格子QCD揭示强子CP违反的关键介子耦合

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本文主要探讨了在量子色动力学（QCD）的格子计算方法（Lattice QCD）背景下，对于强子性CP违规（hadronic CP violation）的理论分析。核电偶极矩（Electric Dipole Moment, EDM）实验中的测量结果常常受到非perturbative矩阵元素带来的理论不确定性的困扰。在标准模型之外的物理模型中，如某些新物理现象，如超对称、额外维度或大电弱耦合，通常假设核和反磁性原子的 EDM主要源于夸克层面上的色电偶极矩（color electric dipole moment,CEDM），这通过π-核子相互作用机制驱动。格子QCD是一种数值模拟方法，它在量子场论中被用来处理在有限空间网格上定义的QCD系统，从而克服了传统解析方法在高能量尺度下的困难。在处理这类强相互作用问题时，它能够提供关于基本粒子性质和相互作用的有效计算。文章的作者们，来自荷兰阿姆斯特丹Nikhef理论组的Jordy de Vries、Emanuele Mereghetti，以及美国洛杉矶洛斯阿拉莫斯国家实验室和上海交通大学的物理学家们，利用这一技术研究了CP违规在强子层面上的具体影响。他们提出，为了减少理论不确定性，有必要通过Lattice QCD的精确计算来估计介子-核子耦合强度，这些耦合是CP违反效应的关键。他们的工作可能涉及对π介子和核子之间的相互作用进行细致的计算，包括CEDM的影响，以便为实验结果提供更准确的理论指导。此外，文章还强调了该研究的时间线，从2016年12月接收初稿，到次年1月修订并接受，最终于1月发布在线，显示了科学交流的严谨性和及时性。这篇论文在理论上拓展了我们对强子CP违规的理解，特别是在面对实验测量中的理论挑战时，利用先进的Lattice QCD技术进行计算，为揭示核EDM背后的CP违变得到了关键性的贡献。这项研究不仅有助于缩小理论与实验之间的差距，而且也为探索新物理现象提供了强有力的工具。

Physics Letters B 766 (2017) 254–262

Contents lists available at ScienceDirect

Physics Letters B

www.elsevier.com/locate/physletb

Lattice QCD spectroscopy for hadronic CP violation

Jordy de Vries

, Emanuele Mereghetti

b,∗

, Chien-Yeah Seng

, André Walker-Loud

Nikhef, Theory Group, Science Park 105, 1098 XG, Amsterdam, The Netherlands

Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA

INPAC, Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, Shanghai, China

Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA

a r t i c l e i n f o a b s t r a c t

Article history:

Received

5 December 2016

Received

in revised form 11 January 2017

Accepted

11 January 2017

Available

online 16 January 2017

Editor:

W. Haxton

The interpretation of nuclear electric dipole moment (EDM) experiments is clouded by large theoretical

uncertainties associated with nonperturbative matrix elements. In various beyond-the-Standard Model

scenarios nuclear and diamagnetic atomic EDMs are expected to be dominated by CP-violating pion–

nucleon

interactions that arise from quark chromo-electric dipole moments. The corresponding CP-

violating

pion–nucleon coupling strengths are, however, poorly known.

this work we propose a strategy to calculate these couplings by using spectroscopic lattice QCD

techniques. Instead of directly calculating the pion–nucleon coupling constants, a challenging task, we

use chiral symmetry relations that link the pion–nucleon couplings to nucleon sigma terms and mass

splittings that are signiﬁcantly easier to calculate. In this work, we show that these relations are reliable

up to next-to-next-to-leading order in the chiral expansion in both SU(2) and SU(3) chiral perturbation

theory. We conclude with a brief discussion about practical details regarding the required lattice QCD

calculations and the phenomenological impact of an improved understanding of CP-violating matrix

elements.

(http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP

1. Introduction

The search for phenomena that can explain the apparent short-

comings

of the Standard Model (SM) takes place over a large range

of energy scales. The LHC explores the high-energy frontier, so

far without ﬁnding any deviations from SM predictions, whereas

low-energy experiments aim to uncover new physics by comparing

high-precision measurements to high-precision theoretical predic-

tions.

Several classes of low-energy experiments have the potential

to probe energy scales comparable to, or even above, the TeV scale

probed by the LHC. Examples of such experiments are proton-

decay

searches, the muon g −2, neutron–antineutron oscillations,

rare decays, and searches for permanent electric dipole moment

(EDMs).

The

search for EDMs is a particularly active ﬁeld of research.

Very strong bounds on the EDMs of different systems, from the

neutron [1], to diamagnetic atoms such as

199

Hg [2], to polar

molecules such as ThO [3], exist, and are projected to improve

by one to two orders of magnitude in the near future. Experi-

Corresponding author.

E-mail

address: emereghetti@lanl.gov (E. Mereghetti).

ments with other heavy diamagnetic systems, such as

225

Ra [4]

and

129

Xe [5] have already set constraints and strong improve-

ments

are expected. Furthermore, exciting progress has been made

on the proposal to investigate the EDMs of light nuclei in storage

rings [6,7]. While a single measurement in any of these systems

would only indicate a so far unmeasured source of CP violation,

measurements of different, complementary systems could point to-

wards

the microscopic source [8–10].

The

interpretation of various EDM experiments relies on the

knowledge of nonperturbative matrix elements that link operators

at the fundamental quark–gluon level to hadronic quantities. An

outstanding challenge is the calculation of the nucleon EDMs in

terms of CP-violating (CPV) sources in the SM (the QCD

term)

and beyond. The latter can be categorized in an effective ﬁeld the-

ory

(EFT) picture, assuming the new physics is heavy, where the

most relevant higher-dimensional operators are the quark elec-

tric

dipole moments (qEDMs), chromo-electric dipole moments

(qCEDMs), the Weinberg three-gluon operator, and several four-

quark

operators. The last year has seen great progress in lattice

QCD (LQCD) calculations of the nucleon EDMs in terms of the

term [11–13] and qEDMs [14,15], while lattice calculations for the

qCEDMs [16] and the Weinberg operator [17] have been initiated.

http://dx.doi.org/10.1016/j.physletb.2017.01.017

0370-2693/

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