ar X iv : h ep - p h / 02 06 18 7 v 2 8 A ug 2 00 2 Bulk viscosity of interacting strange quark matter

The quarks are regarded as quasiparticles, which acquire an effective mass generated by the interaction with the other quarks of the dense system. The bulk viscosity is re-expressed in the case of interacting strange quark matter. We find that the viscosity is a few∼tens times larger than that of non-interacting quark gas due to the small correction of medium effect to the equation of state. The limiting spins of strange stars will rise so significantly that the pulsars with shorter period may exist. PACS numbers: 97.60.Jd, 12.38.Mh, 97.60.Gb As the hypothesis compact objects, strange stars have not been proven by observation yet. Probing strange stars and then identifying them are significant challenges in nuclear physics and astrophysics. It has been shown in a series of papers, that the emission of gravitational radiation due to r-mode instabilities in hot, young neutron stars severely limits the rotation period of these stars[1, 2, 3, 4, 5, 6]. Whereas Madsen found that the r-mode instability does not play any role in a young strange star contrary to young neutron stars[7]. The author reasonably concluded that finding a young pulsar with a rotation period below 5-10 milliseconds would be a strong indication of the existence of strange stars. In another article[8], the author also discussed the evolution of pulsars as strange stars due to r-mode instabilities in rapidly rotating stars. The results revealed that strange stars, perhaps better than neutron stars, explained the apparent lack of very rapid pulsars with frequencies above 642Hz sine existing data are consistent with pulsars being strange stars under some circumstances.All above involve the viscosities of strange quark matter contained in the interior of these stars. This is because of viscosity damping the r-modes. As known, the shear viscosity of quark matter[7, 9] is roughly comparable to that of neutron star matter for the parameter range of our interest where the bulk viscosity of quark matter, which damps the r-modes, is decisive for the localization of the instability, differs from neutron star matter. The bulk viscosity of strange quark matter mainly arises from the non-leptonic weak interactions[10] u+ d ↔ s+ u (1)