arXiv subjects

Y. B. Yu

Publications and source records attributed to Y. B. Yu.

10 recordsLinked to original sources

arXiv2022

Intermittent emission of particles from a Bose-Einstein condensate in a one-dimensional lattice

We investigate particle emission from a Bose-Einstein condensate with periodically modulated interactions in a one-dimensional lattice. Within perturbative analysis, which leads to instabilities for discrete modes, we obtain the main regimes where the system can emit a large particle jet, and find that the emission is distinctly intermittent rather than continuous. The time evolution of the trapped particles exhibits a stair-like decay, and a larger drive induces a more significant intermittency. We further shed light on the dynamics of the stimulating process, and demonstrate that instead of a real suspension, the intermittency represents a build-up stage of the system. The theoretical framework might be generalized to the explorations on multiple-site systems with analogous configurations and couplings, and offer new insights into other fundamental nonequilibrium problems.

cond-mat.quant-gas↗

arXiv2022

Resonant enhancement of particle emission from a parametrically driven condensate in a one-dimensional lattice

Motivated by recent experiments, we investigate particle emission from a Bose-Einstein condensate in a one-dimensional lattice, where the interaction strength is periodically modulated. The modulated interactions parametrically excite a collective mode, leading to density oscillations. These collective oscillations in turn drive particle emission. This multistep process amplifies the drive, producing larger particle jets. We find that the amplitude dependence of the emission rate has a characteristic threshold behavior, as seen in experiments.

cond-mat.quant-gas↗

arXiv2021

Emission of particles from a parametrically driven condensate in a one-dimensional lattice

Motivated by recent experiments, we calculate particle emission from a Bose-Einstein condensate trapped in a single deep well of a one-dimensional lattice when the interaction strength is modulated. In addition to pair emission, which has been widely studied, we observe single-particle emission. Within linear response, we are able to write closed-form expressions for the single-particle emission rates and reduce the pair emission rates to one-dimensional integrals. The full nonlinear theory of single-particle emission is reduced to a single variable integrodifferential equation, which we numerically solve.

cond-mat.quant-gas↗

arXiv2019

Charge nonconservation of molecular devices in the presence of a nonlocal potential

In the presence of a nonlocal potential in molecular device systems, generally the charge conservation cannot be satisfied, and in literatures the modifications of the conventional definition of current were given to solve this problem. We demonstrate that, however, the nonconservation is not due to the invalidation of the conventional definition of current, but originates respectively from the improper approximations to electron-electron interactions and the inappropriate definition of current using pseudo wave functions in pseudopotential implementations. In this work, we propose a nonlocal-potential formulation of the interactions to fulfill the charge conservation and also give a discussion about the calculation of current when the pseudopotential is involved. As an example of application of our formulation, we further present the calculated results of a double-barrier model.

cond-mat.mes-hall↗

arXiv2018

Bimodal distribution of short gamma-ray bursts: evidence for two distinct types of short gamma-ray bursts

Recently, GRB 170817A was confirmed to be associated with GW 170817, which was produced by a neutron star - neutron star merger. It indicates that at least some short gamma-ray bursts come from binary neutron star mergers. Theoretically, it is widely accepted that short gamma-ray bursts can be produced by two distinctly different mechanisms, binary neutron star mergers and neutron star - black hole mergers. These two kinds of bursts should be different observationally due to their different trigger mechanisms. Motivated by this idea, we collect a universal data set constituted of 51 short gamma-ray bursts observed by $Swift$/BAT, among which 14 events have extended emission component. We study the observational features of these 51 events statistically. It is found that our samples are consisted of two distinct groups. They clearly show a bimodal distribution when their peak photon fluxes at 15-150 keV band are plotted against the corresponding fluences. Most interestingly, all the 14 short bursts with extended emission lie in a particular region. When the fluences are plotted against the burst durations, short bursts with extended emission again tend to concentrate in the long duration segment. These features strongly indicate that short gamma-ray bursts really may come from two distinct types of progenitors. We argue that those short gamma-ray bursts with extended emission come from the coalescence of neutron stars, while the short gamma-ray bursts without extended emission come from neutron star - black hole mergers.

astro-ph.HE↗

arXiv2017

Searching for strange quark matter objects in exoplanets

The true ground state of hadronic matter may be strange quark matter (SQM). Consequently, the observed pulsars may actually be strange quark stars, but not neutron stars. However, proving or disproving the SQM hypothesis still remains to be a difficult problem, due to the similarity between the macroscopical characteristics of strange quark stars and neutron stars. Here we propose a hopeful method to probe the existence of strange quark matter. In the frame work of the SQM hypothesis, strange quark dwarfs and even strange quark planets can also stably exist. Noting that SQM planets will not be tidally disrupted even when they get very close to their host stars due to their extreme compactness, we argue that we could identify SQM planets by searching for very close-in planets among extrasolar planetary systems. Especially, we should keep our eyes on possible pulsar planets with orbital radius less than $\sim 5.6 \times 10^{10}$~cm and period less than $\sim 6100$~s. A thorough search in the currently detected $\sim 2950$ exoplanets around normal main sequence stars has failed to identify any stable close-in objects that meet the SQM criteria, i.e. lying in the tidal disruption region for normal matter planets. However, the pulsar planet PSR J1719-1438B, with an orbital radius of $\sim 6 \times 10^{10}$~cm and orbital period of $7837$~s, is encouragingly found to be a good candidate.

