118614193
Reexamination of reaction rates for a key stellar reaction of $^{14}$O($\alpha$,p)$^{17}$F
The reaction rates of the key stellar reaction of O(α,p)F have been reexamined. The previous conclusion, the 6.15-MeV state (Jπ=1−) dominating this reaction rate, has been overthrown by a careful reanalysis of the previous experimental data [J. Gómez del Campo et al., Phys. Rev. Lett. 86, 43 (2001)]. According to the present R-matrix analysis, the previous 1− assignment for the 6.15MeV state is definitely wrong. Most probably, the 6.286-MeV state is the 1− state and the 6.15-MeV state is a 3− one, and hence the resonance at Ex=6.286 MeV (J π=1−) dominates the reaction rates in the temperature region of astrophysical interests. The newly calculated reaction rates for the O(α,p)F reaction are quite different from the previous ones, for instance, it’s only about 1/6 of the previous value around 0.4 GK, while it’s about 2.4 times larger than the previous value around 2 GK. The astrophysical implications have been discussed based on the present conclusions.
15702909
The continuum limit of perturbative coefficients calculated with a large field cutoff
Abstract We report MC calculations of perturbative coefficients for lattice scalar field theory in dimensions l, 2 and 3, where the large field contributions are cutoff. This produces converging (instead of asymptotic) perturbative series. We discuss the statistical errors and the lattice effects and sho-kv that accurate calculations are possible even in a crossover region where no approximation works. We show that the field cutoff is also a UV regulator. We point out the relevance for QCD questions discussed by Tomboulis ad Trottier at this conference.
36263241
New optimization methods for converging perturbative series with a field cutoff
We take advantage of the fact that in lambda phi ^4 problems a large field cutoff phi_max makes perturbative series converge toward values exponentially close to the exact values, to make optimal choices of phi_max. For perturbative series terminated at even order, it is in principle possible to adjust phi_max in order to obtain the exact result. For perturbative series terminated at odd order, the error can only be minimized. It is however possible to introduce a mass shift in order to obtain the exact result. We discuss weak and strong coupling methods to determine the unknown parameters. The numerical calculations in this article have been performed with a simple integral with one variable. We give arguments indicating that the qualitative features observed should extend to quantum mechanics and quantum field theory. We found that optimization at even order is more efficient that at odd order. We compare our methods with the linear delta-expansion (LDE) (combined with the principle of minimal sensitivity) which provides an upper envelope of for the accuracy curves of various Pade and Pade-Borel approximants. Our optimization method performs better than the LDE at strong and intermediate coupling, but not at weak coupling where it appears less robust and subject to further improvements. We also show that it is possible to fix the arbitrary parameter appearing in the LDE using the strong coupling expansion, in order to get accuracies comparable to ours.
15336878
Hot subdwarfs from the stable Roche lobe overflow channel
Context. Hot subdwarfs are core-helium-burning stars with extremely thin envelopes. We discuss the formation and evolution of hot subdwarfs formed through the stable Roche lobe overflow (RLOF) channel of intermediate-mass binaries, although their formation channels are various. Aims. In this study, we concentrate on the formation and evolution of hot subdwarfs binaries through the stable RLOF channel of intermediate-mass binaries. We aim at setting out the properties of hot subdwarfs and their progenitors, so that we can understand the formation and evolution of hot subdwarfs. Methods. Employing Eggleton's stellar evolution code, we have computed conservative and nonconservative population I binary evolution sequences. The initial mass of the primary ranges from 2.2 to 6.3 M(circle dot), spaced by approximately 0.1 in log M, the initial mass ratio q(i) = M(1)/M(2) is between 1.1 and 4.5, and the Roche lobe overflow begins at the main sequence, the Hertzsprung gap and the first giant branch. In nonconservative binary evolution, we assume that 50 percent of the mass lost from the primary leaves the system, carrying away the specific angular momentum of the primary, and the remaining mass is accreted on to the secondary during the RLOF. Also, we have studied the distributions of the mass and orbital periods of hot subdwarfs using the population synthesis approach. Results. We have obtained the ranges of the initial parameters of progenitor binaries and the properties of hot subdwarfs through the stable RLOF channel of intermediate-mass binaries, e. g. mass, envelope mass and age of hot subdwarfs. We have found that hot subdwarfs could be formed through stable Roche lobe overflow at the main sequence and Hertzsprung gap. We have also found that some subdwarf B or OB stars have anomalously high mass (similar to 1 M(circle dot)) with a thick envelope (similar to 0.07 M(circle dot)-similar to 0.16) in our models. By comparing our theoretical results with observations on the hot subdwarfs in open clusters, we suggest that more hot subdwarfs in binary systems might be found in open clusters in the future.
121764664
The DIRC prototype for the WASA experiment at COSY
The implementation of a DIRC (Detector or Internally Reflected Cherenkov light) was planned for the WASA-at-COSY experiment, located at the Forschungszentrum Julich and is a major project for the future PANDA experiment at FAIR. In order to study the components and the behavior of the detector under experimental conditions, a large scale demonstrator made of acrylic glass was built and tested at the external proton beam of the COSY accelerator. The main properties of the components, especially of the newly developed front end electronics and the results of the first tests are presented.
