Overlap fermion papers:


[23]  arXiv:1103.4588 [pdf, other]
Title: Tata lectures on overlap fermions
Authors: R. Narayanan
Comments: 34 pages, 8 figures, Lectures given at the Asian School on Lattice Field Theory 2011 (an ICTS program)
Subjects: High Energy Physics - Lattice (hep-lat)

[7]  arXiv:1102.1000 [ps, pdf, other]
Title: Numerical properties of staggered overlap fermions
Comments: 7 pages, Contribution presented at The XXVIII International Symposium on Lattice Field Theory, Lattice2010, June 14-19, 2010, Villasimius, Italy; v2: added acknowledgement
Subjects: High Energy Physics - Lattice (hep-lat)

[2]  arXiv:1012.0152 [ps, pdf, other]
Title: Direct Proof of Reflection Positivity of Free Overlap Dirac Fermion
Comments: 7 pages, presented at the XXVIII International Symposium on Lattice Field Theory, Lattice 2010, title slightly modified. v2 minor corrections
Subjects: High Energy Physics - Lattice (hep-lat)

[7]  arXiv:1001.1786 [ps, pdf, other]
Title: Exploring chiral dynamics with overlap fermions
Authors: Hidenori Fukaya, for the JLQCD, the TWQCD collaborations
Comments: 21 pages, 15 figures, plenary talk (and poster) at LATTICE 2009
Journal-ref: PoS LAT2009:004,2009
Subjects: High Energy Physics - Lattice (hep-lat)

[30]  arXiv:0903.5521 [ps, pdf, other]
Title: A renormalisation group derivation of the overlap formulation
Authors: Nigel Cundy
Comments: 28 pages
Subjects: High Energy Physics - Lattice (hep-lat)

[5]  arXiv:0811.1257 [ps, pdf, other]
Title: Physics results from dynamical overlap fermion simulations
Authors: Shoji Hashimoto
Comments: 15 pages, a plenary talk presented at the 26th International Symposium on Lattice Field Theory (Lattice 2008), Williamsburg, Virginia, USA, July 14-19, 2008
Subjects: High Energy Physics - Lattice (hep-lat)

[42]  arXiv:0810.1360 [ps, pdf, other]
Title: Light meson spectrum with $N_f=2+1$ dynamical overlap fermions
Comments: 7 pages, 7 figure files. Talk given at the XXVI International Symposium on Lattice Field Theory, July 14 - 19 2008, Williamsburg, Virginia, USA
Subjects: High Energy Physics - Lattice (hep-lat)

[3]  arXiv:0808.3049 [ps, pdf, other]
Title: Topological Summation of Observables Measured with Dynamical Overlap Fermions
Comments: 7 pages, 5 figures
Journal-ref: PoS(LAT2008)079
Subjects: High Energy Physics - Lattice (hep-lat)

[5]  arXiv:0808.2919 [ps, pdf, other]
Title: Universality check of the overlap fermions in the Schroedinger functional
Authors: Shinji Takeda
Comments: 7 pages, 3 figures, talk given at the XXVI International Symposium on Lattice Field Theory, July 14-19 Williamsburg, Virginia, USA
Subjects: High Energy Physics - Lattice (hep-lat)

[8]  arXiv:0806.4744 [ps, pdf, other]
Title: Nucleon sigma term and strange quark content from lattice QCD with exact chiral symmetry
Comments: 26 pages
Subjects: High Energy Physics - Lattice (hep-lat)

[1]  arXiv:0803.0294 [ps, pdf, other]
Title: Topological tunneling with Dynamical overlap fermions
Comments: 17 pages
License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
Subjects: High Energy Physics - Lattice (hep-lat)

[5]  arXiv:0802.2496 [ps, pdf, other]
Title: New overlap construction of Weyl fermions
License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
Subjects: High Energy Physics - Lattice (hep-lat)

[12]  arXiv:0710.4225 [ps, pdf, other]
Title: Exploring the chiral regime with dynamical overlap fermions
Comments: 15 pages, 14 figures, contribution to 25th International Symposium on Lattice Field Theory, Regensburg, Germany, 30 Jul - 4 Aug 2007
Journal-ref: PoS(LATTICE 2007)018
Subjects: High Energy Physics - Lattice (hep-lat)

