CBBN in the CMSSM

Catalyzed big bang nucleosynthesis (CBBN) can lead to an overproduction of ^6Li in gravitino dark matter scenarios in which the lighter stau is the lightest Standard Model superpartner. Based on a treatment using the state-of-the-art result for the catalyzed ^6Li production cross section, we update the resulting constraint within the framework of the constrained minimal supersymmetric Standard Model (CMSSM). We confront our numerical findings with recently derived conservative limits on the gaugino mass parameter and the reheating temperature.Comment: 4 pages, 4 figures; Submitted for the SUSY07 proceeding

Axinos in Cosmology and at Colliders

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.Comment: 64 pages, 22 figure

Supersymmetric Dark Matter Candidates - The Lightest Neutralino, the Gravitino, and the Axino

In supersymmetric extensions of the Standard Model, the lightest neutralino, the gravitino, and the axino can appear as the lightest supersymmetric particle and as such provide a compelling explanation of the non-baryonic dark matter in our Universe. For each of these dark matter candidates, I review the present status of primordial production mechanisms, cosmological constraints, and prospects of experimental identification.Comment: 13 pages, 8 figures; Submitted for the SUSY07 proceedings; revised version (comments and references added, typos corrected

Bremsstrahlung out of the Quark-Gluon Plasma

A systematic investigation of hard thermal photon spectra from central ultra­relativistic heavy ion collisions is presented with emphasis on the effects of bremsstrahlung processes in the quark­gluon plasma (QGP). Bremsstrahlung photon production in the quark­gluon plasma has recently been considered within the Braaten­Pisarski method in thermal QCD, where rates have been found that exhibit the same order in the coupling constants as those describing the lowest order processes, Compton scattering and q¯q­annihilation. The im­ pact of these bremsstrahlung photon production rates on the thermal photon spectra is studied systematically within a simple, well understood one­fluid hydrodynamical model that describes an only longitudinally expanding fireball (1+1 Bjorken scaling hydrody­ namics). A first­order phase transition is implemented in which QGP (simulated by an ideal massless parton gas of two­flavors) \u27hadronizes\u27 according to the Gibbs criteria and Maxwell construction into a hot hadronic gas (HHG) (simulated by an ideal massless pion gas). It is found that the bremsstrahlung processes enhance the thermal photon yield from the QGP by about one order of magnitude over the complete considered p ­range independent of the choice of the model parameters. This results in an enhancement of the total thermal photon yield which is most significant for parameter sets that support a highly contributing QGP phase. The influence of each model parameter on the thermal photon spectra is examined carefully and a thorough understanding of the model is ob­ tained. Experimental upper limits on direct photon production in fixed target 200 A.GeV S + Au collisions at the CERN SPS are also considered and used to extract upper limits for the initial temperature of the QGP, where the QGP bremsstrahlung processes are found to make a difference of about 15 to 20 MeV depending on the temperature at which the phase transition is assumed. In comparison with other theoretical studies, the impor­ tance of reaction features not described in the simple model are estimated and interesting elements for a future extension of this systematic investigation are identified, which will be of great interest in prospect of the upcoming experiments at the BNL RHIC and the CERN LHC

Dark Matter Candidates - Axions, Neutralinos, Gravitinos, and Axinos

The existence of dark matter provides strong evidence for physics beyond the Standard Model. Extending the Standard Model with the Peccei-Quinn symmetry and/or supersymmetry, compelling dark matter candidates appear. For the axion, the neutralino, the gravitino, and the axino, I review primordial production mechanisms, cosmological and astrophysical constraints, experimental searches, and prospects for experimental identification.Comment: 31 pages, 14 figure