Search

At tree-level Higgs production in association with a b-quark pair proceeds through the small Yukawa bottom coupling in the Standard Model. Even in the limit where this coupling vanishes, electroweak one-loop effects, through the top-Higgs Yukawa coupling in particular, can still trigger this reaction. This contribution is small for Higgs masses around 120GeV but it quickly picks up for higher Higgs masses especially because the one-loop amplitude develops a leading Landau singularity and new thresholds open up. These effects can be viewed as the production of a pair of top quarks which rescatter to give rise to Higgs production through WW fusion. We study the leading Landau singularity in detail. Since this singularity is not integrable when the one-loop amplitude is squared, we regulate the cross section by taking into account the width of the internal top and W particles. This requires that we extend the usual box one-loop function to the case of imaginary masses. We show how this can be implemented analytically in our case. We study in some detail the cross section at the LHC as a function of the Higgs mass and show how some distributions can be drastically affected compared to the tree-level result., Comment: 48 pages, 20 figures. Phys.Rev.D accepted version. Conclusions unchanged, minor changes and references added

Despite several indirect confirmations of the existence of dark matter, the properties of a new dark matter particle are still largely unknown. Several experiments are currently searching for this particle underground in direct detection, in space and on earth in indirect detection and at the LHC. A confirmed signal could select a model for dark matter among the many extensions of the standard model. In this paper we present a short review of the public codes for computation of dark matter observables., Comment: 10 pages, 2 figures, to appear in the Proceedings of 13th International Workshop on Advanced Computing and Analysis Techniques in Physics Research, February 2010, Jaipur, India

20 pages, 4 figures, Chapter 16 of the book "Particle Dark Matter: Observations, Models and Searches" edited by G. Bertone, Cambridge University Press, http://cambridge.org/us/catalogue/catalogue.asp?isbn=9780521763684; With present and upcoming SUSY searches both directly, indirectly and at accelerators, the need for accurate calculations is large. We will here go through some of the tools available both from a dark matter point of view and at accelerators. For natural reasons, we will focus on public tools, even though there are some rather sophisticated private tools as well.

These lecture notes describe the micrOMEGAs code for the calculation of Dark Matter observables in extensions of the standard model., Comment: Proceedings of TASI Summer School, Boulder, Colorado, June 2011

We show that current Higgs data permit a significantly enhanced Higgs coupling to charm pairs, comparable to the Higgs to bottom pairs coupling in the Standard Model, without resorting to additional new physics sources in Higgs production. With a mild level of the latter current data even allow for the Higgs to charm pairs to be the dominant decay channel. An immediate consequence of such a large charm coupling is a significant reduction of the Higgs signal strengths into the known final states as in particular into bottom pairs. This might reduce the visible vector-boson associated Higgs production rate to a level that could compromise the prospects of ever observing it. We however demonstrate that a significant fraction of this reduced signal can be recovered by jet-flavor-tagging targeted towards charm-flavored jets. Finally we argue that an enhanced Higgs to charm pairs coupling can be obtained in various new physics scenarios in the presence of only a mild accidental cancellation between various contributions., 8 pages, 3 figures

International audience; The BMSSM framework is an effective theory approach that encapsulates avariety of extensions beyond the MSSM with which it shares the same fieldcontent. The lightest Higgs mass can be much heavier than in the MSSM withoutcreating a tension with naturalness or requiring superheavy stops. Thephenomenology of the Higgs sector is at the same time much richer. Wecritically review the properties of a Higgs with mass around 125GeV in thismodel. In particular, we investigate how the rates in the important inclusive 2photons channel, the 2 photons + 2 jets and the ZZ to 4 leptons (and/or WW) canbe enhanced or reduced compared to the standard model and what kind ofcorrelations between these rates are possible. We consider both a vanilla modelwhere stops have moderate masses and do not mix and a model with large mixingand a light stop. We show that in both cases there are scenarios that lead toenhancements in these rates at a mass of 125GeV corresponding either to thelightest Higgs or the heaviest CP-even Higgs of the model. In all of thesescenarios we study the prospects of finding other signatures either of the125GeV Higgs or those of the heavier Higgses. In most cases the $\oo{\tau}\tau$channels are the most promising. Exclusion limits from the recent LHC Higgssearches are folded in our analyses while the tantalising hints for a Higgssignal at 125GeV are used as an example of how to constrain the BMSSM and/ordirect future searches.

International audience; The extracted value of the relic density has reached the few per-cent level precision. One can therefore no longer content oneself with calculations of this observable where the annihilation processes are computed at tree-level, especially in supersymmetry where radiative corrections are usually large. Implementing full one-loop corrections to all annihilation processes that would be needed in a scan over parameters is a daunting task. On the other hand one may ask whether the bulk of the corrections are taken into account through effective couplings of the neutralino that improve the tree-level calculation and would be easy to implement. We address this issue by concentrating in this first study on the neutralino coupling to i) fermions and sfermions and ii) Z. After constructing the effective couplings we compare their efficiency compared to the full one-loop calculation and comment on the failures and success of the approach. As a bonus we point out that large non decoupling effects of heavy sfermions could in principle be measured in the annihilation process, a point of interest in view of the latest limit on the squark masses from the LHC. We also comment on the scheme dependencies of the one-loop corrected results.

We calculate the one-loop electroweak corrections to e+e- to WWZ and e+e- toZZZ and analyse their impacts on both the total cross section and some keydistributions. These processes are important for the measurements of thequartic couplings of the massive gauge bosons which can be a window on themechanism of spontaneous symmetry breaking. We find that even after subtractingthe leading QED corrections, the electroweak corrections can still be largeespecially as the energy increases. We compare and implement different methodsof dealing with potential instabilities in the routines pertaining to the loopintegrals. For the real corrections we apply a dipole subtraction formalism andcompare it to a phase-space slicing method.

We calculate the full one-loop electroweak corrections to tri-boson production (ZZZ and WWZ) at the ILC. This is important to understand the Standard Model (SM) gauge quartic couplings which can be a window on the mechanism of spontaneous symmetry breaking. We find that even after subtracting the leading QED corrections, the electroweak corrections can still be large especially as the energy increases., Comment: 7 pages, proceedings of the 3rd CPP Workshop, September 23-25, 2010, KEK Tsukuba Japan

We give an extensive description of the renormalisation of the Higgs sector of the minimal supersymmetric model in SloopS. SloopS is an automatised code for the computation of one-loop processes in the MSSM. In this paper, the first in a series, we study in detail the non gauge invariance of some definitions of tan(beta). We rely on a general non-linear gauge fixing constraint to make the gauge parameter dependence of different schemes for tan(beta) at one-loop explicit. In so doing, we update, within these general gauges, an important Ward-Slavnov-Taylor identity on the mixing between the pseudo-scalar Higgs, A^0, and the Z^0. We then compare the tan(beta) scheme dependence of a few observables. We find that the best tan(beta) scheme is the one based on the decay A^0 -> tau^+ tau^- because of its gauge invariance, being unambiguously defined from a physical observable, and because it is numerically stable. The oft used DRbar scheme performs almost as well on the last count, but is usually defined from non-gauge invariant quantities in the Higgs sector. The use of the heavier scalar Higgs mass in lieu of tan(beta) though related to a physical parameter induces too large radiative corrections in many instances and is therefore not recommended., 34 pages, 1 figure, typos corrected, accepted for publication in Phys. Rev. D