Warintorn Sreethawong

Mixed axion/neutralino cold dark matter in supersymmetric models

We consider supersymmetric (SUSY) models wherein the strong CP problem is solved by the Peccei-Quinn (PQ) mechanism with a concommitant axion/axino supermultiplet. We examine R-parity conserving models where the neutralino is the lightest SUSY particle, so that a mixture of neutralinos and axions serve as cold dark matter (a1 CDM). The mixed a1 CDM scenario can match the measured dark matter abundance for SUSY models which typically give too low a value of the usual thermal neutralino abundance, such as models with wino-like or higgsino-like dark matter. The usual thermal neutralino abundance can be greatly enhanced by the decay of thermally-produced axinos (a) to neutralinos, followed by neutralino re-annihilation at temperatures much lower than freeze-out. In this case, the relic density is usually neutralino dominated, and goes as ~ (fa/N)/ma3/2. If axino decay occurs before neutralino freeze-out, then instead the neutralino abundance can be augmented by relic axions to match the measured abundance. Entropy production from late-time axino decays can diminish the axion abundance, but ultimately not the neutralino abundance. In a1 CDM models, it may be possible to detect both a WIMP and an axion as dark matter relics. We also discuss possible modifications of our results due to production and decay of saxions. In the appendices, we present expressions for the Hubble expansion rate and the axion and neutralino relic densities in radiation, matter and decaying-particle dominated universes.

Coupled Boltzmann calculation of mixed axion/neutralino cold dark matter production in the early universe

We calculate the relic abundance of mixed axion/neutralino cold dark matter which arises in R-parity conserving supersymmetric (SUSY) models wherein the strong CP problem is solved by the Peccei-Quinn (PQ) mechanism with a concommitant axion/saxion/axino supermultiplet. By numerically solving the coupled Boltzmann equations, we include the combined effects of 1. thermal axino production with cascade decays to a neutralino LSP, 2. thermal saxion production and production via coherent oscillations along with cascade decays and entropy injection, 3. thermal neutralino production and re-annihilation after both axino and saxion decays, 4. gravitino production and decay and 5. axion production both thermally and via oscillations. For SUSY models with too high a standard neutralino thermal abundance, we find the combined effect of SUSY PQ particles is not enough to lower the neutralino abundance down to its measured value, while at the same time respecting bounds on late-decaying neutral particles from BBN. However, models with a standard neutralino underabundance can now be allowed with either neutralino or axion domination of dark matter, and furthermore, these models can allow the PQ breaking scale fa to be pushed up into the 1014−1015 GeV range, which is where it is typically expected to be in string theory models.

Wh plus missing-ET signature from gaugino pair production at the LHC

In SUSY models with heavy squarks and gaugino mass unification, the gaugino pair production reaction

Same-Sign Diboson Signature from Supersymmetry Models with Light Higgsinos at the LHC

pp\ensuremath{\rightarrow}{\stackrel{\texttildelow{}}{W}}_{1}^{\ifmmode\pm\else\textpm\fi{}}{\stackrel{\texttildelow{}}{Z}}_{2}

Search for the elusive Higgs boson using jet structure at LHC

dominates gluino pair production for

Radiatively-driven natural supersymmetry at the LHC

{m}_{\stackrel{\texttildelow{}}{g}}\ensuremath{\gtrsim}1\text{ }\text{ }\mathrm{TeV}

WZ plus missing-E T signal from gaugino pair production at LHC7

at LHC with

Discriminating electroweak-ino parameter ordering at the LHC and its impact on LFV studies

\sqrt{s}=14\text{ }\text{ }\mathrm{TeV}

Erratum to: Radiatively-driven natural supersymmetry at the LHC

(LHC14). For this mass range, the two-body decays

Testing the gaugino AMSB model at the Tevatron via slepton pair production

{\stackrel{\texttildelow{}}{W}}_{1}\ensuremath{\rightarrow}W{\stackrel{\texttildelow{}}{Z}}_{1}