[10]  arXiv:0710.0929 [ps, pdf, other]
Title: Light meson spectrum with $N_f=2$ dynamical overlap fermions
Comments: 7 pages, 9 figures, contribution to XXV International Symposium on Lattice Field Theory, July 2007, Regensburg
Journal-ref: PoS(LATTICE 2007)126
Subjects: High Energy Physics - Lattice (hep-lat)

[12]  arXiv:0709.0932 [ps, pdf, other]
Title: Localized eigenmodes of the overlap operator and their impact on the eigenvalue distribution
Comments: 16 pages, 6 figures
Subjects: High Energy Physics - Lattice (hep-lat)

[23]  arXiv:0704.3486 [ps, pdf, other] :
Title: An iterative method to compute the sign function of a non-Hermitian matrix and its application to the overlap Dirac operator at nonzero chemical potential
Authors: J. Bloch, A. Frommer, B. Lang, T. Wettig
Comments: 11 pages, 4 figures
 

[16]  arXiv:0704.2433 [ps, pdf, other] :
Title: A simple derivation of the Overlap Dirac Operator
Authors: C. D. Fosco, G. Torroba, H. Neuberger
Comments: 9 pages, LaTeX
 

hep-lat/0702003 [abs, ps, pdf, other] :
Title: Two-flavor lattice QCD simulation in the epsilon-regime with exact chiral symmetry
Authors: JLQCD collaboration: H. Fukaya, S. Aoki, T.W. Chiu, S. Hashimoto, T. Kaneko, H. Matsufuru, J. Noaki, K. Ogawa, M. Okamoto, T. Onogi, N. Yamada
Comments: 10pages, 4figures
 

hep-lat/0610036 [abs, ps, pdf, other] :
Title: JLQCD's dynamical overlap project
Authors: JLQCD Collaboration: T.Kaneko, S.Aoki, H.Fukaya, S.Hashimoto, K-I.Ishikawa, K.Kanaya, H.Matsufuru, M.Okamoto, M.Okawa, T.Onogi, A.Ukawa, N.Yamada, T.Yoshie
Comments: 7 pages, 8 figures, talk presented at Lattice 2006 (Chiral Symmetry)
 

hep-lat/0610011 [abs, ps, pdf, other] :
Title: Dynamical overlap fermion at fixed topology
Authors: JLQCD collaboration: S. Hashimoto, S. Aoki, H. Fukaya, K. Kanaya, T. Kaneko, H. Matsufuru, M. Okamoto, T. Onogi, N. Yamada
Comments: 7 pages, 4 figures, talk presented at Lattice 2006 (chiral symmetry); to appear in Proceedings of Science, PoS(LAT2006)052
 

hep-lat/0609073 [abs, ps, pdf, other] :
Title: Mobility edge and locality of the overlap-Dirac operator with and without dynamical overlap fermions
Authors: JLQCD Collaboration: N. Yamada, S. Aoki, H. Fukaya, S. Hashimoto, K-I. Ishikawa, K. Kanaya, T. Kaneko, H. Matsufuru, M. Okamoto, T. Onogi
Comments: 7 pages, 7 figures, talk presented at Lattice 2006 (chiral symmetry)
 

hep-lat/0609034 [abs, ps, pdf, other] :
Title: On the Locality and Scaling of Overlap Fermions at Coarse Lattice Spacings
Authors: Terrence Draper, Nilmani Mathur, Jianbo Zhang, Andrei Alexandru, Ying Chen, Shao-Jing Dong, Ivan Horvath, Frank X. Lee, Keh-Fei Liu, Sonali Tamhankar
Comments: 17 pages, 18 figures
 

hep-lat/0609033 [abs, ps, pdf, other] :
Title: Simulation of Lattice Gauge Action from the Overlap Operator
Authors: K.F. Liu
Comments: 6 pages
 

hep-lat/0609003 [abs, ps, pdf, other] :
Title: Dynamical overlap fermion simulations with a preconditioned Hybrid Monte Carlo force
Authors: Jan Volkholz, Wolfgang Bietenholz, Stanislav Shcheredin
Comments: 7 pages, 5 figures, talk presented at Lattice2006(Algorithms, machines and networks)
 

hep-lat/0605013 [abs, ps, pdf, other] :
Title: Overlap Hypercube Fermions in QCD Simulations Near the Chiral Limit
Authors: W. Bietenholz, S. Shcheredin
Comments: 41 pages, 20 figures
 

hep-lat/0603029 [abs, ps, pdf, other] :
Title: The Schr\"odinger functional in lattice QCD with exact chiral symmetry
Authors: Martin Lüscher
Comments: Plain TeX source, 20 pages, no figures
 

hep-lat/0603008 [abs, ps, pdf, other] :
Title: Lattice QCD with fixed topology
Authors: Hidenori Fukaya
Comments: Ph.D. thesis, 69pages
 

hep-lat/0510117 [abs, ps, pdf, other] :

