368 research outputs found
The 3-3-1 model with A_4 flavor symmetry
We argue that the A_4 symmetry as required by three flavors of fermions may
well-embed in the SU(3)_C X SU(3)_L X U(1)_X gauge model. The new neutral
fermion singlets as introduced in a canonical seesaw mechanism can be combined
with the standard model lepton doublets to perform SU(3)_L triplets. Various
leptoscalar multiplets such as singlets, doublets, and triplets as played in
the models of A_4 are unified in single SU(3)_L antisextets. As a result,
naturally light neutrinos with various kinds of mass hierarchies are obtained
as a combination of type I and type II seesaw contributions. The observed
neutrino mixing pattern in terms of the Harrison-Perkins-Scott proposal is
obtained by enforcing of the A_4 group. The quark masses and
Cabibbo-Kobayashi-Maskawa mixing matrix are also discussed. By virtue of very
heavy antisextets the nature of the vacuum alignments of scalar fields can be
given.Comment: Version published by PR
One-loop contributions to decays and anomalies, and Ward identity
In this paper, we will present analytic formulas to express one-loop
contributions to lepton flavor violating decays , which are
also relevant to the anomalous dipole magnetic moments of charged leptons
. These formulas were computed in the unitary gauge, using the well-known
Passarino-Veltman notations. We also show that our results are consistent with
those calculated previously in the 't Hooft-Veltman gauge, or in the limit of
zero lepton masses. At the one-loop level, we show that the appearance of
fermion-scalar-vector type diagrams in the unitary gauge will violate the Ward
Identity relating to an external photon. As a result, the validation of the
Ward Identity guarantees that the photon always couples with two identical
particles in an arbitrary triple coupling vertex containing a photon.Comment: The version accepted to Nuclear Physics
Saturn's Seasonal Atmosphere at Northern Summer Solstice
The incredible longevity of Cassini's orbital mission at Saturn has provided
the most comprehensive exploration of a seasonal giant planet to date. This
review explores Saturn's changing global temperatures, composition, and aerosol
properties between northern spring and summer solstice (2015-2017), extending
our previous review of Cassini's remote sensing investigations (2004-14,
Fletcher et al., 2018) to the grand finale. The result is an unprecedented
record of Saturn's climate that spans almost half a Saturnian year, which can
be used to test the seasonal predictions of radiative climate models, neutral
and ion photochemistry models, and atmospheric circulation models. Hemispheric
asymmetries in tropospheric and stratospheric temperatures were observed to
reverse from northern winter to northern summer; spatial distributions of
hydrocarbons and para-hydrogen shifted in response to atmospheric dynamics
(e.g., seasonally-reversing Hadley cells, polar stratospheric vortex formation,
equatorial stratospheric oscillations, and inter-hemispheric transport); and
upper tropospheric and stratospheric aerosols exhibited changes in optical
thickness that modulated Saturn's visible colours (from blue hues to a golden
appearance in the north near solstice), reflectivity, and near-infrared
emission. Numerical simulations of radiative balance and photochemistry do a
good job in reproducing the observed seasonal change and phase lags, but
discrepancies between models and observations still persist, indicating a
crucial role for atmospheric dynamics and the need to couple chemical and
radiative schemes to the next generation of circulation models. With Cassini's
demise, an extended study of Saturn's seasons, from northern summer to autumn,
will require the capabilities of ground- and space-based observatories, as we
eagerly await the next orbital explorer at Saturn.Comment: 24 pages, 18 figures, submitted for publication by Cambridge
University Press as part of a multi-volume work edited by Kevin Baines,
Michael Flasar, Norbert Krupp, and Thomas Stallard, entitled "Cassini at
Saturn: The Grand Finale." The copy of the Chapter, as displayed on this
website, is a draft, pre-publication copy onl
Symmetry Factors of Feynman Diagrams for Scalar Fields
The symmetry factor of Feynman diagrams for real and complex scalar fields is
presented. Being analysis of Wick expansion for Green functions, the mentioned
factor is derived in a general form. The symmetry factor can be separated into
two ones corresponding to that of connected and vacuum diagrams. The
determination of symmetry factors for the vacuum diagrams is necessary as they
play a role in the effective action and phase transitions in cosmology. In the
complex scalar theory the diagrams different in topology may give the same
contribution, hence inverse of the symmetry factor (1/S) for total contribution
is a summation of each similar ones (1/S_i), i.e., 1/S = \sum_i (1/S_i).Comment: Journal version, new references adde
Topological Analysis of Metabolic Networks Integrating Co-Segregating Transcriptomes and Metabolomes in Type 2 Diabetic Rat Congenic Series
Background: The genetic regulation of metabolic phenotypes (i.e., metabotypes) in type 2 diabetes mellitus is caused by complex organ-specific cellular mechanisms contributing to impaired insulin secretion and insulin resistance. Methods: We used systematic metabotyping by 1H NMR spectroscopy and genome-wide gene expression in white adipose tissue to map molecular phenotypes to genomic blocks associated with obesity and insulin secretion in a series of rat congenic strains derived from spontaneously diabetic Goto-Kakizaki (GK) and normoglycemic Brown-Norway (BN) rats. We implemented a network biology strategy approach to visualise shortest paths between metabolites and genes significantly associated with each genomic block. Results: Despite strong genomic similarities (95-99%) among congenics, each strain exhibited specific patterns of gene expression and metabotypes, reflecting metabolic consequences of series of linked genetic polymorphisms in the congenic intervals. We subsequently used the congenic panel to map quantitative trait loci underlying specific metabotypes (mQTL) and genome-wide expression traits (eQTL). Variation in key metabolites like glucose, succinate, lactate or 3-hydroxybutyrate, and second messenger precursors like inositol was associated with several independent genomic intervals, indicating functional redundancy in these regions. To navigate through the complexity of these association networks we mapped candidate genes and metabolites onto metabolic pathways and implemented a shortest path strategy to highlight potential mechanistic links between metabolites and transcripts at colocalized mQTLs and eQTLs. Minimizing shortest path length drove prioritization of biological validations by gene silencing. Conclusions: These results underline the importance of network-based integration of multilevel systems genetics datasets to improve understanding of the genetic architecture of metabotype and transcriptomic regulations and to characterize novel functional roles for genes determining tissue-specific metabolism
Vulnerability to Climate Change: Adaptation Strategies and Layers of Resilience, Quantifying Vulnerability to Climate Change in Vietnam, Research Report No. 25
This paper characterizes eight agro ecological regions of Vietnam based on the vulnerability to climate change. Cross-section data set belonging to a set of variables representing 3 components of vulnerability, ie, exposure, sensitivity and adaptive capacity were selected for this analysis. The vulnerability was computed based on the standard methodology and regions were mapped based on the extent of vulnerability to climate change. This analysis delineated agro-ecological regions based on the degree of vulnerability, ie, Red River Delta (RRD), North West mountainous (NWM), South east region (SER), Central Highland (CHR), Mekong river delta (MRD) as being vulnerable – very highly vulnerable to climate change
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