Effective couplings of axigluons and technicolor pseudo Goldstone bosons

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  • PHYSICAL REVIEW D VOLUME 46, NUMBER 1 1 1 DECEMBER 1992

    Effective couplings of axigluons and technicolor pseudo Goldstone bosons

    Xin-zhou Li East China Institute for Theoretical Physics, 130 Mei Long Road, Shanghai 200237, China

    Jian-zu Zhang China Center of Advanced Science and Technology (World Laboratory), P.O. Box 8730, Beijing 100080, China

    and East China Institute for Theoretical Physics, 130 Mei Long Road, Shanghai 200237, China* (Received 25 March 1991; revised manuscript received 19 June 1992)

    The anomaly-free chiral-color models in the technicolor scheme are discussed. The effective couplings of the low-lying technicolor pseudo Goldstone bosons (PGBs) to the gauge bosons, y , w',z', gluons, and axigluons are constructed in the effective chiral Lagrangian framework. The model suggests a rich phenomenology and shows the new axigluon-PGB coupling G, G, PP which contributes to technion pair production via axigluon fusion and should be accessible to the next generation of accelerators and the Superconducting Super Collider.

    PACS numberk): 12.10.Dm, 12.50.Lr, 14.80.Er, 14.80.Pb

    I. INTRODUCTION

    The recent and forthcoming precision electroweak measurements at the SLAC Linear Collider (SLC), and CERN e + e - collider (LEP), and Fermilab Tevatron col- lider are providing a sensitive probe for possible new physics at and above the Fermi scale MF-250 GeV which could potentially reveal effects outside the minimal standard model. As is well known, the low-energy phe- nomena is well described by a Yang-Mills theory with the gauge group

    This defines the minimal standard model of particle phys- ics which is in good agreement with present experiments ii.e., for ds 5 100 GeV). What is not so clear is what lies beyond this theory. One such proposed extension of the standard model is offered by chiral-color theory [I]. There is a possibility that the SU(31, of the strong in- teraction originates in the chiral-color gauge group SU(3),,@ SU( 3 ),,. The gauge group of strong and elec- troweak interactions above M F is taken to be

    and the SUi3), group is identified with the diagonal sub- group of SU(3),l s SUi 3 ),,. Therefore the chiral-color theory behaves like the standard model after spontaneous breakdown of the chiral-color and electroweak sym- metries below M,. However, the chiral-color theory ex- hibits nonstandard phenomenology above MF [2]. There are many different implementations of chiral-color [l -41 theory. The most important model-independent predic- tion of chiral-color theory is a massive color octet of gauge bosons, the axigluons g A . The chiral-color model

    ailin in^ address.

    can be examined [2,3,5,6] in the technicolor (TC) scheme [7,8]. The range of the axigluon mass M A is fixed by the T C dynamical symmetry-breaking scheme, 280 < M A < 970 GeV [9]. The absence of anomalies in chiral-color theory plays an essential role in constraining the quark spectrum in this theory. For chiral-color mod- els in the T C scheme, both the ordinary and T C fermions must be free of triangle anomalies with respect to SUi3),l@ SUi 3 I,,@ Ui 1 1,. The anomaly-free chiral-color models based on the gauge interaction (1.2) are not as unique as the standard model. In this paper we show some chiral-color models in the T C scheme which are free of anomalies with respect to the gauge group (1.2). In these models there is a rich spectrum of the T C pseudo Goldstone bosons. Some of the low-lying TC bosons may have masses much less than 1 TeV. We argue that chiral-symmetry low-energy-theorem techniques can be expected to work for the chiral-color model in T C phys- ics [2,9,10]. It is quite interesting to consider the new vertices involving axigluons and T C pseudo Goldstone bosons which, in addition to the pure gauge-boson anom- aly vertices [2,10], show the difference between the chiral-color models ( 1.2) and the standard model i 1.1)

    11. EFFECTIVE COUPLINGS OF THE AXIGLUONS

    AND THE TC PSEUDO GOLDSTONE BOSONS

    We consider a T C model with one family of T C fermions [2,3] which have the following SU(3),l@ SU( 3 ),,@ SUi 2 1, @ U( 1 ). representations. T C quarks:

    i u/,D/),: i3,1,2,f ), , (2.la)

    UL: ( 1 , 3 , 1 , + ) R , D L : i1,3,1,-+)R .

    T C leptons:

    46 5092 @ 1992 The American Physical Society

  • EFFECTIVE COUPLINGS OF AXIGLUONS AND TECHNICOLOR . .

    It is convenient to discuss the triangle anomalies in terms of SU(3),.@ SU( 3 ),,a U ( 1 ), rather than the SU(3),,@ SU( 3 I,,@ U ( 1 I,, gauge interactions. This is be- cause the weak hypercharge quantum number Y is the same for all members in a representation, while the elec- tric charge of the members can vary according to their weak-isospin quantum numbers. In the above we assume the T C interactions to be an SU(NTc) vector-gauge theory, t = 1,2,. . . ,NTc ( N T c > 3 ). The indices 1 and r refer to the left- and right-handed chiral-color model, while the indices L and R refer to the helicity. This is an extension of the Farhi-Susskind model [ l l ] . The T C fer- mions have triangle anomalies due to the SU(3),,@ SU(3 I,,@ U ( 1 1 , interactions.

