双线性R宇称破坏超对称中的有效拉氏量及中微子的质量产生

中微子在标准模型中是没有质量的,而在R宇称不守恒的最小超对称标准模型中却可以产生中微子质量。本文采用有效拉氏量方法,给出了希格斯场和费米场双重态,并根据在高能标的最初的双重态和它们的真空期待值定义了标准模型中的希格斯双重态。     

LHC上希格斯与味物理实验进展

希格斯场是标准模型中电弱对称性自发破缺的核心,通过与基本粒子的相互作用直接赋予质量,构建了粒子质量来源的机制.与希格斯相互作用的夸克质量本征态和参与弱相互作用的夸克味道本征态不重合使得不同代的夸克发生混合,即CKM机制,是目前唯一确定的CP破坏来源,但所提供的CP破坏远不足以解释宇宙正反物质不对称性.因此,在实验上对希格斯粒子和CKM矩阵进行精确测量以及寻找新的CP破坏来源是精确检验标准模型、寻找新物理的主要途径之一.正值希格斯粒子发现十周年,本文将介绍标准模型希格斯粒子以及味物理中CKM矩阵参数特别是相角测量在大型强子对撞机LHC实验上的最新进展,回顾北京大学高能物理研究团队在希格斯粒子及味物理实验方面的工作,献礼北京大学物理学科百十周年.     

五种希格斯玻色子与希格斯场之内部结构模型图表解析

现今，“希格斯玻色子”被认为是所有基本粒子质量的来源，也是标准模型预言的最后一种粒子，目前，物理学家普遍认为不排除未来可能会发现其他带电荷的希格斯玻色子。许多物理学家认为：事实上，希格斯玻色子组成希格斯场是一种更加复杂的理论模型，而这些理论模型预言了应有五种不同的希格斯玻色子，它们不仅带有电荷，还有可能带有色荷，而且质量也不相同。希格斯场遍布在宇宙中，该文就这五种不同希格斯玻色子及其组成的希格斯场，作一理论模型预言之图表解析。     

带电的希格斯玻色子与W玻色子在ILC上的联合产生

带有单个电荷和双电荷的希格斯玻色子(H±和H±±)是希格斯三重态模型中的特征粒子.主要研究在高能直线对撞机上带电的希格斯玻色子与W玻色子的联合产生过程:e+e-→W+H+H--.计算了该过程的产生截面、末态粒子的横动量和快度的分布,并分析了标准模型的背景.结果表明,产生截面在一定的参数空间内可以达到几个飞靶的量级.只要带电希格斯玻色子的质量不是很大,在未来的高能直线对撞机上实验中可以通过该过程探测到这些带电希格斯玻色子的信号.     

轻子混合和六层子模型中的弱流混合角问题

最近一些工作讨论了标准的六层子模型中的层子混合角问题,分析了混合角的实验值范围,在这些讨论中都没有考虑中性重轻子和中微子在弱作用中可能存在混合的问题。如果中性轻子只有中微子,并且中微子质量为零,那么由于中微子质量的简并,弱作用的本征态也就是轻子的本征态。但若存在中性重轻子,尽管这种粒子在轻子分类中属于什么地位还不清楚,一般地,轻子就可能以混合的方式参与弱作用。事实上,中微子产生中性重轻子的事例就暗示了可能存在中微子与中性重轻子的混合。如     

有质量的中微子与Weinberg—Salam—Glashow模型

我們发現,如果允許中微子有質量而在标准的弱电統一模型中引入中微子右手单态,在一代輕子的情况下,对中性弱流和带电弱流完全沒有影响,在多代輕子情况下,中性弱流仍然不变,但在带电弱流中将出現中微子左手态的类Cabibbo混合,这可以引起中微子振蕩。     

希格斯粒子与暴涨宇宙

希格斯(Higgs)粒子是迄今为止发现的第一个标量粒子.在粒子物理标准模型中,希格斯粒子起到了非常重要的作用.另一方面,在宇宙暴涨时期,使宇宙加速膨胀的往往是也一个标量场,或者标量粒子,被称为暴涨子.由于能标的不同,希格斯粒子不能直接作为暴涨子,但通过一些间接的手段,暴涨子却有可能是希格斯粒子在高能标时的另一种表现形式.本文作者回顾了希格斯暴涨模型,并且着重讨论了宇宙学常数在暴涨中所起到的作用.     

