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Magnetic Field of a Compact Spherical Star under f(R,T) Gravity
Safiqul Islam, Shantanu Basu
Chin. Phys. Lett.    2018, 35 (9): 099501 .   DOI: 10.1088/0256-307X/35/9/099501
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We present the interior solutions of distributions of magnetized fluid inside a sphere in $f(R,T)$ gravity. The magnetized sphere is embedded in an exterior Reissner–Nordström metric. We assume that all physical quantities are in static equilibrium. The perfect fluid matter is studied under a particular form of the Lagrangian density $f(R,T)$. The magnetic field profile in modified gravity is calculated. Observational data of neutron stars are used to plot suitable models of magnetized compact objects. We reveal the effect of $f(R,T)$ gravity on the magnetic field profile, with application to neutron stars, especially highly magnetized neutron stars found in x-ray pulsar systems. Finally, the effective potential $V_{\rm eff}$ and innermost stable circular orbits, arising out of the motion of a test particle of negligible mass influenced by attraction or repulsion from the massive center, are discussed.
Gravitational constant in f(R) theories of gravity with non-minimal coupling between matter and geometry
Jun Wang, Li-Jia Cao
Chin. Phys. Lett.    2018, 35 (12): 129801 .   DOI: 10.1088/0256-307X/35/12/129801
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We study the effect of the non-minimal coupling between matter and geometry on the gravitational constant in the context of $f(R)$ theories of gravity on cosmic scales. For a class of $f(R)$ models, the result shows that the value of the gravitational constant not only changes over time but also has the dampened oscillation behavior. Compared with the result of the standard ${\it \Lambda}$CDM model, the consequence suggests that the coupling between matter and geometry should be weak.
Global Statistical Study of Ionospheric Waves Based on COSMIC GPS Radio Occultation Data
Xuan-Yun Zeng, Xiang-Hui Xue, Xin-An Yue, Ming-Jiao Jia, Bing-Kun Yu, Jian-Fei Wu, Chao Yu
Chin. Phys. Lett.    2018, 35 (10): 109401 .   DOI: 10.1088/0256-307X/35/10/109401
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Extracting and parameterizing ionospheric waves globally and statistically is a longstanding problem. Based on the multichannel maximum entropy method (MMEM) used for studying ionospheric waves by previous work, we calculate the parameters of ionospheric waves by applying the MMEM to numerously temporally approximate and spatially close global-positioning-system radio occultation total electron content profile triples provided by the unique clustered satellites flight between years 2006 and 2007 right after the constellation observing system for meteorology, ionosphere, and climate (COSMIC) mission launch. The results show that the amplitude of ionospheric waves increases at the low and high latitudes ($\sim$0.15 TECU) and decreases in the mid-latitudes ($\sim$0.05 TECU). The vertical wavelength of the ionospheric waves increases in the mid-latitudes (e.g., $\sim$50 km at altitudes of 200–250 km) and decreases at the low and high latitudes (e.g., $\sim$35 km at altitudes of 200–250 km). The horizontal wavelength shows a similar result (e.g., $\sim$1400 km in the mid-latitudes and $\sim$800 km at the low and high latitudes).
Effect of Tidal Torques on Rotational Mixing in Close Binaries
Zhi Li, Han-Feng Song, Wei-Guo Peng
Chin. Phys. Lett.    2018, 35 (7): 079701 .   DOI: 10.1088/0256-307X/35/7/079701
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The effect of tidal torques on rotational mixing in close binaries is investigated. It is found that spin angular momentum can attain a high value due to a strong tidal torque. Nitrogen and helium enrichment occurs early in the binary system that is triggered by tides. The stellar radius can reach a high value in the single star model with high initial velocities at the early stage of the evolution, but efficient rotational mixing can inhibit stellar expanding at the subsequent evolution. Central compactness is increased by the centrifugal force at the early stage of evolution but is reduced by rotational mixing induced by strong tides. The binary models with weak tides have high values of central temperature and stellar radius. Rotational mixing in single stars can slow down the shrinkage of convective cores, while convective cores can be expanded by strong tides in the binary system. Efficient rotational mixing induced by tides can cause the star to evolve towards high temperature and luminosity.
