Sound velocity in dense stellar matter with strangeness and compact stars

The phase state of dense matter in the intermediate density range (\begin{document}$\sim$\end{document}1-10 times the nuclear saturation density) is both intriguing and unclear and can have important observable effects in the present gravitational wave era of neutron stars. As matter density increases in compact stars, the sound velocity is expected to approach the conformal limit (\begin{document}$c_s/c=1/\sqrt{3}$\end{document}) at high densities and should also fulfill the causality limit (\begin{document}$c_s/c<1$\end{document}). However, its detailed behavior remains a prominent topic of debate. It was suggested that the sound velocity of dense matter could be an important indicator of a deconfinement phase transition, where a particular shape might be expected for its density dependence. In this work, we explore the general properties of the sound velocity and the adiabatic index of dense matter in hybrid stars as well as in neutron stars and quark stars. Various conditions are employed for the hadron-quark phase transition with varying interface tension. We find that the expected behavior of the sound velocity can also be achieved by the nonperturbative properties of the quark phase, in addition to a deconfinement phase transition. Moreover, it leads to a more compact star with a similar mass. We then propose a new class of quark star equation of states, which can be tested by future high-precision radius measurements of pulsar-like objects.     

Quark matter influence on observational properties of compact stars

Densities in compact stars may be such that quarks are no longer confined in hadrons, but instead behave as weakly interacting particles. In this regime perturbative calculations are possible. Yet, due to high pressures and an attractive channel in the strong force, condensation of quarks in a superfluid state is likely. This can have interesting consequences for magnetic fields, especially in relation to the discovery of slow-period free precession in a compact star. In this proceedings there will be a discussion of the mass-radius relations of compact stars made from quark matter and magnetic field behaviour in compact stars with a quark matter core.     

Neutrinos in dense quark matter and cooling of compact stars

We discuss that observational constraints on neutrino cooling processes may restrict the spectrum of quark matter phases admissible for compact star interiors.     

Color superconductivity in dense quark matter

The possible structure of the QCD phase diagram is discussed focusing on color superconducting quark matter in the region of low temperatures and moderately large densities, which could be relevant for compact stars.     

Quark matter nucleation in hot hadronic matter

We study the quark deconfinement phase transition in hot β-stable hadronic matter. Assuming a first order phase transition, we calculate the enthalpy per baryon of the hadron–quark phase transition. We calculate and compare the nucleation rate and the nucleation time due to thermal and quantum nucleation mechanisms. We compute the crossover temperature above which thermal nucleation dominates the finite temperature quantum nucleation mechanism. We next discuss the consequences for the physics of proto-neutron stars. We introduce the concept of limiting conversion temperature and critical mass M_cr for proto-hadronic stars, and we show that proto-hadronic stars with a mass M<M_cr could survive the early stages of their evolution without decaying to a quark star.     

核物质和夸克物质的对称能（英文）

对称能表征了同位旋非对称强相互作用物质状态方程的同位旋相关部分,它对于理解核物理和天体物理中的许多问题有重要意义。简要总结了关于核物质和夸克物质对称能研究的最新进展。对于核物质对称能,通过对核结构,核反应以及中子星的研究,目前对其亚饱和密度的行为已有比较清楚的认识,同时,对饱和密度附近对称能的约束也取得了很好的研究进展。但如何确定核物质对称能的高密行为仍然是一个挑战。另一方面,在极端高重子数密度条件下,强相互作用物质将以退禁闭的夸克物质状态存在。同位旋非对称夸克物质可能存在于致密星内部,也可能产生于极端相对论重离子碰撞中。对最近关于夸克物质对称能对夸克星性质的影响以及重夸克星的存在对夸克物质对称能的约束的研究工作进行了介绍,结果表明同位旋非对称夸克物质中上夸克和下夸克可能感受到很不一样的相互作用,这对于研究极端相对论重离子碰撞中部分子动力学的同位旋效应有重要启发。The symmetry energy characterizes the isospin dependent part of the equation of state of isospin asymmetric strong interaction matter and it plays a critical role in many issues of nuclear physics and astrophysics. In this talk, we briefly review the current status on the determination of the symmetry energy in nucleon (nuclear) and quark matter. For nuclear matter, while the subsaturation density behaviors of the symmetry energy are relatively well-determined and significant progress has been made on the symmetry energy around saturation density, the determination of the suprasaturation density behaviors of the symmetry energy remains a big challenge. For quark matter, which is expected to appear in dense matter at high baryon densities, we briefly review the recent work about the effects of quark matter symmetry energy on the properties of quark stars and the constraint of possible existence of heavy quark stars on quark matter symmetry energy. The results indicate that the u and d quarks could feel very different interactions in isospin asymmetric quark matter, which may have important implications on the isospin effects of partonic dynamics in relativistic heavy-ion collisions.     

