Hybrid stars that masquerade as neutron stars

We show that a hybrid (nuclear + quark matter) star can have a mass-radius relationship very similar to that predicted for a star made of purely nucleonic matter. We show this for a generic parameterization of the quark matter equation of state, and also for an MIT bag model, each including a phenomenological correction based on gluonic corrections to the equation of state. We obtain hybrid stars as heavy as 2 M_solar for reasonable values of the bag model parameters. For nuclear matter, we use the equation of state calculated by Akmal, Pandharipande, and Ravenhall using many-body techniques. Both mixed and homogeneous phases of nuclear and quark matter are considered.Comment: 22 pages, LaTeX. Extra figure and explanation adde

The maximum mass and radius of neutron stars and the nuclear symmetry energy

We calculate the equation of state of neutron matter with realistic two- and three-nucleon interactions using quantum Monte Carlo techniques, and illustrate that the short-range three-neutron interaction determines the correlation between neutron matter energy at nuclear saturation density and higher densities relevant to neutron stars. Our model also makes an experimentally testable prediction for the correlation between the nuclear symmetry energy and its density dependence -- determined solely by the strength of the short-range terms in the three neutron force. The same force provides a significant constraint on the maximum mass and radius of neutron stars.Comment: 5 pages, 3 figures, final versio

The Stability of Strange Star Crusts and Strangelets

We construct strangelets, taking into account electrostatic effects, including Debye screening, and arbitrary surface tension sigma of the interface between vacuum and quark matter. We find that there is a critical surface tension sigma_crit below which large strangelets are unstable to fragmentation and below which quark star surfaces will fragment into a crystalline crust made of charged strangelets immersed in an electron gas. We derive a model-independent relationship between sigma_crit and two parameters that characterize any quark matter equation of state. For reasonable model equations of state, we find sigma_crit typically of order a few MeV/fm^2. If sigma <= sigma_crit, the size-distribution of strangelets in cosmic rays could feature a peak corresponding to the stable strangelets that we construct.Comment: 11 pages, LaTe

A low energy theory for superfluid and solid matter and its application to the neutron star crust

We formulate a low energy effective theory describing phases of matter that are both solid and superfluid. These systems simultaneously break translational symmetry and the phase symmetry associated with particle number. The symmetries restrict the combinations of terms that can appear in the effective action and the lowest order terms featuring equal number of derivatives and Goldstone fields are completely specified by the thermodynamic free energy, or equivalently by the long-wavelength limit of static correlation functions in the ground state. We show that the underlying interaction between particles that constitute the lattice and the superfluid gives rise to entrainment, and mixing between the Goldstone modes. As a concrete example we discuss the low energy theory for the inner crust of a neutron star, where a lattice of ionized nuclei coexists with a neutron superfluid.Comment: 21 pages, 1 figur

Neutrino processes in the K0K^0 condensed phase of color flavor locked quark matter

We study weak interactions involving Goldstone bosons in the neutral kaon condensed phase of color flavor locked quark matter. We calculate the rates for the dominant processes that contribute to the neutrino mean free p ath and to neutrino production. A light $K^+$ state, with a mass $\tilde{m}_{K^+} \propto (\Delta/\mu) (\Delta/m_s)(m_d-m_u)$, where $\mu$ and $\Delta$ are the quark chemical potential and superconducting gap respectively, is shown to play an important role. We identify unique characteristics of weak interaction rates in this novel phase and discuss how they might influence neutrino emission in core collapse supernova and neutron stars.Comment: 21 pages, 4 figure

Quark Matter in Neutron Stars: An apercu

The existence of deconfined quark matter in the superdense interior of neutron stars is a key question that has drawn considerable attention over the past few decades. Quark matter can comprise an arbitrary fraction of the star, from 0 for a pure neutron star to 1 for a pure quark star, depending on the equation of state of matter at high density. From an astrophysical viewpoint, these two extreme cases are generally expected to manifest different observational signatures. An intermediate fraction implies a hybrid star, where the interior consists of mixed or homogeneous phases of quark and nuclear matter, depending on surface and Coulomb energy costs, as well as other finite size and screening effects. In this brief review article, we discuss what we can deduce about quark matter in neutron stars in light of recent exciting developments in neutron star observations. We state the theoretical ideas underlying the equation of state of dense quark matter, including color superconducting quark matter. We also highlight recent advances stemming from re-examination of an old paradigm for the surface structure of quark stars and discuss possible evolutionary scenarios from neutron stars to quark stars, with emphasis on astrophysical observations.Comment: 15 pages, 1 figure. Invited review for Modern Physics Letters

