| 1. |
- Akhmedov, Evgeny, et al.
(författare)
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T violation in neutrino oscillations in matter
- 2001
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Ingår i: Nuclear Physics B. - : Elsevier Science B.V.. - 0550-3213 .- 1873-1562. ; 608:02-jan, s. 394-422
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Tidskriftsartikel (refereegranskat)abstract
- We consider the interplay of fundamental and matter-induced T violation effects in neutrino oscillations in matter. After discussing the general features of these effects we derive a simple approximate analytic expression for the T-violating probability asymmetry DeltaP(ab)(T) for three-flavour neutrino oscillations in a matter with an arbitrary density profile in terms of the two-flavour neutrino amplitudes. Explicit examples are given for the cases of a two-layer medium and for the adiabatic Emit in the general case. We then discuss implications of the obtained results for long baseline experiments. We show, in particular, that asymmetric matter effects cannot hinder the determination of the fundamental CP- and T-violating phase delta (CP) in the long baseline experiments as far as the error in this determination is larger than 1% at 99% CL. Since there are no T-violating effects in the two-flavour case, and in the limits of vanishing theta (13) or Deltam(21)(2) the three-flavour neutrino oscillations effectively reduce to the two-flavour ones, studying the T-violating asymmetries ApT ab can in principle provide us with a complementary means of measuring theta (13) and Deltam(21)(2).
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| 2. |
- Ambjørn, J., et al.
(författare)
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Stochastic confinement and dimensional reduction. (I). Four-dimensional SU(2) lattice gauge theory
- 1984
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Ingår i: Nuclear Physics, Section B. - : Elsevier BV. - 0550-3213. ; 240:2, s. 189-212
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Tidskriftsartikel (refereegranskat)abstract
- By Monte Carlo calculations on a 124 lattice we investigate four-dimensional SU(2) lattice gauge theory with respect to the conjecture that at large distances this theory reduces approximately to two-dimensional SU(2) lattice gauge theory. We find good numerical evidence for this conjecture. As a by-product we also measure the SU(2) string tension and find reasonable agreement with scaling. The "adjoint string tension" is also found to have a reasonable scaling behaviour.
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| 3. |
- Ambjørn, J., et al.
(författare)
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Stochastic confinement and dimensional reduction (II). Three-dimensional SU(2) lattice gauge theory
- 1984
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Ingår i: Nuclear Physics, Section B. - : Elsevier BV. - 0550-3213. ; 240:4, s. 533-542
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Tidskriftsartikel (refereegranskat)abstract
- We study 3-dimensional SU(2) lattice gauge theory with respect to dimensional reduction. By Monte Carlo calculations we find that this reduction is valid to a good approximation (within ≈10%). The adjoint string tension is found to scale approximately. We also compare the adjoint string tension with a string theory.
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| 4. |
- Ambjørn, J., et al.
(författare)
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The complex langevin equation and Monte Carlo simulations of actions with static charges
- 1986
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Ingår i: Nuclear Physics, Section B. - 0550-3213. ; 275:3, s. 375-397
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Tidskriftsartikel (refereegranskat)abstract
- We explore the possibilities of using the complex Langevin equation to Monte Carlo generate configurations of gauge theories with static charges present in the action. Successful results are obtained for systems that possess nontrivial saddle-point (classical) solutions. For that reason the algorithm works impressively for two-dimensional U(1) in the entire β-range whereas for three- and four-dimensional U(1) the applicability is limited to the weak coupling regime (large β). The method fails completely for SU(2) and SU(3).
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| 5. |
- Ambjørn, J., et al.
(författare)
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Three-dimensional lattice gauge theory and strings
- 1984
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Ingår i: Nuclear Physics, Section B. - : Elsevier BV. - 0550-3213. ; 244:1, s. 262-276
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Tidskriftsartikel (refereegranskat)abstract
- We consider SU(2) lattice gauge theory in three dimensions. The Wilson loops are found to be well described by a simple string model in the approximate scaling region.
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| 6. |
- Amoros, G., et al.
(författare)
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QCD isospin breaking in meson masses, decay constants and quark mass ratios
- 2001
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Ingår i: Nuclear Physics B. - 0550-3213. ; 602:1-2, s. 87-108
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Tidskriftsartikel (refereegranskat)abstract
- The procedure to calculate masses and matrix-elements in the presence of mixing of the basis states is explained in detail. We then apply this procedure to the two-loop calculation in Chiral Perturbation Theory of pseudoscalar masses and decay constants including quark mass isospin breaking. These results are used to update our analysis of Kℓ4 done previously and obtain a value of mu/md in addition to values for the low-energy-constants Li r.
