118508611
The state of cold quark matter: a model-independent view
From a model-independent point of view, we address the possibility that quark clustering could occur in cold quark matter at realistic baryon densities because of the likely strong coupling between quarks in compact stars.
118446912
Radio and gamma-ray emission from pulsars
The radiation of pulsars have been observed for many years. A few pulsars are discovered to have both radio and gamma-ray emission. Many models on pulsar radiation have been developed, but so far we are still lacking an elaborate model which can explain the emission from radio to gamma-rays in detail. In this paper we present a joint model for radio and gamma-ray emission, in which both the dominate emission mechanisms are inverse Compton scattering. The pulse profiles at radio and gamma-ray bands are reproduced for the Crab-like, Vela-like and Geminga-like pulsars, in good agreement with observations.
117027180
Plateaus of gamma-ray bursts and supernovae: A unified correlation?
119299830
On Hoyle-Narlikar-Wheeler mechanism of vibration energy powered magneto-dipole emission of neutron stars
We revisit the well-known Hoyle-Narlikar-Wheeler proposition that neutron star emerging in the magnetic-flux-conserving process of core-collapse supernova can convert the stored energy of Alfvén vibrations into power of magneto-dipole radiation. We show that the necessary requirement for the energy conversion is the decay of internal magnetic field. In this case the loss of vibration energy of the star causes its vibration period, equal to period of pulsating emission, to lengthen at a rate proportional to the rate of magnetic field decay. These prediction of the model of vibration powered neutron star are discussed in juxtaposition with data on pulsating emission of magnetars whose radiative activity is generally associated with the decay of ultra strong magnetic field.
124675777
PRIMORDIAL STRANGE QUARK MATTER
Strange quark nuggets (SQNs) could be the relics of the cosmological QCD phase transition, and they could very likely be the candidate of cold dark matter if survived the cooling of the later Universe, although the formation and evolution of these SQNs depend on the physical state of the hot QGP (quark-gluon plasma) phase and the state of cold quark matter. We reconsider the possibility of SQNs as cold dark matter, and discuss the astrophysical consequences of primordial SQNs in the early and present universe. In the early Universe, the formation of black holes inside primordial halos could be faster than that in the standard scenario, and speed up the formation of the supermassive black holes at high redshift. In the present Universe, the capture of SQNs by pulsars could trigger star-quakes, which could be the mechanism for pulsar-glitches.
18183996
Is PSR B0943+10 a Low-Mass Quark Star?
A recent X-ray observation has shown that the radio pulsar PSR B0943+10, with clear drifting subpulses, has a much smaller polar cap area than that of conventional pulsars with mass of ~1 M☉ and radius of ~10 km. Zhang and coworkers have addressed the fact that this new result conflicts with the standard vacuum gap model. Nonetheless, the discrepancy could be explained if PSR B0943+10 is actually a low-mass quark star. We find that the potential drop in the open field line region of oblique pulsars (i.e., inclination angle α ≠ 0) might be ~102 times that of aligned pulsars, and that PSR B0943+10 with α = 124 could be well above the death line. We thus conclude that the Ruderman-Sutherland-type vacuum gap model still works well for this pulsar if it is a bare quark star with a mass of ~0.02 M☉ and a radius of ~2.6 km.
18317704
Measurement of Tau branching ratios
Using the data accumulated at LEP in 1989 and 1990 with the ALEPH detector, the inclusive and exclusive branching ratios of the τ lepton have been measured assuming lepton universality inZ0 decays. The inclusive branching fractions for the τ decay into one, three, and five charged particles have been determined to be (85.45±0.97)%, (14.35±0.48)%, and (0.10±0.05)%, respectively, in agreement with the world averages. New undetected decay modes are determined to have a branching fraction of less than 2.1% at 95% CL. The measured branching ratios for quasi-exclusive channels are slightly larger than, but consistent with the world averages, except for the modes τ→3 hadrons+vτ andτ→hadron+2π0vτ, which are significantly larger. These latter branching ratios have been found to be (9.5±0.7)% and (10.2±1.1)%, respectively. The sum of all the measured quasi-exclusive branching ratios is (100.4±1.8)%. A fully exclusive analysis of modes with neutral pions shows no evidence for new photonic decay modes with a branching fraction limit of 3.4% at 95% CL.
121366770
Measurement of the strong coupling constant using τ decays
The strong coupling constant is determined from the leptonic branching ratios, the lifetime, and the invariant mass distribution of the hadronic final state of the τ lepton, using data accumulated at LEP with the ALEPH detector. The strong coupling constant measurement, αs(mτ2) = 0.330±0.046, evolved to the Z mass yields αs(MZ2) = 0.188±0.005. The error includes experimental and theoretical uncertainties, the latter evaluated in the framework of the Shifman, Vainshtein and Zakharov (SVZ) approach. The method allows the non-perturbative contribution to the hadronic decay rate to be determined to be 0.3±0.5%.
9662073
Effect of asymmetric strange–antistrange sea to the NuTeV anomaly
Abstract We calculate the strange quark and antiquark distributions of the nucleon by using the effective chiral quark model, and find that the strange–antistrange asymmetry can bring a contribution of about 60–100% to the NuTeV deviation of sin 2 θ w from the standard value measured in other electroweak processes. The results are insensitive to different inputs. The light-flavor quark asymmetry of d ¯ – u ¯ is also investigated and found to be consistent with the experimental measurements. Therefore the chiral quark model provides a successful picture to understand the NuTeV anomaly, as well as the light-flavor quark asymmetry and the proton spin problem in previous studies.
123529844
Observation of charmless hadronic B decays
Abstract Four candidates for charmless hadronic B decay are observed in a data sample of four million hadronic Z decays recorded by the aleph detector at lep . The probability that these events come from background sources is estimated to be less than 10 −6 . The average branching ratio of weakly decaying B hadrons (a mixture of B d 0 , B s 0 and Λ b weighted by their production cross sections and lifetimes, here denoted B) into two long-lived charged hadrons (pions, kaons or protons) is measured to be Br (B → h + h − ) = (1.7 −0.7 +1.0 ± 0.2) × 10 −5 . The relative branching fraction Br( B d(s) 0 → π + π − (K − )) Br( B d(s) 0 → h + h − ) is measured to be 1.0 −0.3 −0.1 +0.0 +0.0 . In addition, branching ratio upper limits are obtained for a variety of exclusive charmless hadronic two-body decays of B hadrons.
120315427
Performance of the ALEPH detector at LEP
The performance of the ALEPH detector at the LEP e+e− collider is reviewed. The accuracy of the tracking detectors to measure the impact parameter and momentum of charged tracks is specified. Calorimeters are used to measure photons and neutral hadrons, and the accuracy obtained in energy and angle is given. An essential property of the detector is its ability to identify particles; the performance in identification of electrons, muons, neutrinos (from missing energy), charged hadrons, π0's and V0's is described.