Michel H. G. Tytgat

The Inert Doublet Model: An Archetype for Dark Matter

The inert doublet model (IDM), a two Higgs extension of the standard model with an unbroken Z2 symmetry, is a simple and yet rich model of dark matter. We present a systematic analysis of the dark matter abundance and investigate the potentialities for direct and gamma indirect detection. We show that the model should be within the range of future experiments, like GLAST and ZEPLIN. The lightest stable scalar in the IDM is a perfect example, or archetype of a weakly interacting massive particle.

Inflation from a tachyon fluid

Motivated by recent works of Sen [hep-th/0203211, hep-th/0203265] and Gibbons [hep-th/0204008], we study the evolution of a flat and homogeneous universe dominated by tachyon matter. In particular, we analyze the necessary conditions for inflation in the early roll of a single tachyon field. Comparison with string theory reveals that the potential is too steep to explain the fluctuations in the CMBR. We suggest a scenario based on the simultaneous decay of many branes and comment on the issue of reheating of the universe after tachyon rolling.

Electroweak symmetry breaking induced by dark matter

Abstract The mechanism behind electroweak symmetry breaking (EWSB) and the nature of dark matter (DM) are currently among the most important issues in high energy physics. Since a natural dark matter candidate is a weakly interacting massive particle or WIMP, with mass around the electroweak scale, it is clearly of interest to investigate the possibility that DM and EWSB are closely related. In the context of a very simple extension of the Standard Model, the inert doublet model, we show that dark matter could play a crucial role in the breaking of the electroweak symmetry. In this model, dark matter is the lightest component of an inert scalar doublet. The coupling of the latter with the Standard Model Higgs doublet breaks the electroweak symmetry at one-loop, a la Coleman–Weinberg . The abundance of dark matter, the breaking of the electroweak symmetry and the constraints from electroweak precision measurements can all be accommodated by imposing (an exact or approximate) custodial symmetry.

WIMP dark matter, Higgs exchange and DAMA

In the WIMP scenario, there is a one-to-one relation between the dark matter (DM) relic density and spin-independent direct detection rate if both the annihilation of DM and its elastic scattering on nuclei go dominantly through Higgs exchange. In particular, for DM masses much smaller than the Higgs boson mass, the ratio of the relevant cross sections depends only on the DM mass. Assuming DM mass and direct detection rate within the ranges allowed by the recent DAMA collaboration results—taking account of the channelling effect on energy threshold and the null results of the other direct detection experiments—gives a definite range for the relic density. For scalar DM models, like the Higgs portal models or the inert doublet model, the relic density range turns out to be in agreement with WMAP. This scenario implies that the Higgs boson has a large branching ratio to pairs of DM particles, a prediction which might challenge its search at the LHC.

Light scalar WIMP through the Higgs portal and CoGeNT

If dark matter (DM) simply consists in a scalar particle interacting dominantly with the Higgs boson, the ratio of its annihilation cross section---which is relevant both for the relic abundance and indirect detection---and its spin-independent scattering cross section on nuclei depends only on the DM mass. It is an intriguing result that, fixing the mass and direct detection rate to fit the annual modulation observed by the DAMA experiment, one obtains a relic density in perfect agreement with its observed value. In this article we update this result and confront the model to the recent CoGeNT data, tentatively interpreting the excess of events in the recoil energy spectrum as being due to DM. CoGeNT, as DAMA, points toward a light DM candidate, with somewhat different (but not necessarily incompatible) masses and cross sections. For the CoGeNT region too, we find an intriguing agreement between the scalar DM relic density and direct detection constraints. We give the

Phenomenological evidence for the gluon content of η and η

1\ensuremath{\sigma}

Invisible Z ′ and dark matter: LHC vs LUX constraints

region favored by the CDMS-II events, and our exclusion limits for the Xenon10 (2009) and Xenon100 data, which, depending on the scintillation efficiency, may exclude CoGeNT and DAMA. Assuming CoGeNT and/or DAMA to be due to scalar singlet DM leads to definite predictions regarding indirect detection and at colliders. We specifically emphasize the limit on the model that might be set by the current Fermi-LAT data on dwarf galaxies, and the implications for the search for the Higgs at the LHC.

Confined hidden vector dark matter

We discuss the effect of η-η′ mixing and of axial current anomalies on various decay processes. We describe the 2γ decays of η and η′, the radiative decays of low-lying vector mesons as well as the decays η → 3π, Jψ → ηγ and Jψ → η′γ in one unified framework, in which they are related to the electromagnetic and strong axial current anomalies, respectively. We also discuss briefly the enhancement of η′ in Ds decays and suggest a possible relation to gluon-mediated processes. The importance of the decays of the glueball candidates f0(1500) and f0(1590) into ηη′ channels is also stressed.

IDM & iDM or the inert doublet model and inelastic dark matter

A bstractWe consider a simple, yet generic scenario in which a new heavy Z′ gauge boson couples both to SM fermions and to dark matter. In this framework we confront the best LHC limits on an extra gauge boson Z′ to the constraints on couplings to dark matter from direct detection experiments. In particular we show that the LHC searches for resonant production of dileptons and the recent exclusion limits obtained by the LUX collaboration give complementary constraints. Together, they impose strong bounds on the invisible branching ratio and exclude a large part of the parameter space for generic Z′ models. Our study encompasses many possible Z′ models, including SSM, E6-inspired or B-L scenario.

Are leptogenesis and dark matter related

Abstract We argue that the lightest vector bound states of a confining hidden sector communicating with the Standard Model through the Higgs portal are stable and are viable candidates of dark matter. The model is based on an SU ( 2 ) gauge group with a scalar field in its fundamental representation and the stability of the lightest vector bound state results from the existence of a custodial symmetry. As the relic density depends essentially on the scale of confinement in the hidden sector, Λ HS , agreement with WMAP abundance requires Λ HS in the 20–120 TeV range.