Title: Topology with Dynamical Overlap Fermions
Authors: G. I. Egri, Z. Fodor, S. D. Katz, K.K. Szabo
Comments: 15 pages, 3 figures
 

hep-lat/0510116 [abs, ps, pdf, other] :

Title: Topology conserving gauge action and the overlap-Dirac operator
Authors: H.Fukaya, S.Hashimoto, T.Hirohashi, K.Ogawa, T.Onogi
Comments: 26pages, 11figures
 

hep-lat/0511003 [abs, ps, pdf, other] :

Title: Localization and lattice fermions
Authors: Benjamin Svetitsky (Tel Aviv University)
Comments: Talk given at the Workshop on Computational Hadron Physics, Nicosia, Cyprus, September 2005. 6 pp., 3 figs
 

hep-lat/0510095 [abs, ps, pdf, other] :

Title: Overlap fermion with the topology conserving gauge action
Authors: H. Fukaya, S. Hashimoto, T. Hirohashi, H. Matsufuru, K. Ogawa, T. Onogi
Comments: Poster presented at Lattice 2005 (Chiral fermions), 6 pages, 14 figures
Journal-ref: PoS(LAT2005)123
 

hep-lat/0508025 [abs, ps, pdf, other] :

Title: Dynamical overlap fermions: techniques and results
Authors: Stefan Schaefer, Thomas DeGrand
Comments: 10 pages, 5 figures, submitted to Lattice 2005 (chiral fermions)
 

hep-ph/0508085 [abs, ps, pdf, other] :

Title: Continuum physics with overlap fermions
Authors: Stephan Durr, Christian Hoelbling
Comments: 10 pages, 5 figures
 

hep-lat/0506021 [abs, ps, pdf, other] :

Title: Chiral properties of two-flavor QCD in small volume and at large lattice spacing
Authors: Thomas DeGrand, Stefan Schaefer
Comments: 16 pages, 12 figures
 

hep-lat/0412024 [abs, ps, pdf, other] :

Title: Schroedinger functional formalism with Ginsparg-Wilson fermion
Authors: Yusuke Taniguchi
Comments: 18 pages
 

hep-lat/0412005 [abs, ps, pdf, other] :

Title: Physics issues in simulations with dynamical overlap fermions
Authors: Thomas DeGrand, Stefan Schaefer
Comments: 14 pages, 10 figures
 

hep-lat/0409070 [abs, ps, pdf, other] :

Title: Dynamical overlap fermions, results with HMC algorithm
Authors: Z. Fodor, S.D. Katz, K.K. Szabo
Comments: Lattice2004(chiral)
 

hep-lat/0409030 [abs, ps, pdf, other] :

Title: Improving Inversions of the Overlap Operator
Authors: S. Krieg, N. Cundy, J.van den Eshof, A. Frommer, Th. Lippert, K. Schäfer
Comments: lattice2004(machines)
 

hep-lat/0409029 [abs, ps, pdf, other] :

Title: Dynamical overlap simulations using HMC
Authors: N. Cundy, S. Krieg, A. Frommer, Th. Lippert, K. Schilling
Comments: Lattice2004(machines)
 

hep-lat/0311010 [abs, ps, pdf, other] :

Title: Dynamical overlap fermions, results with hybrid Monte-Carlo algorithm
Authors: Z. Fodor, S.D. Katz, K.K. Szabo
Comments: 13 pages, 2 figures
 

hep-lat/0311002 [abs, ps, pdf, other] :

Title: Staggered versus overlap fermions: a study in the Schwinger model with $N_f=0,1,2$
Authors: Stephan Dürr, Christian Hoelbling
Comments: 15 pages, 7 figures
 

hep-lat/0306022 [abs, ps, pdf, other] :

