Effective interactions of axion supermultiplet and thermal production of axino dark matter

TL;DR

This paper analyzes the effective interactions of the axion supermultiplet, emphasizing the importance of correctly distinguishing related quantities for accurate thermal axino production calculations in supersymmetric models.

Contribution

It clarifies the differences between key quantities affecting axino production and evaluates the relic axino density considering these effects in DFSZ and KSVZ models.

Findings

Axino production at T > M_Φ is dominated by matter supermultiplet interactions.

The axino production rate is significantly reduced if M_Φ << v_PQ.

Relic axino density calculations are revised to include suppression effects.

Abstract

We discuss the effective interactions of axion supermultiplet, which might be important for analyzing the cosmological aspect of supersymmetric axion model. Related to axino cosmology, it is stressed that three seemingly similar but basically different quantities, the Wilsonian axino-gluino-gluon coupling, the 1PI axino-gluino-gluon amplitude, and the PQ anomaly coefficient, should be carefully distinguished from each other for correct analysis of the thermal production of axinos in the early Universe. It is then noticed that the 1PI axino-gluino-gluon amplitude at energy scale p in the range M_\Phi < p < v_{PQ} is suppressed by (M_\Phi ^2)/(p^2) in addition to the well-known suppression by p/(16\pi^2 v_{PQ}), where M_\Phi is the mass of the heaviest PQ-charged and gauge-charged matter supermultiplet in the model, which can be well below the PQ scale v_{PQ}. As a result, axino production at temperature T>M_\Phi is dominated by the production by matter supermultiplet, not by the production by gauge supermultiplet. Still the axino production rate is greatly reduced if M_\Phi << v_{PQ}, which would make the subsequent cosmology significantly altered. This would be most notable in the supersymmetric DFSZ model in which M_\Phi corresponds to the Higgsino mass which is around the weak scale, however a similar reduction is possible in the KSVZ model also. We evaluate the relic axino density for both the DFSZ and KSVZ models while including the axino production in the processes involving the heaviest PQ-charged and gauge-charged matter supermultiplet.