Neutrino interactions in dense stellar matter

Weak-interaction rates play an important role in the birth of neutron stars in core collapse supernova and their subsequent thermal evolution. In this paper, I highlight the role of strong interactions and phase transitions in calculations of neutrino scattering and emission rates in dense stellar matter.Received: 1 November 2002, Published online: 15 July 2003PACS: 13.15.+g Neutrino interactions - 13.20.-v Leptonic and semileptonic decays of mesons - 26.50.+x Nuclear physics aspects of novae, supernovae, and other explosive environments - 26.60.+c Nuclear matter aspects of neutron starsPresent address: Los Alamos National Laboratory, P.O. Box 1663, MS B283, Los Alamos, NM 87545, USA     

Vacuum fluctuation effects on hyperonic neutron star matter

The vacuum fluctuation （VF） effects on the properties of the hyperonic neutron star matter are investigated in the framework of the relativistic mean field （RMF） theory. The VF corrections result in the density dependence of in-medium baryon and meson masses. We compare our results obtained by adopting three kinds of meson-hyperon couplings. The introduction of both hyperons and VF corrections softens the equation of state （EoS） for the hyperonic neutron star matter and hence reduces hyperonic neutron star masses. The presence of the δ field enlarges the masses and radii of hyperonic neutron stars. Taking into account the uncertainty of meson-hyperon couplings, the obtained maximum masses of hyperonic neutron stars are in the range of 1.33M⊙-1.55M⊙.     

固态夸克星星震模型的研究

Glitch指脉冲星发生的自转角速度突然增大的现象,在许多脉冲星中都探测到了。Glitch的产生机制与脉冲星内部结构相关,而后者依然是待解决的难题。天文观测和理论研究均不能排除一类可能性,即脉冲星类天体本质上是固态夸克集团星,而固态星体发生Glitch的最自然的解释就是星震。本工作在星震模型下研究了固态脉冲星的Glitch现象。固态星体在自转减慢过程中,会发生应力能（或弹性能）的积累,当积累的应力超过星体能承受的限度,星体会发生碎裂,即发生星震,此时由于转动惯量突然减小而导致自转角速度突然增大,表现为Glitch现象。根据此模型可得到Glitch的幅度与时间间隔的关系。如果星体的质量较大而自转较慢,星震过程可能同时伴随体积的减小,即体积改变的星震,此时通常会有显著的引力能释放,可以解释观测到的反称X射线脉冲星/软伽马射线重复暴（AXPs/SGRs）;如果星体转速较快,星震过程可能只表现为形状即扁率的微小变化,此时不会有显著的能量释放。这两类Glitches可以解释观测现象。进一步的理论研究结合更多观测,有望使人们利用Glitch现象来检验固态夸克集团星这一理论猜想。The author demonstrates that how to understand the Glitches of solid pulsars in the starquake model. Glitch is the sudden spin-up during the normal spin-down process, which has been observed in many pulsars. The mechanism of Glitches is still a matter of debate because it depends on the unsolved problem that what is the nature of pulsars. One of the models of pulsars, the so-called solid quark-cluster stars, could not be ruled out by neither the astrophysics observations nor theoretical considerations. The Glitches of solid quarkcluster stars could naturally be the result of starqukes. During the spinning-down of the solid star, the strain energy develops until the stress reaches the critical value, then some parts of the star fragment, which would suddenly decrease the moment of inertia of the star, leading to the sudden increase of the rotation frequency that manifests as a Glitch. If the star has high mass or rotates slowly, the shrink of radius would happen during the starquake, leading to a huge amount of energy releasing which accounts for AXPs/SGRs. On the other hand, if the star rotates fast, only the oblateness of the star changes during the starquake, which would lead to negligible releasing of energy. This paper discusses the phenomenon of Glitches for solid quark-cluster stars, including the physical processes and consequences of starquakes, as well as the reasons for different energy releasing during Glitches. Further theoretical study combined with more observations about Glitches would be helpful for us to test the conjecture of sold quark-clusters.     

Effects of Δ-Isobars on Neutron Stars

We have investigated the possibility of the presence of the deltas in neutron star matter and their effects on neutron stars. Δ-meson couplings of the theoretical predictions are only restricted in a region where the deltas can be present and even a first-order phase transition may take place, making the EOS sorer and the maximum mass of neutron stars smaller. The presence of the deltas leads to the rapid decrease of neutrino mean free paths.     

Adiabatic index of hot dense stellar matter

We calculate the adiabatic index of hot dense stellar matter taking into account the full nuclear interaction in all possible channels.     