Title: Spectral Properties of the Overlap Dirac Operator in QCD
Authors: W. Bietenholz, K. Jansen, S. Shcheredin
Comments: 22 pages, 8 figures

hep-lat/0206007 [abs, src, ps, other] :

Title: A note on Zolotarev optimal rational approximation for the overlap Dirac operator
Authors: Ting-Wai Chiu, Tung-Han Hsieh, Chao-Hsi Huang, Tsung-Ren Huang
Comments: 23 pages, 5 eps figures

hep-lat/0204016 [abs, src, ps, other] :

Title: Convergence Rate and Locality of Improved Overlap Fermions
Authors: W. Bietenholz
Comments: 31 pages, 15 figures

hep-lat/0202025 [abs, src, ps, other] :

Title: Numerical Methods for the QCD Overlap Operator: I. Sign-Function and Error Bounds
Authors: J. van den Eshof, A. Frommer, Th. Lippert, K. Schilling, H. A. van der Vorst
Comments: 30 pages, 2 figures

hep-lat/0112042 [abs, src, ps, other] :

Title: Improving the low-lying spectrum of the overlap kernel
Authors: W. Kamleh, D. Adams, D.B. Leinweber, A.G. Williams
Comments: 5 pages, 8 figures

hep-lat/0112041 [abs, src, ps, other] :

Title: Accelerated Overlap Fermions
Authors: W. Kamleh, D. Adams, D.B. Leinweber, A.G. Williams
Comments: 13 pages, 6 figures

hep-lat/0110218 [abs, src, ps, other] :

Title: Ginsparg-Wilson fermions: practical aspects and applications
Author: P. Hernandez (CERN)
Comments: 6 pages, Talk at Lattice 2001(plenary)

hep-lat/0110184 [abs, src, ps, other] :

Title: Quenched Results for Light Quark Physics with Overlap Fermions
Authors: L. Giusti, C. Hoelbling, C. Rebbi
Comments: LATTICE2001(Chiral Fermions and Gauge Theories), 9 pages, 5 figure, CPT 2001/P.4250

hep-lat/0110009 [abs, src, ps, other] :

Title: A new fermion Hamiltonian for lattice gauge theory
Authors: Michael Creutz (Brookhaven), Ivan Horváth (Kentucky), Herbert Neuberger (Rutgers)
Comments: Lattice2001(chiral), 3 pages, 4 figures

hep-lat/0110005 [abs, src, ps, other] :

Title: Understanding chiral symmetry breaking with the overlap action
Authors: Thomas DeGrand
Comments: Lattice2001(confinement)

hep-lat/0109037 [abs, src, ps, other] :

Title: Unquenching the topological susceptibility with an overlap action
Authors: Tamas G. Kovacs (NIC/DESY Zeuthen, & Pecs U.)
Comments: 3 pages, LaTeX with 3 eps figures, Lattice2001(confinement)

hep-lat/0108028 [abs, src, ps, other] :

Title: Perturbative renormalization for overlap fermions
Authors: Stefano Capitani (MIT)
Comments: 3 pages, Lattice2001(improvement)

hep-lat/0101015 [abs, src, ps, other] :

Title: Schwinger Model with the Overlap-Dirac Operator: exact results versus a physics motivated approximation
Authors: L. Giusti, Ch. Hoelbling, C. Rebbi (Boston University)
Comments: Latex, 30 pages, 18 figures included

hep-lat/0011017 [abs, src, ps, other] :

Title: Recent results using the overlap Dirac operator
Authors: Rajamani Narayanan
Comments: 4 pages, Talk given at DPF2000, Columbus, Ohio

hep-lat/0011014 [abs, src, ps, other] :

Title: Exact results and approximation schemes for the Schwinger model with the overlap Dirac operator
Authors: L. Giusti, C. Hoelbling, C. Rebbi
Comments: Lattice 2000 (Chiral Fermions)

hep-lat/0011012 [abs, src, ps, other] :

Title: Constructing Improved Overlap Fermions in QCD
Authors: W. Bietenholz, N. Eicker, I. Hip, K. Schilling
Comments: 5 pages, poster presented at Lattice 2000 (Improvement and Renormalisation)

hep-lat/0009033 [abs, src, ps, other] :

