Dai, Slough, and Coleman reply

Dai, Zhenzi; Slough, C. G.; Coleman, R. V.

doi:10.1103/physrevlett.67.1472

Cited by 32 publications

(35 citation statements)

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“…We may make a connection with the nonleptonic interactions between octet baryons and the pseudo-Goldstone bosons. It was realized in [26,27] that a non-zero strange axial matrix element in the nucleon may impact nuclear parity violation. Non-strange operators are suppressed by custodial symmetries of the standard model of electroweak interactions in the limit sin 2 θ w → 0, while strange operators are not.…”

mentioning

confidence: 99%

SU(3) breaking in neutral current axial matrix elements and the spin content of the nucleon

Savage

Walden

1997

Phys. Rev. D

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We examine the effects of SU͑3͒ breaking in the matrix elements of the flavor-diagonal axial-vector currents between octet baryon states. Our calculations of K, , and loops indicate that the SU͑3͒ breaking may be substantial for some matrix elements and at the very least indicate large uncertainties. In particular, the strange axial matrix element in the proton determined from the measurements of g 1 (x) is found to have large uncertainties and might yet be zero. We estimate the strange axial matrix element in the proton to be Ϫ0.35Շ⌬sՇ0 and the matrix element of the flavor-singlet current in the proton to be Ϫ0.1Շ⌺Շϩ0.3 from the E143 measurement of ͐dxg 1 (x)ϭ0.127Ϯ0.004Ϯ0.010. The up-quark content of the ⌶ Ϫ is discussed and its implications for nonleptonic weak processes discussed. We also estimate the matrix element of the axialvector current coupling to the Z 0 between all octet baryon states. This may be important for neutrino interactions in dense nuclear environments, where hyperons may play an important role. ͓S0556-2821͑97͒00709-1͔ PACS number͑s͒: 12.15. Ji, 12.39.Fe, 14.20.Dh One of the more exciting realizations in hadronic physics of the last few years is that the strange quark may play an important role in the structure of the nucleon ͓1͔. While this may seem somewhat unnatural in the context of the most naive quark model, it is perfectly natural from the standpoint of QCD. Matrix elements of the strange vector current must vanish at zero-momentum transfer between states with zero net strangeness; however, matrix elements of the axial-vector current need not. Recent measurements suggest that the matrix element of the strange axial-vector current in the proton is ⌬sϭϪ0.12Ϯ0.04 ͓2͔. In addition, one would like to know what fraction of the nucleon spin is carried by the quarks themselves, which is equivalent to determining the matrix element of flavor-singlet axial-vector current in the proton ⌺. This is, of course, intimately related to the matrix element of the strange axial-vector current and present analysis suggests that ⌺ϭ0.2Ϯ0.1 ͓2͔, much smaller than the quark model estimate of ⌺ϳ0.58. There have been intense theoretical and experimental efforts to extract ⌬s and ⌺ to address the present ''spin crisis'' and such efforts continue ͑for recent reviews, see ͓3,4͔͒.A vital ingredient in the present determination of ⌺ and ⌬s is the matrix element of the j 5 ,8 ϭū␥ ␥ 5 uϩd␥ ␥ 5 d Ϫ2s␥ ␥ 5 s axial-vector current in the nucleon, which cannot be measured directly but must be inferred from the approximate SU͑3͒ symmetry observed in nature. The question of SU͑3͒ breaking in the matrix element of the j 5 ,8 current and its impact upon the extraction of ⌬s and ⌺ has been previously addressed ͓5-10͔. In ͓5,6͔ it was assumed that the breaking in the matrix elements of the axial-vector currents was proportional to the breaking in the octet baryon masses and in ͓7͔ a model of the SU͑3͒ breaking was employed. Studies in the Skyrme model ͓9͔ suggest that ⌺ is relatively insensitive to SU͑3͒ breaking while ⌬s sh...

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confidence: 99%

SU(3) breaking in neutral current axial matrix elements and the spin content of the nucleon

Savage

Walden

1997

Phys. Rev. D

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“…The tunneling parameters used for Ta2NiSe7 are very similar to those used [3][4][5][6] for the semimetal NbSea and electronic structural changes appear to dominate the STM scans of both materials below the CDW transitions. However, in contrast to NbSes, the CDW amplitude modulation along the chain is extremely weak in Ta2NiSe7 and the STM image is dominated by a very strong charge transfer between the two chains in the unit cell.…”

mentioning

confidence: 99%

“…The impurities and defects appear to affect [1] both the amplitude and phase of the CDW in Ta2NiSe7 while in NbSea only the phase is affected until very large impurity concentrations are reached [4]. quasi-one-dimensional systems.…”

