Flavor symmetry breaking in quark magnetic moments

Zeitschrift für Physik C Particles and Fields - We discuss the magnetic moments of the baryons allowing for flavor symmetry breaking in the quark magnetic moments. We show that there is a...     

Flavor symmetry breaking and strangeness in the nucleon

We suggest that breaking of SU(3) flavor symmetry mainly resides in the baryon wave functions while the charge operators have no (or only small) explicit symmetry-breaking components. We utilize the collective coordinate approach to chiral soliton models to support this picture. In particular we compute the g _A /g _V ratios for hyperon beta-decay and the strangeness contribution to the nucleon axial current matrix elements and analyze their variation with increasing flavor symmetry breaking.Received: 30 September 2002, Published online: 22 October 2003PACS: 12.39.Dc Skyrmions - 12.39.Fe Chiral Lagrangians - 13.30.Ce Leptonic, semileptonic, and radiative decays - 14.20.Jn HyperonsH. Weigel: Heisenberg-Fellow;     

Flavor symmetry breaking and scaling for improved staggered actions in quenched QCD

We present a study of the flavor symmetry breaking in the pion spectrum for the p4-improved fermion action. Three different variants of the p4 action – p4fat3, p4fat7, and p4fat7tad – are compared to the Asqtad and naive staggered actions. To study the pattern of symmetry breaking, we measure all 15 pion masses in the four-flavor staggered theory. The measurements are done on a quenched gauge background, generated using a one-loop improved Symanzik action with β=10/g²=7.40, 7.75, and 8.00, corresponding to lattice spacings of approximately a= 0.31 fm, 0.21 fm, and 0.14 fm. PACS 11.15.Ha; 11.30.Rd; 12.38.Aw; 12.38.-t; 12.38.Gc     

Solvent-induced symmetry breaking

Symmetry breaking can be induced in a number of ways including interactions with a solvent. An example is the triiodide ion which is centrosymmetric in the gas phase. Molecular dynamics simulations of the triiodide ion in solution have been used to investigate the extent of symmetry breaking in a variety of solvents. We find that the triiodide ion loses its symmetry in water, ethanol, and methanol which form hydrogen bonds with the ion. This results in a localization of charge at one end of the ion and breaking of the geometric symmetry. The extent of symmetry breaking increases as the temperature is lowered. Correlation times for interconversion are reported and the energetics of symmetry breaking are presented. Analogies are made with second-order phase transitions.     

电荷对称破缺

1930年 ,物理学家海森伯曾认为 ,中子与质子实质上是在质量上具有微小差别的同一种粒子 ,他将两者统称为“核子” .近代的核物理学家赞同这样的观点 ,即在大量的核反应中 ,如果用中子来代替质子时 ,核反应过程将以相同方式继续进行下去 ,反之亦然 .但这种相似性在某些情况下会发生破坏 ,因为它将导致电荷对称破缺 ,简称为CSB .2 0 0 3年 4月 ,在美国费城召开的美国物理学会的会议上 ,有两个实验室分别独立地宣布 ,他们完成了对电荷对称破缺的实验观测 .一个是美国印第安那大学回旋加速器实验室 (IUCF) .IUCF的E .Stephenson教授宣…     

Spontaneous symmetry breaking in QCD

We study dynamical chiral symmetry breaking in massless QCD by the use of the generalized Hartree-Fock method. As the order parameter of chiral symmetry we choose the dynamical quark mass in the zero momentum limit which we call low energy quark mass. We calculate the low energy mass to the second order of diagrammatic expansion around shifted perturbative vacuum. We then show that the mass is finite and renormalization group invariant. After the improvement of the result by the method of effective charges we estimate the mass in the true vacuum under the gap and stationarity conditions and demonstrate that both of them produce non-zero mass proportional to a conventional scale, which breaks down the chiral symmetry.     

Chiral symmetry breaking in SQCD

Using a spectral function sum rules approach, we derive some constraints among the Goldstone parameters, the lowest dimension vacuum condensates and the mass of the chiral matter superfield in supersymmetric QCD (SQCD). These relations are consistent with previous results on SQCD and complement them.     

Chiral symmetry breaking in QCD

By applying bifurcation theory to a truncated Dyson-Schwinger equation for the quark propagator in massless QCD, we show that dynamical symmetry breaking occurs at a certain critical value of the coupling constant. Essential ingredients are (a) an effective dynamical mass for the gluon, and (b) a running coupling constant.     

Dynamical electroweak symmetry breaking

In theories of dynamical electroweak symmetry breaking, the electroweak interactions are broken to electromagnetism by the vacuum expectation value of a fermion bilinear. These theories may thereby avoid the introduction of fundamental scalar particles, of which we have no examples in nature. In this note, we review the status of experimental searches for the particles predicted in technicolor, topcolor, and related models.     

Flavour symmetry breaking in antiquark distributions

We show that knowledge of the valence quark distribution of a proton at one value of q², enables one to calculate a contribution to the difference between the distribution of anti-up quarks $\text{(}\text{u}{}_{\mathrm{<mtext>p</mtext>}}\text{)}$ and anti-down quarks $\text{(}\text{d}{}_{\mathrm{<mtext>p</mtext>}}\text{)}$ in the sea of the proton at higher values of q². This difference can be expressed as a linear combination of the structure functions F₁, for νp → νX and e^?p → e^?p (for which one knows the q² behaviour of the moments) and for $\text{ν}\text{p}\text{→ μ}{}^{\mathrm{?}}\text{X}\text{and}\text{ν}\text{p}\text{→ μ}{}^{\mathrm{+}}\text{X}$ (for which one knows the q² behaviour of the odd moments). The calculable contribution involves a non-trivial continuation of the even (odd) moments of the neutral (charged) current structure functions to odd (even) moments. We calculate this contribution and although we find that its sign is negative we point out that this cannot be interpreted as a consequences of the Pauli exclusion principle. We discuss the constraints our results impose on antiquark distributions.     

Gauge symmetry breaking in matrix models

We argue that some features of the standard model, in particular the fermion assignment and symmetry breaking, can be obtained in matrix model which describes noncommutative gauge theory as well as gravity in an emergent way. The mechanism is based on the presence of some extra (matrix) dimensions. These extra dimensions are different from the usual ones which give to a noncommutative geometry of the Grönewold-Moyal type, and are reminiscent of the Connes-Lott model, although the action is very different.     

Radiative symmetry breaking in supersymmetric models

We propose a scheme where the three relevant physics scales related to the supersymmetry, electroweak, and baryon minus lepton (B−L) breakings are linked together and occur at the TeV scale. The phenomenological implications in the Higgs and leptonic sectors are discussed.     

Chiral symmetry breaking in dense matter

The quark condensate in nuclear matter is studied. We relate it to the nuclear sigma commutator, and then treat it as sigma commutator for quasi- particles in a self-consistent way. We find that the deviation from the linear expression is large at high density. Received: 20 November 1997 / Revised version: 24 February 1998 / Published online: 16 September 1998