A running spectral index in supersymmetric dark-matter models with quasistable charged particles
We show that charged particles decaying in the early Universe can induce a scale-dependent or running spectral index in the small-scale linear and nonlinear matter power spectrum and discuss examples of this effect in minimal supersymmetric models in which the lightest neutralino is a viable cold-dark-matter candidate. We find configurations in which the neutralino relic density is set by coannihilations with a long-lived stau and the late decay of staus partially suppresses the linear matter power spectrum. Nonlinear evolution on small scales then causes the modified linear power spectrum to evolve to a nonlinear power spectrum similar to (but different in detail) models parametrized by a constant running alphas = dns/dlnk by redshifts of 2 to 4. Thus, Lyman-alpha forest observations, which probe the matter power spectrum at these redshifts, might not discriminate between the two effects. However, a measurement of the angular power spectrum of primordial 21-cm radiation from redshift z[approximate]30–200 might distinguish between this charged-decay model and a primordial running spectral index. The direct production of a long-lived charged particle at future colliders is a dramatic prediction of this model.
Additional Information© 2005 The American Physical Society (Received 29 October 2004; published 20 January 2005) We thank R. R. Caldwell and U. Seljak for useful discussions. S. P. acknowledges fruitful help and elucidations from Y. Mambrini about the SDECAY package. K. S. acknowledges the support of the Canadian NSERC. This work was supported in part by NASA NAG5-9821 and DoE DE-FG03-92-ER40701.
Published - PROprd05.pdf