246 research outputs found
Minimal Scalar Sector of 3-3-1 Models without Exotic Electric Charges
We study the minimal set of Higgs scalars, for models based on the local
gauge group which do not contain
particles with exotic electric charges. We show that only two Higgs
triplets are needed in order to properly break the symmetry. The exact
tree-level scalar mass matrices resulting from symmetry breaking are calculated
at the minimum of the most general scalar potential, and the gauge bosons are
obtained, together with their couplings to the physical scalar fields. We show
how the scalar sector introduced is enough to produce masses for fermions in a
particular model which is an subgroup. By using experimental results we
constrain the scale of new physics to be above 1.3 TeV.Comment: LaTeX, 22 pages, 1 figure include
How to determine an effective potential for a variable cosmological term
It is shown that if a variable cosmological term in the present Universe is
described by a scalar field with minimal coupling to gravity and with some
phenomenological self-interaction potential , then this potential
can be unambiguously determined from the following observational data: either
from the behaviour of density perturbations in dustlike matter component as a
function of redshift (given the Hubble constant additionally), or from the
luminosity distance as a function of redshift (given the present density of
dustlike matter in terms of the critical one).Comment: Latex, 7 pages, JETP Lett., in press, 199
Fermion Masses and Mixing in 331 Models with Horizontal Symmetry
The possibility of adding an SU(2) horizontal symmetry to the 331 model is
studied. It is found that simple, anomaly-free fermion assignments can be made
which lead to plausible results for fermion masses and mixings. In particular,
all particles of the first generation are massless at tree-level, and the CKM
matrix acquires a realistic form.Comment: 11 pages, no figures. Typos correcte
Quantum Symmetries and Marginal Deformations
We study the symmetries of the N=1 exactly marginal deformations of N=4 Super
Yang-Mills theory. For generic values of the parameters, these deformations are
known to break the SU(3) part of the R-symmetry group down to a discrete
subgroup. However, a closer look from the perspective of quantum groups reveals
that the Lagrangian is in fact invariant under a certain Hopf algebra which is
a non-standard quantum deformation of the algebra of functions on SU(3). Our
discussion is motivated by the desire to better understand why these theories
have significant differences from N=4 SYM regarding the planar integrability
(or rather lack thereof) of the spin chains encoding their spectrum. However,
our construction works at the level of the classical Lagrangian, without
relying on the language of spin chains. Our approach might eventually provide a
better understanding of the finiteness properties of these theories as well as
help in the construction of their AdS/CFT duals.Comment: 1+40 pages. v2: minor clarifications and references added. v3: Added
an appendix, fixed minor typo
Two-loop Radiative Neutrino Mechanism in an Gauge Model
By using the - - symmetry, we construct an
gauge model that provides two-loop radiative neutrino
masses as well as one-loop radiative neutrino masses. The generic smallness of
two-loop neutrino masses leading to compared with one-loop
neutrino masses leading to successfully explains by invoking the - -
breaking. The Higgs scalar () that initiates radiative mechanisms is
unified into a Higgs triplet together with the standard Higgs scalar (,
) to form (, , ), which calls for three families
of lepton triplets: (, , ) (i = 1,2,3), where
denote heavy neutral leptons. The two-loop radiative mechanism is
found possible by introducing a singly charged scalar, which couples to
(i,j = 2,3).Comment: with 10 pages, revtex, including 2 figures, accepted for publication
in Phys. Rev. D (with undefined latex citation indices removed
Supersymmetric One-family Model without Higgsinos
The Higgs potential and the mass spectrum of the N=1 supersymmetric extension
of a recently proposed one-family model based on the local gauge group , which is a subgroup of the electroweak-strong
unification group , is analyzed. In this model the slepton multiplets play
the role of the Higgs scalars and no Higgsinos are needed, with the consequence
that the sneutrino, the selectron and six other sleptons play the role of the
Goldstone bosons. We show how the problem is successfully addressed in
the context of this model which also predicts the existence of a light CP-odd
scalar.Comment: REVTeX 4, 10 pages. Included discussions about constraints coming
from the rho-parameter and from Muon (g-2). References added. Version to
appear in Phys. Rev.
