28535306
Implications of a cosmological constant varying as R-2.
We advocate the possibility that the (effective) cosmological constant {Lambda} varies in time as {ital R}{sup {minus}2}, {ital R} being the scale factor of our expanding Universe. This behavior can be obtained under some simple and general assumptions in conformity with quantum cosmology. After pointing out several advantages worth noticing, we show that such a time-varying {Lambda} leads to no conflict with existing observations. However, it does change the predictions of the standard cosmology in the matter-dominated epoch and alleviates some problems in reconciling observations with the inflationary scenario. In particular, this medium'' time variation of {Lambda} leads to creation of matter with a rate at present which is comparable to that in the steady-state cosmology.
119207670
PHASE-RESOLVED SPECTRAL ANALYSIS OF 4U 1901+03 DURING ITS OUTBURST
The high-mass X-ray binary 4U 1901+03 is reported to have a pulse profile evolving with the X-ray luminosity and energy during its outburst in 2003 February-July: the pulse peak changed from double to single along with the decreasing luminosity. We have carried out a detailed analysis on the contemporary phase-resolved energy spectrum of 4U 1901+03 as observed by the Rossi X-ray Timing Explorer. We find that the spectra are phase dependent. At the beginning of the outburst, the maximum of the optical depth for Compton scattering is near the major phase peak. During the decay of the outburst, the optical depth has the maximum away from the main peak of the pulse profile. For each observation, Fe Kα emission line is detected in the phase-resolved spectra, and its flux is constant across the pulse phases. This suggests that the origin of the Fe emission is from the accretion disk, not the surface of the neutron star.
44727684
BRST quantization of topological field theory.
The canonical quantization of the topological field-theory model {Sigma}, proposed by Horowitz, is examined through the Becchi-Rouet-Stora-Tyutin approach. With this approach we have a manifestly covariant description of a certain class of topological quantum field theories. However, if {ital M} in the present model is any orientable four-dimensional manifold, one would end up with different theories when different polarizations are chosen. Therefore a restriction {ital M}={ital R}{sup 1}{times}{Sigma}, as pointed out by Horowitz, is required for consistency.
119850463
Charged Pion Photoproduction
We extracted the differential cross section for the γn→π−p process from a deuterium target using the CLAS detector at Jefferson Lab in Hall B for photon energies between 1.0 and 3.5 GeV and pion center‐of‐mass (c.m.) angles (θc.m.) between 50° and 115°. We confirm a previous indication of a broad enhancement around a c.m. energy (s) of 2.1 GeV at θc.m. = 90° in the scaled differential cross section, s7dσdt and a rapid fall‐off in a center‐of‐mass energy region of about 400 MeV following the enhancement. Our data show an angular dependence of this enhancement as the suggested scaling region is approached for θc.m. from 70° to 105°.
17527105
Four-Fermion theory and the conformal bootstrap
We employ the conformal bootstrap to re-examine the problem of finding the critical behavior of four-fermion theory at its strong coupling fixed point. Existence of a solution of the bootstrap equations indicates self-consistency of the assumption that, in space-time dimensions less than four, the renormalization group flow of the coupling constant of a four-fermion interaction has a nontrivial fixed point which is generally out of the perturbative regime. We exploit the hypothesis of conformal invariance at this fixed point to reduce the set of the Schwinger-Dyson bootstrap equations for four-fermion theory to three equations which determine the scale dimension of the fermion field ψ, the scale dimension of the composite field ψψ and the critical value of the Yukawa coupling constant. We solve the equations assuming this critical value to be small. We show that this solution recovers the fixed point for the four-fermion interaction with N-component fermions in the limit of large N at (Euclidean) dimension d between two and four. We perform a detailed analysis of the 1/N-expansion in d = 3 and demonstrate full agreement with the conformal bootstrap. We argue that this is a useful starting point for more sophisticated computation of the critical indices.
16855657
Critical statistical charge for anyonic superconductivity.