Reissner-Nordstr9 m几何中自旋场的统计熵

用brick-wall模型计算了Reissner-Nordstr9m几何中的引力场、电磁场和中微子场的统计熵.结果表明玻色场的主项熵是标量场主项熵的整数倍,其倍数等于自旋态引起的简并度,有理由推测费密场也应有类似的性质,其中中微子场的熵为最小.     

CP对称性破坏 中国科学家谈科学

贮存环中子衰变的中微子工厂为研究CP破坏效应提供了条件;超对称性模型在宇宙中产生物质的能力的假设提高了通过希格斯玻色子衰变的研究用来揭示CP对称性破坏的一种新的可能性。     

2018年粒子物理学热点回眸

 粒子物理是研究物质的基本组成和相互作用的前沿学科。从希格斯物理、新物理寻找、中微子物理、暗物质寻找、新强子态和强作用力机制研究、以及未来对撞机研究等方面回顾了2018年粒子物理学取得的重大进展及突破。     

最小超对称模型中希格斯势的真空稳定性

讨论了量子场论对希格斯有效势的单圈阶修正与重整化群方程的改进方法,并将这些理论应用于最小超对称模型(minimum supersymmetric model,MSSM).在MSSM框架下讨论了稳定的希格斯有效势对敏感参数tan β的限制,通过重整化群方程的双圈阶数值解,在不同能标下对希格斯势的真空稳定性进行了研究并作出了分析.结果表明,随能标增长希格斯势行为有所变化,但没有出现标准模型那样的不稳定势.     

超形变核态的相对论对称性研究

相对论对称性在原子核的壳层结构及其演化中扮演重要角色.探讨超形变核态的相对论对称性,利用相对论平均场理论计算超形变核态的结合能、单粒子能级,提取单粒子能级的自旋和赝自旋能量劈裂,分析这些能量劈裂与原子核形变及自旋和赝自旋双重态量子数间的关系,进而研究超形变核态的自旋和赝自旋对称性及其随形变变化的规律,结果表明超形变核态的自旋和赝自旋对称性与双重态量子数和形变都相关.     

Quadratic Yukawa coupling and matrix Yukawa coupling in the large N expansion

In this article, we study three types of new Yukawa couplings (the boson field is coupled to the fermion field). Two of them are quadratic Yukawa couplings (the boson field is in the form of a vector), and the other one is the matrix Yukawa coupling (the boson field is in the form of a matrix). Based on the above three couplings, we introduce the Higgs mechanism, and find out the properties of the generated mass for the fermions with multiple flavors. For the matrix boson, we introduce its coupling with non-Abelian gauge field. It turns out that the generated mass of the gauge field through the Higgs mechanism is unique. In the large N limit, using the method of auxiliary field, we study the dynamical behaviors of the quadratic Yukawa couplings, including the poles of some dressed propagators.     

Higgs机制的历史发展研究

Ｈｉｇｇｓ真空对称性自发破缺的思想在现代物理学中占有十分重要的地位，本文揭示了这一重要思想是如何从固体物理研究中移植到粒子物理学中的；并成为粒子物理学的重要观念的，最后指出：这一思想的发展改变了人们对对称性探索的传统方式；以及我们应从Ｈｉｇｇｓ机制发展中所获得的启示。     

非Abel规范场的Noether流

本文从规范场的拉氏函数出发,直接导出了规范场的定城守恒流,找到了外源流,自源流和规范条件与定域流守恒的关系。文中还讨论了Higgs场对Noether流结构的影响和Noether流的对偶荷问题。     

