Improved Light-Cone QCD Sum Rule Analysis of Rare Decays Λ_b → Λ_γ and Λ_b → Λl~+ l~-

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.     

Phenomenological Λ-nuclear interactions

Variational Monte-Carlo calculations have been performed for the ligh s-shell hypernuclei, namely, _Λ ⁴ H, _Λ ⁴ H^*, and _Λ ⁵ He. The main aim of the study has been to give more insight into the Λ-nuclear interactions. Our study shows that the three-body ANN force has a larger share in the splitting energy of _Λ ⁴ H (0⁺–1⁺) compared to the two-body AN force. The analyses on Λ-binding to nuclear matter based on our s-shell results demonstrate that the three-body ANN correlations need to be incorporated suitably to describe these systems.     

Alpha Cluster Structure of Hypernuclei and Λ-Seperate Energy of Λ17O

By using the alpha cluster structure model of hypernuclei and the phenomenological interaction potential between Λ hyperon and α-particle, the Λ seperate energy of the hypernucleus 13ΛC is calculated. A good agreement with the experimental data is achieved. Based on this the Λ-seperate energy of the hypernucleus 17ΛO is predicted. It is consistent with the empirical value of 17ΛO and advantages over the existing theoretical calculation made up-to-date.     

Effects of vector leptoquarks on Λ_b→ Λ_c?■_? decay

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.     

On cosmological mass with positive Λ

For asymptotically flat space-times, a very satisfactory expression for the total mass/energy of a system defined at future null infinity was provided by Bondi and Sachs, in the early 1960s. A generalization of this to space-times that are asymptotically de Sitter now has particular relevance in view of observational evidence, from 1998 onwards, indicating the presence of a positive cosmological constant Λ. In this article, some of the issues involved in such a definition are examined, showing that a somewhat different attitude to mass/energy must be taken, from that which was appropriate for asymptotically flat space-times. Two tentative suggestions are put forward for a retarded mass/energy definition with positive Λ, one based on a conformally invariant integral expression whose advanced time-derivative gives the Bondi–Sachs definition in the asymptotically flat case and the other, on the author’s 1982 approach to quasi-local energy. Such expressions could have some direct relevance to the proposal of Conformal Cyclic Cosmology, for which recent analysis of the CMB has provided some striking support.     

Tachyonization of the ΛCDM cosmological model

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.     

Non-spectator Contributions to Lifetime of Λb

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.     

Double Λ-hypernuclei at the PANDA experiment

Hypernuclear research will be one of the main topics addressed by the PANDA experiment at the planned Facility for Antiproton and Ion Research FAIR at Darmstadt (Germany). Thanks to the use of stored $\overline{p}$ beams, copious production of double ?? hypernuclei is expected at the PANDA experiment, which will enable high precision ?? spectroscopy of such nuclei for the first time. At PANDA excited states of ??^?? hypernuclei will be used as a starting point for the formation of double ?? hypernuclei. In order to predict the yield of particle stable double hypernuclei a microcanonical decay model was developed. For the detection of these nuclei, a devoted hypernuclear detector setup is planned. This set-up consists, in addition to the general purpose of the PANDA set-up, of a primary nuclear target for the production of $\Xi^{-}+\overline{\Xi}$ pairs, a secondary active target for the hypernuclei formation and the identification of associated decay products and a germanium array detector to perform ?? spectroscopy. Furthermore, the presence of $\overline{\Xi}$ can be used as an alternative to tag the strangeness in the $\Xi^{-}+\overline{\Xi}$ . All systems need to operate in the presence of a high magnetic field and a large hadronic background. In the present talk details concerning simulations, the identification procedure of double hypernuclei and the suppression of background will be presented. In addition, the present status of the detector developments for this programme will be briefly given.     

Flat FRW models with variableG and Λ

We consider Einstein's equations with variable gravitational couplingG and cosmological term . For a power-law time-dependence ofG, the cosmological term varies in proportion to the inverse square of the time, provided the equation of state is not that of vacuum. There is then no dimensional constant associated with . For a vacuum equation of state the model is compatible with classical inflation for a wide class of functionsG(t) and (t). For non-power-law behaviour ofG(t), it is possible to have a scale factor that increases exponentially without a vacuum equation of state. For this case the energy density associated with decreases exponentially, while at time zero it is equal with opposite sign to the regular energy density, so there is zero total energy initially.     

J~P assignments of Λ_c~+ baryons

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.     