Title: Regulated chiral gauge theories
Authors: Herbert Neuberger (Rutgers)
Comments: 9 pages, LaTeX, includes esfconf.sty

hep-lat/0009032 [abs, src, ps, other] :

Title: Exact Chiral Symmetry with a non-perturbative cutoff
Authors: Herbert Neuberger (Rutgers)
Comments: 12 pages, LaTeX, includes sprocl.sty

hep-lat/0009004 [abs, src, ps, other] :

Title: Lattice QCD with the Overlap-Dirac Operator: Its $\Lambda$ Parameter, and One-Loop Renormalization of Fermionic Currents
Authors: C. Alexandrou (1), E. Follana (1), H. Panagopoulos (1), E. Vicari (2) ((1) Univ. of Cyprus, (2) Univ. of Pisa)
Comments: 3 pages, LATeX with 2 PS figure files. Talk presented at Confinement IV, Vienna, July 2000. Longer write-ups in: hep-lat/9909158 (NPB 571 (2000) 257), hep-lat/0002010 (NPB 580 (2000) 394)

hep-lat/0008002 [abs, src, ps, other] :

Title: Lattice QCD with the Overlap Fermions at Strong Gauge Coupling (II)
Authors: Ikuo Ichinose, Keiichi Nagao
Comments: Latex 17 pages, the extended version of hep-lat/0001030, the discussion of symmetries and species doubling added

hep-lat/0007021 [abs, src, ps, other] :

Title: Overlap-Dirac fermions with a small hopping parameter
Authors: Maarten Golterman, Yigal Shamir
Comments: 14 pages, 1 figure, minor changes

hep-lat/0006004 [abs, src, ps, other] :

Title: Chiral Symmetry, Quark Mass, and Scaling of the Overlap Fermions
Authors: S. J. Dong, F. X. Lee, K. F. Liu, J. B. Zhang
Comments: 8 pages, 5 figures

hep-lat/0002010 [abs, src, ps, other] :

Title: One-loop renormalization of fermionic currents with the overlap-Dirac operator
Authors: C. Alexandrou (1), E. Follana (1), H. Panagopoulos (1), E. Vicari (2) ((1) Univ. of Cyprus, (2) Univ. of Pisa)
Comments: 14 pages, LATeX with 2 PS figure files

hep-lat/0001030 [abs, src, ps, other] :

Title: Pions in Lattice QCD with the Overlap Fermions at Strong Gauge Coupling
Authors: Ikuo Ichinose, Keiichi Nagao
Comments: Latex 11 pages

hep-lat/0001019 [abs, src, ps, other] :

Title: Fast methods for computing the Neuberger Operator
Authors: Artan Borici
Comments: 12 pages, 2 figures. Talk given at the ``Interdisciplinary Workshop on Numerical Challenges to Lattice QCD'', Wuppertal, 22-24 August 1999

hep-lat/0001013 [abs, src, ps, other] :

Title: The Overlap-Dirac Operator: Topology and Chiral Symmetry Breaking
Authors: R. G. Edwards, U. M. Heller, R. Narayanan
Comments: latex, 12 pages, 8 postscript figures. Talk given at CHIRAL '99, Taipei, Taiwan, Sept. 13-18, 1999

hep-lat/0001008 [abs, src, ps, other] :

Title: A numerical treatment of Neuberger's lattice Dirac operator
Authors: P. Hernandez, K. Jansen, L. Lellouch
Comments: Latex2e file, 3 figures, 14 pages

hep-lat/9912043 [abs, src, ps, other] :

Title: First experiences with HMC for dynamical overlap fermions
Authors: Achim Bode, Urs M. Heller, Robert G. Edwards, Rajamani Narayanan
Comments: 4 pages with 1 ps figure; crckapb.sty included; to appear in the proceedings of the workshop "Lattice Fermions and Structure of the Vacuum", Oct 5-9, Dubna, Russia

hep-lat/9912042 [abs, src, ps, other] :

Title: Topology and Chiral Symmetry in QCD with Overlap Fermions
Authors: Robert G. Edwards, Urs M. Heller, Joe Kiskis, Rajamani Narayanan
Comments: 12 pages with 6 ps figures; crckapb.sty included; to appear in the proceedings of the workshop "Lattice Fermions and Structure of the Vacuum", Oct 5-9, Dubna, Russia

hep-lat/9912033 [abs, src, ps, other] :

