Detection of dark matter
189
x
x
x
x
q
q
q
q
(b)
q
x~x
IH,h
q~q
Figure 6.3. Lowest-order Feynman diagrams for neutralino--quark elastic scattering: (a)
and (b) contribute to the spin-dependent amplitude; (b) and (c) contribute to the scalar
amplitude.
and for the spin-dependent cross section. as D.
2 x 10- 7 pb ~ aSD ~ 10- 5 pb
(6.63)
If the g - 2 constraint is dropped and IL < 0 is tolerated. then there is no lower
limit on aSI. In general. it is found that aSI is relatively large in the bulk region
but falls off in the co-annihilation tail. There is strong cancellation in aSI when
IL < O.
6.6.2 WIMP annihilation in the sun or earth
If the galactic halo is composed of neutralino WIMPs, the WIMPs have a small
probability of elastic scattering with the sun and/or the earth. The WIMPs that
scatter to a velocity smaller than the escape velocity become gravitationally bound
to that body 1 • Once captured. the WIMPs undergo further scattering from the
elements of that body and settle to the core in a relatively short time period.
Thus. the sun and earth are like (inefficient) cosmological vacuum cleaners.
constantly sucking in WIMPs that are then stored in their cores. WIMPs that
have accumulated in this way can annihilate. essentially at rest, to produce
standard model particles most of whose decay products are absorbed without
any observable consequences. However. some of the decay products include
energetic muonic neutrinos (v". v,,) that can pass through the sun and earth and
1 For the sun, the escape velocity at the centre is Vc = 1354 km s-I and at the surface Vs
795 kms- 1 ; for the earth Vc = 14.8 kms- I , V$ = 11.2 kms- I .
189
x
x
x
x
q
q
q
q
(b)
q
x~x
IH,h
q~q
Figure 6.3. Lowest-order Feynman diagrams for neutralino--quark elastic scattering: (a)
and (b) contribute to the spin-dependent amplitude; (b) and (c) contribute to the scalar
amplitude.
and for the spin-dependent cross section. as D.
2 x 10- 7 pb ~ aSD ~ 10- 5 pb
(6.63)
If the g - 2 constraint is dropped and IL < 0 is tolerated. then there is no lower
limit on aSI. In general. it is found that aSI is relatively large in the bulk region
but falls off in the co-annihilation tail. There is strong cancellation in aSI when
IL < O.
6.6.2 WIMP annihilation in the sun or earth
If the galactic halo is composed of neutralino WIMPs, the WIMPs have a small
probability of elastic scattering with the sun and/or the earth. The WIMPs that
scatter to a velocity smaller than the escape velocity become gravitationally bound
to that body 1 • Once captured. the WIMPs undergo further scattering from the
elements of that body and settle to the core in a relatively short time period.
Thus. the sun and earth are like (inefficient) cosmological vacuum cleaners.
constantly sucking in WIMPs that are then stored in their cores. WIMPs that
have accumulated in this way can annihilate. essentially at rest, to produce
standard model particles most of whose decay products are absorbed without
any observable consequences. However. some of the decay products include
energetic muonic neutrinos (v". v,,) that can pass through the sun and earth and
1 For the sun, the escape velocity at the centre is Vc = 1354 km s-I and at the surface Vs
795 kms- 1 ; for the earth Vc = 14.8 kms- I , V$ = 11.2 kms- I .