# Bulk viscosity for interacting strange quark matter and r-mode instability windows for strange stars

• We investigate the bulk viscosity of strange quark matter in the framework of the equivparticle model, where analytical formulae are obtained for certain temperature ranges, which can be readily applied to those with various quark mass scalings. In the case of adopting a quark mass scaling with both linear confinement and perturbative interactions, the obtained bulk viscosity increases by $1 \sim 2$ orders of magnitude compared with those in bag model scenarios. Such an enhancement is mainly due to the large quark equivalent masses adopted in the equivparticle model, which are essentially attributed to the strong interquark interactions and are related to the dynamical chiral symmetry breaking. Due to the high bulk viscosity, the predicted damping time of oscillations for a canonical 1.4 ${\rm M}_\odot$ strange star is less than one millisecond, which is shorter than previous findings. Consequently, the obtained $r$-mode instability window for the canonical strange stars well accommodates the observational frequencies and temperatures for pulsars in low-mass X-ray binaries (LMXBs).

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Jian-Feng Xu, Dong-Biao Kang, Guang-Xiong Peng and Cheng-Jun Xia. Bulk viscosity for interacting strange quark matter and r-mode instability windows for strange stars[J]. Chinese Physics C. doi: 10.1088/1674-1137/abc0cd
Jian-Feng Xu, Dong-Biao Kang, Guang-Xiong Peng and Cheng-Jun Xia. Bulk viscosity for interacting strange quark matter and r-mode instability windows for strange stars[J]. Chinese Physics C.
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Revised: 2020-08-18
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沈阳化工大学材料科学与工程学院 沈阳 110142

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## Bulk viscosity for interacting strange quark matter and r-mode instability windows for strange stars

• 1. School of Physics & Electrical Engineering, AnYang Normal University, AnYang 455000, China
• 2. School of Nuclear Science and Technology, University of Chinese Academy of Sciences, Beijing 100049, China
• 3. Synergetic Innovation Center for Quantum Effects and Application, Hunan Normal University, Changsha 410081, China
• 4. School of Information Science and Engineering, Ningbo Tech University, Ningbo 315100, China

Abstract: We investigate the bulk viscosity of strange quark matter in the framework of the equivparticle model, where analytical formulae are obtained for certain temperature ranges, which can be readily applied to those with various quark mass scalings. In the case of adopting a quark mass scaling with both linear confinement and perturbative interactions, the obtained bulk viscosity increases by $1 \sim 2$ orders of magnitude compared with those in bag model scenarios. Such an enhancement is mainly due to the large quark equivalent masses adopted in the equivparticle model, which are essentially attributed to the strong interquark interactions and are related to the dynamical chiral symmetry breaking. Due to the high bulk viscosity, the predicted damping time of oscillations for a canonical 1.4 ${\rm M}_\odot$ strange star is less than one millisecond, which is shorter than previous findings. Consequently, the obtained $r$-mode instability window for the canonical strange stars well accommodates the observational frequencies and temperatures for pulsars in low-mass X-ray binaries (LMXBs).

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