astro-ph.HE↗

arXiv2016

Delayed Energy Injection Model For Gamma-Ray Burst Afterglows

The shallow decay phase and flares in the afterglows of gamma-ray bursts (GRBs) is widely believed to be associated with the later activation of central engine. Some models of energy injection involve with a continuous energy flow since the GRB trigger time, such as the magnetic dipole radiation from a magnetar. However, in the scenario involving with a black hole accretion system, the energy flow from the fall-back accretion may be delayed for a fall-back time $\sim t_{\rm fb}$. Thus we propose a delayed energy injection model, the delayed energy would cause a notable rise to the Lorentz factor of the external shock, which will "generate" a bump in the multiple band afterglows. If the delayed time is very short, our model degenerates to the previous models. Our model can well explain the significant re-brightening in the optical and infrared light curves of GRB 081029 and GRB 100621A. A considerable fall-back mass is needed to provide the later energy, this indicates GRBs accompanied with fall-back material may be associated with a low energy supernova so that fraction of the envelope can be survived during eruption. The fall-back time can give meaningful information of the properties of GRB progenitor stars.

astro-ph.HE↗

arXiv2015

Signature of a spin-up magnetar from multi-band afterglow rebrightening of GRB 100814A

In recent years, more and more gamma-ray bursts with late rebrightenings in multi-band afterglows unveil the late-time activities of the central engines. GRB 100814A is a special one among the well-sampled events, with complex temporal and spectral evolution. The single power-law shallow decay index of the optical light curve observed by GROND between 640 s and 10 ks is $α_{\rm opt} = 0.57 \pm 0.02$, which apparently conflicts with the simple external shock model expectation. Especially, there is a remarkable rebrightening in the optical to near infrared bands at late time, challenging the external shock model with synchrotron emission coming from the interaction of the blast wave with the surrounding interstellar medium. In this paper, we invoke a magnetar with spin evolution to explain the complex multi-band afterglow emission of GRB 100814A. The initial shallow decay phase in optical bands and the plateau in X-ray can be explained as due to energy injection from a spin-down magnetar. At late time, with the falling of materials from the fall-back disk onto the central object of the burster, angular momentum of the accreted materials is transferred to the magnetar, which leads to a spin-up process. As a result, the magnetic dipole radiation luminosity will increase, resulting in the significant rebrightening of the optical afterglow. It is shown that the observed multi-band afterglow emission can be well reproduced by the model.

astro-ph.HE↗

arXiv2015

Reduced spin-down rate of PSR J0738-4042 explained as due to an asteroid disruption event

Long term observations by Brook et al. reveal that the derivative of rotational frequency of PSR J0738-4042 changed abruptly in 2005. Originally, the spin-down rate was relatively stable, with the rotational frequency derivative of $-1.14 \times 10^{-14}~\rm s^{-2}$. After September 2005, the derivative began to rise up. About 1000 days later, it arrived at another relatively stable value of about $-0.98 \times 10^{-14}~\rm s^{-2}$, indicating that the pulsar is spinning-down relatively slowly. To explain the observed spin-down rate change, we resort to an asteroid disrupted by PSR J0738-4042. In our model, the orbital angular momentum of the asteroid is assumed to be parallel to that of the rotating pulsar, so that the pronounced reduction in the spin-down rate can be naturally explained as due to the transfer of the angular momentum from the disrupted material to the central pulsar. The derived magnetospheric radius is about $4.0 \times 10^{9}$ cm, which is smaller than the tidal disruption radius ($4.9 \times 10^{10}$ cm). Our model is self-consistent. It is shown that the variability of the spin-down rate of PSR J0738-4042 can be quantitatively accounted for by the accretion from the asteroid disrupted by the central pulsar.

astro-ph.HE↗

arXiv2015

Fall back accretion and energy injections in gamma-ray bursts

Intense flares that occur at late times relative to the prompt phase have been observed by the $Swift$ satellite in the X-ray afterglows of gamma-ray bursts (GRBs). Here, we present a detailed analysis on the fall back accretion process to explain the intense flare phase in the very early X-ray afterglow light curves. To reproduce the afterglow at late times, we resort to the external shock by engaging energy injections. By applying our model to GRBs 080810, 081028 and 091029, we show that their X-ray afterglow light curves can be reproduced well. We then apply our model to the ultra-long $Swift$ GRB 111209A, which is the longest burst ever observed. The very early X-ray afterglow of GRB 111209A showed many interesting features, such as a significant bump observed at around 2000 s after the $Swift$/BAT trigger. We assume two constant energy injection processes in our model. These can explain the observed plateau at X-ray wavelength in the relatively early stage ($8.0\times10^{3}$ s) and a second X-ray plateau and optical rebrightening at about $10^{5}$ s. Our analysis supports the scenario that a significant amount of material may fall back toward the central engine after the prompt phase, causing an enhanced and long lived mass accretion rate powering a Poynting-flux-dominated outflow.

astro-ph.HE↗