Strange Quark Matter and Strangelets in a Strong Magnetic Field

We study the stability properties of magnetized strange quark matter and strangelets under a strong magnetic field in the MIT bag model. The free energy per baryon of strange quark matter feels a great influence from the magnetic field. At the field strength about 10¹⁷G, the magnetized strange quark matter becomes more stable. Considering the finite size effect, the magnetic influence on strangelets becomes complicated. For a given magnetic field, there exists a critical baryon number, below which the magnetized strangelets have lower energy than the non-magnetized strangelets. For the field strength of 5× 10¹⁷G, the critical baryon number is A_c ～ 100. Generally, the critical baryon number increases with the decreasing external magnetic field. When the field strength is smaller than 10¹⁷G, the critical baryon number goes up to A_c～ 10⁵. The stable radius, electric charge, and quark flavor fractions of magnetized strangelets are shown.     

Color-Flavor Locked Strangelets in a New Quark Model with Linear Confinement and Coulomb-Type Interactions

The color-flavor locked (CFL) strangelets have been investigated in a new quark model with linear confinement and one-gluon-exchange interactions. Considering Coulomb energy, we have studied the properties of three kinds of CFL strangelets, namely, positively charged, negatively charged and nearly neutral CFL strangelets. It is found that the one-gluon-exchange effect lowers the energy of a strangelet considerably and thus makes it much more stable than without considering the effect. The charge of a positive strangelet is larger than 0.15A^2/3 with A being the baryon number, but smaller than that in bag model. The charge of a negatively charged or nearly neutral CFL strangelet is nearly proportional to A^1/3.     

新的质量标度下奇异夸克物质的电荷与临界密度

应用自恰的热力学方式确定夸克质量公式中的参数,并进一步证明,在新的质量标度下,适量的负电荷仍然可以降低奇异夸克物质的临界密度,从而有利于在重离子碰撞实验中寻找strangelets.当然,过量的负电荷仍将使味平衡成为不可能.     

Colour-Charged Quark Matter in Astrophysics？

Colour confinement is only a supposition, which has not yet been proven in QCD. Here we propose that macroscopic quark-gluon plasma in astrophysics could hardly maintain colourless because of causality. It is expected that the existence of chromatic strange quark stars as well as chromatic strangelets preserved from the QCD phase transition in the early Universe could be unavoidable if their colourless correspondents do exist.     

Dark matter, neutron stars, and strange quark matter

We show that self-annihilating weakly interacting massive particle (WIMP) dark matter accreted onto neutron stars may provide a mechanism to seed compact objects with long-lived lumps of strange quark matter, or strangelets, for WIMP masses above a few GeV. This effect may trigger a conversion of most of the star into a strange star. We use an energy estimate for the long-lived strangelet based on the Fermi-gas model combined with the MIT bag model to set a new limit on the possible values of the WIMP mass that can be especially relevant for subdominant species of massive neutralinos.     

Strange star surface: a crust with nuggets

We reexamine the surface composition of strange stars. Strange quark stars are hypothetical compact stars which could exist if strange quark matter was absolutely stable. It is widely accepted that they are characterized by an enormous density gradient (10(26) g/cm4) and large electric fields at the surface. By investigating the possibility of realizing a heterogeneous crust, comprised of nuggets of strange quark matter embedded in an uniform electron background, we find that the strange star surface has a much reduced density gradient and negligible electric field. We comment on how our findings will impact various proposed observable signatures for strange stars.     

Emission of droplets of strange quark matter in RHIC

We demonstrate that strangeness separates in the quark-hadron coexistence (even atT=0) and prompt kaon emission results in a strong enhancement of thes-quark abundance in the quark phase during the phase transition to hadron matter. Condensation into stabilized droplets of strange quark matter (“strangelets”) does occur during the phase transition. The so formed cool, compact, long-lived clusters could be experimentally observed by their smallZ/A-ratio. If the late quark matter phase is unstable, it should be observable by the delayed, correlated emission of several hyperons.     

Non-Spherical Gravitational Collapse of Strange Quark Matter

We study the non-spherical gravitational collapse of the strange quark null fluid. The interesting feature which emerges is that the non-spherical collapse of charged strange quark matter leads to a naked singularity whereas the gravitational collapse of neutral quark matter proceeds to form a black hole. We extend the earlier work of Harko and Cheng [Phys. Lett. A 266 （2000） 249] to the non-spherical case.     

