Exotic bulk viscosity and its influence on neutron star r-modes

We investigate the effect of exotic matter in particular, hyperon matter on neutron star properties such as equation of state (EoS), mass-radius relationship and bulk viscosity. Here we construct equations of state within the framework of a relativistic field theoretical model. As hyperons are produced abundantly in dense matter, hyperon-hyperon interaction becomes important and is included in this model. Hyperon-hyperon interaction gives rise to a softer EoS which results in a smaller maximum mass neutron star compared with the case without the interaction. Next we compute the coefficient of bulk viscosity and the corresponding damping time scale due to the non-leptonic weak process including $\Lambda$ hyperons. Further, we investigate the role of the bulk viscosity on gravitational radiation driven r-mode instability in a neutron star of given mass and temperature and find that the instability is effectively suppressed.Comment: 5 pages, 3 figure, presented in the Conference on Isolated Neutron Stars: From the Interior to The Surface, London, UK, 24-28 April, 2006; revised and final version to appear in Astrophys. Space Sc

Linear Paul trap design for an optical clock with Coulomb crystals

We report on the design of a segmented linear Paul trap for optical clock applications using trapped ion Coulomb crystals. For an optical clock with an improved short-term stability and a fractional frequency uncertainty of 10^-18, we propose 115In+ ions sympathetically cooled by 172Yb+. We discuss the systematic frequency shifts of such a frequency standard. In particular, we elaborate on high precision calculations of the electric radiofrequency field of the ion trap using the finite element method. These calculations are used to find a scalable design with minimized excess micromotion of the ions at a level at which the corresponding second- order Doppler shift contributes less than 10^-18 to the relative uncertainty of the frequency standard

Color superconducting quark matter core in the third family of compact stars

We investigate first order phase transitions from $\beta$-equilibrated hadronic matter to color flavor locked quark matter in compact star interior. The hadronic phase including hyperons and Bose-Einstein condensate of $K^-$ mesons is described by the relativistic field theoretical model with density dependent meson-baryon couplings. The early appearance of hyperons and/or Bose-Einstein condensate of $K^-$ mesons delays the onset of phase transition to higher density. In the presence of hyperons and/or $K^-$ condensate, the overall equations of state become softer resulting in smaller maximum masses than the cases without hyperons and $K^-$ condensate. We find that the maximum mass neutron stars may contain a mixed phase core of hyperons, $K^-$ condensate and color superconducting quark matter. Depending on the parameter space, we also observe that there is a stable branch of superdense stars called the third family branch beyond the neutron star branch. Compact stars in the third family branch may contain pure color superconducting core and have radii smaller than those of the neutron star branch. Our results are compared with the recent observations on RX J185635-3754 and the recently measured mass-radius relationship by X-ray Multi Mirror-Newton Observatory.Comment: 24 pages, RevTex, 9 figures included; section II shortened, section III elaborated, two new curves in Fig. 9 and acknowledgements added; version to bepublished in Phys. Rev.

Quark Stars: Features and Findings

Under extreme conditions of temperature and/or density, quarks and gluons are expected to undergo a deconfinement phase transition. While this is an ephemeral phenomenon at the ultra-relativistic heavy-ion collider (BNL-RHIC), quark matter may exist naturally in the dense interior of neutron stars. Herein, we present an appraisal of the possible phase structure of dense quark matter inside neutron stars, and the likelihood of its existence given the current status of neutron star observations. We conclude that quark matter inside neutron stars cannot be dismissed as a possibility, although recent observational evidence rules out most soft equations of state.Comment: Contribution to proceedings of Hot Quarks 2006, Villasimius, Italy; 5 pages (TeX), 2 .eps figure

Spin Down of Rotating Compact Magnetized Strange Stars in General Relativity

We find that in general relativity slow down of the pulsar rotation due to the magnetodipolar radiation is more faster for the strange star with comparison to that for the neutron star of the same mass. Comparison with astrophysical observations on pulsars spindown data may provide an evidence for the strange star existence and, thus, serve as a test for distinguishing it from the neutron star.Comment: 6 pages; Accepted for publication in Astrophysics and Space Scienc