An evolutionary game based particle swarm optimization algorithm

AbstractParticle swarm optimization (PSO) is an evolutionary algorithm used extensively. This paper presented a new particle swarm optimizer based on evolutionary game (EGPSO). We map particles’ finding optimal solution in PSO algorithm to players’ pursuing maximum utility by choosing strategies in evolutionary games, using replicator dynamics to model the behavior of particles. And in order to overcome premature convergence a multi-start technique was introduced. Experimental results show that EGPSO can overcome premature convergence and has great performance of convergence property over traditional PSO

On joint analysing XMM-NuSTAR spectra of active galactic nuclei

A recently released XMM-Newton technical note has revealed a significant calibration issue between NuSTAR and XMM-Newton EPIC, and provided an empirical correction to EPIC effective area. To quantify the bias caused by the calibration issue to joint analysis of XMM-NuSTAR spectra and verify the effectiveness of the correction, in this work we perform joint-fitting of NuSTAR and EPIC-pn spectra for a large sample of 104 observation pairs of 44 X-ray bright AGN. The spectra were extracted after requiring perfect simultaneity between XMM-Newton and NuSTAR exposures (merging GTIs from two missions) to avoid bias due to rapid spectral variability of AGN. Before the correction, the EPIC-pn spectra are systematically harder than corresponding NuSTAR spectra by $\Delta \Gamma \sim 0.1$, subsequently yielding significantly underestimated cutoff energy $E_{\rm cut}$ and the strength of reflection component R when performing joint-fitting. We confirm the correction is highly effective and can commendably erase the discrepancy in best-fit $\Gamma$, $E_{\rm cut}$ and R, and thus we urge the community to apply the correction when joint-fitting XMM-NuSTAR spectra. Besides, we show that as merging GTIs from two missions would cause severe loss of NuSTAR net exposure time, in many cases joint-fitting yields no advantage compared with utilizing NuSTAR data alone. We finally present a technical note on filtering periods of high background flares for XMM-Newton EPIC-pn exposures in the Small Window mode.Comment: 14 pages, 8 figures, submitted. Comments are very welcome

What can be learnt from a highly informative X-ray occultation event in NGC 6814? A marvellous absorber

A unique X-ray occultation event in NGC 6814 during an XMM-Newton observation in 2016 has been reported, providing useful information of the absorber and the corona. We revisit the event with the aid of the hardness ratio (HR) - count rate (CR) plot and comparison with two other absorption-free XMM exposures in 2009 and 2021. NGC 6814 exhibits a clear "softer-when-brighter" variation pattern during the exposures, but the 2016 exposure significantly deviates from the other two in the HR - CR plot. While spectral fitting does yield transient Compton-thin absorption corresponding to the eclipse event in 2016, rather than easing the tension between exposures in the HR - CR plot, correcting the transient Compton-thin absorption results in new and severe deviation within the 2016 exposure. We show that the eclipsing absorber shall be clumpy (instead of a single Compton-thin cloud), with an inner denser region composed of both Compton-thin and Compton-thick clouds responsible for the previously identified occultation event, and an outer sparser region with Compton-thin clouds which eclipses the whole 2016 exposure. With this model, all the tension in the HR - CR plots could be naturally erased, with the observed spectral variability during the 2016 exposure dominated by the variation of absorption. Furthermore, the two warm absorbers (with different ionization and column densities but similar outflowing velocities) detected in the 2016 exposure shall also associate with the transient absorber, likely due to ablated or tidal stretched/disrupted fragments. This work highlights the unique usefulness of the HR - CR plot while analysing rare occultation events.Comment: 13 pages, 9 figures, accepted by MNRAS. For the video of the eclipsing cloud, see https://drive.google.com/file/d/1CEsPEWE-b5W8PfZINyI5K1sE6klHaYMa/view?usp=sharing . Comments are welcome

