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Register a new userAxino abundances in high-scale supersymmetry
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We consider the thermal production of axino dark matter in high-scale supersymmetry where all the superpartners except the axino are heavier than the maximum and reheating temperatures. In this case, the axinos are produced dominantly in pairs from the scattering of SM particles in thermal plasma in the early Universe after inflation. We find that the thermal averaged scattering cross section for the axino pair production is given by $langlesigma vrangle propto T^4$ in Kim-Shifman-Vainstein-Zakharov (KSVZ) axion model, while it does not depend on the temperature in Dine-Fischler-Srednicki-Zhitnitski (DFSZ) axion model. As a result, the axinos produced during the early matter domination is diluted by the entropy production, so the axino abundance is determined mainly by the reheating temperature, unlike the case with gravitino dark matter. We show that the axino pair production in DFSZ model opens up new parameter space for axino dark matter, due to non-decoupled Higgsino interactions at tree level.
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In hybrid inflation, the inflaton generically has a tadpole due to gravitational effects in supergravity, which significantly changes the inflaton dynamics in high-scale supersymmetry. We point out that the tadpole can be cancelled if there is a supersymmetry breaking singlet with gravitational couplings, and in particular, the cancellation is automatic in no-scale supergravity. We consider the LARGE volume scenario as a concrete example and discuss the compatibility between the hybrid inflation and the moduli stabilization. We also point out that the dark radiation generated by the overall volume modulus decay naturally relaxes a tension between the observed spectral index and the prediction of the hybrid inflation.
No-scale supergravity provides a successful framework for Starobinsky-like inflation models. Two classes of models can be distinguished depending on the identification of the inflaton with the volume modulus, $T$ (C-models), or a matter-like field, $phi$ (WZ-models). When supersymmetry is broken, the inflationary potential may be perturbed, placing restrictions on the form and scale of the supersymmetry breaking sector. We consider both types of inflationary models in the context of high-scale supersymmetry. We further distinguish between models in which the gravitino mass is below and above the inflationary scale. We examine the mass spectra of the inflationary sector. We also consider in detail mechanisms for leptogenesis for each model when a right-handed neutrino sector, used in the seesaw mechanism to generate neutrino masses, is employed. In the case of C-models, reheating occurs via inflaton decay to two Higgs bosons. However, there is a direct decay channel to the lightest right-handed neutrino which leads to non-thermal leptogenesis. In the case of WZ-models, in order to achieve reheating, we associate the matter-like inflaton with one of the right-handed sneutrinos whose decay to the lightest right handed neutrino simultaneously reheats the Universe and generates the baryon asymmetry through leptogenesis.
We revisit the limits on $R$-parity violation in the minimal supersymmetric standard model. In particular, we focus on the high-scale supersymmetry scenario in which all the sparticles are in excess of the inflationary scale of approximately $10^{13}$ GeV, and thus no sparticles ever come into thermal equilibrium. In this case the cosmological limits, stemming from the preservation of the baryon asymmetry that have been previously applied for weak scale supersymmetry, are now relaxed. We argue that even when sparticles are never in equilibrium, $R$-parity violation is still constrained via higher dimensional operators by neutrino and nucleon experiments and/or insisting on the preservation of a non-zero $B-L$ asymmetry.
We examine axino dark matter in the regime of a low reheating temperature T_R after inflation and taking into account that reheating is a non-instantaneous process. This can have a significant effect on the dark matter abundance, mainly due to entropy production in inflaton decays. We study both thermal and non-thermal production of axinos in the context of the MSSM with ten free parameters. We identify the ranges of the axino mass and the reheating temperature allowed by the LHC and other particle physics data in different models of axino interactions. We confront these limits with cosmological constraints coming the observed dark matter density, large structures formation and big bang nucleosynthesis. We find a number of differences in the phenomenologically acceptable values of the axino mass and the reheating temperature relative to previous studies. In particular, an upper bound on the axino mass becomes dependent on T_R, reaching a maximum value at T_R~10^2 GeV. If the lightest ordinary supersymmetric particle is a wino or a higgsino, we obtain lower a limit of approximately 10 GeV for the reheating temperature. We demonstrate also that entropy production during reheating affects the maximum allowed axino mass and lowest values of the reheating temperature.
Various theoretical and experimental considerations motivate models with high scale supersymmetry breaking. While such models may be difficult to test in colliders, we propose looking for signatures at much lower energies. We show that a keV line in the X-ray spectrum of galaxy clusters (such as the recently disputed 3.5 keV observation) can have its origin in a universal string axion coupled to a hidden supersymmetry breaking sector. A linear combination of the string axion and an additional axion in the hidden sector remains light, obtaining a mass of order 10 keV through supersymmetry breaking dynamics. In order to explain the X-ray line, the scale of supersymmetry breaking must be about $10^{11-12}$ GeV. This motivates high scale supersymmetry as in pure gravity mediation or minimal split supersymmetry and is consistent with all current limits. Since the axion mass is controlled by a dynamical mass scale, this mass can be much higher during inflation, avoiding isocurvature (and domain wall) problems associated with high scale inflation. In an appendix we present a mechanism for dilaton stabilization that additionally leads to $mathcal{O}(1)$ modifications of the gaugino mass from anomaly mediation.
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