The 'Higgs' amplitude mode at the two-dimensional superfluid/Mott insulator transition

Spontaneous symmetry breaking plays a key role in our understanding of nature. In relativistic quantum field theory, a broken continuous symmetry leads to the emergence of two types of fundamental excitation: massless Nambu-Goldstone modes and a massive 'Higgs' amplitude mode. An excitation of Higgs type is of crucial importance in the standard model of elementary particle physics, and also appears as a fundamental collective mode in quantum many-body systems. Whether such a mode exists in low-dimensional systems as a resonance-like feature, or whether it becomes overdamped through coupling to Nambu-Goldstone modes, has been a subject of debate. Here we experimentally find and study a Higgs mode in a two-dimensional neutral superfluid close to a quantum phase transition to a Mott insulating phase. We unambiguously identify the mode by observing the expected reduction in frequency of the onset of spectral response when approaching the transition point. In this regime, our system is described by an effective relativistic field theory with a two-component quantum field, which constitutes a minimal model for spontaneous breaking of a continuous symmetry. Additionally, all microscopic parameters of our system are known from first principles and the resolution of our measurement allows us to detect excited states of the many-body system at the level of individual quasiparticles. This allows for an in-depth study of Higgs excitations that also addresses the consequences of the reduced dimensionality and confinement of the system. Our work constitutes a step towards exploring emergent relativistic models with ultracold atomic gases.     

Molecular architecture of axonemal microtubule doublets revealed by cryo-electron tomography

The axoneme, which forms the core of eukaryotic flagella and cilia, is one of the largest macromolecular machines, with a structure that is largely conserved from protists to mammals. Microtubule doublets are structural components of axonemes that contain a number of proteins besides tubulin, and are usually found in arrays of nine doublets arranged around two singlet microtubules. Coordinated sliding of adjacent doublets, which involves a host of other proteins in the axoneme, produces periodic beating movements of the axoneme. We have obtained a three-dimensional density map of intact microtubule doublets using cryo-electron tomography and image averaging. Our map, with a resolution of about 3 nm, provides insights into locations of particular proteins within the doublets and the structural features of the doublets that define their mechanical properties. We identify likely candidates for several of these non-tubulin components of the doublets. This work offers insight on how tubulin protofilaments and accessory proteins attach together to form the doublets and provides a structural basis for understanding doublet function in axonemes.     

探索质量起源与2013年诺贝尔物理学奖

 本文首先介绍1964年Peter Higgs及Francois Englert等提出的Higgs机制及其在电弱标准模型的建立中所起的重要作用,说明为什么2012年实验上发现一个Higgs玻色子后,2013年的诺贝尔奖就颁给Englert和Higgs。然后指出,接下来重要的是在实验上进一步探测这个Higgs玻色子对标准模型预言的偏离,和探索可能的新物理。LHC的升级实验和将来的高能对撞机对实现这个目标至关重要。最后展望粒子物理的发展前景。     

On extra neutral and charged Higgs bosons at the LHC

The properties of 125 GeV new particle, which was discovered in 2012 at the Large Hadron Collider (LHC), are found to be consistent with those of the Higgs boson in the standard model (SM). Hereafter the new particle is dubbed as SM-like Higgs boson. However there is still spacious room for physics beyond the SM (BSM) due to the limited energy and luminosity of the LHC. With more data, experiments will scrutinize whether the new particle is indeed the SM one or not. At the same time, one believes that discovery of the SM-like Higgs boson is just the start of the new era of particle physics. The predominant topic is whether there are other new Higgs bosons as speculated in various BSM models. In this short review, we will describe the current status of Higgs physics at the LHC and several BSM models which contain more Higgs sectors. In literatures, there are numerous studies on extended Higgs sector and a comprehensive review is beyond the scope of this review. Instead, we will present two latest studies on Higgs physics: (1) how to detect the charged Higgs boson and measure \(\tan \beta \) after including the top polarization information, and (2) how to discover the extra neutral Higgs boson via the pair production of SM-like Higgs boson.