View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by CERN Document Server NON-SUPERSYMMETRIC EXTENSIONS OF THE STANDARD MODEL KENNETH LANE Department of Physics, Boston University, 590 Commonwealth Ave, Boston, MA 02215, USA The motivations for studying dynamical scenarios of electroweak and avor symmetry breaking are reviewed and the latest ideas, esp ecially top color-assisted technicolor, are summarized. Several technicolor signatures at the Tevatron and Large Hadron Collider are describ ed and it is emphasized that all of them are well within the reach of these colliders. 1 Intro duction troweak interactions have b een in place for almost 4 25 years. In all this time, the standard mo del has The title of my talk was chosen by the organizers withsto o d extremely stringent exp erimental tests, and, while it was not their intention, they have the latest round b eing describ ed at this conference 5 6 7 de ned my sub ject by what it is not. That leaves by Bro ck, Tipton, and Blondel. Down to dis- 16 it for me to de ne what it is. So, in this talk tances of at least 10 cm, the basic constituents 1 \non-sup ersymmetric extensions of the standard of matter are known to b e spin- quarks and lep- 2 mo del" means Dynamical Electroweak and Flavor tons. These interact via the exchange of spin-one Symmetry Breaking. To be sp eci c, I will dis- gauge b osons: the massless gluons of QCD and the 1 0 cuss asp ects of technicolor and extended techni- massless photon and massive W and Z b osons 2 ; 3 color . of electroweak interactions. There are six avors I b egin in Sec. 2 by reiterating why it is still each of quarks and leptons|identical except for imp ortant to study scenarios in which electroweak mass, charge and color|group ed into three gen- and avor symmetry are broken by strong dynam- erations. ics at mo derate, accessible energy scales. This The fact that the QCD gauge symmetry is ex- is followed in Sec. 3 by a review of technicolor act in b oth the Lagrangian and the ground state of and extended technicolor, fo cusing on the more the theory implies that quarks and gluons are con- mo dern asp ects|walking technicolor, multiscale ned at large distances into color-singlet hadrons technicolor, and top color-assisted technicolor. In and that they are almost noninteracting at small Sec. 4, I will discuss several imp ortant signatures distances. However, con nement and asymptotic of these strong dynamics that can b e soughtover freedom are not the only dynamical outcomes for the next 10-15 years at the upgraded Tevatron gauge theories. Even though gauge b osons nec- Collider and the Large Hadron Collider. For the essarily app ear in the Lagrangian without mass, most part, these signatures involve the pro duc- interactions can make them heavy. This happ ens tion of technihadrons and ! and their de- T T 0 to the W and Z b osons: electroweak gauge sym- cay into pairs of technipions, , W and T T L T metry is spontaneously broken in the ground state Z , and p ossibly dijets. I restrict myself to L T of the theory, a phenomenon known as the \Higgs these hadron colliders not only b ecause they are 8 mechanism". Finally, fermions in the standard the only new high-energy machines anywhere near mo del also must start out massless. To make a the real axis, but also b ecause they have the quarks and leptons massive, new forces beyond greatest reach of all machines under consideration the SU (3) SU (2) U (1) gauge interactions are for the unknown physics of the TeV energy scale. required. These additional interactions explicitly break the fermions' avor symmetry and commu- 2 Why Study Strong Electroweak and Fla- nicate electroweak symmetry breaking to them. vor Dynamics? Despite this great b o dy of knowledge, the in- teractions underlying electroweak and avor sym- The theoretical elements of the standard SU (3) metry breakdowns remain unknown . The most SU (2) U (1) gauge mo del of strong and elec- imp ortant element still missing from this descrip- a Some might view mysaying this as the kiss of death. tion of particle interactions is directly connected to 1 electroweak symmetry breaking. This may mani- to search for technicolor and extended technicolor fest itself as one or more elementary scalar \Higgs as well as the standard mo del Higgs b oson, its sim- b osons". This happ ens in sup ersymmetry, the ple extensions, sup ersymmetry, and so on. Hadron scenario for the physics of electroweak symme- colliders have powerful reach by virtue of their 9 try breaking that is by far