核子中奇异夸克分布不对称性与轻味夸克碎裂效应

核子中奇异－反奇异夸克分布的不对称性是核子结构研究中的重要非微扰效应, 然而至今未被实验所直接检验.为了探讨测量这种奇异分布不对称性的有效方法,考察了轻味夸克碎裂效应对测量奇异分布不对称性的影响.建议通过直接测量高能中微子和反中微子的带电流深度非弹散射中的带电和中性D介子的微分截面来测量奇异分布的不对称性.这种方法能够使奇异分布不对称性与轻味夸克碎裂的效应相分离.     

An Exact Family of Einstein–Maxwell Wyman–Adler Solution in General Relativity

This paper presents a family of two-parametric interior solutions of Einstein–Maxwell field equations in general relativity for a static spherically symmetric distribution of a charged perfect fluid with particular choice of charge distribution and the metric component g ₀₀. This family gives us wide range of parameters, n and K, for which the solutions are regular and acceptable on physical grounds and hence suitable for modeling of charged compact star. The maximum allowable mass and corresponding radius, for this family of solutions with the particular form of charge distribution, is determined to be 2.48M _⊙ and 10.56 km respectively by assuming the stellar “surface” density equal to strange (quark) matter density at zero pressure. It is hoped that our investigation may be of some importance in connection with the study of internal structure of electrically charged strange (quark) star.     

Strangelets as cosmic rays beyond the Greisen-Zatsepin-Kuzmin cutoff

Strangelets (stable lumps of quark matter) can have masses and charges much higher than those of nuclei, but have very low charge-to-mass ratios. This is confirmed in a relativistic Thomas-Fermi model. The high charge allows astrophysical strangelet acceleration to energies orders of magnitude higher than for protons. In addition, strangelets are much less susceptible to the interactions with the cosmic microwave background that suppress the flux of cosmic ray protons and nuclei above energies of 10(19)-10(20) eV (the Greisen-Zatsepin-Kuzmin cutoff). This makes strangelets an interesting possibility for explaining ultrahigh energy cosmic rays.     

Exotic decays of strangelets

The stability of strange matter depends on the implicit assumption that baryon number is conserved. We examine the relevant effective operators which allow strangelets to decay by violating the conservation of baryon number. From the experimental lower limit of 10²⁵ years on the stability of nuclei, we find a lower limit of the order 10⁶ years on the stability of strangelets against such exotic decays.     

Strange-quark matter within the Nambu-Jona-Lasinio model

The equation of state of baryon-rich quark matter is studied within the SU(3) Nambu-Jona-Lasinio model with flavor-mixing interaction. Possible bound states (strangelets) and chiral phase transitions in this matter are investigated at various values of the strangeness fraction r _s. Model predictions are very sensitive to the ratio of the vector and scalar coupling constants, ξ=G _V/G _S. At ξ=0.5 and zero temperature, the binding energy takes a maximum value of about 15 MeV per baryon at r _s?0.4. Such strangelets are negatively charged and have typical lifetimes of about 10^?7s. Calculations are performed at finite temperatures as well. According to these calculations, bound states exist up to temperatures of about 15 MeV. The model predicts a first-order chiral phase transition at finite baryon densities. The parameters of this phase transition are calculated as functions of r _s.     

Thermal evolution and light curves of young bare strange stars

We study numerically the cooling of a young bare strange star and show that its thermal luminosity, mostly due to e(+)e(-) pair production from the quark surface, may be much higher than the Eddington limit. The mean energy of photons far from the strange star is approximately 10(2) keV or even more. This differs both qualitatively and quantitatively from the thermal emission from neutron stars and provides a definite observational signature for bare strange stars. It is shown that the energy gap of superconducting quark matter may be estimated from the light curves if it is in the range from approximately 0.5 MeV to a few MeV.     