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confidence: 99%

Charge-density-wave formation inTa2NiSe7studied by scanning tun

et al. 1992

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the various linear chain materials when they are in the CDW phase.The crystals of TaaNiSey grow as needles up to 20 mm in length and have monoclinic symmetry with lattice parameters of ao = 13.827 A, bo = 3AS2 A, co = 18.577 A, and j8 = 108.8°. The crystal structure has been analyzed in detail by Sunshine and Ibers [7]. The chains are oriented along the b axis and there are four formula units Scanning tunneling microscope images of Ta2NiSe7 taken at 77 and 4.2 K show a complex electronic rearrangement occurring below the charge-density-wave (CDW) onset temperature of 52.5 K. A large energy gap of 41.0 ±3.0 meV is observed and a CDW amplitude modulation of wavelength ~2^o is detected. The electronic transfer between chains appears to drive the CDW formation.PACS numbers: 61.16. Di, 71.45.Lr, 73.20.Dx, 73.40.Gk A scanning tunneling microscope (STM) study of the compound Ta2NiSe7 shows that electronic modifications characteristic of a charge-density wave (CDW) are observed at 4.2 K. The electronic spectrum measured at 4.2 K shows a large energy gap of ACDW =41.0 ± 3.0 meV and the local density of states (LDOS) shows a modulation with a wavelength of --2bo, consistent with the wave vector of q = (0,0.483,0) measured by Fleming et al.[1] using x-ray and electron diffraction. The STM scans at 4.2 K also show a significant rearrangement of electron density on the chains compared to the uniform density observed at 77 K.The CDW transition occurs at 52.5 K and the resulting electronic rearrangement produces STM scans which show a very complex LDOS within the unit cell characterized by one chain with very strong intensity, and one much weaker chain. However, the CDW modulation along the chains as detected by the STM at 4.2 K is very weak, in contrast to the strong electronic rearrangement between chains. This suggests that the CDW may in fact be driven by the initial electron transfer between chains rather than a simple nesting of the high-temperature Fermi surface, a significantly different sequence than observed in other linear chain CDW materials such as NbSe3.Ta2NiSe7 is a linear chain compound similar in some respects to FeNbaSeio, although the latter is driven into a metal-insulator transition [2] by the formation of a CDW while TaiNiSev remains a semimetal below the CDW transition. The tunneling parameters used for Ta2NiSe7 are very similar to those used [3-6] for the semimetal NbSea and electronic structural changes appear to dominate the STM scans of both materials below the CDW transitions. However, in contrast to NbSes, the CDW amplitude modulation along the chain is extremely weak in Ta2NiSe7 and the STM image is dominated by a very strong charge transfer between the two chains in the unit cell. This gives rise to a strong difference in STM response for the two chains in the unit cell, even though the chains are equivalent with respect to height and atomic structure. Above the CDW transition at 52.5 K they appear equivalent in both STM and AFM images (see Fig. 2 for STM image). In this respect the STM results on...

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“…[4,5]. To study the resonances in a given scattering process, one needs dispersion relations to continue the amplitude from the real s-axis (the physical region) to the complex-s plane [6][7][8][9], where the pole locations and their couplings are extracted. Following this method, some work on the light scalars can be found in [10][11][12][13][14][15], where the accurate pole locations and residues of the σ and κ mesons are given.…”

Section: Introductionmentioning

confidence: 99%

“…In Refs. [7,8] the l.h.c is estimated by crossed-channel exchange of resonances, where chiral effective field theory (χEFT) is used to calculate the amplitude. And the contribution of r.h.c.…”

Section: Introductionmentioning

confidence: 99%

A Study on the Correlation Between Poles and Cuts in ππ Scattering*

Dai¹,

Kang²,

Luo³

et al. 2019

Commun. Theor. Phys.

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In this paper we propose a dispersive method to describe two-body scattering with unitarity imposed. This approach is applied to elastic ππ scattering. The amplitudes keep single-channel unitarity and describe the experimental data well, and the low-energy amplitudes are consistent with that of chiral perturbation theory. The pole locations of the σ, f0(980), ρ(770) and f2 (1270) and their couplings to ππ are obtained. A virtual state appearing in the isospin-two S-wave is confirmed. The correlations between the left (and right) hand cut and the poles are discussed. Our results show that the poles are more sensitive to the right hand cut rather than the left hand cut. The proposed method could be used to study other two-body scattering processes.

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Dai, Slough, and Coleman reply

Cited by 32 publications

References 3 publications

SU(3) breaking in neutral current axial matrix elements and the spin content of the nucleon

SU(3) breaking in neutral current axial matrix elements and the spin content of the nucleon

Charge-density-wave formation inTa2NiSe7studied by scanning tun

A Study on the Correlation Between Poles and Cuts in ππ Scattering*

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