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arXiv 2409.14764hep-phnucl-exnucl-th
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同位旋标量标量场与同位旋矢量标量场对核物质中重子半轻衰变的影响

Effect of isoscalar and isovector scalar fields on baryon semileptonic decays in nuclear matter

Koichi Saito, Tsuyoshi Miyatsu, Myung-Ki Cheoun

AI总结:

该研究利用QMC模型探究同位旋标量、矢量标量场对非对称核物质中重子半轻衰变耦合常数的影响,发现δ场对中子β衰变矢量耦合常数的偏差影响达当前测量不确定度水平,指出核内重子衰变需考虑两类标量场效应。

摘要:

精确测定卡比博-小林-益川(Cabibbo-Kobayashi-Maskawa,CKM)矩阵元具有重要意义,因为它可能是探寻标准模型之外新物理的线索,其中$V_{ud}$尤为关键——它是CKM矩阵元幺正性条件的主要贡献项。目前,涉及$V_{ud}$的幺正性检验精度已达$10^{-4}$量级。由于$V_{ud}$的精确数据通常从超允许核β衰变中提取,因此研究核物质中弱矢量耦合常数的SU(3)味对称性破缺具有重要价值。\n本文旨在探究同位旋标量标量($σ$)平均场与同位旋矢量标量($δ$或$a_0$)平均场,如何影响非对称核物质中半轻重子(中子、$Λ$或$Ξ^-$)衰变的弱矢量耦合常数与轴矢耦合常数。为此,我们采用夸克-介子耦合(quark-meson coupling,QMC)模型,该模型中核物质由包含夸克自由度的核子组成,核子通过标量介子与矢量介子的自洽交换结合。我们仔细考虑了核物质中夸克流的质心修正。\n研究发现,对于非对称核物质中的中子β衰变,在核饱和密度下,$δ$场导致的矢量耦合常数偏差可达$10^{-4}$量级,与当前测量的不确定度水平相当。此外一个有趣的结果是,在富中子物质中,存在某一低密度值可使同位旋对称性恢复,即u-d夸克质量差消失。我们的结论是,在研究原子核内的重子半轻衰变时,必须考虑同位旋标量标量场与同位旋矢量标量场的效应。

英文摘要:

The precise determination of the Cabibbo-Kobayashi-Maskawa (CKM) matrix elements is very important, because it could be a clue to new physics beyond Standard Theory. This is particular true of $V_{ud}$, because it is the main contribution to the unitary condition of the CKM matrix elements. The level of accuracy for the test of the unitarity involving the element $V_{ud}$ is now of the order of $10^{-4}$. Because the precise data for $V_{ud}$ is usually extracted from super-allowed nuclear $β$ decay, it is quite significant to investigate the breaking of SU(3) flavor symmetry on the weak vector coupling constant in nuclear matter. The purpose of this paper is to investigate how the isoscalar scalar ($σ$) and the isovector scalar ($δ$ or $a_0$) mean-fields affect the weak vector and axial-vector coupling constants for semileptonic baryon (neutron, $Λ$ or $Ξ^-$) decay in asymmetric nuclear matter. To do so, we use the quark-meson coupling (QMC) model, where nuclear matter consists of nucleons including quark degrees of freedom bound by the self-consistent exchange of scalar and vector mesons. We pay careful attention to the center of mass correction to the quark currents in matter. We then find that, for neutron $β$ decay in asymmetric nuclear matter, the defect of the vector coupling constant due to the $δ$ field can be of the order of $10^{-4}$ at the nuclear saturation density, which is the same amount as the level of the current uncertainty in the measurements. It is also interesting that, in neutron-rich matter, there exists a certain low density at which isospin symmetry is restored, that is, the $u$-$d$ quark mass difference vanishes. We conclude that the effect of the isoscalar scalar and the isovector scalar fields should be considered in baryon semileptonic decays in nuclei.

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