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1.
Summary Triple differential cross-section (TDCS) of hydrogen atom in its metastable (2S) state is studied theoretically by electron and positron impact for coplanar and asymmetric geometry. The final-state wave
function in the present model satisfies the asymptotic boundary condition for asymmetric geometry (i.e. fork
1≫k
2). In the absence of experiment, present results are compared with other existing theoretical results. Apart from the double-peaked
structure of the TDCS as in ground-state ionization, some interesting secondary structures are found, in conformity with other
theories for ionization from 2S state. 相似文献
2.
Results of number projected quasiparticle calculations for Sn isotopes in large and in small model spaces are compared when the force strengths and single-particle energies are determined consistently within each model space. When extending the model space, one observes that the model parameters extracted from the odd nuclei become more satisfactory. For even nuclei the collective states are not lowered in energy although electromagnetic transition rates increase considerably. Spectroscopic factors for one-nucleon transfer reactions change noticeably only for shells close to the Fermi level. Two-nucleon transfer cross-sections are strongly increased for ground state to ground state transitions only. We criticize a usual approximation formula for theL=0 two-nucleon transfer cross-section. 相似文献
3.
4.
The state of the art Mössbauer spectroscopy has made unquestionable advance possible in the solid microstructure study. Apart from that application of the Mössbauer effect, another domain of investigations has been outlined since the outset, in the sixties, wherein the properties of gamma-radiation interaction with resonant nuclei in a recoilless mode are stressed. There were these recoilless processes that enabled to distinguish the gamma-radiation of natural width, and greatly encouraged the arising of traditional optics problems in the gamma range. The subject of interest in this article deals as well with the Mössbauer gamma optics. Essentially it is a gamma-ray (Mössbauer) susceptibility of the excited, non-equilibrium state of the nuclear spin system. We analyze the Mössbauer transitions in the strong coherent excitation of nuclear spins regime and the possibilities to deliberately vary the polarization, spectral and/or temporal properties of gamma-radiation propagating through a time-modulated medium. 相似文献
5.
Some Considerations on the Derivation of the Nonlinear Quantum Boltzmann Equation II: The Low Density Regime 总被引:1,自引:0,他引:1
D. Benedetto F. Castella R. Esposito M. Pulvirenti 《Journal of statistical physics》2006,124(2-4):951-996
In this paper we analyse the asymptotic dynamics of a system of N identical quantum particles in a low-density regime. Our approach follows the strategy introduced by the authors in a previous work,(2) to treat the simpler weak coupling regime. The time evolution of the Wigner transform of the one-particle reduced density matrix is represented by means of a perturbative series. The expansion is obtained upon iterating the Duhamel formula, in the spirit of the paper by Lanford.(32) For short times and small interaction potential, we rigorously prove that a subseries of the complete perturbative series, converges to the solution of the nonlinear Boltzmann equation that is physically relevant in the context. An important point is that we completely identify the cross-section entering the limiting Boltzmann equation, as being the Born series expansion of quantum scattering.As in ref. 2, our convergence result is only partial, in that we merely characterize the asymptotic behaviour of a subseries of the complete original perturbative expansion. We only have plausibility arguments in the direction of proving that the terms we neglect, when going from the original series to its associated subseries, are indeed vanishing in the limit.The present study holds in any dimension d ≥ 3. 相似文献
6.
Jean Farago 《Physica D: Nonlinear Phenomena》2008,237(8):1013-1020
We study the thermal equilibrium of nonlinear Klein-Gordon chains at the limit of small coupling (anticontinuum limit). We show that the persistence distribution associated to the local energy density is a useful tool to study the statistical distribution of the so-called thermal breathers, mainly when the equilibrium is characterized by long-lived pinned excitations; in that case, the distribution of persistence intervals turns out to be a power law. We demonstrate also that this generic behaviour has a counterpart in the power spectra, where the high-frequencies domains nicely collapse if properly rescaled. These results are also compared to nonlinear Klein-Gordon chains with a soft nonlinearity, for which the thermal breathers are rather mobile entities. Finally, we discuss the possibility of a breather-induced anomalous diffusion law, and show that despite a strong slowing down of the energy diffusion, there are numerical evidences for a normal asymptotic diffusion mechanism, but with exceptionally small diffusion coefficients. 相似文献
7.