Effect of Kinetic Alfvén Waves on Electron Transport in an Ion-Scale Flux Rope
Bin-Bin Tang, Wen-Ya Li, Chi Wang, Lei Dai, Jin-Peng Han
Chin. Phys. Lett.    2018, 35 (11): 119401 .   DOI: 10.1088/0256-307X/35/11/119401
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At the Earth's magnetopause, the electron transport due to kinetic Alfvén waves (KAWs) is investigated in an ion-scale flux rope by the Magnetospheric Multiscale mission. Clear electron dropout around 90$^{\circ}$ pitch angle is observed throughout the flux rope, where intense KAWs are identified. The KAWs can effectively trap electrons by the wave parallel electric field and the magnetic mirror force, allowing electrons to undergo Landau resonance and be transported into more field-aligned directions. The pitch angle range for the trapped electrons is estimated from the wave analysis, which is in good agreement with direct pitch angle measurements of the electron distributions. The newly formed beam-like electron distribution is unstable and excites whistler waves, as revealed in the observations. We suggest that KAWs could be responsible for the plasma depletion inside a flux rope by this transport process, and thus be responsible for the formation of a typical flux rope.
Neutrino Emission and Cooling of Dark-Matter-Admixed Neutron Stars
Wen-Bo Ding, Zi Yu, Yan Xu, Chun-Jian Liu, Tmurbagan Bao
Chin. Phys. Lett.    2019, 36 (4): 049701 .   DOI: 10.1088/0256-307X/36/4/049701
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The GW170817 binary neutron star merger event in 2017 has raised great interest in the theoretical research f neutron stars. The structure and cooling properties of dark-matter-admixed neutron stars are studied here using relativistic mean field theory and cooling theories. The non-self-annihilating dark matter (DM) component is assumed to be ideal fermions, among which the weak interaction is considered. The results show that pulsars J1614-2230, J0348+0432 and EXO 0748-676 may all contain DM with the particle mass of 0.2–0.4 GeV. However, it is found that the effect of DM on neutron star cooling is complicated. Light DM particles favor the fast cooling of neutron stars, and the case is converse for middle massive DM. However, high massive DM particles, around 1.0 GeV, make the low mass (around solar mass) neutron star still undergo direct Urca process of nucleons at the core, which leads the DM-admixed stars cool much more quickly than the normal neutron star, and cannot support the direct Urca process with a mass lower than 1.1 times solar mass. Thus, we may conjecture that if small (around solar mass) and super cold (at least surface temperature 5–10 times lower than that of the usual observed data) pulsars are observed, then the star may contain fermionic DM with weak self-interaction.
Comparison of Proton Shower Developments in the BGO Calorimeter of the Dark Matter Particle Explorer between GEANT4 and FLUKA Simulations
Wei Jiang, Chuan Yue, Ming-Yang Cui, Xiang Li, Qiang Yuan, Francesca Alemanno, Paolo Bernardini, Giovanni Catanzani, Zhan-Fang Chen, Ivan De Mitri, Tie-Kuang Dong, Giacinto Donvito, David Francois Droz, Piergiorgio Fusco, Fabio Gargano, Dong-Ya Guo, Dimitrios Kyratzis, Shi-Jun Lei, Yang Liu, Francesco Loparco, Peng-Xiong Ma, Giovanni Marsella, Mario Nicola Mazziotta, Xu Pan, Wen-Xi Peng, Antonio Surdo, Andrii Tykhonov, Yi-Yeng Wei, Yu-Hong Yu, Jing-Jing Zang, Ya-Peng Zhang, Yong-Jie Zhang, and Yun-Long Zhang
Chin. Phys. Lett.    2020, 37 (11): 119601 .   DOI: 10.1088/0256-307X/37/11/119601
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The DArk Matter Particle Explorer (DAMPE) is a satellite-borne detector for high-energy cosmic rays and $\gamma$-rays. To fully understand the detector performance and obtain reliable physical results, extensive simulations of the detector are necessary. The simulations are particularly important for the data analysis of cosmic ray nuclei, which relies closely on the hadronic and nuclear interactions of particles in the detector material. Widely adopted simulation softwares include the GEANT4 and FLUKA, both of which have been implemented for the DAMPE simulation tool. Here we describe the simulation tool of DAMPE and compare the results of proton shower properties in the calorimeter from the two simulation softwares. Such a comparison gives an estimate of the most significant uncertainties of our proton spectral analysis.
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