Minimal violation of flavour and custodial symmetries in a vectophobic Two-Higgs-Doublet-Model

Tree-level accidental symmetries are known to play a fundamental role in the phenomenology of the Standard Model (SM) for electroweak interactions. So far, no significant deviations from the theory have been observed in precision, flavour and collider physics. Consequently, these global symmetries are expected to remain quite efficient in any attempt beyond the SM. Yet, they do not forbid rather unorthodox phenomena within the reach of current LHC experiments. This is illustrated with a vectophobic Two-Higgs-Doublet-Model (2HDM) where effects of a light, flavour-violating and custodian (pseudo)scalar might be observed in the $B_s\to\mu^+\mu^-$ decay rate and in the diphoton invariant mass spectrum at around 125 GeV.Comment: 13 pages, 3 figures, v2: constraints from B_s -> mu+mu- updated, references added, to appear in Phys.Lett.

Further Issues in Fundamental Interactions

Driven by the mass problem, we raise some issues of the fundamental interactions in terms of non trivial commutation relations implemented within toy theories

Three-generation baryon and lepton number violation at the LHC

One of the most puzzling questions in particle physics concerns the status of the baryon (B) and lepton (L) quantum numbers. On the theoretical side, most new physics scenarios naturally lead to their non-conservation and some amount of violation is actually needed to explain the baryon asymmetry of the Universe. On the experimental side, low-energy constraints such as those on proton decay are so stringent that it is generally believed that no B and L violation will ever be seen in laboratories. We observe that this apparent contradiction, however, disappears when the flavor symmetries involving all three generations are taken into account. We then identify model-independent classes of B and/or L violating six-fermion-based processes that indeed simultaneously satisfy low-energy constraints and produce clearly identifiable signals at the LHC. Finally, through simplified models, we study two classes characterized by (\Delta B;\Delta L) = (\pm 1;\pm 3) and (\pm 2; 0), that lead to particularly striking signatures (t \mu^+ e^+ and \bar t \bar t + jets, respectively).Comment: 5 pages, 2 figures, 1 table; v2: version to appear in Phys.Lett.

Faisabilité économique du parquet massif de Chêne vert

La faisabilité économique de la fabrication de parquet en chêne vert, essence très abondante sur le pourtour méditerranéen, a été analysée par le Cirad-Forêt à la demande du Conseil Général de l’Hérault. Le prix de revient global de la transformation a été calculé en se référant à une opération expérimentale de production et fabrication avec mise en oeuvre en conditions réelles d’utilisation. La rentabilité de l’opération a été analysée en cohérence avec des marchés déjà existants. Une analyse de sensibilité des paramètres qui caractérisent la faisabilité économique de la fabrication a mis en évidence le rôle essentiel du prix de vente du produit fini, du rendement matière au sciage, et du prix d’achat de la matière première. Une variation de 1 % de chacun de ces trois paramètres peut induire une variation de plus de 35 % de la marge d’exploitation. La rentabilité de la fabrication de parquet en chêne vert est directement dépendante de la construction d’un réseau de fournisseurs réguliers pour sécuriser l’approvisionnement.

Cosmological perturbations of a perfect fluid and noncommutative variables

We describe the linear cosmological perturbations of a perfect fluid at the level of an action, providing thus an alternative to the standard approach based only on the equations of motion. This action is suited not only to perfect fluids with a barotropic equation of state, but also to those for which the pressure depends on two thermodynamical variables. By quantizing the system we find that (1) some perturbation fields exhibit a noncommutativity quite analogous to the one observed for a charged particle moving in a strong magnetic field, (2) local curvature and pressure perturbations cannot be measured simultaneously, (3) ghosts appear if the null energy condition is violated.Comment: 4 pages, uses RevTeX. Title modified, references and comments added

Cosmological perturbation in f(R,G) theories with a perfect fluid

In order to classify modified gravity models according to their physical properties, we analyze the cosmological linear perturbations for f(R,G) theories (R being the Ricci scalar and G, the Gauss-Bonnet term) with a minimally coupled perfect fluid. For the scalar type perturbations, we identify in general six degrees of freedom. We find that two of these physical modes obey the same dispersion relation as the one for a non-relativistic de Broglie wave. This means that spacetime is either highly unstable or its fluctuations undergo a scale-dependent super-luminal propagation. Two other modes correspond to the degrees of freedom of the perfect fluid, and propagate with the sound speed of such a fluid. The remaining two modes correspond to the entropy and temperature perturbations of the perfect fluid, and completely decouple from the other modes for a barotropic equation of state. We then provide a concise condition on f(R,G) theories, that both f(R) and R+f(G) do fulfill, to avoid the de Broglie type dispersion relation. For the vector type perturbation, we find that the perturbations decay in time. For the tensor type perturbation, the perturbations can be either super-luminal or sub-luminal, depending on the model. No-ghost conditions are also obtained for each type of perturbation.Comment: 12 pages, uses RevTe