Rodrigo Vargas 《Journal of statistical physics》2008,133(3):491-511
We establish the existence of two weak coupling regime effective dynamics for an open quantum system of repeated interactions
(vanishing strength and individual interaction duration, respectively). This generalizes known results (Attal and Joye in
J. Stat. Phys. 126:1241–1283, 2007) in that the von Neumann algebras describing the system and the chain element may not be of finite type. Then (but now assuming
that the small system is of finite type), we prove that both effective dynamics capture the long-term behavior of the system:
existence of a unique asymptotic state for them implies the same property for the respective exact dynamics—provided that
the perturbation parameter is sufficiently small. The zero-th order term in a power series expansion in the perturbation parameter
of such an asymptotic state is given by the asymptotic state of the effective dynamics. We conclude by working out the case
in which the small system and the chain element are spins.
Dedicated to Mariana Huerta.
This work was partially funded by Nucleus Millennium Information and Randomness P04-069-F. 相似文献
8.
Reactive scattering of O atoms with ICl molecules has been studied at an initial translational energy E = 40 kJ mol-1 using a supersonic beam of O atoms seeded in He and at E = 15 kJ mol-1 using O atoms seeded in Ne. Velocity distributions of OI product were measured by cross-correlation time-of-flight analysis. Full contour maps of the differential reaction cross-section have been obtained which show peaking almost equally in the forward and backward directions at both initial translational energies. The product translational energy distributions are consistent with a long-lived O-I-Cl collision complex dissociating via a loose transition state. The stability of the O-I-Cl complex is attributed to the low electronegativity of the central I atom compared with the peripheral atoms. This electronegativity ordering rule also determines the stability of the intermediates in the other reactions of oxygen atoms with halogen molecules. The mild peaking of the product angular distributions for O + ICl and IBr indicates that collision complexes have quite modest collision angular momenta L ~ 40 ? corresponding to impact parameters b ~ 1·4 Å and that the angular momentum of the OI molecule in the loose transition state may be approximately half the product orbital angular momentum. 相似文献
9.
Angular and velocity distribution measurements of IO reactive scattering from crossed beams of O atoms and halogen molecules I2, ICl are reported. Angular distribution measurements are reported for BrO from O + Br2. The O atom beam was generated at ~350 K from a microwave discharge source and the halogen molecule beam from a supersonic nozzle source at ~380 K. The product time-of-flight distribution was recorded at each laboratory scattering angle by a mini-computer. The scattering data are found to be in excellent agreement with the RRKM-AM model of reactive scattering via a long-lived collision complex. The observation of IO product from O + ICl identifies the complex with a bound O-I-Cl triplet state, previously observed for O-Cl-Cl in matrix isolation studies, as proposed by Herschbach. The maximum centrifugal barrier B m′ for dissociation of the long-lived complex can be accurately determined, particularly for O + I2. The B m′ values indicate that both the entrance and exit valleys of the potential energy surface are governed by centrifugal barriers in the region of long-range van der Waals potentials. The comparatively small reaction cross section (e.g. Q ~ 2 Å2 for O + Br2 from discharge flow measurements) is attributed primarily to an orientation requirement for reaction. The RRKM-AM model indicates a ‘tight linear’ transition state for dissociation of the O-I-I complex, corresponding to significant long-range IO orienting forces in the exit valley of the potential energy surface. 相似文献
10.
We explore the possibility of distinguishing the SM-like MSSM Higgs boson from the SM Higgs boson via Higgs boson pair production
at future muon collider. We study the behavior of the production cross-section in SM and MSSM with Higgs boson mass for various
MSSM parameters tan β and m
A
. We observe that at fixed CM energy, in the SM, the total cross-section increases with the increase in Higgs boson mass whereas
this trend is reversed for the MSSM. The changes that occur for the MSSM in comparison to the SM predictions are quantified
in terms of the relative percentage deviation in cross-section. The observed deviations in cross-section for different choices
of Higgs boson masses suggest that the measurements of the cross-section could possibly distinguish the SM-like MSSM Higgs
boson from the SM Higgs boson.
相似文献
11.
