Abstract
Some variants of the MSSM feature a strip in parameter space where the lightest neutralino χ is identified as the lightest supersymmetric particle (LSP), the gluino $$ \tilde{g} $$ is the next-to-lightest supersymmetric particle (NLSP) and is nearly degenerate with χ, and the relic cold dark matter density is brought into the range allowed by astrophysics and cosmology by coannihilation with the gluino NLSP. We calculate the relic density along this gluino coannihilation strip in the MSSM, including the effects of gluino-gluino bound states and initial-state Sommerfeld enhancement, and taking into account the decoupling of the gluino and LSP densities that occurs for large values of the squark mass $$ {m}_{\tilde{q}} $$ . We find that bound-state effects can increase the maximum m χ for which the relic cold dark matter density lies within the range favoured by astrophysics and cosmology by as much as ∼ 50% if $$ {m}_{\tilde{q}}/{m}_{\tilde{g}}=1.1 $$ , and that the LSP may weigh up to ∼ 8 TeV for a wide range of $$ {m}_{\tilde{q}}/{m}_{\tilde{g}}\lesssim 100 $$ .
Highlights
If R parity is conserved and the lightest supersymmetric particle (LSP) is present in the Universe today as a relic from the Big Bang, it is expected to be electromagnetically neutral and have only weak interactions
Some variants of the minimal supersymmetric extension of the Standard Model (MSSM) feature a strip in parameter space where the lightest neutralino χ is identified as the lightest supersymmetric particle (LSP), the gluino gis the next-to-lightest supersymmetric particle (NLSP) and is nearly degenerate with χ, and the relic cold dark matter density is brought into the range allowed by astrophysics and cosmology by coannihilation with the gluino NLSP
We find that bound-state effects can increase the maximum mχ for which the relic cold dark matter density lies within the range favoured by astrophysics and cosmology by as much as ∼ 50% if mq/mg = 1.1, and that the LSP may weigh up to ∼ 8 TeV for a wide range of mq/mg 100
Summary
Before discussing the formation and effects of gluino-gluino bound states, we first discuss briefly Sommerfeld effects in gluino-gluino annihilation, which may enhance annihilation rates at low velocities, and are relevant in the case of the strongly-interacting gluino. Initial-state interactions modify s-wave cross-sections by factors [31,32,33,34,35]. Where α is the coefficient of a Coulomb-like potential whose sign convention is such that the attractive case has α < 0, and β is the velocity of one of the annihilating particles in the centre-of-mass frame of the collision. Denotes an average over the thermal distributions of the annihilating particles, the coefficient a and b represent the contributions of the s- and p-wave cross-sections, x ≡ m/T , and the dots represent terms of higher order in 1/x. The expressions for the matrix elements for the coannihilation processes are given in detail in appendix B
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