We examine a criterion for the anyonic superconductivity at zero temperature in Abelian matter-coupled Chern-Simons gauge-field theories in three dimensions. By solving the Dyson-Schwinger equations, we obtain a critical value of the statistical charge for the superconducting phase in a massless fermion-Chern-Simons model. {copyright} {ital 1996 The American Physical Society.}
64414878
IN-VACUUM UNDULATOR CONTROLLER DESIGN FOR SSRF
Two 25mm period in-vacuum undulators (IVU25) have been installed in SSRF 3.5 GeV storage ring. The controller for IVU25 based on Siemens S7-300 PLC is used to control two stepper motors for the gap and tapper of magnetic pole array. The controller monitors cooling water’s temperature and flux, monitor the array’s temperature, too. And configure Ethernet access for remote control as well as MPS and PPS interlock. A simple user interface supports routine operation and detail information is showed at cascading windows. With real time feedback of the linear absolute encoders (LAEs) the tracking precision of gap and taper are less than 1 micron. This paper describes the design of controller hardware and software.
42826202
Observation of the Top Quark.
The D0 collaboration reports on a search for the Standard Model top quark in p{bar p} collisions at {radical}s = 1.8 TeV at the Fermilab Tevatron, with an integrated luminosity of approximately 50 pb{sup {minus}1}. We have searched for t{bar t} production in the dilepton and single lepton decay channels, with and without tagging of b quark jets. We observe 17 events with an expected background of 3.8 {plus_minus} 0.6 events. The probability for an upward fluctuation of the background to produce the observed signal is 2 {times} 10{sup {minus}6} (equivalent to 4.6 standard deviations). The kinematic properties of the excess events are consistent with top quark decay. We conclude that we have observed the top quark and measure its mass to be 199{sub {minus}21}{sup +19} (stat.) {plus_minus}22 (syst.) GeV/c{sup 2} and its production cross section to be 6.4 {plus_minus} 2.2 pb.
28164273
General theory of quantum statistics with internal degrees of freedom in two dimensions.
The general theory of θ statistics with internal degrees of freedom is presented. The intrinsic parts of wave functions are expressed by means of the irreducible representations of the quantum group SU(2,q) with q=e −iθ . We show that the violation of P or T reflection symmetry is involved in two kinds of coproduct for constructing these representations
42992975
Study of the strong coupling constant using W+jet processes.
The ratio of the number of W + 1 jet to W + 0 jet events is measured with the D0 detector using data from, the 1992--93 Tevatron Collider run. For the W {yields} e{nu} channel with a minimum jet E{sub T} cutoff of 25 GeV, the experimental ratio is 0.065 {+-} 0.003(stat) {+-} 0.007(sys). Next-to-Leading order QCD predictions for various parton distributions agree well with each other and are all over one standard deviation below the measurement. Varying the strong coupling constant {alpha}{sub s} in both the parton distributions and the partonic cross sections simultaneously does not remove this discrepancy.
43203688
Remark on charm quark fragmentation to D** mesons.
The observed [ital D][sup **] mesons have [ital c[bar q]] flavor quantum numbers and a spin-parity of the light degrees of freedom [ital s][sub [ital l]][sup [pi]][sub [ital l]]=3/2[sup +]. In the [ital m][sub [ital c]][r arrow][infinity] limit the spin of the charm quark is conserved and the [ital c][r arrow][ital D][sup **] fragmentation process is characterized by the probability for the charm quark to fragment to a [ital D][sup **] meson with a given helicity for the light degrees of freedom. We consider the calculated [ital b][r arrow][ital B][sub [ital c]][sup **] fragmentation functions in the limit [ital m][sub [ital c]]/[ital m][sub [ital b]][r arrow]0 as a qualitative model for the [ital c][r arrow][ital D][sup **] fragmentation functions. We find that in this model charm quark fragmentation to [ital s][sub [ital l]][sup [pi]][sub [ital l]]=3/2[sup +] light degrees of freedom with helicities [plus minus]1/2 is favored over fragmentation to [ital s][sub [ital l]][sup [pi]][sub [ital l]]=3/2[sup +] light degrees of freedom with helicities [plus minus]3/2.