N. V. Krasnikov 《JETP Letters》1996,63(7):503-509
We construct a SUSY electroweak model with superweak R-parity violation. The scale of R-parity violation in our model is determined by the Majorana mass of the neutrino and is very small, leading to the existence
of a long-lived (T≫O(10−4) sec) lightest superparticle. If the lightest superparticle is a right-handed charged slepton, as can occur within the gaugino-dominated
scenario, then the phenomenology of such a model differs in a drastic way from the standard SUSY phenomenology; in particular,
long-lived charged sleptons can form bound states with ordinary matter—quasistable supermatter (SUSY analogs of mu-atoms and
muonium). We also discuss possible manifestations of the existence of such a long-lived charged particle at LEP2, TEVATRON
and LHC.
Pis’ma Zh. éksp. Teor. Fiz. 63, No. 7, 481–486 (10 April 1996)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
12.
It is the aim of this paper to describe two different linearization procedures for the Boltzmann equation in ak=0 Robertson-Walker space-time. These procedures are discussed with a view to obtaining an asymptotic form of the Boltzmann equation for the late stages of cosmic expansion where the behavior appropriate to a nonrelativistic gas is encountered. Using the asymptotic kinetic equations, a necessary and sufficient condition is formulated under which every small perturbation of the equilibrium distribution function, either classical or relativistic, decays to zero as time goes on. The same condition can be extracted from each of two linearization procedures, and in this sense a comparison is made of these approaches which reveals mutual agreement. Also, applying an asymptotic theory of the Einstein-Boltzmann system, we show that the final state of a gas is dust (i.e., a fluid with zero temperature and pressure). Comparison with the predictions of the Eckart fluid model is briefly presented. 相似文献
13.
C. Adloff et al. 《The European Physical Journal C - Particles and Fields》2002,25(4):495-509
Signals of QCD instanton-induced processes are searched for in deep-inelastic scattering (DIS) at the electron-proton collider
HERA in a kinematic region defined by the Bjorken-scaling variables x > 10-3, 0.1 < y < 0.6 and photon virtualities < 100 GeV2. Several observables characterising hadronic final state properties of QCD instanton-induced events are exploited to identify
a potentially instanton-enriched domain. While an excess of events with instanton-like topology is observed it cannot be claimed
significant given the uncertainty of the standard DIS background simulation. Upper limits on the cross-section for instanton-induced
processes of between 60 pb and 1000 pb are set dependent on the kinematic domain considered. The data do not exclude the cross-section
predicted by instanton perturbation theory for small instanton sizes. At large instanton sizes a naive extrapolation of instanton
perturbation theory yields a cross-section in the range of sensitivity of this study. Such a cross-section is not observed,
in agreement with non-perturbative lattice simulations of the QCD vacuum.
Received: 27 May 2002 / Published online: 24 September 2002 相似文献
14.
We study the relaxation of force distributions in the q-model, assuming a uniform q-distribution. We show that diffusion of correlations makes this relaxation very slow. On a d-dimensional lattice, the asymptotic state is approached as l
(1–d)/2, where l is the number of layers from the top. Furthermore, we derive asymptotic modes of decay, along which an arbitrary short-range correlated initial distribution will decay towards the stationary state. 相似文献
15.
T. Sekihara A. Martínez Torres D. Jido E. Oset 《The European Physical Journal A - Hadrons and Nuclei》2012,48(1):10
We study the photoproduction of φ mesons in deuteron, paying attention to the modification of the cross-section from bound
protons to the free ones. For this purpose we take into account Fermi motion in single scattering and rescattering of φ to
account for φ absorption on a second nucleon as well as the rescattering of the proton on the neutron. We find that the contribution
of the double scattering for φ is much smaller than the typical cross-section of γp → φp in free space, which implies a very small screening of the φ production in deuteron. The contribution from the proton rescattering,
on the other hand, is found to be not negligible compared to the cross-section of γp → φp in free space, and leads to a moderate reduction of the φ photoproduction cross-section on a deuteron at forward angles if
the LEPS set-up is taken into account. The Fermi motion allows contribution of the single scattering in regions forbidden
by phase-space in the free case. In particular, we find that for momentum transfer squared close to the maximum value, the
Fermi motion changes drastically the shape of dσ/dt, to the point that the ratio of this cross-section to the free one becomes very sensitive to the precise value of t chosen, or the size of the bin used in an experimental analysis. Hence, this particular region of t does not seem to be the most indicated to find effects of a possible φ absorption in the deuteron. This reaction is studied
theoretically as a function of t and the results are contrasted with recent experiments at LEPS and Jefferson Lab. The effect of the experimental angular
cuts at LEPS is also discussed, providing guidelines for future experimental analyses of the reaction. 相似文献
16.
