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1.
The KNΛ and KNΣ coupling constants have been calculated in the framework of the Chiral Bag Model(CBM). We find −3.88 ≤g
KNΛ≤−3.67 and 1.15 ≤g
KNΣ≤ 1.24 by taking into account pseudoscalar mesons (π, K) and vector mesons (ρ, ω, K
*) field effects. Particularly, it is shown that vector mesons make significant contributions to the coupling constants g
KNΛ and g
KNΣ. Our values are existing within the experimental limits compared to the phenomenological values extracted from the kaon photoproduction
and kaon-nucleon scattering experiments. Also, form factors are suggested for the πNN, πNΔ, KNΛ and KNΣ couplings.
Received: 17 August 1998 / Revised version: 22 December 1998 相似文献
2.
Yu-Ming Wang Ying Li Cai-Dian Lü 《The European Physical Journal C - Particles and Fields》2009,59(4):861-882
The weak decays of Λ
b
→Λ+γ and Λ
b
→Λ+l
+
l
− are investigated in the standard model using the light-cone sum-rule approach. The higher-twist distribution amplitudes of
the Λ baryon to the leading conformal spin are included in the sum rules for the transition form factors. Our results indicate
that the higher-twist distribution amplitudes almost have no influence on the transition form factor f
2(q
2) defined by the tensor current, while such corrections can have a significant impact on the form factors g
2(q
2) defined by a vector current. Two phenomenological models (COZ and FZOZ) for the wave function of the Λ baryon are also employed in the sum rules for comparison, which can give rise to form factors approximately five times larger
than that in terms of conformal expansion. Utilizing the form factors calculated in LCSR, the physical observables like the
decay rate, the polarization asymmetry and forward–backward asymmetry are analyzed for the decays of Λ
b
→Λ
γ, Λ
l
+
l
−. 相似文献
3.
Mahmood Mian 《Pramana》1993,41(2):145-149
The binding energy of the double hypernucleus
ΛΛ
6
is calculated in α + 2Λ cluster model using the method of translation invariant basis TIMO. As regards the required interaction
potentials we use a density dependent effective ΛN force and a gaussian form for ΛΛ potential. With these interactions a very reasonable value ofB
ΛΛ is obtained if the oscillator states up to the excitation quantum numberN=12 are taken into account in the expansion of wavefunction of the hypernucleus. This value ofN is much smaller than that obtained in an earlier study. This lowering inN value is attributed to a much better choice of ΛN potential used in the present study. 相似文献
4.
Jai Kumar Singhal 《Pramana》2004,62(5):1029-1040
We examine the effects of mixing induced light heavy charged lepton neutral currents on the partial wave amplitude for the
process l+l− →ZZ (withl = e,μ or τ). By imposing the constraints that the amplitude should not exceed the perturbative unitarity limit at high energy (√s
= Λ), we obtain bounds on light heavy charged lepton mixing parameter sin2(2θ
L
a
) where θ
L
a
is the mixing angle of the ordinary charged lepton with its exotic partner. For Λ = 1 TeV, no bound is obtained on sin2 (2θ
L
a
) form
E < 0.69 TeV. However, sin2 (2θ
L
a
) ≤ 1.52×10−5 form
E = 5 TeV, sin2 (2θ
L
a
) ≤ 2.41 ×10−7 form
E = 10 TeV. Similarity for Λ = ∞ no bound is obtained on sin2 (2θ
L
a
) for mE < 1.97 TeV and sin2 (2θ
L
a
) ≤ 0.15 form
E = 5 TeV and sin2 (2θ
L
a
) ≤ 3.88×10-2 form
E = 10 TeV. 相似文献
5.
Variational Monte Carlo calculations of the ground state separation energiesB
Λ of thes-shell hypernuclei and also of
Λ
9
Be have been made for an Urbana-type central space-exchange ΛN potential consistent with Λp scattering, and also including three-body ΛNN forces. Thes-shell hypernuclei are treated asA-body systems (A = baryon number), and
Λ
9
Be is analysed as a partially nine-body problem in the Λ — 2α model. The reduction ofB
Λ due to the space-exchange ΛN potential has been calculated for thes-shell hypernuclei for a range of interactions: both ΛN and ΛN + ΛNN forces. ForA = 3,4,5 the exchange energy is approximately, 0.04, 0.15 and 0.50 MeV, respectively. For
Λ
9
Be a much more limited study gives ≅ 1.3 MeV. These values are much larger than that for ‘soft’ ΛN +NN potentials when the correlations are weak.
