14342177
Disk Accretion onto Magnetized Neutron Stars: The Inner Disk Radius and Fastness Parameter
It is well known that the accretion disk around a magnetized compact star can penetrate inside the magnetospheric boundary, so that the magnetospheric radius R0 does not represent the true inner edge Rin of the disk, but controversies exist in the literature concerning the relation between R0 and Rin. In the model of Ghosh & Lamb, the width of the boundary layer is given by δ=R0-RinR0, or RinR0, while Li & Wickramasinghe recently argued that Rin could be significantly smaller than R0 in the case of a slow rotator. Here we show that if the star is able to absorb the angular momentum of the disk plasma at R0, appropriate for binary X-ray pulsars, the inner disk radius can be constrained by 0.8Rin/R01, and the star reaches spin equilibrium with a relatively large value of the fastness parameter (~0.7-0.95). For accreting neutron stars in low-mass X-ray binaries (LMXBs), R0 is generally close to the stellar radius, Rs, so that the toroidal field cannot transfer the spin-up torque efficiently to the star. In this case, the critical fastness parameter becomes smaller, but Rin is still near R0.
44450113
Static magnetization and ac susceptibility measurements of the copper-oxygen cluster compound BaCuO2+x.
The clusters are in their ground states below {similar_to}40 K. The AF ordering at at {ital T}{sub {ital N}} arises from AF ordering of the Cu{sub 6} spin 3 magnetic moments only; this aspect of our model has been confirmed by magnetic neutron diffraction measurements. Remarkably, the Cu{sub 18} clusters and lone Cu ions do not participate in this ordering and remain paramagnetic down to at least 2 K. Each Cu{sub 18} cluster is antiferromagnetically coupled to three lone Cu ions, and each lone Cu ion to one Cu{sub 18} cluster, with AF coupling constant 2{ital J}{sub AF}/{ital k}{sub {ital B}}={minus}0.33 K. The Cu{sub 18} clusters (with spin {ital S}{sub {ital s}}=9) are predicted to undergo ferromagnetic intercluster ordering below {similar_to}1 K.
119270278
Strongly correlated topological superconductors and topological phase transitions via Green's function
We propose several topological order parameters expressed in terms of Green's function at zero frequency for topological superconductors, which generalizes the previous work for interacting insulators. The coefficient in topological field theory is expressed in terms of zero frequency Green's function. We also study topological phase transition beyond noninteracting limit in this zero frequency Green's function approach.
18351437
Search for the Optical Counterparts of Southern Anomalous X-Ray Pulsars and Radio-Quiet Neutron Stars in Young Supernova Remnants
We report on our search for the optical counterparts of the Southern Hemisphere anomalous X-ray pulsar 1E1048.1-5937 and the radio-quiet neutron stars in supernova remnants Puppis A, RCW 103, and PKS 1209-52. The observations were carried out with the new MIT/CfA MagIC camera on the Magellan-I 6.5 m telescope in Chile. We present deep multiband optical images of the X-ray error circles for each of these targets and discuss the resulting candidates and limits.
4372235
A debris disk around an isolated young neutron star
Pulsars are rotating, magnetized neutron stars that are born in supernova explosions following the collapse of the cores of massive stars. If some of the explosion ejecta fails to escape, it may fall back onto the neutron star or it may possess sufficient angular momentum to form a disk. Such ‘fallback’ is both a general prediction of current supernova models and, if the material pushes the neutron star over its stability limit, a possible mode of black hole formation. Fallback disks could dramatically affect the early evolution of pulsars, yet there are few observational constraints on whether significant fallback occurs or even the actual existence of such disks. Here we report the discovery of mid-infrared emission from a cool disk around an isolated young X-ray pulsar. The disk does not power the pulsar's X-ray emission but is passively illuminated by these X-rays. The estimated mass of the disk is of the order of 10 Earth masses, and its lifetime (≥ 106 years) significantly exceeds the spin-down age of the pulsar, supporting a supernova fallback origin. The disk resembles protoplanetary disks seen around ordinary young stars, suggesting the possibility of planet formation around young neutron stars.
1162741
Low-Mass X-Ray Binary as the Progenitor of PSR J1713 + 0747
We have calculated the evolution of low-mass X-ray binaries that leads to the formation of the binary radio pulsars like PSR J1713+0747. We show that the mass transfer is most likely to be nonconservative, due to unstable disk accretion, to account for the mass of PSR J1713+0747, which is close to its initial value. We assume that part of the lost material from the binary may form a circumbinary disk, and find that it can significantly influence the mass transfer processes. We briefly discuss the implications of the circumbinary disks on the evolution of low-mass X-ray binaries and the formation of low-mass binary pulsars.
121984241
Representation of the propagator and Schwinger functions of Dirac fields in terms of Brownian motions
A mathematical path integral representation of the propagator and Schwinger functions of the Dirac fields on R4 interacting with a smooth non‐Abelian gauge field is presented. The representation is essentially in terms of expectations with respect to the Brownian motion on R4.