–1–
DYNAMICAL ELECTROWEAK SYMMETRY
BREAKING
Revised August 2009 by R.S. Chivukula (Michigan State Uni
versity), M. Narain (Brown University), and J. Womersley
(STFC, Rutherford Appleton Laboratory).
In theories of dynamical electroweak symmetry breaking,
the electroweak interactions are broken to electromagnetism
by the vacuum expectation value of a fermion bilinear. These
theories may thereby avoid the introduction of fundamental
scalar particles, of which we have no examples in nature. In
this note, we review the status of experimental searches for the
particles predicted in technicolor, topcolor, and related models.
The limits from these searches are summarized in Table 1.
I. Technicolor
The earliest models [1,2] of dynamical electroweak symme
try breaking [3] include a new asymptotically free nonabelian
gauge theory (“technicolor”) and additional massless fermions
(“technifermions” transforming under a vectorial representation
of the gauge group) which feel this new force. The global chiral
symmetry of the fermions is spontaneously broken by the for
mation of a technifermion condensate, just as the approximate
chiral SU(2)
×
SU
(2) symmetry in QCD is broken down to SU(2)
isospin by the formation of a quark condensate. If the quantum
numbers of the technifermions are chosen correctly (
e.g.
,b
y
choosing technifermions in the fundamental representation of
an SU(
N
) technicolor gauge group, with the lefthanded tech
nifermions being weak doublets and the righthanded ones weak
singlets), this condensate can break the electroweak interactions
down to electromagnetism.
The breaking of the global chiral symmetries implies the
existence of Goldstone bosons, the “technipions” (
π
T
). Through
the Higgs mechanism, three of the Goldstone bosons become
the longitudinal components of the
W
and
Z
,andth
ew
e
ak
gauge bosons acquire a mass proportional to the technipion
decay constant (the analog of
f
π
in QCD). The quantum
numbers and masses of any remaining technipions are model
dependent. There may be technipions which are colored (octets
and triplets), as well as those carrying electroweak quantum
CITATION: K. Nakamura
et al.
(Particle Data Group), JPG
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document–2–
Table 1:
Summary of the mass limits. Sym
bols are deFned in the text.
Process
Excluded mass range
Decay channels Ref.
p
p
→
ρ
T
→
Wπ
T
170
<m
ρ
T
<
215 GeV
ρ
T
→
Wπ
T
[19]
and 80
<m
π
T
<
115 GeV
π
0
T
→
b
b
for
M
V
= 500 GeV
π
±
T
→
b
c
p
p
→
ω
T
→
γπ
T
140
<m
ω
T
<
290 GeV
ω
T
→
γπ
T
[20]
for
m
π
T
≈
m
ω
T
/
3
π
0
T
→
b
b
and
M
T
= 100 GeV
π
±
T
→
b
c
p
p
→
ω
T
/ρ
T
m
ω
T
=
m
ρ
T
<
203 GeV
ω
T
/ρ
T
→
±
+
±
−
[21]
for
m
ω
T
<m
π
T
+
m
W
or
M
T
>
200 GeV
m
ω
T
=
m
ρ
T
<
280 GeV
ω
T
/ρ
T
→
±
+
±
−
[22]
for
m
ω
T
<m
π
T
+
m
W
or
M
T
>
500 GeV
e
+
e
−
→
ω
T
/ρ
T
90
<m
ρ
T
<
206
.
7GeV
ρ
T
→
WW
,
[23]
m
π
T
<
79
.
8GeV
Wπ
T
,π
This is the end of the preview.
Sign up
to
access the rest of the document.
 Spring '11
 Kutter
 Higgs boson, GeV

Click to edit the document details