Non-thermal Dark Matter Production Research Articles

Boltzmann equation for non-equilibrium particles and its application to non-thermal dark matter production

We consider a scalar field (called $\phi$) which is very weakly coupled to thermal bath, and study the evolution of its number density. We use the Boltzmann equation derived from the Kadanoff-Baym equations, assuming that the degrees of freedom in the thermal bath are well described as "quasi-particles." When the widths of quasi-particles are negligible, the evolution of the number density of $\phi$ is well governed by a simple Boltzmann equation, which contains production rates and distribution functions both evaluated with dispersion relations of quasi-particles with thermal masses. We pay particular attention to the case that dark matter is non-thermally produced by the decay of particles in thermal bath, to which the above mentioned formalism is applicable. When the effects of thermal bath are properly included, the relic abundance of dark matter may change by $O(10-100%)$ compared to the result without taking account of thermal effects.

Effects ofp-wave annihilation on the angular power spectrum of extragalactic gamma-rays from dark matter annihilation

We present a formalism for estimating the angular power spectrum of extragalactic gamma-rays produced by dark matter annihilating with any general velocity-dependent cross section. The relevant density and velocity distribution of dark matter is modeled as an ensemble of smooth, universal, rigid, disjoint, spherical halos with distribution and universal properties constrained by simulation data. We apply this formalism to theories of dark matter with $p$-wave annihilation, for which the relative-velocity-weighted annihilation cross section is $\ensuremath{\sigma}v=a+b{v}^{2}$. We determine that this significantly increases the gamma-ray power if $b/a\ensuremath{\gtrsim}{10}^{6}$. The effect of $p$-wave annihilation on the angular power spectrum is very similar for the sample of particle physics models we explored, suggesting that the important effect for a given $b/a$ is largely determined by the cosmic dark matter distribution. If the dark matter relic from strong $p$-wave theories is thermally produced, the intensities of annihilation gamma-rays are strongly $p$-wave suppressed, making them difficult to observe. If an angular power spectrum consistent with a strong $p$ wave were to be observed, it would likely indicate nonthermal production of dark matter in the early Universe.

Split supersymmetry and dark matter generation

We analyze a simple Split Supersymmetry scenario where fermion masses come from anomaly mediation, yielding m_s ~ 1000 TeV, m_{3/2} ~ 100 TeV, and m_f ~ 1 TeV. We consider non-thermal dark matter production in the presence of moduli, and we find that the decay chains of moduli to LSPs and moduli to gravitinos to LSPs generate dark matter more efficiently than perturbative freeze-out, allowing for a light, LHC visible spectrum. These decaying moduli can also weaken cosmological constraints on the axion decay constant. With squark masses of order 1000 TeV, LHC gluinos will decay millimeters from their primary vertices, resulting in a striking experimental signature, and the suppression of Flavor Changing Neutral Currents is almost sufficient to allow arbitrary mixing in squark mass matrices.

Nonthermal production of dark matter from a late-decaying scalar field at an intermediate scale

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.