Summary We reveal the fallacies in recent gamma-ray laser schemes that propose to obtain gain by stimulating transitions from a long-lived
upper to a short-lived lower nuclear state. We point out the errors in recent derivations of the stimulated-emission coefficients,
derive the correct formulae, and submit an alternative explanation for an experiment purported to observe stimulated emission
from a long-lived isomer. 相似文献
17.
We have calculated thef-sum rule for magnetic neutron scattering off electrons. Correlations alter the cross-section significantly at intermediate scattering vectors. Field induced effects are most significant at small scattering vectors, and the sum rule diverges in the limit of zero scattering vector. This feature is attributed to the field induced coupling of neutrons to the lowest energy Landau level and the collective density oscillation (hybrid mode). Our interpretation is based on an RPA calculation of the response function for neutron scattering from a magnetized plasma. The contribution to the cross-section from the electron-phonon interaction is also assessed, and it is found to increase with decreasing scattering vector. 相似文献
18.
M. Zawisza 《Physics of Particles and Nuclei Letters》2011,8(9):924-927
Correlations between non-identical particles at small relative velocity probe asymmetries in the average space-time emission
points at freeze-out. The origin of such asymmetries may be from long-lived resonances, bulk collective effects, or differences
in the freeze-out scenario for the different particle species. STAR has extracted pion-proton correlation functions from a
dataset of Au+Au collisions at √s
NN
= 200 GeV. We present correlation functions in the spherical harmonic decomposition representation, for different centralities
and for different combinations of pions and (anti-)protons. 相似文献
19.
Orest?Hrycyna Jakub?Mielczarek Marek?Szyd?owski 《General Relativity and Gravitation》2009,41(5):1025-1049
In this paper, we investigate dynamics of the modified loop quantum cosmology models using dynamical systems methods. Modifications
considered come from the choice of the different field strength operator F̂ and result in different forms of the effective Hamiltonian. Such an ambiguity of the choice of this expression from some
class of functions is allowed in the framework of loop quantization. Our main goal is to show how such modifications can influence
the bouncing universe scenario in the loop quantum cosmology. In effective models considered we classify all evolutional paths
for all admissible initial conditions. The dynamics is reduced to the form of a dynamical system of the Newtonian type on
a two-dimensional phase plane. These models are equivalent dynamically to the FRW models with the decaying effective cosmological
term parameterized by the canonical variable p (or by the scale factor a). We demonstrate that the evolutional scenario depends on the geometrical constant parameter Λ as well as the model parameter
n. We find that for the positive cosmological constant there is a class of oscillating models without the initial and final
singularities. The new phenomenon is the appearance of curvature singularities for the finite values of the scale factor,
but we find that for the positive cosmological constant these singularities can be avoided. The values of the parameter n and the cosmological constant differentiate asymptotic states of the evolution. For the positive cosmological constant the
evolution begins at the asymptotic state in the past represented by the de Sitter contracting (deS−) spacetime or the static Einstein universe H = 0 or H = − ∞ state and reaches the de Sitter expanding state (deS+), the state H = 0 or H = + ∞ state. In the case of the negative cosmological constant we obtain the past and future asymptotic states as the Einstein
static universes. 相似文献
20.
The ground state and the lowest excited states of the spin 1/2-Heisenberg model are investigated by exact diagonalization and variational Monte Carlo techniques. Our trial state represents a generalization of a wave function introduced by Hulthen, Kasteleijn and Marshall. The long range character of the spin-correlation function is in excellent agreement with exact diagonalization and also with recent neutron scattering results for La2CuO4. The asymptotic behavior of the spin-correlation function is found to differ from spin-wave theory. From the exact (N<=20 spins) and variational (N<=400) ground state energies we determine as asymptotic values 1.3025 and 1.288, respectively. We calculate the dispersion for the spin-wave excitations and identify an excited triplet which becomes degenerate with the ground state in the thermodynamic limit. This triplet state allows spontaneous symmetry breaking to occur atT=0 K. Quantum fluctuations reduce the sublattice magnetization to an effective value of 0.195 (3) as compared to the Néel-state value of 1/2. 相似文献