28 research outputs found
Breaking democracy with non renormalizable mass terms
The exact democratic structure for the quark mass matrix, resulting from the
action of the family symmetry group , is broken by the
vaccum expectation values of heavy singlet fields appearing in non
renormalizable dimension 6 operators. Within this specific context of breaking
of the family symmetry we formulate a very simple ansatz which leads to correct
quark masses and mixings.Comment: 6 pages, RevTe
CP Violation and Flavour Mixings in Orbifold GUTs
We address the flavour problem by incorporating the hypothesis of universal
strength of Yukawa couplings in the framework of a 5D GUT model compactified on
an orbifold. We show that a quantitatively
successful picture of fermion masses and mixings emerges from the interplay
between the bulk suppression factors of geometric origin and the phases of the
Yukawa matrices. We give an explicit example, where we obtain a good fit for
both the CKM and PMNS matrices.Comment: 8 pages, no figures; v2: minor changes, published in Phys Rev D
(Rapid Communication
Symmetries, Large Leptonic Mixing and a Fourth Generation
We show that large leptonic mixing occurs most naturally in the framework of
the Sandard Model just by adding a fourth generation. One can then construct a
small discrete symmetry, instead of the large ,
which requires that the neutrino as well as the charged lepton mass matrices be
proportional to a democratic mass matrix, where all entries are
equal to unity. Without considering the see-saw mechanism, or other more
elaborate extensions of the SM, and contrary to the case with only 3
generations, large leptonic mixing is obtained when the symmetry is broken.Comment: 6 pages, ReVTeX, no figure
Flavour physics of the RS model with KK masses reachable at LHC
The version of the higher-dimensional Randall-Sundrum (RS) model with matter
in the bulk, which addresses the gauge hierarchy problem, has additional
attractive features. In particular, it provides an intrinsic geometrical
mechanism that can explain the origin of the large mass hierarchies among the
Standard Model fermions. Within this context, a good solution for the gauge
hierarchy problem corresponds to low masses for the Kaluza-Klein (KK)
excitations of the gauge bosons. Some scenarios have been proposed in order to
render these low masses (down to a few TeV) consistent with precision
electroweak measurements. Here, we give specific and complete realizations of
this RS version with small KK masses, down to 1 TeV, which are consistent with
the entire structure of the fermions in flavour space: (1) all the last
experimental data on quark/lepton masses and mixing angles (including massive
neutrinos of Dirac type) are reproduced, (2) flavour changing neutral current
constraints are satisfied and (3) the effective suppression scales of
non-renormalizable interactions (in the physical basis) are within the bounds
set by low energy flavour phenomenology. Our result, on the possibility of
having KK gauge boson modes as light as a few TeV, constitutes one of the first
theoretical motivations for experimental searches of direct signatures at the
LHC collider, of this interesting version of the RS model which accommodates
fermion masses.Comment: 27 pages, Latex file. References and comments adde
The Problem of Large Leptonic Mixing
Unlike in the quark sector where simple permutation symmetries can
generate the general features of quark masses and mixings, we find it
impossible (under conditions of hierarchy for the charged leptons and without
considering the see-saw mechanism or a more elaborate extension of the SM) to
guarantee large leptonic mixing angles with any general symmetry or
transformation of only known particles. If such symmetries exist, they must be
realized in more extended scenarios.Comment: RevTeX, 4 pages, no figure
Successful Yukawa structures in Warped Extra Dimensions
For a RS model, with SM fields in the bulk and the Higgs boson on the
TeV-brane, we suggest two specific structures for the Yukawa couplings, one
based on a permutation symmetry and the other on the Universal Strength of
Yukawa couplings hypothesis (USY). In USY, all Yukawa couplings have equal
strength and the difference in the Yukawa structure lies in some complex phase.
In both scenarios, all Yukawa couplings are of the same order of magnitude.
Thus, the main features of the fermion hierarchies are explained through the RS
geometrical mechanism, and not because some Yukawa coupling is extremely small.
We find that the RS model is particularly appropriate to incorporate the
suggested Yukawa configurations. Indeed, the RS geometrical mechanism of
fermion locations along the extra dimension, combined with the two Yukawa
scenarios, reproduces all the present experimental data on fermion masses and
mixing angles. It is quite remarkable that in the USY case, only two complex
phases of definite value +-Pi/2 are sufficient to generate the known neutrino
mass differences, while at same time, permitting large leptonic mixing in
agreement with experiment.Comment: 11 page
TRY plant trait database â enhanced coverage and open access
Plant traits - the morphological, anatomical, physiological, biochemical and phenological characteristics of plants - determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of traitâbased plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits - almost complete coverage for âplant growth formâ. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and traitâenvironmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives
Pervasive gaps in Amazonian ecological research
Biodiversity loss is one of the main challenges of our time,1,2 and attempts to address it require a clear understanding of how ecological communities respond to environmental change across time and space.3,4 While the increasing availability of global databases on ecological communities has advanced our knowledge of biodiversity sensitivity to environmental changes,5,6,7 vast areas of the tropics remain understudied.8,9,10,11 In the American tropics, Amazonia stands out as the world's most diverse rainforest and the primary source of Neotropical biodiversity,12 but it remains among the least known forests in America and is often underrepresented in biodiversity databases.13,14,15 To worsen this situation, human-induced modifications16,17 may eliminate pieces of the Amazon's biodiversity puzzle before we can use them to understand how ecological communities are responding. To increase generalization and applicability of biodiversity knowledge,18,19 it is thus crucial to reduce biases in ecological research, particularly in regions projected to face the most pronounced environmental changes. We integrate ecological community metadata of 7,694 sampling sites for multiple organism groups in a machine learning model framework to map the research probability across the Brazilian Amazonia, while identifying the region's vulnerability to environmental change. 15%â18% of the most neglected areas in ecological research are expected to experience severe climate or land use changes by 2050. This means that unless we take immediate action, we will not be able to establish their current status, much less monitor how it is changing and what is being lost