Preliminary results were presented at the DAE Symp. on ‘Nuclear Physics’ Vol. 32B (1989). 相似文献
6.
Vilson Tonin-Zanchin Erasmo Recami José A. Roversi Luis A. Brasca-Annes 《Foundations of Physics Letters》1994,7(2):167-179
Within a purely classical formulation of “strong gravity,” we associated hadron constituents (and even hadrons themselves)
with suitable stationary, axisymmetric solutions of certain new Einsteintype equations supposed to describe the strong field
inside hadrons. Such equations are nothing but Einstein equations—with cosmological term—suitably scaled down. As a consequence,
the cosmological constant Λ and the massesM result in our theory to be scaled up, and transformed into a “hadronic constant” and into “strong masses,” respectively.
Due to the unusual range of Λ andM values considered, we met a series of solutions of the Kerr-Newman-de Sitter (KNdS) type with rather interesting properties:
aim of the present work is putting forth such results, while “translating” them into the more popular language of ordinary
gravity.
The requirement that those solutions be stable, i.e., that their temperature (or surface gravity) bevanishingly small, implies the coincidence of at least two of their (in general, three) horizons. Imposing the stability condition of a certain
horizon does yield (once chosen the values ofJ, q and Λ) mass and radius of the associated black hole.
In the case of ordinary Einstein equations and for stable blackholes of the KNdS type, we get in particular Regge-like relations
among massM, angular momentumJ, chargeq and cosmological constant Λ; which did not receive enough attention in the previous literature. For instance, with the standard
definitionsQ
2 = Gq2/(4πε
0
c
4), a ≡ J/(Mc), m ≡GM/c
2, in the case Λ=0 in whichm
2=a2+Q2 and ifq is negligible, we findm
2=J. When considering, for simplicity, Λ>0 andJ=0 (andq still negligible), then we obtainm
2 = 1/(9Λ). In the most general case, the condition, for instance, of “triple coincidence” among the three horizons yields
for |Λa
2|<< 1 the couple of independent relationsm
2 = 2/(9Λ) andm
2 = 8(a
2 + Q2.
Another interesting point is that—with few exceptions—all such relations (amongM, J, q, Λ) lead to solutions that can be regarded as (stable) cosmological models.
Work partially supported by INFN, MURST, and CNR and by CNPq, FAPESP, and CAPES. 相似文献
7.
The weak radiative decay Λ
b
→Λγ is studied in the heavy quark effective theory treatings-quark as heavy. This rare decay is induced by the short distance electromagnetic penguins. Including corrections of the order
of (1/m
Q), we obtain the transition matrix element and the corresponding decay width. The Isgur-Wise function is evaluated in the
largeN
c limit and the branching ratio obtained is 1.48×10−5. 相似文献
8.
Yong-Lu Liu Ming-Qiu Huang Dao-Wei Wang 《The European Physical Journal C - Particles and Fields》2009,60(4):593-601
We present the light-cone QCD sum rules up to twist 6 for the electromagnetic form factors of the Λ baryon. To estimate the magnetic moment of the baryon, the magnetic form factor is fitted by the dipole formula. The numerical
value of our estimation is μ
Λ
=−(0.64±0.04)μ
N
, which is in accordance with the experimental data and the existing theoretical results. We find that it is twist 4 but not
the leading twist distribution amplitudes that dominate the results. 相似文献
9.
M.P. Rekalo E. Tomasi-Gustafsson 《The European Physical Journal A - Hadrons and Nuclei》2003,16(4):563-567
We discuss the applicability of pQCD to the elastic scattering of electrons on protons and deuterons. We analyze the Q2-dependence of the reduced deuteron form factor, taking into account the recent data on the electric proton form factor and
we find that the value of the QCD-scale parameter Λ differs essentially from the value Λ = 0.1 GeV, previously found using
the dipole parametrization of the electromagnetic nucleon form factors GE and GM. Moreover, the predicted scaling behavior of the reduced deuteron form factor cannot be recovered in the Dirac and Pauli
representations for the nucleon electromagnetic form factors.
Received: 14 October 2002 / Accepted: 12 November 2002 / Published online: 11 March 2003
RID="a"
ID="a"Permanent address: National Science Center KFTI, 310108 Kharkov, Ukraine.
