1,425 research outputs found
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 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
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