    Let the general coupling between the gauge boson and fermion be

    where ra may involve y5 and satisfies the Lie algebra

    where the fabc are the structure constants of the underly- ing Lie algebra. The triangle graph with three-gauge- boson vertices has an anomaly given by [12,13]

    It is convenient to write ra in terms of left- and right- handed couplings

    where T ; are Hermitian matrices and satisfy the same commutation relations as (2.3), i.e.,

    Then (2.4) can be rewritten as

    The anomalies are of the type [SU(3),,13 - [SU(3),,I3 and Y [ S U ( ~ ),, 1 2 - Y [ SU( 3 ), , I2 . All other anomalies either cancel between quarks and leptons or are zero. Let the gauge fields belonging to SU(3),,, SU(3),,, SU(2),, and U ( l ) , be denoted by G I , G,, W L , and Y. The nonvanish- ing anomaly coefficients are

    (3,1,2, f )L T C quarks:

    ( 1,3,1, I R T C quarks:

    (1 ,3 ,1 , - ) )R T C quarks:

    (1,1,2, - 1 ), T C leptons:

    ( 1,1,1,-2)R TC leptons: A,( y3)=8

    The chiral-color anomalies in the T C quark sector can be canceled by that in the ordinary quark sector [2,3]. This is based on the fact that the anomaly is mass independent [14,15]; i.e., anomalies due to a fermion with a large sepa- ration in masses can cancel against each other, which is not prohibited by the decoupling theorem [16]. Thus, for the ordinary-fermion sector, we assume that there are n generations and each generation has chiral-color repre- sentations opposite to that of T C quarks, i.e., for quarks,

    and for leptons,

    If we relate the number n of ordinary quark generations to the rank NTC of the TC gauge group, n =NTC( =4), the cancellation of the chiral-color anomalies of the type [su(~) , , ]~-[ S U ( ~ ) , , ] ~ and Y [ S U ( ~ ) , , ] ~ - Y [ S U ( ~ ) , , ] ~ is achieved between the T C and ordinary quarks.

    The general form of the low-energy chiral Lagrangians of T C theory is expected to be a valid phenomenological framework for new strong physics between 1 TeV and around the Fermi scale M F . This low-energy effective chiral Lagrangian allows us to describe interactions among low-lying T C pseudo Goldstone bosons and the gauge bosons y , w', z O , gluons, and axigluons. It is useful to represent (2.1) as the eight-component left- and right-handed fermion fields

    Above the T C condensate scale AT,- 1 TeV, the chiral- color and electroweak interactions are negligible, and the T C fermions have an SU(8), 0 SU( 8 ), global chiral sym- metry. Below ATc, the T C interaction becomes strong and T C fermion condensate appears, ( qLqR )# 0, which breaks SU(8),@ SU(8 ), into SU(81, + R . Then there ap- pear 63 Goldstone bosons. Among them, three color- singlet weak-triplet Goldstone bosons n f + n ~ = & y 5 7 i ~ + Q y 5 ~ i ~ (i=1,2,3) are absorbed by W' and Z O to give W' and Z O masses, and the eight color-octet weak-singlet neutral Goldstone bosons n$=Dy5haQ ( a = 1,2, ..., 8 ) are absorbed by the axi- gluons to give the axigluon masses, where Q denotes the T C quarks, Q = ( U,D), and L denotes the T C leptons, L = ( N , El . Among the rest, there are four color-singlet T C pseudo Goldstone bosons (technions): the isotriplet #= 0 y s ~ i ~ - 3&y ,T'L ( i = 1,2,3 ) and the isosinglet ~ 0 = ~ y 5 ~ - 3 ~ y , ~ . They may have masses much less than 1 TeV (a rough estimation is 2 GeV < mpo, m,,. < 40

  • 5094 XIN-ZHOU LI AND JIAN-ZU ZHANG 46

    GeV, 8 < m,+ < 40 GeV [17]) and have unusual produc- tion and decay characteristics [ l l ] . Because of their ex- pected low masses, we are motivated to study their cou- plings to gauge bosons.

    Now we discuss the low-energy effective Lagrangian for technions which takes the form [18,10]

    where U( 4 ) - ( $L qR ) is a phenomenological field which is related to the matrix-valued T C pseudoscalar mesons 4. The phenomenological reasonable form for U ( 4 ) is

    U ( d ) = exp(2i4/FT) . (2.12)

    In (2.1 1) and (2.121, the technion decay constant FT is the anologue of the pion decay constant f ,, but it is related to the scale of a T C force-induced condensate and can be determined by its relationship to the weak W' (and z O ) boson masses

    where g is the SU(2) gauge coupling and r is the number of the doublet of technicolor fermions. In order to keep the local gauge invariance, a,U(4) in (2.1 1) should be re- placed by the covariant derivative.

    For the gauge group (1.2), the left- and right-handed gauge fields are

    For the gauge group (1.21, the left- and right-handed gauge fields are

    where Wf, ( i=1 ,2 ,3 )