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Cll Unification: Its Implications for Present and Future High Energy-Experimentation

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Cll Unification: Its Implications for Present and Future High Energy-Experimentation 624 H. TERAZAWA der Heyde: contributed paper No. 236 (Univ. of Spinor Theory," in this Proceedings, C9. Colonge and Tel-Aviv Univ.). 24. J. D. Bjorken: Ann. Phys. 24 (1963) 174. 21. H. Terazawa, K. Akama and Y. Chikashige: 25. M. Gell-Mann and F. E. Low: Phys. Rev. 95 Progr. theor. Phys. 56 (1976) 1935; Phys. Rev. (1954) 1300. D15 (1977) 480; see also T. Saito and K. Shige- 26. P. R. Phillips: Phys. Rev. 146 (1966) 966; see moto: Progr. theor. Phys. 57 (1977) 242; 57 also A. D. Sakharov: Dokl. Acad. Nauk (1977) 643. SSSR 177 (1967) 70. 22. H. Terazawa, Y. Chikashige, K. Akama and T. 27. L. Landau: in Niels Bohr and the Development of Matsuki: Phys. Rev. D15 (1977) 1118; Progr. Physics, edited by W. Pauli (McGraw-Hill, New theor. Phys. 60 (1978) 868; contributed paper York, 1955) p. 52. No. 103, KEK-78-11 (National Lab. for High 28. H. Terazawa: Phys.. Rev. D16 (1977) 2373. Energy Phys., July, 1978). 23. K. Kikkawa: Progr. theor. Phys. 56 (1976) Note added in proof: Recently, J. Arafune has 947; T. Kugo: ibid., 55 (1976) 2032; see also pointed out that the baryon-number non conservation T. Eguchi and H. Sugawara: Phys. Rev. D10 claimed by Yoshimura violates CPT invariance and (1974) 4257; H. Sugawara: "Gauge Invariant unitarity. PROC. 19th INT. CONF. HIGH ENERGY PHYSICS TOKYO, 1978 Cll Unification: Its Implications for Present and Future High Energy-Experimentation J. C. PATI Department of Physics and Astronomy, University of Maryland, College Park, Maryland 20742 manifest at present energies through the dis­ §1, Introduction covery of neutral current interactions, what Since the last International Conference held new phenomena and correspondingly fun­ in Hamburg a year ago, there is one marked damentally new physics may one look forward difference in the experimental situation regard­ to discover next at higher energies through ing the status of the structure of neutral current high energy accelerators to be completed in interactions. At present all experiments, the near future and within the decade? Speci­ which include neutrino-nucleon-scattering, neu­ fically, assuming that the three basic forces— trino-charged lepton scattering as well as parity weak, electromagnetic as well as strong—have violation in electron-deuteron-scattering, agree a common origin, and so also do quarks and remarkably well with the predictions of the leptons,2'3 one might look forward to discover simple gauge-unification based on the sym­ next tangible evidence of such a "grand" 1 metry-structure SU(2)LxU(l). unification. This evidence would arise if This raises two important questions: one could see traces of the new class of interac­ (1) Do the set of data noted above single tions (analogous to neutral current interac­ out SU(2)£xU(l) as the only allowed sym­ tions) that are needed for putting quarks and metry relevant for low energy electro-weak leptons into one multiplet. The pertinent force, or do they allow for possible alternative question is: can these new interactions and symmetries, which would differ from the correspondingly "grand" unification manifest predictions of SU(2)LxU(l) even in the low at an energy or mass-scale, within experi­ energy regime in areas yet to be explored mental reach in the near or conceivable experimentally? future? (2) Given that a gauge unification of the The purpose of my talk is two fold: weak and electromagnetic forces is already (i) First, to note that the present set of Unified Theories Including Strong Interactions 625 data, which test only (a) left handed neutrino- unifying symmetries such as [SU(4)]4, which or right handed antineutrino-scattering, and (b) gauge chiral color, such a unification can the parity violating part of the electron-quark manifest at an energy scale as low as about neutral current (nc) interaction do not single 10M06 GeV, provided chiral color SU(3)ix out SU(2)LxU(l) as the only allowed low SU(3% rather than vector color emerges as energy electro-weak-symmetry, since they have a good low energy symmetry.6 This raises the not yet probed sensitively into the parity con­ possibility that "grand" unification may in serving part of the nc interaction. fact be testable within the present generation. The present set of data permit two alternative I shall remark that chiral color brings with it low energy forms for the electro-weak sym­ intriguing signatures without disturbing the metry: (i) The left handed GL = $U(2)L X U(l), familiar successes of the standard vector QCD; 4 as well as (ii) the left-right symmetric GLR It supplements the familiar octet of vector EESU(2)xXSU(2)*XU(1)lXU(1)*. Both of color gluons with an octet of relatively light these arise as