Reflection symmetry
w
q
mg
F
b
<
b
c
b
>
b
c
BROKEN
Free energy:
F=K+P
= 2sin
2
(
q/2)
(1-
b
cos
2
(
q/2))
Extrema:
dF/d
q =
sin
q (1-
b
cos
q )=0
b
c
=1
(K~P)