Neutron electric dipole moment with external electric field method in lattice QCD
Neutron electric dipole moment with external electric field method in lattice QCD
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DOI：
10.1103/physrevd.75.034507
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发表时间：
2006-11
影响因子：
5
通讯作者：
E. Shintani;S. Aoki;N. Ishizuka;K. Kanaya;Y. Kikukawa;Y. Kuramashi;M. Okawa;A. Ukawa;T. Yoshi'e-T.-Yoshi
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文献类型：
--
作者：
E. Shintani;S. Aoki;N. Ishizuka;K. Kanaya;Y. Kikukawa;Y. Kuramashi;M. Okawa;A. Ukawa;T. Yoshi'e-T.-Yoshi
我们讨论了在晶格QCD模拟中存在$CP$ -违反$\ensuremath{\theta}$项时计算中子电偶极矩（NEDM）的可能性。本文测量了均匀静态外电场下中子自旋向上和自旋向下状态的能量差。我们首先在一个相对重的夸克质量$({m}_{PS}/{m}_{V}\ensuremath{\simeq}0.85)$处，使用两种不同的晶格费米子公式，即域壁费米子和夸克的三叶草费米子，在${a}^{\ensuremath{-}1}\ensuremath{\simeq}2\text{ }\text{ }\mathrm{GeV}$处的${16}^{3}\ifmmode\times\else\texttimes\fi{}32$晶格上，用重整化群改进的规范作用在淬灭的QCD中测试了这种方法。我们从两个费米子公式的计算中得到了NEDM的非零值。接下来，我们考虑我们的NEDM方法的一些系统不确定性，使用${24}^{3}\ifmmode\times\else\texttimes\fi{}32$晶格与三叶草费米子在相同的晶格间距。我们最后研究了NEDM的夸克质量依赖性，并观察到NEDM在接近手性极限时的不消失行为。我们将这种行为解释为在淬火近似中病理的表现。
We discuss a possibility that the neutron electric dipole moment (NEDM) can be calculated in lattice QCD simulations in the presence of the $CP$-violating $\ensuremath{\theta}$ term. In this paper we measure the energy difference between spin-up and spin-down states of the neutron in the presence of a uniform and static external electric field. We first test this method in quenched QCD with the renormalization group improved gauge action on a ${16}^{3}\ifmmode\times\else\texttimes\fi{}32$ lattice at ${a}^{\ensuremath{-}1}\ensuremath{\simeq}2\text{ }\text{ }\mathrm{GeV}$, employing two different lattice fermion formulations, the domain-wall fermion and the clover fermion for quarks, at relatively heavy quark mass $({m}_{PS}/{m}_{V}\ensuremath{\simeq}0.85)$. We obtain nonzero values of the NEDM from calculations with both fermion formulations. We next consider some systematic uncertainties of our method for the NEDM, using ${24}^{3}\ifmmode\times\else\texttimes\fi{}32$ lattice at the same lattice spacing only with the clover fermion. We finally investigate the quark mass dependence of the NEDM and observe a nonvanishing behavior of the NEDM toward the chiral limit. We interpret this behavior as a manifestation of the pathology in the quenched approximation.