共查询到20条相似文献,搜索用时 31 毫秒
1.
We present a systematic light-cone QCD sum rule study of the exclusive rare radiative decay Λ b →Λγ and rare semileptonic decay Λ b →Λl + l within the framework of the standard model. Although some light-cone sum rule (LCSR) studies on these rare processes can be found in different literatures, it is necessary to reanalyze them systematically for the reason that either the baryonic distribution amplitudes are improved or different interpolating currents for the Λ b baryon may lead to quite different results. In addition, the rare process Λ b →Λγ has not yet been analyzed by LCSR with the Ioffe-type current. Taking all these reasons into account, we perform LCSR calculations of both the processes with two types of interpolating currents. Our calculations show that the choice of the interpolating current for the Λ b baryon can affect the predictions significantly, especially for the rare radiative decay process. 相似文献
2.
3.
The structures of the lightp-shell hypernuclei \({}_\Lambda ^6 He,{}_\Lambda ^7 Li,{}_\Lambda ^9 Liand{}_\Lambda ^9 Be\) are studied by using a realistic effectiveΛN interaction (YNG), and compared to those with the use of the simple one-range Gaussian (ORG) interaction. The YNG interaction, which simulates theΛNG-matrix for the Nijmegen OBE modelD, is characterized by the inner repulsive core and the density-dependence along with the space-exchange and spin-spin components. The framework we adopt is the microscopic α +x + Λ (x=n, d, t or α) three-cluster model, where nucleon antisymmetrization is exactly treated. The characteristic behaviors ofΛ?x andΛ?(αx) interactions derived from the YNG are displayed and discussed. In spite of the remarkable characteristic of YNG, the calculated energy levels of the four hypernuclei are very similar to those previous obtained by using the simple ORG interaction. The stabilization and contraction of the hypernuclear system due to the glue-like role ofΛ-particle persists in the present calculation, though the repulsive core of theΛN interaction tends to prevent from too much contraction. 相似文献
4.
Luis P. Chimento Mónica Forte Gilberto M. Kremer Marlos O. Ribas 《General Relativity and Gravitation》2010,42(6):1523-1535
In this work a tachyonization of the ΛCDM model for a spatially flat Friedmann–Robertson–Walker space–time is proposed. A
tachyon field and a cosmological constant are considered as the sources of the gravitational field. Starting from a stability
analysis and from the exact solutions for a standard tachyon field driven by a given potential, the search for a large set
of cosmological models which contain the ΛCDM model is investigated. By the use of internal transformations two new kinds
of tachyon fields are derived from the standard tachyon field, namely, a complementary and a phantom tachyon fields. Numerical
solutions for the three kinds of tachyon fields are determined and it is shown that the standard and complementary tachyon
fields reproduces the ΛCDM model as a limiting case. The standard tachyon field can also describe a transition from an accelerated
to a decelerated regime, behaving as an inflationary field at early times and as a matter field at late times. The complementary
tachyon field always behaves as a matter field. The phantom tachyon field is characterized by a rapid expansion where its
energy density increases with time. 相似文献
5.
In this work, we study the contributions of non-spectator effects to the lifetimes of Λb and B-mesons comparatively. Based on the well-established theoretical framework about the effective weak Lagrangian, we derive the formulation of the non-spectator effects at the quark level. Especially, for Λb we have considered two pictures: the three-valence-quark picture and the quark-diquark picture. In the two pictures, the interference contributions to the total width are different, in this work, we investigate the interference effects in detail. As a preliminary estimate on the lifetimes, we evaluate the hadronic matrix elements appearing in the final formulas of the lifetimes by means of a simple phenomenological model for both pictures. Our results show that the contributions of the non-spectator effects can reduce the ratio of lifetime of Λb to that of B-mesons by 5 ~ 7%. It is noted that in the quark-diquark picture the ratio can be further reduced if excited states of the diquark system are taken into account. We conclude that the measured ratio τ(Λb)/τ(B0)(≈)0.79 [The Data Group, Phys. Rev. D66 (2002) 010001] can be partly understood by the non-spectator effects, although the problem on the discrepancy between theoretical prediction and experimental measurement is not fully solved. 相似文献
6.
