254 research outputs found

    Isovector axial-vector form factors of octet baryons in QCD

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    We compute the diagonal isovector axial-vector as well as induced pseudoscalar form factors of nucleon, Σ\Sigma and Ξ\Xi baryons by employing the light-cone QCD sum rules to leading order in QCD and including distribution amplitudes up to twist 6. Extrapolating our sum-rules results to low-momentum transfers, we make a comparison with experimental and lattice-QCD results where we can achieve a nice qualitative and quantitative agreement.Comment: 9 pages, 3 figure

    On the calculation of covariant expressions for Dirac bilinears

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    In this article, various approaches to calculate covariant expressions for the bilinears of Dirac spinors are presented. For this purpose, algebraic equations defining Dirac spinors are discussed. Following that, a covariant approach for spacetime parameterization is presented and the equations defining Dirac spinors are written fully in terms of Lorentz scalars. After presenting how the tensorial bilinears can be reduced to combinations of scalar bilinears with appropriate Lorentz structures, a covariant recipe for the calculation of scalar bilinears is provided.Comment: 10 pages, 1 figur

    New Unitary Relations between the QCD sum rules

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    Abstract. New unitary symmetry relations are obtained between the QCD sum rules for ΣΛ transitions. Also for QCD SR's with baryon distribution amplitudes the unitary relations are constructed, proved in a simple quark model and found to be consistent with the existing calculations

    X(3872) and Its Heavy Quark Spin Symmetry Partners in QCD Sum Rules

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    X(3872) presents many surprises after its discovery more than ten years ago. Understanding its properties is crucial to understand the spectrum of possible exotic mesons. In this work, X(3872) meson and its heavy quark spin symmetry (HQSS) partners (including the mesons in the bottom sector) are studied within the QCD Sum Rules approach using a current motivated by the molecular picture of X(3872). We predict four heavy partners to X(3872) and bottomonium with the masses and J^PC quantum numbers. Obtained results are in good agreement with the previous studies and available experimental data within errors.Comment: 18 pages, 12 figures, 3 tables, Accepted by European Physical Journal

    Tensor form factors of nucleon in QCD

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    We extract the isovector tensor nucleon form factors, which play an important role in understanding the transverse spin structure of the nucleon when related to the quark helicity-flip generalized parton distributions via their first moments. We employ the light-cone QCD sum rules to leading order in QCD and include distribution amplitudes up to twist 6 in order to calculate the three tensor form factors HTH_T, ETE_T and H~T\tilde{H}_T. Our results agree well with those from other approaches in the low and high momentum-transfer regions.Comment: 8 pages, 1 figure; minor changes, matches journal versio

    Q-ball formation in the wake of Hubble-induced radiative corrections

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    We discuss some interesting aspects of the Q\rm Q-ball formation during the early oscillations of the flat directions. These oscillations are triggered by the running of soft (mass)2({\rm mass})^2 stemming from the nonzero energy density of the Universe. However, this is quite different from the standard Q\rm Q-ball formation. The running in presence of gauge and Yukawa couplings becomes strong if m1/2/m0m_{1/2}/m_0 is sufficiently large. Moreover, the Q\rm Q-balls which are formed during the early oscillations constantly evolve, due to the redshift of the Hubble-induced soft mass, until the low-energy supersymmtery breaking becomes dominant. For smaller m1/2/m0m_{1/2}/m_0, Q\rm Q-balls are not formed during early oscillations because of the shrinking of the instability band due to the Hubble expansion. In this case the Q\rm Q-balls are formed only at the weak scale, but typically carry smaller charges, as a result of their amplitude redshift. Therefore, the Hubble-induced corrections to the flat directions give rise to a successful Q\rm Q-ball cosmology.Comment: 7 revtex pages, few references corrected and added, final version to appear in Phys. Rev.

    Juxtaposing BTE and ATE – on the role of the European insurance industry in funding civil litigation

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    One of the ways in which legal services are financed, and indeed shaped, is through private insurance arrangement. Two contrasting types of legal expenses insurance contracts (LEI) seem to dominate in Europe: before the event (BTE) and after the event (ATE) legal expenses insurance. Notwithstanding institutional differences between different legal systems, BTE and ATE insurance arrangements may be instrumental if government policy is geared towards strengthening a market-oriented system of financing access to justice for individuals and business. At the same time, emphasizing the role of a private industry as a keeper of the gates to justice raises issues of accountability and transparency, not readily reconcilable with demands of competition. Moreover, multiple actors (clients, lawyers, courts, insurers) are involved, causing behavioural dynamics which are not easily predicted or influenced. Against this background, this paper looks into BTE and ATE arrangements by analysing the particularities of BTE and ATE arrangements currently available in some European jurisdictions and by painting a picture of their respective markets and legal contexts. This allows for some reflection on the performance of BTE and ATE providers as both financiers and keepers. Two issues emerge from the analysis that are worthy of some further reflection. Firstly, there is the problematic long-term sustainability of some ATE products. Secondly, the challenges faced by policymakers that would like to nudge consumers into voluntarily taking out BTE LEI

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