122970197
Multijet production in neutral current deep inelastic scattering at HERA and determination of alpha(s)
Multijet production rates in neutral current deep inelastic scattering (DIS) have been measured in the range of exchanged boson virtualities 10<Q2<5000 GeV2. The data were taken at the ep collider HERA with centre-of-mass energy using the ZEUS detector and correspond to an integrated luminosity of 82.2 pb-1. Jets were identified in the Breit frame using the kT cluster algorithm in the longitudinally invariant inclusive mode. Measurements of differential multijet cross sections are presented as functions of jet transverse energy , pseudorapidity and Q2 with and . Next-to-leading-order QCD calculations describe the data well. The value of the strong coupling constant αs(MZ), determined from the ratio of the trijet to dijet cross sections, is .
36299978
Jet Collimation by Small-Scale Magnetic Fields
A popular model for jet collimation is associated with the presence of a large-scale and predominantly toroidal magnetic field originating from the central engine (a star, a black hole, or an accretion disk). Besides the problem of how such a large-scale magnetic field is generated, in this model the jet suffers from the fatal long-wave mode kink magnetohydrodynamic instability. In this paper we explore an alternative model: jet collimation by small-scale magnetic fields. These magnetic fields are assumed to be local, chaotic, and tangled, but are dominated by toroidal components. Just as in the case of a large-scale toroidal magnetic field, we show that the "hoop stress" of the tangled toroidal magnetic fields exerts an inward force which confines and collimates the jet. The magnetic "hoop stress" is balanced either by the gas pressure of the jet or by centrifugal force if the jet is spinning. Since the length scale of the magnetic field is small (< the cross-sectional radius of the jet the length of the jet), in this model the jet does not suffer from the long-wave mode kink instability. Many other problems associated with the large-scale magnetic field are also eliminated or alleviated for small-scale magnetic fields. Though it remains an open question how to generate and maintain the required small-scale magnetic fields in a jet, the scenario of jet collimation by small-scale magnetic fields is favored by the current study on disk dynamo which indicates that small-scale magnetic fields are much easier to generate than large-scale magnetic fields.
116604013
QCD inspired relativistic bound state model and meson structures
A QCD inspired relativistic effective Hamiltonian model for the bound states of mesons has been constructed, which integrates the advantages of several QCD effective Hamiltonian models. Based on light-front QCD effective Hamiltonian model, the squared invariant mass operator of meson is used as the effective Hamiltonian. The model has been improved significantly in four major aspects: i)it is proved that in center of mass frame and in internal coordinate Hilbert subspace, the total angular momentum $J$ of meson is conserved and the mass eigen equation can be expressed in total angular momentum representation and in terms of a set of coupled radial eigen equations for each $J$. ii)Based on lattice QCD results, a relativistic confining potential is introduced into the effective interaction and the excited states of mesons can be well described. iii)an SU(3) flavor mixing interaction is introduced phenomenologically to describe the flavor mixing mesons and the mass eigen equations contain the coupling among different flavor components. iv)the mass eigen equations are of relativistic covariance and the coupled radial mass eigen equations take full account of $L-S $ coupling and tensor interactions. The model has been applied to describe the whole meson spectra of about 265 mesons with available data. The agreement of the calculated masses, squared radii, and decay constants with data is quite well. For the mesons whose mass data have large experimental uncertainty, the model produces certain mass values for test. For some mesons whose total angular momenta and parity are not assigned experimentally, the model gives a prediction of the spectroscopic configuration$^{2S+1}L_J$. The connection between our model and the recent low energy QCD issues-the infrared conformal scaling invariance and holographic QCD hadron models is discussed.
122891080
THE GENERALIZED CHAPLYGIN GAS MODEL WITH INTERACTION
A two-fluid generalized Chaplygin gas (GCG) model including two different cases is considered in this paper. Concretely, the evolution of the GCG model with interaction is discussed and the statefinder diagnostic for the GCG models is performed, respectively. By analysis, we show that the effective state parameter of dark energy can cross the so-called phantom divide ω = -1, the behavior of GCG will be like ΛCDM in the future and therefore our Universe will not end up with the Big Rip in the future. In addition, we find that the statefinder diagnostic can differentiate the GCG model with or without interaction. Also, trajectories of both the GCG model mixed with cold dark matter (CDM) and the pure GCG model in the parameter plane are illustrated to be significantly different.
123281558
Understanding nuclear shape phase transitions within SD-pair shell model
15632846
Energetics of a Black Hole-Accretion Disk System with Magnetic Connection: Limit of Low Accretion Rate
We consider the energetics of a black hole-accretion disk system with magnetic connection: a Keplerian disk is connected to a Kerr black hole by a large-scale magnetic field. We assume that 1) the magnetic field is locked to the inner boundary of the disk and corotates with it, and 2) the accretion rate is low, but the accretion from the disk can still provide a sufficient amount of cold plasma particles in the transition region so that the magnetohydrodynamics approximation is valid. By finding solutions that smoothly pass the fast critical point near the equatorial plane, we find that a system with a fast rotating black hole and that with a slow rotating black hole behave very differently. For ab lack hole with a>a cr ≡ 0.3594 M ,w hereM is the mass and a is the specific angular momentum of the black hole, the spinning energy of the black hole is efficiently extracted and transported to the disk, thus increasing the radiation efficiency of the disk by orders of magnitude. For a black hole with 0 ≤ a<a cr, the inner region of the disk is disrupted by the magnetic field and the inner boundary moves out to a radius where the angular velocity of the disk is equal to the spinning angular velocity of the black hole. As a result, the disk may have an extremely low radiation efficiency if 0 ≤ a/M � 1.