The "good" diquark is employed to study Λ_c~+ baryons within a mass loaded flux tube model. The study indicates that all Λ_c~+ baryons candidates in the 2008 review by the Particle Data Group (PDG) are well described in the mass loaded flux model. The quantum numbers J~P of these Λ_c~+ candidates are assigned. If Λ_c(2765)~+ is an orbitally excited Λ_c~+, it is likely the J~P=3~+/2 one. If Λ_c(2765)~+ is an orbitally excited Σ_c, there ought to be another J~P = 3~+/2 Λ_c~+ with mass ≈ 2770 MeV. In the model, there exists no J~P = 1~+/2 Λ_c~+ (≈ 2700) predicted in existing literature. Λ_c(2940)~+ is very possible the orbitally excited baryon with J~P = 5~-/2. 相似文献
7.
《中国物理C(英文版)》2021,(1)
Experimental data on R(D~((*))),R(K~((*))),and R(J/Ψ),provided by different collaborations,show sizable deviations from the standard model predictions.To describe these anomalies,many new physics scenarios have been proposed.One of them is the leptoquark model,which introduces the simultaneous coupling of vector and scalar leptoquarks to quarks and leptons.To look for similar possible anomalies in the baryonic sector,we investigate the effects of a vector leptoquark U3(3,3,2/3) on various physical quantities related to the tree-level ∧_b→∧_c■ decays(■=μτ),which proceed via b→ c■ transitions at the quark level.We calculate the differential branching ratio,forward-backward asymmetry,and longitudinal polarizations of leptons and ∧c baryons at the μ and τ lepton channels in the leptoquark model and compare their behavior to the predictions of the SM in terms of q~2.In the calculations,we use the form factors calculated in full QCD as the main input and account for all errors coming from the form factors and model parameters.We observe that at the τ channel,the R_A fit solution to data related to the leptoquark model sweeps some regions out of the SM band;nevertheless,the fit has a considerable intersection with the SM predictions.The R_B type solution gives roughly the same results as the SM on DBR(q~2)-q~2.At the μ channel,the leptoquark model gives results that are consistent with the SM predictions and existing experimental data on the behavior of DBR(q~2) with respect to q~2.Concerning the q2 behavior of the A_(FB)(q~2),the two types of fits for τand the predictions at the μ channel in the leptoquark model give exactly the same results as the SM.We also investigate the behavior of the parameter R(q~2) with respect to q~2 and the value of R(∧_C) in both the vector leptoquark and SM models.Both fit solutions lead to results that deviate considerably from the SM predictions for R(q~2)-q~2 and R(∧_C).Future experimental data on R(q~2)-q~2 and R(∧_C),made available by measurements of the ∧_b→∧_cτ■τ channel,will be particularly helpful.Any experimental deviations from the SM predictions in this channel would emphasize the importance of tree-level hadronic weak transitions as good probes of new physics effects beyond the SM. 相似文献
8.
It is noted that in the new Particle Data Group(PDG) version the rare decays of the Λ_b baryon have been revised with more accuracy. The new results show that most of the existing theoretical results on the process Λ_b→Λ_γ Lgbare larger than those of experiments. With the improved higher-order light-cone distribution amplitudes of the Λ baryon, we reanalyze the process in the framework of light-cone quantum chromodynamics sum rules and the branching ratio is estimated to be Br (Λ_b→Λ_γ)=(7.38_(-0.39)~(+0.40))×10~(16), which is consistent with the new experimental result. Furthermore, another process Λ_b→Λl~+l~- is also analyzed in the same frame. The final branching ratio is calculated to be Br (Λ_b→Λl~+l~-)=1.20×10~(-6), which is in good accordance with the data from the PDG and other theoretical predictions. 相似文献
9.
V. A. Filimonov 《Russian Physics Journal》1981,24(2):194-197
The model of one-boson exchange is used to calculate the spin-orbit component of the -nucleus and nucleon-nucleus optical potential. For the hyperon, the spin-orbit interaction is approximately an order of magnitude weaker than for the nucleon.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 102–105, February, 1981. 相似文献
10.
E. A. Gazazyan G. G. Grigoryan V. O. Chaltykyan D. Schraft 《Journal of Contemporary Physics (Armenian Academy of Sciences)》2012,47(5):216-221
An optical Toffoli gate is the essential logical element, which permits the implementation of a reversible optical processor. We propose a simple realization of such a gate in films of crystals doped with rare-earth ions. The proposed scheme is based on adiabatic population transfer in a ??-system by means of counterintuitive and intuitive sequences of short laser pulses. We also discuss possibilities for experimental realization of the proposed gate. 相似文献
11.
