The axino, the fermionic superpartner of the axion, is a well-motivated candidate for cold dark matter if it is the lightest supersymmetric particle. Since the axino couples very weakly to the matter multiplets, the next-to-lightest supersymmetric particle (NLSP) has a long lifetime, which has important consequences for both cosmology and collider phenomenology. Assuming that a charged slepton is the NLSP, we calculate the complete leading one-and two-loop contributions to its decay. We analyze in detail constraints on the parameters space from cosmology and discuss how this scenario can be probed at colliders. Scenarios in which both the axino and the gravitino are lighter than the long-lived charged slepton are also explored with particular emphasis on cosmological constraints and collider phenomenology.

Considering axino cold dark matter scenarios with a long-lived charged slepton, we study constraints on the Peccei-Quinn scale fa and on the reheating temperature TR imposed by the dark matter density and by big bang nucleosynthesis (BBN). For an axino mass compatible with largescale structure, m e a 100 keV, temperatures above 10 9 GeV become viable for fa > 3 × 10 12 GeV. We calculate the slepton lifetime in hadronic axion models. With the dominant decay mode being two-loop suppressed, this lifetime can be sufficiently large to allow for primordial bound states leading to catalyzed BBN of lithium-6 and beryllium-9. This implies new upper limits on fa and on TR that depend on quantities which will be probed at the Large Hadron Collider.PACS numbers: 98.80. Cq, 95.35.+d, 12.60.Jv, 95.30.Cq

Taking into account effects of late energy injection, we examine big bang nucleosynthesis (BBN) constraints on axino dark matter scenarios with long-lived charged sleptons. We calculate 4-body slepton decays into the axino, a lepton, and a quark-antiquark pair since they govern late hadronic energy injection and associated BBN constraints. For supersymmetric hadronic axion models, we present the obtained hadronic BBN constraints and show that they can be more restrictive than the ones associated with catalyzed BBN via slepton-bound-state formation. From the BBN constraints on hadronic and electromagnetic energy release, we find new upper limits on the Peccei-Quinn scale.PACS numbers: 98.80. Cq, 95.35.+d, 12.60.Jv, 95.30.Cq

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