alternative low energy forms axial color gluons ((mA)eS<(1/2—2) GeV), relevant for electro-weak interactions within which generate spin-spin force in the leading unifying symmetries3 such as [SU(4)]4. The term. This may help resolve some of the two sub-symmetries GL and GLR coincide in lingering discrepancies as regards level-splitt­ their predictions as regards low energy neutri­ ing and transitions in charmonium physics. no-scattering as well as parity violating part In the course of my talk I shall briefly of the nc interaction. But they can differ in allude to a) left-right symmetry and CP general substantially from each other in their violation, b) spontaneous breakdown of sym­ predictions as regards the parity conserving metry structures of the form [SU(4)]4, in parti­ part of the nc interaction, and simultaneously cular some new results7 exhibiting that there as regards the masses and the number of the is an intimate link between the emergence of relatively light weak neutral gauge bosons. the GIM-mechanism and the degree of nc The symmetry GLR permits in general a weak parity violation within such a symmetry- gauge boson ZA substantially lighter than the structure, and c) the question of liberation Z°(m°z^85 GeV) of SU(2)L X U(l) con­ versus confinement of quarks and gluons, sistent with all available data. Such dif­ especially the possible links between liberated ferences, in case they exist, can be probed color and the excess prompt neutrinos observed sensitively through a measurement of the in beam dump experiments on the one hand 2 parity conserving forward-backward asym­ and the indicated rise in vW2 at high W > + + 2 metry-parameters for e~e ->/w"~/M scattering 100 GeV for /^p-scattering reported at this at PETRA and PEP energies and also for high conference on the other. energy pp and pp-^/j+x scatterings. The topics appear in the following sequence: In other words, discovery of new physics, II. Grand Unification: Comparative Sum­ which could signal a structure beyond $\J{2)L x mary of Alternative Approaches U(l), may still be awaiting PETRA and PEP III. Salient Features of [SU(4)]4: Left- experiments as well as high energy pp and pp Right-Symmetry CP Violation: Link Between experiments under planning. Any indication GIM-Mechanism and Neutral Current Parity for the presence of the extra U(l)iXU(l)r Violation: Integer Versus Fractional Quark- factor in the low energy electro-weak symmetry Charges: Liberated Versus Confined Quarks would be important in that it would greatly and Gluons narrow down the choice of the superstructure IV. Role of Chiral Color in Low Mass G unifying weak, electromagnetic as well as Unification: Possible Signatures of Chiral strong forces. Color in Quarkonium-Physics and Deep (ii) The second and main point of my talk Inelastic scattering would be to emphasize that a manifestation of V. Summary: Important Questions: New the postulated strong-electro-weak-unification Discoveries Within the Decade need not necessarily await realization of Due to lack of space, I include only the ultrahigh centre of mass energies exceeding second and last chapters in this Proceeding, 1015GeV, as traditionally claimed.5 Within which provide motivations, a comparative 626 J. C. PATI summary and experimental consequences of metry in the ground state; these distinctions grand unification. A complete outline may be should disappear at appropriately high ener­ found in the Proceedings of the Seoul Sym­ gies. posium on Elementary Particle Physics held Such a broad view calls for the existence of September, 1978. a new class of interactions mediated by gauge particles (X) coupled for example to quark- §11. Grand Unification lepton-currents. These exotic gauge particles The motivations for going beyond electro- need in general to be much heavier than weak weak unification (exemplified by the symmetry- W± and Z° bosons both on grounds of absence structure SU(2)z<xU(l)) are that within the of exotic interactions (such as KL-±fte and for premises of electroweak unification: (a) there some cases decay of the proton) as well as the are more than one gauge coupling constants, observed low energy disparity between effective which are unrelated; thus the weak angle strong and electromagnetic coupling constants. tan2 Ow^ig'/g)2 is an arbitrary parameter; (b) It is these exotic gauge particles (generically there is no rationale for the existence of referred to as X) and the interactions generated quarks and leptons; (c) there is no rationale by them, which are the hall marks of grand for the existence of weak, electromagnetic and unification. One thus needs to achieve centre strong interactions: (d) there is no prediction of mass energies of order Mx to feel the effects for the charges of leptons vis-a-vis those of of the new class of interactions and therefore quarks; electric charge is not quantized; (e) of grand unification.
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