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| 7. |
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| 8. |
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| 9. |
- Andersson, B., et al.
(författare)
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A statistical model for quark fragmentation into mesons with emphasis on vector meson contributions
- 1978
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Ingår i: Nuclear Physics, Section B. - : Elsevier BV. - 0550-3213. ; 135:2, s. 273-284
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Tidskriftsartikel (refereegranskat)abstract
- This paper is the first part of a program to deal with the relative importance of the different effects in a colour dipole field when the field energy is transformed into hadrons according to a statistical scheme with the sole constraints coming from energy and momentum conservation and the requirements of scaling. In this paper we treat the meson distributions from quark fragmentation with particular emphasis on the importance of a vector meson production of the size observed at present. We neglect diquark formation and the baryon distributions as a first approximation. The simplicity of the approach will make it possible to easily understand the size and the shape of the different contributions.
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| 10. |
- Andersson, Bo, et al.
(författare)
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Bose-Einstein correlations in the Lund model
- 1998
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Ingår i: Nuclear Physics B. - 0550-3213. ; 513:3, s. 627-644
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Tidskriftsartikel (refereegranskat)abstract
- By providing the Lund Model fragmentation process with a quantum-mechanical framework we extend the results of previous work to situations where there are very many identical bosons. We investigate the features of the weight distributions in some detail and in particular exhibit three-particle BE-correlations, the influence on the rho-spectrum and the difference between charged and neutral pion correlations.
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| 11. |
- Andersson, Bo, et al.
(författare)
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Gluon Splitting in the Color Dipole Cascades
- 1990
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Ingår i: Nuclear Physics B. - 0550-3213. ; 339:2, s. 393-405
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Tidskriftsartikel (refereegranskat)abstract
- We present a method to implement the gluon splitting process, g → QQ, into the dipole approximation to QCD cascades. It is known that due to the uncertainties in the interpolation between the pole regions, there are large uncertainties in the results. We show that there are further uncertainties due to the ordering in phase space of the gluon emission and gluon splitting processes. We present two options called the IO scheme (for independent dipoles) and another, the DO scheme (corresponding to an ordering in transverse momentum of the emissions) both of which lead to enhanced (hard) QQ-pair production, as compared to conventional cascades. We compare to present experimental data and give predictions for LEP energies.
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| 12. |
- Andersson, Bo, et al.
(författare)
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The lambda-measure and the generalised dipoles in the Lund model
- 2002
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Ingår i: Nuclear Physics, Section B. - 0550-3213. ; 646:1-2, s. 102-126
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate that the multiple gluon emission phase space in the dipole cascade model has a strong linear correlation with the number of gluons emitted. The number of gluons per unit available phase space at a certain resolution scale is found to be remarkably independent of the cms energy and global event properties like thrust, and even changes in the ordering variable or resolution scale. We show that the distribution of sizes of gluon-gluon dipoles in a parton cascade has stability properties which are sufficient to account for those of the phase space variable. We observe that certain more abstract entities, defined in the context of hadronisation and related to the gluon emission phase space, share those properties of colour dipoles and name them generalised dipoles. We also present an analytical model to qualitatively describe our findings. (C) 2002 Elsevier Science B.V. All rights reserved.
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| 13. |
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| 14. |
- Bengtsson, Mats, et al.
(författare)
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QCD effects on the event structure in leptoproduction
- 1988
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Ingår i: Nuclear Physics, Section B. - : Elsevier BV. - 0550-3213. ; 301:4, s. 554-582
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Tidskriftsartikel (refereegranskat)abstract
- Perturbative QCD corrections to leptoproduction events can be introduced either in the form of matrix elements or of parton showers. Each of these approaches has its advantages and disadvantages, making a comparison of the two interesting. At present energies, both methods can be made to agree reasonably well with data, whereas differences appear at higher energies. The influence of these QCD effects on the expected event structure at ep colliders, HERA in particular, is investigated in detail. This includes multiplicity and momentum distributions, transverse momentum flow and correlations, as well as jet properties.
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| 15. |
- Bijnens, Johan, et al.
