5 research outputs found
Constraining pre Big-Bang-Nucleosynthesis Expansion using Cosmic Antiprotons
A host of dark energy models and non-standard cosmologies predict an enhanced
Hubble rate in the early Universe: perfectly viable models, which satisfy Big
Bang Nucleosynthesis (BBN), cosmic microwave background and general relativity
tests, may nevertheless lead to enhancements of the Hubble rate up to many
orders of magnitude. In this paper we show that strong bounds on the pre-BBN
evolution of the Universe may be derived, under the assumption that dark matter
is a thermal relic, by combining the dark matter relic density bound with
constraints coming from the production of cosmic-ray antiprotons by dark matter
annihilation in the Galaxy. The limits we derive can be sizable and apply to
the Hubble rate around the temperature of dark matter decoupling. For dark
matter masses lighter than 100 GeV, the bound on the Hubble-rate enhancement
ranges from a factor of a few to a factor of 30, depending on the actual
cosmological model, while for a mass of 500 GeV the bound falls in the range
50-500. Uncertainties in the derivation of the bounds and situations where the
bounds become looser are discussed. We finally discuss how these limits apply
to some specific realizations of non-standard cosmologies: a scalar-tensor
gravity model, kination models and a Randall-Sundrum D-brane model.Comment: 19 pages, 15 figures, LaTex, uses revtex
Direct versus indirect detection in mSUGRA with self-consistent halo models
We perform a detailed analysis of the detection prospects of neutralino dark
matter in the mSUGRA framework. We focus on models with a thermal relic
density, estimated with high accuracy using the DarkSUSY package, in the range
favored by current precision cosmological measurements. Direct and indirect
detection rates are computed implementing two models for the dark matter halo,
tracing opposite regimes for the phase of baryon infall, with fully consistent
density profiles and velocity distribution functions. This has allowed, for the
first time, a fully consistent comparison between direct and indirect detection
prospects. We discuss all relevant regimes in the mSUGRA parameter space,
underlining relevant effects, and providing the basis for extending the
discussion to alternative frameworks. In general, we find that direct detection
and searches for antideuterons in the cosmic rays seems to be the most
promising ways to search for neutralinos in these scenarios.Comment: 26 pages, 9 figure
Supersymmetric Dark Matter : aspects of sfermion coannihilations
There is very strong evidence that ordinary matter in the Universe is outweighed by almost ten times as much so-called dark matter. Dark matter does neither emit nor absorb light and we do not know what it is. One of the theoretically favoured candidates is a so-called neutralino from the supersymmetric extension of the Standard Model of particle physics. A theoretical calculation of the expected cosmic neutralino density must include the so-called coannihilations. Coannihilations are particle processes in the early Universe with any two supersymmetric particles in the initial state and any two Standard Model particles in the final state. In this thesis we discuss the importance of these processes for the calculation of the relic density. We will go through some details in the calculation of coannihilations with one or two so-called sfermions in the initial state. This includes a discussion of Feynman diagrams with clashing arrows, a calculation of colour factors and a discussion of ghosts in non-Abelian field theory. Supersymmetric models contain a large number of free parameters on which the masses and couplings depend. The requirement, that the predicted density of cosmic neutralinos must agree with the density observed for the unknown dark matter, will constrain the parameters. Other constraints come from experiments which are not related to cosmology. For instance, the supersymmetric loop contribution to the rare b -> sγ decay should agree with the measured branching fraction. The principles of the calculation of the rare decay are discussed in this thesis. Also on-going and planned searches for cosmic neutralinos can constrain the parameters. In one of the accompanying papers in the thesis we compare the detection prospects for several current and future searches for neutralino dark matter