Title: Techniques for using the overlap-Dirac operator to calculate hadron spectroscopy
Authors: UKQCD Collaboration: Craig McNeile
Comments: Talk given at CHIRAL '99, Taipei, Sep. 13-18, 1999. 9 pages

hep-lat/9912026 [abs, src, ps, other] :

Title: Heat-Kernel Approach to the Overlap Formalism
Authors: Shoichi Ichinose
Comments: Talk at CHIRAL'99, 9 pages, No figures

hep-lat/9912011 [abs, src, ps, other] :

Title: Gauged Gross Neveu model with overlap fermions
Authors: Ikuo Ichinose, Keiichi Nagao
Comments: Latex 9 pages, sty file included, talk by K.Nagao at Chiral'99, Taipei, Taiwan, Sep.13-18, 1999. (To be pubished in the Proceedings)

hep-lat/9911037 [abs, src, ps, other] :

Title: One-loop analyses of lattice QCD with the overlap Dirac operator
Authors: M. Ishibashi (U. of Tokyo), Y. Kikukawa (Nagoya U), T. Noguchi (Kyoto U), A. Yamada (U. of Tokyo)
Comments: 19pages, latex

hep-lat/9911022 [abs, src, ps, other] :

Title: Overlap
Authors: H. Neuberger (Rutgers)
Comments: 12 pages, Latex, sty file included, talk at CHIRAL '99, Taipei, Sep. 13-18, 1999

hep-lat/9910040 [abs, src, ps, other] :

Title: The Overlap Dirac Operator
Authors: H. Neuberger (Rutgers)
Comments: 17 pages, Latex, cls file included

hep-lat/9909158 [abs, src, ps, other] :

Title: Lambda-parameter of lattice QCD with the overlap-Dirac operator
Authors: C. Alexandrou, H. Panagopoulos, E. Vicari
Comments: 11 pages, 2 figures

hep-lat/9909061 [abs, src, ps, other] :

Title: Hadron Masses and Quark Condensate from Overlap Fermions
Authors: K. F. Liu, S. J. Dong, F. X. Lee, J. B. Zhang
Comments: LATTICE99(Chiral Fermions), 3 pages, 6 figures

hep-lat/9909059 [abs, src, ps, other] :

Title: Feasibility study of using the overlap-Dirac operator for hadron spectroscopy
Authors: UKQCD Collaboration: Craig McNeile, Alan Irving, Chris Michael
Comments: LATTICE99(Chiral Fermions) 3 pages, 2 figures

hep-lat/9909024 [abs, src, ps, other] :

Title: Overlap Dirac Operator, Eigenvalues and Random Matrix Theory
Authors: Robert G. Edwards, Urs M. Heller, Joe Kiskis, Rajamani Narayanan
Comments: 3 pages latex with 1 postscript figure. Talk presented at LATTICE99(topology)

hep-lat/9908012 [abs, src, ps, other] :

Title: Improved Overlap Fermions
Authors: W. Bietenholz, I. Hip
Comments: Talk presented at LATTICE99(chiral fermions), 3 pages, 6 figures

hep-lat/9801031 [abs, src , ps, other] :

Title: More about exactly massless quarks on the lattice
Authors: H. Neuberger (Rutgers)
Comments: 4 pages, plain TeX
Journal-ref: Phys.Lett. B427 (1998) 353-355

hep-lat/9712022 [abs, src, ps, other] :

Title: Exponential suppression of radiatively induced mass in the truncated overlap
Authors: Y. Kikukawa, H. Neuberger, A. Yamada
Comments: 26 pages, plain TeX
Journal-ref: Nucl.Phys. B526 (1998) 572-596

hep-lat/9710089 [abs, src, ps, other] :

Title: Vector like gauge theories with almost massless fermions on the lattice
Authors: Herbert Neuberger (Rutgers)
Comments: 35 pages, TeX, 4 figures using epsf
Journal-ref: Phys.Rev. D57 (1998) 5417-5433

hep-lat/9707022 [abs, src, ps, other] :

Title: Exactly massless quarks on the lattice
Authors: Herbert Neuberger (Rutgers)
Comments: 7 pages, plain TeX; references corrected
Journal-ref: Phys.Lett. B417 (1998) 141-144