The dynamics ofatomic populations in the field of a single femtosecond pulse is numerically investigated in the frameworks of the resonant approximation and beyond it. It is shown that for the pulses with the extremely short duration the violation of resonant approximation leads not only to the quantitative but also to the qualitative changes in the behavior of the three-level atom. 相似文献
12.
We propose alternative methods for measurement of the global polarization of Λ hyperons. These methods involve event averages of proton and Λ momenta in the laboratory frame. We carry out simulations using these methods and show that all of them work equally well in obtaining the global polarization of Λ hyperons. 相似文献
13.
A. Z. Dubničková S. Dubnička M. E. Biagini A. Castro 《Czechoslovak Journal of Physics》1991,41(12):1177-1188
The behaviour of the -hyperon electric and magnetic form factors is predicted within the modified three resonance ((783), (1020), (1680)) vector-meson dominance (VMD) model with correct analytic properties and the asymptotic behaviour predestinated by the quark model for baryons. The resonance couplings to are evaluated from the known couplings to nucleons by utilizing theSU(3) symmetry and normalization conditions for Dirac and Pauli form factors. The masses and widths of the considered vector mesons are fixed at the world averaged values. The optimal position of the effective inelastic threshold, common for Dirac and Pauli form factors, is determined from the fit of the only existing Orsay DM2 point on the
cross section att=5·693 GeV2. The mean square charge and magnetic radii of the -hyperon are found to be r
E
2
=0·018 F2 and r
M
2
=–0·027 F2, respectively.The authors are very much indebted to Prof. R. Baldini-Ferroli for calling their attention to the problem of -hyperon e.m. ff 's in connection with the FENICE experiment. 相似文献
14.
Martiros Khurshudyan 《Central European Journal of Physics》2014,12(5):348-366
In this article we will consider several phenomenological models for the Universe with varying G and Λ(t), where G is the gravitational ”constant” and Λ(t) is a varying cosmological ”constant”. Two-component fluid model are taken into account. An interaction of the phenomenological form between a barotropic fluid and a quintessence DE is supposed. Three different forms of Λ(t) will be considered. The problem is analysed numerically and behavior of different cosmological parameters investigated graphically. Conclusion and discussions are given at the end of the work. In an Appendix information concerning to the other cosmological parameters is presented. 相似文献
15.
Harpreet Kaur 《Pramana》1999,52(4):395-400
We study some nonleptonic decays of Λb-baryon involving transition of a heavy to light quark, using nonrelativistic quark model for form factors. The decay rates
for two such decays are consistent with the data available. Also these decays can give us information on the CKM matrix element
|VUb|. 相似文献
16.
17.
Based on the beyond-mean-field Skyrme-Hartree-Fock model,impurity effects of the Λ hyperon in the hypernuclear systems Λ25Mg and Λ29Si are investigated,respecti... 相似文献
18.
An extrapolation to the physical limit for the lattice data of Λ_b →Λ_c form factors computed in the nonphysical region is made in this work through a class of fitting functions proposed by us with nonlinear dependence on m2/π derived in the chiral perturbative theory(ChPT) and the heavy quark effective theory(HQET) framework. Then the results are applied to calculate the differential and integrated Λ_b →Λ_c semileptonic decay rates. Meanwhile, a comparison between our results and those obtained through the extrapolation functions with naive linear dependenceon m2/π is made.It is shown that the difference between the extrapolated central values of these two cases is about 5%.The total uncertainties(depending on the momentum transfer q~2) in the linear case are about 5% ~10%(caused by the uncertainties of lattice data) and those in the nonlinear case are about 10% ~ 20%(caused by the uncertainties of both lattice data and input parameters in Ch PT and HQET). More accurate lattice data and parameters in ChPT and HQET are needed to reduce the uncertainties of the extrapolated results. 相似文献
19.
We theoretically investigate the emission spectrum for a Λ-type three-level atom trapped in the node of a standing wave. We show that the atomic center-of-mass motion not only directly affects the peak number, peak position, and peak height in the atomic emission spectrum, but also influences the effects of the cavity field and the atomic initial state on atomic emission spectrum. 相似文献
20.
Li Xungui 《中国物理C(英文版)》1994,18(1):81-84
This paper extends the method of the harmonic-oscillator product state as basis function to the hypernucleus A6Li which is of non-zero spin. we have studied the characteristic of the ground state of the hypernucleus A6Li with this method and an α+ p + A three cluster model. The calculated result shows the method can be used to calculate the energy level of the system in which the interaction between the constituent clusters is spin-dependent. 相似文献