Flavor symmetry breaking in DTU

The implications of the breaking of SU (N) flavor symmetry are studied at the planar and cylinder levels of the Dual Topological Unitarization scheme. It is shown that the ρ intercept is constrained to lie between 0.51 and 0.54, and that SU (4) symmetry is necessarily more strongly broken that SU (3). The matrix structure of the cylinder bootstrap equations is shown to suppress many of the problems of the “cylinder extinction of the planar poles”, and to lead to a sensible singularity spectrum.     

Dynamical symmetry breaking in the sea of the nucleon

We derive the nonanalytic chiral behavior of the flavor asymmetry d - u. Such behavior is a unique characteristic of Goldstone boson loops in chiral theories, including QCD, and establishes the unambiguous role played by the Goldstone boson cloud in the sea of the proton. Generalizing the results to the SU(3) sector, we show that strange chiral loops require that the s - s distribution be nonzero.     

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 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     

On the instanton-induced portion of the nucleon strangeness

We calculate the instanton contribution to the proton strangeness in an MIT bag enriched by the presence of a dilute instanton liquid. The evaluation is based on the expression of the nucleon matrix elements of bilinear strange-quark operators in terms of a model valence nucleon state and the interactions producing quark–antiquark fluctuations on top of that valence state. Our method combines use of the the evolution operator containing a strangeness source and the Feynman–Hellmann theorem. It enables one to evaluate the strangeness in different Lorentz channels in essentially the same way. Only the scalar channel is found to be affected by the interaction induced by the random instanton liquid. Received: 12 February 1999 / Published online: 30 June 1999     

Meson cloud and nucleon strangeness: An update

We use a version of the meson cloud model, including kaon, κ and K^* contributions, to estimate the electric and magnetic strange form factors of the nucleon. We compare our results with the recent measurements of the strange-quark contribution to parity-violating asymmetries in electron-proton scattering experiments.     

Neutrino dimuon production and the strangeness asymmetry of the nucleon

We have performed the first global QCD analysis to include the CCFR and NuTeV dimuon data, which provide direct constraints on the strange and antistrange parton distributions, s(x) and . To explore the strangeness sector, we adopt a general parametrization of the non-perturbative functions satisfying basic QCD requirements. We find that the strangeness asymmetry, as represented by the momentum integral , is sensitive to the dimuon data provided the theoretical QCD constraints are enforced. We use the Lagrange multiplier method to probe the quality of the global fit as a function of [S ^-] and find -0.001 < [S ^-] < 0.004. Representative parton distribution sets spanning this range are given. Comparisons with previous work are made.Received: 15 January 2004, Revised: 23 November 2004, Published online: 15 February 2005PACS: 11.30.Hv, 12.15.-y, 13.15. + g, 12.38.-t, 13.60.Hb     

Non-standard physics and nucleon strangeness in low-energy PV electron scattering

Contributions from physics beyond the Standard Model, strange quarks in the nucleon, and nuclear structure effects to the left-right asymmetry measured in parity-violating (PV) electron scattering from¹²C and the proton are discussed. It is shown how lack of knowledge of the distribution of strange quarks in the nucleon, as well as theoretical uncertainties associated with higher-order dispersion amplitudes and nuclear isospin-mixing, enter the extraction of new limits on the electroweak parametersS andT from these PV observables. It is found that a series of elastic PV electron scattering measurements using⁴He could significantly constrain thes-quark electric form factor if other theoretical issues are resolved. Such constraints would reduce the associated form factor uncertainty in the carbon and proton asymmetries below a level needed to permit extraction of interesting low-energy constraints onS andT from these observables. For comparison, the much smaller scale ofs-quark contributions to the weak charge measured in atomic PV is quantified. It is likely that only in the case of heavy muonic atoms could nucleon strangeness enter the weak charge at an observable level.     

Precise determination of the strangeness magnetic moment of the nucleon

By combining the constraints of charge symmetry with new chiral extrapolation techniques and recent low mass quenched lattice-QCD simulations of the individual quark contributions to the magnetic moments of the nucleon octet, we obtain a precise determination of the strange magnetic moment of the proton. The result, namely, G(s)(M)=(-0.046 +/- 0.019)mu(N) is consistent with the latest experimental measurements but an order of magnitude more precise. This poses a tremendous challenge for future experiments.     

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…     

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.