RID="b"
ID="b"e-mail: etomasi@cea.fr
Communicated by V.V. Anisovich 相似文献
10.
A generalized set of strain variablesq
r
N
, has been defined to develop the expression for a generalized set of second order and third-order elastic moduliC
rs
N
andC
rst
N
for a cubic crystal deformed to orthorhombic structure. The HessainC
rs
N
δqrδqs andC
rst
N
δqrδqsδqt (r=1, 2……6; summation convention) are calculated in the new variables and compared withG-strength andS-strength, for both positive and negative loading environment.
The convexity of the internal energy relative to various choice of strain measure is examined considering up to third degree
terms in the internal energy expression. The computational results forbcc iron is presented according to the new moduli. The stable ranges thus obtained for iron under hydrostatic compressive and
tensile stresses is found to generate the classical stable range, green-stable range and stretch-stable range as the specific
cases. However,bcc iron does not seem to follow any conventional stable ranges under hydrostatic compression, where the present generalized
stable range is found satisfactory. 相似文献
11.
The electromagnetic form factors for pions and nucleons are considered within the model of quark-gluon strings, where the momentum-transfer dependence of hadronic form factors is determined by the intercepts of the corresponding Regge trajectories and by the Sudakov form factor. Analytic expressions found for form factors in the timelike region admit an analytic continuation to the spacelike region. The resulting form factors for pions and nucleons comply well with experimental data both for positive and for negative values of the squared momentum transfer q 2. It is shown that the distinctions between the absolute values of the pion and nucleon form factors F π(q 2), G m (q 2), and F 2(q 2) at positive values of q 2 and those at negative values of this variable are associated with the analytic properties of the double-logarithmic term in the exponent of the Sudakov form factor. The spin structure of the amplitudes for quark transitions into hadrons that is proposed in the present study makes it possible to describe fairly well available experimental data on the Pauli form factor F 2 and on the ratio G e /G m . 相似文献
12.
Timothy M. Garoni Giovanni Ossola Marco Polin Alan D. Sokal 《Journal of statistical physics》2011,144(3):459-518
We study, via Monte Carlo simulation, the dynamic critical behavior of the Chayes–Machta dynamics for the Fortuin–Kasteleyn
random-cluster model, which generalizes the Swendsen–Wang dynamics for the q-state Potts ferromagnet to non-integer q≥1. We consider spatial dimension d=2 and 1.25≤q≤4 in steps of 0.25, on lattices up to 10242, and obtain estimates for the dynamic critical exponent z
CM. We present evidence that when 1≤q≲1.95 the Ossola–Sokal conjecture z
CM≥β/ν is violated, though we also present plausible fits compatible with this conjecture. We show that the Li–Sokal bound z
CM≥α/ν is close to being sharp over the entire range 1≤q≤4, but is probably non-sharp by a power. As a byproduct of our work, we also obtain evidence concerning the corrections to
scaling in static observables. 相似文献
13.
We study the chromatic polynomial PG(q) for m× n square- and triangular-lattice strips of widths 2≤ m ≤ 8 with cyclic boundary conditions. This polynomial gives the zero-temperature limit of the partition function for the antiferromagnetic
q-state Potts model defined on the lattice G. We show how to construct the transfer matrix in the Fortuin–Kasteleyn representation for such lattices and obtain the accumulation
sets of chromatic zeros in the complex q-plane in the limit n→∞. We find that the different phases that appear in this model can be characterized by a topological parameter. We also compute
the bulk and surface free energies and the central charge. 相似文献
14.
A. A. Tolchennikov 《Russian Journal of Mathematical Physics》2008,15(1):128-139
For the kernel of the Laplace operator ΔΛ with potential Σ
j=1
k
c
j
δ
q
j
(x) on a manifold, (the operator is given by a Lagrangian plane Λ ⊂ ℂ
k
⊕ ℂ
k
), an isomorphism Γ: ker ΔΛ → Λ ∩ L is described, where L is a special Lagrangian plane (whose explicit form is evaluated). A similar assertion holds for the Laplace operator on a decorated graph; for such a graph (obtained by decorating a connected finite graph with n edges and v vertices) with “continuity” conditions, the inequality 1 ≤ dimker ≤ n − v + 2 is obtained. It is also proved that the quantity n − v + 1-dim ker cannot reduce when adding new edges and manifolds. The first terms of the expansion of Tr(exp(-tH
Λ)) are found.
Dedicated to the memory of V. A. Geyler 相似文献
15.