Periodontal Status amongst Substance Abusers in Indian Population

Background. In India there have been limited number of studies on periodontal status among drug addicts, and thus this study aims to assess the Oral hygiene and periodontal status in substance abusers and compare it with non-substance abusers. Methods. A comparative study was conducted to assess the periodontal status in substance abusers. Non-substance abusers were procured from the general population of Bangalore. From the control group 250 non-substance abusers were age and sex matched with the study population of substance abusers. The oral hygiene and periodontal condition of all subjects was assessed using Oral hygiene index- simplified (OHI-S), Russell's periodontal indices and Gingival bleeding index. Results. The mean of OHI-S and Periodontal Index (Russell's Index) scores were higher (2.70 and 3.68, resp.) in substance abusers than the control group (2.45 and 2.59, resp.). The mean Gingival bleeding score was lower (9.69) in substance abusers than the control group (22.7) and found to be statistically significant. A positive correlation found between OHI-S and Russell's periodontal index whereas negative correlation was found between OHI-S and Gingival bleeding in substance abusers. Conclusions. Though the oral hygiene was fair, more periodontal destruction and less of gingival bleeding were observed in substance abusers as compared to control group

First Order Kaon Condensation in Neutron Stars: Finite Size Effects in the Mixed Phase

We study the role of Coulomb and surface effects on the phase transition from dense nuclear matter to a mixed phase of nuclear and kaon-condensed matter. We calculate corrections to the bulk calculation of the equation of state (EOS) and the critical density for the transition by solving explicitly for spherical, cylindrical, and planar structures. The importance of Debye screening in the determination of the charged particle profiles is studied in some detail. We find that the surface and Coulomb contributions to the energy density are small, but that they play an important role in the determination of the critical pressure for the transition, as well as affecting the size and geometry of favored structures. This changes the EOS over a wide range of pressure and consequently increases the maximum mass by about 0.1 solar masses. Implications for transport properties of the mixed phase are also discussed.Comment: 18 pages, 6 figure

Neutrino Propagation In Color Superconducting Quark Matter

We calculate the neutrino mean free path in color superconducting quark matter, and employ it to study the cooling of matter via neutrino diffusion in the superconducting phase as compared to a free quark phase. The cooling process slows when quark matter undergoes a second order phase transition to a superconducting phase at the critical temperature $T_c$. Cooling subsequently accelerates as the temperature decreases below $T_c$. This will directly impact the early evolution of a newly born neutron star should its core contain quark matter. Consequently, there may be observable changes in the early neutrino emission which would provide evidence for superconductivity in hot and dense matter.Comment: 12 pages, 5 figure

Differential attenuation of Marek's disease virus-induced tumours and late-Marek's disease virus-induced immunosuppression

Marek's disease virus (MDV) is a herpesvirus that induces lymphoma and a variety of non-neoplastic syndromes in chickens. Furthermore, very virulent plus (vv+) MDVs induce a form of immunosuppression (late-MDV-IS) that might involve both neoplastic and non-neoplastic mechanisms. The objective of this study was to evaluate whether the attenuation of MDV-induced tumours and late-MDV-IS occurs simultaneously or can be dissociated. The immunosuppressive ability of three viruses derived from vv+ MDV strain 686 (wild-type 686, the somewhat attenuated molecular clone 686-BAC, and the nononcogenic molecular clone lacking the two copies of the oncogene meq 686-BACΔMEQ) was evaluated. Late-MDV-IS was evaluated indirectly by assessing the negative effect of MDV strains on the protection conferred by infectious laryngotracheitis (ILT) vaccines. Our results showed that the ability to induce late-MDV-IS was attenuated before the ability to induce tumours. Strain 686 induced both tumours and late-MDV-IS, 686-BAC induced tumours but did not induce late-MDV-IS and 686-BACΔMEQ did not induce either tumours or late-MDV-IS. Further comparison of strains 686 and 686-BAC revealed that strain 686 reduced the humoral immune responses to ILTV (1132 vs 2167) more severely, showed higher levels of meq transcripts (2.1E+09 vs 4.98E+8) and higher expression of MDV microRNAs (mdv1-miR-M4-5p and mdv1-miR-M2-3p) in the spleen, and further reduced the percentage of CD45+-MHC-I+splenocytes (13 vs32 %) compared to molecular clone 686-BAC. This study suggests that the immunosuppressive ability of MDV might follow a continuous spectrum and only the most virulent MDVs can overcome a certain threshold level and induce clinical MDV-IS in the ILT model