the most p opular. high energy and luminosity, but extracting clear Notwithstanding its p opularity, there is no ex- signals from them can b e quite demanding. Thus, 10 ; b p erimental evidence for sup ersymmetry. We detectors should be designed to be sensitive to, do not know the origin of electroweak symmetry and exp erimenters should be prepared to search breaking. for, the signatures of dynamical electroweak and avor symmetry breaking. So far, there is little If the dynamics of the Higgs mechanism are indication of this in the large LHC detector col- unknown in detail, those of avor are completely lab orations. obscure. We don't even have a prop er name, much less a b elievable and venerable \mechanism", for avor symmetry breaking. Mo dels with elemen- 3 Summary of Technicolor and Extended tary Higgs b osons, whether sup ersymmetric or Technicolor not, o er no explanation at all for the quark-lepton content of the generations, the numb er of genera- Technicolor|the strong interaction of fermions tions, why they are identical, and why avor sym- and gauge b osons at the scale 1TeV | TC metry is broken|the bizarre pattern of quark and describ es the breakdown of electroweak symme- lepton masses. try to electromagnetism without elementary scalar Dynamical electroweak and avor symmetry 1 b osons. Technicolor has a great precedent in breaking|technicolor and extended technicolor| QCD. The chiral symmetry of massless quarks is are plausible, attractive, natural, and nontrivial sp ontaneously broken by strong QCD interactions, scenarios for this physics that involve new inter- resulting in the app earance of massless Goldstone actions at sp eci ed, exp erimentally accessible en- c b osons, , K , . In fact, if there were no Higgs 11 ergy scales. Technicolor is a strong gauge inter- b osons, this chiral symmetry breaking would itself action mo deled after QCD. Its characteristic en- cause the breakdown of electroweak SU (2) U (1) < ergy is 1TeV , so it may be sought in exp eri- to electromagnetism. Furthermore, the W and Z ments of the coming decade. Extended technicolor 2 2 2 masses would be given by M = cos M = W W Z (ETC) emb eds technicolor, color and avor into a 1 2 2 g N f , where g is the weak SU (2) coupling, F 8 larger gauge symmetry; this emb edding is neces- N the numb er of massless quark avors, and f , F sary to pro duce the nonzero \current-algebraic" the pion decay constant, is only 93 MeV. or \hard" masses of quarks and leptons. At the In its simplest form, technicolor is a scaled same time, ETC o ers a simple group-theoretic up version of QCD, with massless technifermions explanation of avor in terms of the representa- whose chiral symmetry is sp ontaneously broken at tion content of fermions. As we explain shortly, . If left and right-handed technifermions are TC the scale at which ETC symmetry is broken down assigned to weak SU (2) doublets and singlets, re- to color technicolor is O (100 TeV). Neverthe- 1 sp ectively, then M = cos M = gF , where W W Z 2 less, the e ects of this interaction are observable F = 246 GeV is the weak technipion decay con- at the TeV energy scale in terms of the masses and d stant. decay mo des of the technihadrons, and , that T T The principal signals in hadron collider ex- p opulate technicolor mo dels. p eriments of \classical" technicolor were discussed Because we are so completely ignorant of 12 ; 13 long ago. In the minimal technicolor mo del, electroweak and avor dynamics, exp eriments at with just one technifermion doublet, the only TeV energies, which for now means those planned c for the Tevatron and the LHC, must have the The hard masses of quarks explicitly break chiral sym- metry and give mass to , K , , which are then referred to greatest p ossible discovery p otential. They ought as pseudo-Goldstone b osons. d b The technipions in minimal technicolor are the linear Those who would cite the apparent uni cation of the 16 combinations of massless Goldstone b osons that b ecome, SU (3) SU (2) U (1) couplings near 10 GeV as evidence via the Higgs mechanism, the longitudinal comp onents W now have to incorp orate the scenario of sup ersymmetry L 0 and Z of the weak gauge b osons. breaking mediated by new gauge interactions. L 2 prominent collider signals are the mo dest enhance- M : ET C ments in longitudinally-p olarized weak b oson pro- 2 g duction. These are the s-channel color-singlet ET C m (M ) ' m (M ) ' hTTi ; q ET C ` ET C ET C 2 0 M technirho resonances near 1.5{2 TeV: ! ET C T 1 + 0 2 (1) W W and ! W Z .