Strong decays of low-lying DD-wave Ξb/Ξb′\Xi_b/\Xi_b' baryons with QPC model

For further decoding the inner structure of the two excited $\Xi_b$ states observed by LHCb, we perform a systematical study of the strong decays of the low-lying $1D$-wave $\Xi_b$ and $\Xi_b'$ excitations using the quark pair creation model within the $j-j$ coupling scheme. Combining with the measured masses and decay properties of $\Xi_{b}(6327)^{0}$ and $\Xi_{b}(6327)^{0}$, the two excited states can be explained as $1D$ $\lambda$-mode $\Xi_b$ states $\Xi_{b}|J^{P}=\frac{3}{2}^{+},2\rangle_{\lambda\lambda}$ and $\Xi_{b}|J^{P}=\frac{5}{2}^{+},2\rangle_{\lambda\lambda}$, respectively. If such a view were correct, $\Xi_b'\pi$ and $\Xi_b'^*\pi$ could be another interesting channels for experimental exploring of the $\Xi_{b}(6327)^{0}$ and $\Xi_{b}(6327)^{0}$, respectively. Those calculations are good consistent with the results within the chiral quark model. In addition, for the other missing $1D$-wave $\Xi_b$ and $\Xi_b'$ excitations, our predictions indicate that:(i) the two $\rho$-mode $1D$ $\Xi_b$ states are likely to be moderate states with a width of $\Gamma\sim50$ MeV. The $J^P=3/2^+$ state dominantly decays into $\Sigma_bK$ and $\Xi_b'\pi$, while the $J^P=5/2^+$ state decays primarily through $\Sigma_b^*K$ and $\Xi_b'^*\pi$. (ii) The $\lambda$-mode $1D$ $\Xi_b'$ states may be moderate states with a widths of about several to dozens of MeV. Most of the $\lambda$-mode $1D$ $\Xi_b'$ states mainly decay into the $1P$-wave bottomed baryon via the pionic decay processes. Meanwhile, several $\lambda$-mode $1D$ $\Xi_b'$ states have significant decay rates into $\Lambda B$. (iii) While, the $\rho$-mode $1D$ $\Xi_b'$ states are predicted to be very broad states with a width of about several hundreds MeV. It will be a great challenge to explore the $\rho$-mode $1D$ $\Xi_b'$ states in experiments for their broad widths.Comment: 11 pages, 5 figure

Strong decays of the low-lying 1P1P- and 1D1D-wave Σc\Sigma_c baryons

In this work, we systematically study the OZI-allowed two-body strong decay properties of $1P$- and $1D$-wave $\Sigma_c$ baryons within the $j$-$j$ coupling scheme in the framework of the quark pair creation model. For a comparison, we also give the predictions of the chiral quark model. Some model dependencies can be found in the predictions of two models. The calculations indicate that: (i) The $1P$-wave $\lambda$-mode $\Sigma_c$ states most likely to be relatively narrow states with a width of $\Gamma<80$ MeV. Their main decay channels are $\Lambda_c\pi$, or $\Sigma_c\pi$, or $\Sigma_c^*\pi$. The $1P$-wave $\rho$-mode states most might be broad states with a width of $\Gamma\sim 100-200$ MeV. They dominantly decay into $\Sigma_c\pi$ and $\Sigma_c^*\pi$ channels. Some evidences of these $1P$-wave states are most likely to be observed in the $\Lambda_c\pi$ and $\Lambda_c\pi\pi$ invariant mass spectra around the energy range of $2.75-2.95$ GeV. (ii) The $1D$-wave $\lambda$-mode $\Sigma_c$ excitations may be moderate states with a width of about dozens of MeV. The $1D$-wave $\lambda$-mode states mainly decay into the $1P$-wave charmed baryon via the pionic decay processes. Meanwhile, several $1D$-wave $\lambda$-mode states have significant decay rates into $DN$ or $D^*N$. Hence, the $DN$ and $D^*N$ are likely to be interesting channels for experimental exploration. (iii) Furthermore, the two $1D$-wave $\rho$-mode excitations $\Sigma_c|J^P=5/2^+,3\rangle_{\rho\rho}$ and $|J^P=7/2^+,3\rangle_{\rho\rho}$ are most likely to be fairly narrow state with a width of dozens of MeV, and they mainly decay into $\Lambda_c\pi$. Some evidences of them might be observed in the $\Lambda_c\pi$ invariant mass spectra around the energy range of $3.1-3.2$ GeV.Comment: 12 pages,5 figures, 4 tables. arXiv admin note: text overlap with arXiv:2208.1011