Strange hadrons – strangeness in strongly interacting particles Strangeness production with KAOS at MAMI

In 2007 the Mainz Microtron MAMI has been upgraded to 1.5 GeV electron beam energy, crossing the energy threshold for open strangeness production. The strangeness quantum number, as carried by the strange quark, provides valuable information on the contribution of individual quark flavours to hadronic processes. Theoretically, the strange quark with its rest energy of order 150 MeV is particularly interesting because it can neither be treated as a massless nor as a heavy quark. Experimentally, an instrument of central importance for the charged kaon electro-production off the proton or light nuclei at MAMI is the magnetic spectrometer Kaos that was installed recently and is now routinely operated by the A1 collaboration.     

Strangelet search and particle production studies in Pb+Pb collisions at 158 AGeV/c at CERN SPS

We searched for long-lived strange quark matter particles, so-calledstrangelets, and studied particle and antiparticle production in Pb+Pb collisions at 158 GeV/c per nucleon at zero degree production angle. We give upper limits for the production of strangelets covering a mass to charge ratio up to 120 GeV/c ² and lifetimest _lab>1.2 μs and plot invariant differential production cross sections as a function of rapidity for a variety of particles.     

Effects of Density-Dependent Quark Mass on Phase Diagram of Color-Flavor-Locked Quark Matter

Considering the density dependence of quark mass, we investigate the phase transition between the (unpaired) strange quark matter and the color-flavor-locked matter, which are supposed to be two candidates for the ground state of strongly interacting matter. We find that if the current mass of strange quark ms is small, the strange quark matter remains stable unless the baryon density is very high. If ms is large, the phase transition from the strange quark matter to the color-flavor-locked matter in particular to its gapless phase is found to be different from the results predicted by previous works. A complicated phase diagram of three-flavor quark matter is presented, in which the color-flavor-locked phase region is suppressed for moderate densities.     

Neutron star in the presence of strong magnetic field

Compact stars such as neutron stars (NS) can have either hadronic or exotic states like strange quark or colour superconducting matter. Stars can also have a quark core surrounded by hadronic matter, known as hybrid stars (HS). The HS is likely to have a mixed phase in between the hadron and the quark phases. Observational results suggest huge surface magnetic field in certain NS. Therefore, we study here the effect of strong magnetic field on the respective equation of states (EOS) of matter under extreme conditions. We further study the hadron–quark phase transition in the interiors of NS giving rise to HS in the presence of strong magnetic field. The hadronic matter EOS is described based on RMF theory and we include the effects of strong magnetic fields leading to Landau quantization of the charged particles. For quark phase, we use the simple Massachusetts Institute of Technology (MIT) bag model, assuming density-dependent bag pressure and magnetic field. The magnetic field strength increases from the surface to the centre of the star. We construct the intermediate mixed phase using Glendenning conjecture. The magnetic field softens the EOS of both the matter phases. We finally study, the mass–radius relationship for such types of mixed HS, calculating their maximum mass, and compare them with the recent observations of pulsar PSR J1614-2230, which is about 2 solarmass.     

Leading particle production in light flavour jets

The energy distribution and type of the particle with the highest momentum in quark jets are determined for each of the five quark flavours making only minimal model assumptions. The analysis is based on a large statistics sample of hadronic decays collected with the OPAL detector at the LEP collider. These results provide a basis for future studies of light flavour production at other centre-of-mass energies. We use our results to study the hadronisation mechanism in light flavour jets and compare the data to the QCD models JETSET and HERWIG. Within the JETSET model we also directly determine the suppression of strange quarks to be by comparing the production of charged and neutral kaons in strange and non-strange light quark events. Finally we study the features of baryon production. Received: 19 November 1999 / Published online: 8 May 2000     

密度依赖口袋常数下奇异物质的热力学自洽处理及其对混合星性质的影响

在MTT口袋模型的基础上采用密度依赖口袋常数,给出了奇异夸克物质的热力学关系,并用于描述奇异夸克物质及混合星内的夸克相,研究了奇异星、混合星的性质.结果表明,密度依赖口袋常数下,奇异夸克物质的压强公式中有一个附加项,而能量密度中则没有,从而保证了系统的热力学自洽性.在新的热力学关系下,奇异夸克物质的状态方程变软,相应的奇异星的引力质量和对应的半径均变小;混合星的状态方程也变软,其质量变小,而对应的半径也变小.说明经热力学自洽处理后该模型对中子星的状态方程及相应的质量-半径关系等都有显著的影响.