Maximum stellar iron core mass

An analytical method of estimating the mass of a stellar iron core, just prior to core collapse, is described in this paper. The method employed depends, in part, upon an estimate of the true relativistic mass increase experienced by electrons within a highly compressed iron core, just prior to core collapse, and is significantly different from a more typical Chandrasekhar mass limit approach. This technique produced a maximum stellar iron core mass value of 269 × 10³⁰ kg (1.35 solar masses). This mass value is very near to the typical mass values found for neutron stars in a recent survey of actual neutron star masses. Although slightly lower and higher neutron star masses may also be found, lower mass neutron stars are believed to be formed as a result of enhanced iron core compression due to the weight of non-ferrous matter overlying the iron cores within large stars. And, higher mass neutron stars are likely to be formed as a result of fallback or accretion of additional matter after an initial collapse event involving an iron core having a mass no greater than 2.69 × 10³⁰ kg     

Dark matter with chiral symmetry admixed with hadronic matterin compact stars

Using the two-fluid Tolman-Oppenheimer-Volkoff equation, the properties of dark matter (DM) admixed neutron stars (DANSs) have been investigated. In contrast to previous studies, we find that an increase in the maximum mass and a decrease in the radius of 1.4 \begin{document}$ M_\odot $\end{document} NSs can occur simultaneously in DANSs. This stems from the ability of the equation of state (EOS) for DM to be very soft at low density but very stiff at high density. It is well known that the IU-FSU and XS models are unable to produce a neutron star (NS) with a maximum mass greater than 2.0 \begin{document}$ M_\odot $\end{document}. However, by considering the IU-FSU and XS models for DANSs, there are interactions with DM that can produce a maximum mass greater than 2.0 \begin{document}$ M_\odot $\end{document} and a radius of 1.4 \begin{document}$ M_\odot $\end{document} NSs below 13.7 km. When considering a DANS, the difference between DM with chiral symmetry (DMC) and DM with meson exchange (DMM) becomes obvious when the central energy density of DM is greater than that of nuclear matter (NM). In this case, the DMC model with a DM mass of 1000 MeV can still produce a maximum mass greater than 2.0 \begin{document}$ M_\odot $\end{document} and a radius of a 1.4 \begin{document}$ M_\odot $\end{document} NS below 13.7 km. Additionally, although the maximum mass of the DANS using the DMM model is greater than 2.0 \begin{document}$ M_\odot $\end{document}, the radius of a 1.4 \begin{document}$ M_\odot $\end{document} NS can surpass 13.7 km. In the two-fluid system, the maximum mass of a DANS can be larger than 3.0 \begin{document}$ M_\odot $\end{document}. Consequently, the dimensionless tidal deformability \begin{document}$ \Lambda_{CP} $\end{document} of a DANS with 1.4 \begin{document}$ M_\odot $\end{document}, which increases with increasing maximum mass, may be larger than 800 when the radius of the 1.4 \begin{document}$ M_\odot $\end{document} DANS is approximately 13.0 km.     

Quark distribution in light nuclei

The distribution of quarks in light nuclei is given using the quark cluster wave function. An analytic expression for the nucleus⁴He is obtained. The distribution so obtained is compared with the one obtained using a different theoretical formulation called mapping.     

Bose-Einstein condensation in dense quark matter

We consider the problem of Bose condensation of charged pions in QCD at finite isospin chemical potential μ_I using the O(4)-symmetric linear sigma model as an effective field theory for two-flavor QCD. Using the 2PI 1/N-expansion, we determine the quasiparticle masses as well as the pion and chiral condensates as a function of the temperature and isospin chemical potential in the chiral limit and at the physical point. The calculations show that there is a competition between the condensates. At T=0, Bose condensation takes place for chemical potentials larger than μ_π. In the chiral limit, the chiral condensate vanishes for any finite value of μ_I.     

Quark mixing in the discrete dark matter model

We consider a model in which dark matter is stable as it is charged under a Z₂ symmetry that is residual after an A₄ flavour symmetry is broken. We consider the possibility to generate the quark masses by charging the quarks appropriately under A₄. We find that it is possible to generate the CKM mixing matrix by an interplay of renormalisable and dimension-six operators. In this set-up, we predict the third neutrino mixing angle to be large and the dark matter relic density to be in the correct range. Low energy observables - in particular meson-antimeson oscillations - are hard to facilitate. We find that only in a situation where there is a strong cancellation between the Standard Model contribution and the contribution of the new Higgs fields, B meson oscillations are under control.     

浅谈近场光学

简要地介绍了近场光学的历史及现状，讨论了近场光学显微镜的构造、工作原理、工作方式及实际应用，并支近场光学的一些理论问题作了简明扼要的介绍，指出理论和实验上需要进一步发展的地方以及可能的途径。