(författare)
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Comment on the pion pole part of the light-by-light contribution to the muon g-2
- 2002
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Ingår i: Nuclear Physics, Section B. - 0550-3213. ; 626:1-2, s. 410-411
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Tidskriftsartikel (refereegranskat)abstract
- We comment on the recent calculations of the pion pole part of the light-by-light contribution to the muon anomalous magnetic moment and we point out where the analysis in our previous work was mistaken.
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| 16. |
- Bijnens, Johan, et al.
(författare)
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K -> 3 pi decays in chiral perturbation theory
- 2003
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Ingår i: Nuclear Physics, Section B. - 0550-3213. ; 648:1-2, s. 317-344
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Tidskriftsartikel (refereegranskat)abstract
- The CP conserving amplitudes for the decays K --> 3pi are calculated in chiral perturbation theory at the next-to-leading order. We present the expressions in a compact form with single parameter functions only. These expressions are then fitted to all available K --> 2pi and K --> 3pi data to obtain a fit of the parameters that occur. We compare with the work of Kambor, Missimer and Wyler. (C) 2002 Elsevier Science B.V. All rights reserved.
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| 17. |
- Bijnens, Johan, et al.
(författare)
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K-l3 decays in chiral perturbation theory
- 2003
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Ingår i: Nuclear Physics, Section B. - 0550-3213. ; 669:1-2, s. 341-362
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Tidskriftsartikel (refereegranskat)abstract
- The process K-l3 is calculated to two-loop order (p(6)) in chiral perturbation theory (ChPT) in the isospin conserved case. We present expressions suitable for use with previous work in two-loop ChPT where the order p(4) parameters (L-i(r)) were determined from experiment. We point out that all the order p(6) parameters (C-i(r)) that appear in the value of f(+)(0) relevant for the determination of V-us can be determined from K-l3 measurements via the slope and the curvature of the scalar form-factor. As by product we update the value of the CKM matrix element V-us. (C) 2003 Elsevier B.V. All rights reserved.
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| 18. |
- Bijnens, Johan, et al.
(författare)
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Obtaining K → ππ from off-shell K → π amplitudes
- 1998
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Ingår i: Nuclear Physics B. - 0550-3213. ; 521:1-2, s. 305-333
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Tidskriftsartikel (refereegranskat)abstract
- We properly define off-shell K → π transition amplitudes and use them to extract information for on-shell K → ππ amplitudes within Chiral Perturbation Theory. At order p2 in the chiral expansion all three parameters of weak interaction can be determined. At order p4 we are able to fix eleven additional constants out of thirteen contributing to off-shell K → π transitions, which leaves four undetermined constants in the on-shell K → ππ amplitudes. All script O sign(p4) contributions have been exactly derived with m2 π ≠ 0. We finally discuss the weak mass term issue and find contributions to on-shell ΔS = ±1 kaon decays, in particular to transitions like KL → γγ, KL → μ+μ- and KS → π0γγ at the lowest non-zero order.
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| 19. |
- Bijnens, J., et al.
(författare)
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Pion-pion scattering at low energy
- 1997
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Ingår i: Nuclear Physics B. - 0550-3213. ; 508:1-2, s. 263-310
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Tidskriftsartikel (refereegranskat)abstract
- We present technical details of the evaluation of the elastic ππ scattering amplitude to two loops in chiral perturbation theory. In particular, we elaborate on the renormalization procedure at the two-loop order and on the evaluation of the relevant Feynman diagrams that can all be expressed in terms of elementary functions. For the sake of clarity, we discuss these matters both in the N-component φ4 theory (in its symmetric phase) and in chiral perturbation theory. Estimates for the relevant low-energy constants of O(p6) are presented. Threshold parameters and phase shifts are then calculated for two sets of O(p4) coupling constants and compared with experiment. We comment on the extraction of threshold parameters from phase shift data.
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| 20. |
- Bijnens, J., et al.
(författare)
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Vector meson masses in chiral perturbation theory
- 1997
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Ingår i: Nuclear Physics B. - 0550-3213. ; 501:2, s. 495-517
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Tidskriftsartikel (refereegranskat)abstract
- We discuss the vector meson masses within the context of chiral perturbation theory performing an expansion in terms of the momenta, quark masses and 1/Nc. We extend the previous analysis to include isospin breaking effects and also include up to order p4. We discuss vector meson chiral perturbation theory in some detail and present a derivation from a relativistic Lagrangian. The unknown coefficients are estimated in various ways. We also discuss the relevance of electromagnetic corrections and the implications of the present calculation for the determination of quark masses.