Finslerian Perturbation for the ΛCDM Model

We present Finslerian perturbation for the ΛCDM model, which breaks the isotropic symmetry of the universe. The analysis on the Killing vectors shows that the Randers–Finsler spacetime breaks the isotropic symmetry even if the scalar perturbations of the FRW metric vanish. In Randers–Finsler spacetime, the modified geodesic equation deduces a modified Boltzmann equation. We propose a perturbational version of the gravitational field equation in Randers–Finsler spacetime, where we have omitted the curvature tensor that does not belong to the base space of the tangent bundle. The gravitational field equations for the gravitational wave are also presented. The primordial power spectrum of the gravitational wave is investigated. We show that the primordial power spectrum for super-horizon perturbations is unchanged. For sub-horizon perturbations, however, the power spectrum is modified.     

Magnetised Strings in Λ-Dominated Anisotropic Universe

In this paper, we have searched the existence of Λ-dominated anisotropic universe filled with magnetized strings. The observed acceleration of universe has been explained by introducing a positive cosmological constant Λ in the Einstein’s field equation which is mathematically equivalent to dark energy with equation of state (EOS) parameter set equal to ?1. The present values of the matter and the dark energy parameters (Ω_m)₀ & (Ω_Λ)₀ are estimated for high red shift (.3 ≤ z ≤ 1.4) SN Ia supernova data’s of observed apparent magnitude along with their possible error taken from Union 2.1 compilation. It is found that the best fit value for (Ω_m)₀ & (Ω_Λ)₀ are 0.2920 & 0.7076 respectively which are in good agreement with recent astrophysical observations in the latest surveys like WMAP and Plank. Various physical parameters such as the matter and dark energy densities, the present age of the universe and the present value of deceleration parameter have been obtained on the basis of the values of (Ω_m)₀ & (Ω_Λ)₀.Also, we have estimated that the acceleration would have begun in the past at z = 0.6845 i. e. 6.2341 Gyrs before from now.     

ELECTROMAGNETICALLY INDUCED FOCUSING IN A Λ-TYPE MEDIUM

Electromagnetlcally induced transparency (EIT) in an inhomogenously broadened medium consisting of Λ-type three-level atoms has been analyzed. It is shown that the A system can induce a transparency of the medhun when the probe laser and the coupling laser have the same frequency detunings (including zero). Across the EIT window, the radial variation of the strong coupling laser radiation may lead to electromagnetically induced focusing or defocusing of the weak probe laser at separate probe frequency detuning points.     

Hyperons Analogous to the Λ(1405)

The low mass of the Λ(1405) hyperon with j ^P =  1/2^?, which is higher than the ground state Λ(1116) mass by 290 MeV, is difficult to understand in quark models. We analyze the hyperon spectrum in the bound state approach of the Skyrme model that successfully describes both the Λ(1116) and the Λ(1405). This model predicts that several hyperon resonances of the same spin but with opposite parity form parity doublets that have a mass difference of around 300 MeV, which is indeed realized in the observed hyperon spectrum. Furthermore, the existence of the ${\Xi(1620)}$ and the ${\Xi(1690)}$ of j ^P  = 1/2^? is predicted by this model. Comments on the Ω baryons and heavy quark baryons are made as well.     

Spin-orbit part of the Λ-nucleus optical potential

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.     

Induced magnetic monopole from trapped Λ-type atom

We investigate the spatial motion of the trapped atom with the electromagnetically induced transparency (EIT) configuration where the two Rabi transitions are coupled to two classical light fields respectively with the same detuning. When the internal degrees of freedom can be decoupled adiabatically from the spatial motion of the center of mass via the Born-Oppenheimer approximation, it is demonstrated that the lights of certain profile can provide the atom with an effective field of magnetic monopole, which is the so-called induced gauge field relevant to the Berry's phase. Such an artificial magnetic monopole structure manifests itself in the characterizing energy spectrum.     

Analysis of the Λb → Λ?+?? transition in the SM4 using form factors from full QCD

Using the responsible form factors calculated via full QCD, we analyze the ?? _b ?? ???⁺?^? transition in the standard model containing fourth-generation quarks (SM4). We discuss the effects of the presence of the t?? fourth-family quark on related observables like branching ratio, forward-backward asymmetry, baryon polarization as well as double-lepton polarization asymmetries. We also compare our results with those obtained in the SM as well as with predictions of the SM4 but using form factors calculated within heavy-quark effective theory. The obtained results on the branching ratio indicate that the ? transition is more probable in full QCD comparing to the heavy-quark effective theory. It is also shown that the results on all considered observables in the SM4 deviate considerably from the SM predictions when m _t?? ?? 400 GeV.