61 +- 0.17 (random) +- 0.13 (systematic) Mpc, consistent with previous measurements reported in the literature with uncertainties. In addition, the reddening to NGC 1313 is found to be small.

astro-ph.SR↗

arXiv2016

White-Light Flares on Close Binaries Observed with Kepler

Based on Kepler data, we present the results of a search for white-light flares on 1049 close binaries. We identify 234 flare binaries, on which 6818 flares are detected. We compare the flare-binary fraction in different binary morphologies ("detachedness"). The result shows that the fractions in over-contact and ellipsoidal binaries are approximately 10-20 percent lower than those in detached and semi-detached systems. We calculate the binary flares activity level (AL) of all the flare binaries, and discuss its variations along the orbital period (P_orb) and rotation period (P_rot, calculated for only detached binaries). We find that AL increases with decreasing P_orb or P_rot up to the critical values at P_orb near 3 days or P_rot near 1.5 days, thereafter, the AL starts decreasing no matter how fast the stars rotate. We examine the flaring rate as a function of orbital phase in 2 eclipsing binaries on which a large number of flares are detected. It appears that there is no correlation between flaring rate and orbital phase in these 2 binaries. In contrast, when we examine the function with 203 flares on 20 non-eclipse ellipsoidal binaries, bimodal distribution of amplitude weighted flare numbers shows up at orbital phase 0.25 and 0.75. Such variation could be larger than what is expected from the cross-section modification.

astro-ph.SR↗

arXiv2016

Fault Tolerant Filtering and Fault Detection for Quantum Systems Driven By Fields in Single Photon States

The purpose of this paper is to solve a fault tolerant filtering and fault detection problem for a class of open quantum systems driven by a continuous-mode bosonic input field in single photon states when the systems are subject to stochastic faults. Optimal estimates of both the system observables and the fault process are simultaneously calculated and characterized by a set of coupled recursive quantum stochastic differential equations.

quant-ph↗

arXiv2015

Fault Tolerant Quantum Filtering and Fault Detection for Quantum Systems

This paper aims to determine the fault tolerant quantum filter and fault detection equation for a class of open quantum systems coupled to a laser field that is subject to stochastic faults. In order to analyze this class of open quantum systems, we propose a quantum-classical Bayesian inference method based on the definition of a so-called quantum-classical conditional expectation. It is shown that the proposed Bayesian inference approach provides a convenient tool to simultaneously derive the fault tolerant quantum filter and the fault detection equation for this class of open quantum systems. An example of two-level open quantum systems subject to Poisson-type faults is presented to illustrate the proposed method. These results have the potential to lead to a new fault tolerant control theory for quantum systems.

math-ph↗

arXiv2015

The Phase-space analysis of scalar fields with non-minimally derivative coupling

We perform a dynamical analysis for the exponential scalar field with non-minimally derivative coupling. For the quintessence case, the stable fixed points are the same with and without the non-minimally derivative coupling. For the phantom case, the attractor with dark energy domination exists for the minimal coupling only. For the non-minimally derivative coupling without the standard canonical kinetic term, only the de-Sitter attractor exists, and the dark matter solution is unstable.

gr-qc↗

arXiv2015

Modified Lyth bound and implications of BICEP2 results

To reconcile the BICEP2 measurement on the tensor-to-scalar ratio $r$ with Planck constraint, a large negative running of scalar spectral index $n_s$ is needed. So the inflationary observable such as $n_s$ should be expanded at least to the second-order slow-roll parameters for single-field inflationary models. The large value of $r$ and the Lyth bound indicate that it is impossible to obtain the sub-Planckian excursion for the inflaton. However, we derive an absolutely minimal bound $Δϕ/M_{\rm Pl}>\sqrt{r/2}$ on the inflaton excursion for single-field inflationary models, which can be applied to non-slow-roll inflationary models as well. This bound excludes the possibility of the small-field inflation with $Δϕ<0.1 M_{\rm Pl}$ if the BICEP2 result on $r$ stands and it opens the window of sub-Planckian excursion with $Δϕ<M_{\rm Pl}$ even if $r$ is as large as $0.1$. To get the sub-Planckian excursion with $Δϕ<0.1 M_{\rm Pl}$, our modified bound requires $r<0.02$. Using a fifth-order polynomial potential as an explicit example, we show that it not only agrees with the observational results, but also violates the Lyth bound.

gr-qc↗