matter particle is such a relic particle, the interaction cross section governing the particle-antiparticle annihilation can be no larger than the cross section for the weak interaction. If this model is correct, the dark matter particle would have the properties of the WIMP. Indirect detection Because WIMPs may only interact through gravitational and weak forces, they are extremely difficult to detect. However, there are many experiments underway to attempt to detect WIMPs both directly and indirectly. Indirect detection refers to the observation of annihilation or decay products of WIMPs far away from Earth. Indirect detection efforts typically focus on locations where WIMP dark matter is thought to accumulate the most: in the centers of galaxies and galaxy clusters, as well as in the smaller satellite galaxies of the Milky Way. These are particularly useful since they tend to contain very little baryonic matter, reducing the expected background from standard astrophysical processes. Typical indirect searches look for excess gamma rays, which are predicted both as final-state products of annihilation, or are produced as charged particles interact with ambient radiation via inverse Compton scattering. The spectrum and intensity of a gamma ray signal depends on the annihilation products, and must be computed on a model-by-model basis. Experiments that have placed bounds on WIMP annihilation, via the non-observation of an annihilation signal, include the Fermi-LAT gamma ray telescope and the VERITAS ground-based gamma ray observatory. Although the annihilation of WIMPs into Standard Model particles also predicts the production of high-energy neutrinos, their interaction rate is too low to reliably detect a dark matter signal at present. Future observations from the IceCube observatory in Antarctica may be able to differentiate WIMP-produced neutrinos from standard astrophysical neutrinos; however, by 2014, only 37 cosmological neutrinos had been observed, making such a distinction impossible. Another type of indirect WIMP signal could come from the Sun. Halo WIMPs may, as they pass through the Sun, interact with solar protons, helium nuclei as well as heavier elements. If a WIMP loses enough energy in such an interaction to fall below the local escape velocity, it would not have enough energy to escape the gravitational pull of the Sun and would remain gravitationally bound. As more and more WIMPs thermalize inside the Sun, they begin to annihilate with each other, forming a variety of particles, including high-energy neutrinos. These neutrinos may then travel to the Earth to be detected in