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Non-thermal Production of Dark Matter from Late-Decaying Scalar Field at Intermediate Scale

Motoi Endo, Fuminobu Takahashi

TL;DR

This work tackles non-thermal dark matter production from late-decaying scalars by highlighting D=5 operators that mediate decays into SM particles and their superpartners. It demonstrates that decays into SM particles and SM superpartners are generically comparable, which can lead to excessive gravitino production if the decay proceeds through Planck-suppressed modulus-like couplings. By invoking an intermediate-scale cutoff with saxion decays, the model boosts the decay rate and suppresses gravitino production, enabling the right relic abundance for wino/higgsino DM (m_χ ∼ 100–300 GeV) with an axion decay constant F_A ∼ 10^9–10^12 GeV. The saxion scenario thus provides a natural, robust alternative to modulus decay, linking axion physics with non-thermal DM and avoiding BBN- and gravitino-related cosmological constraints.

Abstract

We examine non-thermal dark matter production from a late-decaying scalar field, with a particular attention on non-renormalizable operators of D=5 through which the scalar field decays into the standard model particles and their superpartners. We show that almost the same number of superparticles as that of particles are generally produced from the decay. To avoid the gravitino overproduction problem, the decay is favored to proceed via interactions with an intermediate cut-off scale M << M_P. This should be contrasted to the conventional scenario using the modulus decay. The bosonic supersymmetry partner of the axion, i.e., saxion, is proposed as a natural candidate for such late-decaying scalar fields. We find that a right amount of the wino/higgsino dark matter with a mass of O(100) GeV is obtained for the saxion mass around the weak scale and axion decay constant, F_A = O(10^{9-12}) GeV.

Non-thermal Production of Dark Matter from Late-Decaying Scalar Field at Intermediate Scale

TL;DR

This work tackles non-thermal dark matter production from late-decaying scalars by highlighting D=5 operators that mediate decays into SM particles and their superpartners. It demonstrates that decays into SM particles and SM superpartners are generically comparable, which can lead to excessive gravitino production if the decay proceeds through Planck-suppressed modulus-like couplings. By invoking an intermediate-scale cutoff with saxion decays, the model boosts the decay rate and suppresses gravitino production, enabling the right relic abundance for wino/higgsino DM (m_χ ∼ 100–300 GeV) with an axion decay constant F_A ∼ 10^9–10^12 GeV. The saxion scenario thus provides a natural, robust alternative to modulus decay, linking axion physics with non-thermal DM and avoiding BBN- and gravitino-related cosmological constraints.

Abstract

We examine non-thermal dark matter production from a late-decaying scalar field, with a particular attention on non-renormalizable operators of D=5 through which the scalar field decays into the standard model particles and their superpartners. We show that almost the same number of superparticles as that of particles are generally produced from the decay. To avoid the gravitino overproduction problem, the decay is favored to proceed via interactions with an intermediate cut-off scale M << M_P. This should be contrasted to the conventional scenario using the modulus decay. The bosonic supersymmetry partner of the axion, i.e., saxion, is proposed as a natural candidate for such late-decaying scalar fields. We find that a right amount of the wino/higgsino dark matter with a mass of O(100) GeV is obtained for the saxion mass around the weak scale and axion decay constant, F_A = O(10^{9-12}) GeV.

Paper Structure

This paper contains 5 sections, 38 equations, 1 figure.

Table of Contents

  1. Introduction
  2. Heavy Scalar Decay via $D=5$ Operators
  3. Difficulties in Modulus Decay
  4. Dark Matter from Saxion Decay
  5. Conclusions and Discussion

Figures (1)

  • Figure 1: Contours of the wino LSP abundance, $\Omega_\chi h^2 = 0.3,\,0.1,\,0.03,\,0.01$, for $m_\chi = 300$ GeV. The shaded regions are excluded; the LSPs are only thermally produced and therefore too small relic density for $m_\sigma < 2 m_\chi$; the upper left triangle region is excluded since the saxion decays after the BBN starts, i.e., $T_d < 5$MeV, while the lower right one corresponds to the decay temperature higher than the decoupling temperature of the wino, i.e., $T_d > m_\chi/20$; $\Omega_\chi h^2 > 0.13$ is from the LSP overproduction in the light of WMAP; $F_{\cal A}<10^9$ GeV from the SN bound. Also the region above the dashed line is disfavored by the axion overclosure limit if no entropy production occurs after the QCD phase transition.