Ref HAL: hal-00377710_v1
Ref Arxiv: 0707.4511
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We reanalyse the gamma-gamma scattering data and conclude that in the massregion below 1 GeV the cross section for gamma-gamma to pi^0-pi^0 can belargely explained by the one pion exchange process with pi-pi rescattering. Theradiative width of the sigma is estimated and a model dependent separation intocontributions from direct gamma-gamma decay and decay through rescattering isobtained. We confront these findings with QCD spectral sum rule (QSSR)predictions and conclude that the sigma can have a large gluonium component inits wave function.

Ref HAL: hal-00288517_v1
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Je parlerai de densité de relique de matière noire dans le modèle supersymétrique non minimal (NMSSM) avec des paramètres semi- universels à l'échelle de grande unification.

Ref HAL: hal-00288516_v1
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I will present the fortran code NMHDECAY which calculates the NMSSM sparticle and Higgs masses and decay widths starting from general (electroweak scale) free parameters, as well as the code NMSPEC which does the same for mSUGRA type (GUT scale) parameters. I will also discuss the link between these programs and the relic density computation program micrOMEGAs.

Ref HAL: hal-00288413_v1
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The epoch of Big Bang nucleosynthesis presents a precision observational test of cosmic conditions at cosmic temperatures below a few MeV. Comparison of theoretically predicted abundances of $^2$H, $^3$He, $^4$He, and $^7$Li with observationally inferred primordial abundances has led to the standard model of Big Bang nucleosythesis (SBBN). In this talk I review the observational determination of light-element abundances, with particular focus on $^7$Li and $^2$H. It is found that predicted $^7$Li production in SBBN is around a factor three higher than the observationally inferred abundance of this isotope. Astrophysical effects, as well as nuclear reaction rate uncertainties, which may or may not explain such a discrepancy are reviewed. Recent observations of $^6$Li abundances in low-metallicity halo stars have revealed a surprisingly high $^6$Li abundance in disaccord with expectations of $^6$Li production by galactic cosmic rays. I review the proposed astrophysical scenarios which may reproduce the data. In the second part of this talk, it is assumed that the $^6$Li and $^7$Li anomalies are signs of physics beyond the standard model of particle physics and BBN. The currently proposed modifications to BBN to account for these anomalies are reviewed. Particularly promising may be the possible existence of supersymmetry with the superpartner of the graviton, the gravitino, being the dark matter. In this case, the decay of either the superpartner of the U(1) hypercharge gauge boson, or the superpartner of the tau-lepton may decay during BBN, thereby solving both problems at once. The resulting cosmology, implications for the LHC, and the physics entering the BBN calculations are highlighted.

Ref HAL: hal-00258401_v1
Ref Arxiv: 0801.4321
DOI: 10.1088/1126-6708/2008/07/002
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60 citations
Résumé:

We discuss constrained and semi--constrained versions of the next--to--minimal supersymmetric extension of the Standard Model (NMSSM) in which a singlet Higgs superfield is added to the two doublet superfields that are present in the minimal extension (MSSM). This leads to a richer Higgs and neutralino spectrum and allows for many interesting phenomena that are not present in the MSSM. In particular, light Higgs particles are still allowed by current constraints and could appear as decay products of the heavier Higgs states, rendering their search rather difficult at the LHC. We propose benchmark scenarios which address the new phenomenological features, consistent with present constraints from colliders and with the dark matter relic density, and with (semi--)universal soft terms at the GUT scale. We present the corresponding spectra for the Higgs particles, their couplings to gauge bosons and fermions and their most important decay branching ratios. A brief survey of the search strategies for these states at the LHC is given.

Ref HAL: in2p3-00252151_v1
Ref Arxiv: 0712.3151
DOI: 10.1103/PhysRevD.77.055014
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6 citations
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We study the complementarity between the indirect detection of dark matter with gamma-rays in H.E.S.S. and the supersymmetry searches with ATLAS at the Large Hadron Collider in the Focus Point region within the mSUGRA framework. The sensitivity of the central telescope of the H.E.S.S. II experiment with an energy threshold of ~ 20 GeV is investigated. We show that the detection of gamma-ray fluxes of O(10^-12) cm-2s-1 with H.E.S.S. II covers a substantial part of the Focus Point region which may be more difficult for LHC experiments. Despite the presence of multi-TeV scalars, we show that LHC will be sensitive to a complementary part of this region through three body NLSP leptonic decays. This interesting complementarity between H.E.S.S. II and LHC searches is further highlighted in terms of the gluino mass and the two lightest neutralino mass difference.

Commentaires: 11 pages, 6 figures, accepted for publication in Phys. Rev. D on February 7, 2008 (slight modifications: references updated and text improved)

Ref HAL: in2p3-00186368_v1
Ref Arxiv: 0711.1067
DOI: 10.1142/S0217751X08039839
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10 citations
Résumé:

We write explicit and self-contained asymptotic expressions for the tensorial B, C and D Passarino-Veltman functions. These include quadratic and linear logarithmic terms, as well as subleading constant terms. Only mass-suppressed O(m^2/s) contributions are neglected. We discuss the usefulness of such expressions, particularly for studying one-loop effects in 2-to-2 body processes at high energy.

Commentaires: 25 pages, 9 eps figures. Soumis Journal of High Energy Physics (JHEP)