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| 21. |
- Coste, Antoine, et al.
(författare)
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Finite Size Effects and Twisted Boundary Conditions
- 1987
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Ingår i: Nuclear Physics B. - : Elsevier BV. - 0550-3213. ; 287, s. 569-588
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Tidskriftsartikel (refereegranskat)abstract
- We explore the possibility of reducing finite size effects in the weak coupling region of glueball correlations and Wilson loops. Our analysis indicates that twisted boundary conditions do diminish finite size effects and numerical evidence for this is given for the glueball correlation.
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| 22. |
- Fjelstad, Jens, 1971-, et al.
(författare)
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CFT description of three-dimensional Kerr-de Sitter space-time
- 2002
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Ingår i: Nuclear Physics B. - : Elsevier. - 0550-3213 .- 1873-1562. ; 641:1-2, s. 376-392
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Tidskriftsartikel (refereegranskat)abstract
- We describe three-dimensional Kerr-de Sitter space using similar methods as recently applied to the BTZ black hole. A rigorous form of the classical connection between gravity in three dimensions and two-dimensional conformal field theory is employed, where the fundamental degrees of freedom are described in terms of two dependent SL(2,C) currents. In contrast to the BTZ case, however, quantization does not give the Bekenstein-Hawking entropy connected to the cosmological horizon of Kerr-de Sitter space.
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| 23. |
- Fjelstad, Jens, 1971-, et al.
(författare)
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Sectors of solutions in three-dimensional gravity and black holes
- 2002
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Ingår i: Nuclear Physics B. - : Elsevier. - 0550-3213 .- 1873-1562. ; 628:1-2, s. 331-360
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Tidskriftsartikel (refereegranskat)abstract
- We examine the connection between three dimensional gravity with negative cosmological constant and two-dimensional CFT via the Chern-Simons formulation. A set of generalized spectral flow transformations are shown to yield new sectors of solutions. One implication is that the microscopic calculation of the entropy of the Banados-Teitelboim-Zanelli (BTZ) black hole is corrected by a multiplicative factor with the result that it saturates the Bekenstein-Hawking expression.
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| 24. |
- Flensburg, M., et al.
(författare)
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String model potentials and lattice gauge theories
- 1987
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Ingår i: Nuclear Physics, Section B. - : Elsevier BV. - 0550-3213. ; 283, s. 141-164
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Tidskriftsartikel (refereegranskat)abstract
- The static potentials from bosonic string models are examined to the two-loop level. Available MC data for 4-dimensional SU(3) are in approximate agreement with the universal leading order predictions but fail to reproduce the Nambu string when the two-loop terms are included in the analysis. We also confront Nambu string model predictions for Tc σ with SU(2), SU(3) and SU(N → ∞) MC data. In the SU(2) case, impressive agreement is found both in 3 and 4 dimensions. In contrast, the data for SU(3) and SU(N → ∞) differ from the string model prediction. These theories have identical values for Tc σ, indicating that N → ∞ is a good approximation to N = 3.
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| 25. |
- Friberg, Christer, et al.
(författare)
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Colour Connections in e+e- annihilation
- 1997
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Ingår i: Nuclear Physics, Section B. - 0550-3213. ; B490, s. 289-305
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Tidskriftsartikel (refereegranskat)abstract
- We have a very limited knowledge about how the confinement mechanism works in processes like $\epea\epe\ra\epq\epqa\ggn\ldots\ggn$, when there are identical colour charges. In this case the partons can be colour connected by a string or a cluster chain in several different ways. We do not know if in such a situation Nature chooses a particular configuration at random, or if some configuration is dynamically favoured. Also in the perturbative parton cascade we have no well founded recipe for describing the interference effects, which correspond to non planar diagrams and are caused by identical colour charges. We have studied two different models, and are in particular interested in the possibility that a colour singlet gluon system hadronizes isolated from the remainder of the state. Using double tagged events with heavy $\epc\epca$ or $\epb\epba$ quarks, it appears to be possible to find a significant signal, if such events appear in Nature. If this type of (re)connected states appear in Z decays it may also be an indication that reconnection might appear between the decay products of two W's in the reaction $\epea\epe\ra\gwp\gwm\ra\epq_1\epqa_2\epQ_1\epQa_2$ at LEP2. This would be important e.g. for a precision measurement of the W mass.
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