First-Order Electroweak Phase Transition in the Standard Model with a Low Cutoff

We study the possibility of a first-order electroweak phase transition (EWPT) due to a dimension-six operator in the effective Higgs potential. In contrast with previous attempts to make the EWPT strongly first-order as required by electroweak baryogenesis, we do not rely on large one-loop thermally generated cubic Higgs interactions. Instead, we augment the Standard Model (SM) effective theory with a dimension-six Higgs operator. This addition enables a strong first-order phase transition to develop even with a Higgs boson mass well above the current direct limit of 114 GeV. The phi^6 term can be generated for instance by strong dynamics at the TeV scale or by integrating out heavy particles like an additional singlet scalar field. We discuss conditions to comply with electroweak precision constraints, and point out how future experimental measurements of the Higgs self couplings could test the idea.Comment: 5 pages, 4 figures. v2: corrected typos, improved discussion of the case lambda<0 and added references. To be published in PR

Le laboratoire de diagnostic foliaire de l'IRHO : organisation et activités

Depuis sa création en 1949 et devant le succès rencontré par l'application de la méthode du diagnostic foliaire à l'étude des carences et des besoins en engrais de l'arachide, puis du palmier et du cocotier, la demande d'analyses et le nombre des éléments à déterminer n'ont cessé de croître, ce qui a conduit le laboratoire spécialisé de l'I. R. H. O. à modifier à plusieurs reprises ses techniques analytiques. Un article publié en 1952 (1] a donné sommairement le principe des méthodes utilisées alors, ainsi que l'organisation adoptée pour réaliser en 1951environ3500 déterminations de N, P, K, Ca et Mg. En 1972, le laboratoire a traité plus de 8 500 échantillons sur lesquels il a effectué environ 35 000 dosages d'éléments majeurs, Na compris, et près de 15 000 déterminations de Cl et de S et des oligoéléments suivants : Fe, Cu, Mn, Zn, Al, B, Mo. Le, présent article se propose de décrire dans les grandes lignes l'organisation actuelle de cette section des laboratoires de l'I. R. H. O., qui comprend essentiellement, outre des salles de broyage et de stockage, une salle des balances, des laboratoires spécialisés, l'un pour les éléments majeurs, l'autre pour les oligoéléments, S et Cl, et un laboratoire pour la photométrie de flamme et la spectrophotométrie d'absorption atomique. Il a semblé intéressant de suivre pour cela le cheminement de l'échantillon depuis sa réception par le laboratoire jusqu'à l'envoi des résultats des mesures au service de calcul du Département Statistique de l'I. R. H. O., dont le fonctionnement et en particulier l'intervention dans le calcul et le contrôle des analyses ont été récemment décrits [2]. (Résumé d'auteur

Dirac Neutrino Dark Matter

We investigate the possibility that dark matter is made of heavy Dirac neutrinos with mass in the range [O(1) GeV- a few TeV] and with suppressed but non-zero coupling to the Standard Model Z as well as a coupling to an additional Z' gauge boson. The first part of this paper provides a model-independent analysis for the relic density and direct detection in terms of four main parameters: the mass, the couplings to the Z, to the Z' and to the Higgs. These WIMP candidates arise naturally as Kaluza-Klein states in extra-dimensional models with extended electroweak gauge group SU(2)_L* SU(2)_R * U(1). They can be stable because of Kaluza-Klein parity or of other discrete symmetries related to baryon number for instance, or even, in the low mass and low coupling limits, just because of a phase-space-suppressed decay width. An interesting aspect of warped models is that the extra Z' typically couples only to the third generation, thus avoiding the usual experimental constraints. In the second part of the paper, we illustrate the situation in details in a warped GUT model.Comment: 35 pages, 25 figures; v2: JCAP version; presentation and plots improved, results unchange

Distributional reaction time properties in the Eriksen task: marked differences or hidden similarities with the Simon task?

In conflict tasks, the irrelevant stimulus attribute needs to be suppressed for the correct response to be produced. In the Simon task, earlier researchers have proposed that this suppression is the reason that, after an initial increase, the interference effect decreases for longer RTs, as reflected by late, negative-going delta plots. This view has been challenged by observations of positive-going delta plots, even for long RTs, in other conflict tasks, despite a similar necessity for suppression. For late negative-going delta plots to be interpreted as reflecting suppression, a necessary, although maybe not sufficient, condition is that similar patterns should be observed for other conflict tasks. We reasoned that a similar suppression could be present, but hidden, in the Eriksen flanker task. By recording and analyzing electromyograms of the muscles involved in response execution, we could compute delta plots separately for trials that elicited a subthreshold incorrect response activation (partial error). Late negative-going delta plots were observable on partial-error trials, although they were weaker than for the Simon task, reducing the impact of this inversion on the overall distribution. We further showed that this pattern is modulated by time pressure. Those results indicate that mechanisms leading to negative-going delta plots, similar to those observed in the Simon task, are also at play in the Eriksen task. The link between negative-going delta plots and executive online control is discussed

Gamma-ray lines and One-Loop Continuum from s-channel Dark Matter Annihilations

The era of indirect detection searches for dark matter has begun, with the sensitivities of gamma-ray detectors now approaching the parameter space relevant for weakly interacting massive particles. In particular, gamma ray lines would be smoking gun signatures of dark matter annihilation, although they are typically suppressed compared to the continuum. In this paper, we pay particular attention to the 1-loop continuum generated together with the gamma-ray lines and investigate under which conditions a dark matter model can naturally lead to a line signal that is relatively enhanced. We study generic classes of models in which DM is a fermion that annihilates through an s-channel mediator which is either a vector or scalar and identify the coupling and mass conditions under which large line signals occur. We focus on the "forbidden channel mechanism" advocated a few years ago in the "Higgs in space" scenario for which tree level annihilation is kinematically forbidden today. Detailed calculations of all 1-loop annihilation channels are provided. We single out very simple models with a large line over continuum ratio and present general predictions for a large range of WIMP masses that are relevant not only for Fermi and Hess II but also for the next generation of telescopes such as CTA and Gamma-400. Constraints from the relic abundance, direct detection and collider bounds are also discussed.Comment: 32 pages, 13 figures; v2: minor clarifications, summary paragraph added; v3: matches published version, minor clarifications, results unchange