The K-matrix approach with effective Lagrangians is used to describe the S and P pion-nucleon partial-wave amplitudes in the energy range E
lab≤ 1 GeV. It is demonstrated, that treating the resonance as K-matrix a pole gives the natural way to separate the resonance and non-resonance parts of the πN amplitude. The model includes all the four-star πN resonances, the non-resonance contributions are calculated from relevant Feynman graphs without any phenomenological form
factors. Different contributions to the inelastic π−
p→ηn amplitude are estimated.
Received: 9 July 1998 相似文献
16.
The electron yield per ion charge-state γ/q was measured for emission of electrons from clean polycrystalline gold induced due to impact of Ta
q+ (11≤q≤41) ions with kinetic energy per chargeE
i/q from 15 keV/q to 150 keV/q. The dependence of γ on angle of incidence was analyzed with use of relation γ(ϑ)=γ0 cos−f
ϑ. The fitting of experimental data gives a range of γ0/q from 1 to 1.75 for Ta13+ and from 1.5 to 1.73 for Ta39+. The dependence of γ0/q onq andE
i is discussed with respect to measurement of ion currents emitted from laser-produced plasmas with an ion collector with unsuppressed
secondary electron emission.
This work was supported by the Division of Chemical Sciences, Office of Basic Energy Sciences, Office of Energy Research,
U.S. Department of Energy, and by grant A1010819 from the Grant Agency of the Academy of Sciences of the Czech Republic. 相似文献
17.
We further extend the cosmological scenario with energy exchange by Barrow and Clifton and our previous work to the more complex
case with energy exchange between three fluids: radiation, matter and vacuum energy. By prescribing the form of energy exchange
function, we construct an infinitely cyclic cosmological model, in which the universe undergoes an endless sequence of cosmic
epoch and each consisting of expansion and contraction, and the cosmological parameters, such as the Hubble parameter H, deceleration parameter q, transition red-shift Z
T, and densities ρ
r
,ρ
m
, and ρ
Λ are consistent with the present observed values. 相似文献
18.
R. Brazis L. Safonova R. Narkowicz 《International Journal of Infrared and Millimeter Waves》1997,18(8):1575-1584
Non-transmission bands of electromagnetic waves propagating along the layers in periodic structures are studied in the steady
magnetic field perpendicular both to the uniaxis and the direction of propagation. The band control range (36÷75 GHz) inn-InSb/Al2O3 structures with the carrier densities 4 1013 ≤n ≤ 8 1014 cm−3 in magnetic fieldsB
o ≤ 2 T at temperatures 77 ≤T ≤ 200 K is found to agree with the calculated in the effective medium approximation. Attenuation down to −50 dB within the
band is observed. The band lineshape is found to indicate additional effects related to the finite layer thickness and periodicity
termination predicted by a more rigorous theory of dispersion. 相似文献
19.
T.Yu. Tretyakova D.E. Lanskoy 《The European Physical Journal A - Hadrons and Nuclei》1999,5(4):391-398
Properties of light neutron-rich Λ hypernuclei (16
ΛC, 12
ΛBe, and 11
ΛLi) are calculated within the Skyrme-Hartree-Fock approach. Interplay between hypernuclear interaction features and properties
of these hypernuclei is studied. Response of weakly bound neutron states to hyperon addition depends generally on core distortion
by hyperon, and it is essentially different for the different states. This response is especially sensitive to details of
the ΛN interaction for 1p
1/2 states. Implications of the nuclear spin-orbit potential and nuclear incompressibility in the neutron-rich system properties
are inferred. Dependence of the Λ binding energies in hypernuclei on Z at fixed A is discussed.
Received: 16 December 1998 相似文献
20.
S. Choe 《The European Physical Journal A - Hadrons and Nuclei》1998,3(1):65-73
In the QCD sum rule approach we predict the Λ (1405) mass by choosing the π0Σ0 multiquark interpolating field. It is found that the mass is about 1.419 GeV from Π1 (q
2) sum rule which is more reliable than Πq (q
2) sum rule, where Πq (q
2) and Π1 (q
2) are two invariant functions of the correlator Π (q
2). We also present the sum rules for the K
+
p and the π+Σ+ multiquark states, and compare to those for the π0Σ0 multiquark state. The mass of the Λ (1600) can be also reproduced in our approach.
Received: 11 November 1997 / Revised version: 28 April 1998 相似文献