The Aurora B specificity switch is required to protect from non-disjunction at the metaphase/anaphase transition
The Aurora B abscission checkpoint delays cytokinesis until resolution of DNA trapped in the cleavage furrow. This process involves PKCε phosphorylation of Aurora B S227. Assessing if this PKCε-Aurora B module provides a more widely exploited genome-protective control for the cell cycle, we show Aurora B phosphorylation at S227 by PKCε also occurs during mitosis. Expression of Aurora B S227A phenocopies inhibition of PKCε in by-passing the delay and resolution at anaphase entry that is associated with non-disjunction and catenation of sister chromatids. Implementation of this anaphase delay is reflected in PKCε activation following cell cycle dependent cleavage by caspase 7; knock-down of caspase 7 phenocopies PKCε loss, in a manner rescued by ectopically expressing/generating a free PKCε catalytic domain. Molecular dynamics indicates that Aurora B S227 phosphorylation induces conformational changes and this manifests in a profound switch in specificity towards S29 TopoIIα phosphorylation, a response necessary for catenation resolution during mitosis.This work was supported by the Francis Crick Institute, which receives its core funding from Cancer Research UK (FC001130), the UK Medical Research Council (FC001130) and the Wellcome Trust (FC001130).Peer reviewe
Perturbation evolution in cosmologies with a decaying cosmological constant
Structure formation models with a cosmological constant are successful in
explaining large-scale structure data, but are threatened by the
magnitude-redshift relation for Type Ia supernovae. This has led to discussion
of models where the cosmological `constant' decays with time, which might
anyway be better motivated in a particle physics context. The simplest such
models are based on scalar fields, and general covariance demands that a
time-evolving scalar field also supports spatial perturbations. We consider the
effect of such perturbations on the growth of adiabatic energy density
perturbations in a cold dark matter component. We study two types of model, one
based on an exponential potential for the scalar field and the other on a
pseudo-Nambu Goldstone boson. For each potential, we study two different
scenarios, one where the scalar field presently behaves as a decaying
cosmological constant and one where it behaves as dust. The initial scalar
field perturbations are fixed by the adiabatic condition, as expected from the
inflationary cosmology, though in fact we show that the choice of initial
condition is of little importance. Calculations are carried out in both the
zero-shear (conformal newtonian) and uniform-curvature gauges. We find that
both potentials allow models which can provide a successful alternative to
cosmological constant models.Comment: 14 pages RevTeX file with three figures incorporated (uses RevTeX and
epsf). Also available by e-mailing ARL, or by WWW at
http://star-www.maps.susx.ac.uk/papers/lsstru_papers.html Revised version
corrects an error in Eq10; results unchange
A novel approach for rapid screening of mitochondrial D310 polymorphism
BACKGROUND: Mutations in the mitochondrial DNA (mtDNA) have been reported in a wide variety of human neoplasms. A polynucleotide tract extending from 303 to 315 nucleotide positions (D310) within the non-coding region of mtDNA has been identified as a mutational hotspot of primary tumors. This region consists of two polycytosine stretches interrupted by a thymidine nucleotide. The number of cytosines at the first and second stretches are 7 and 5 respectively, according to the GeneBank sequence. The first stretch exhibits a polymorphic length variation (6-C to 9-C) among individuals and has been investigated in many cancer types. Large-scale studies are needed to clarify the relationship between cytosine number and cancer development/progression. However, time and money consuming methods such as radioactivity-based gel electrophoresis and sequencing, are not appropriate for the determination of this polymorphism for large case-control studies. In this study, we conducted a rapid RFLP analysis using a restriction enzyme, BsaXI, for the single step simple determination of 7-C carriers at the first stretch in D310 region. METHODS: 25 colorectal cancer patients, 25 breast cancer patients and 41 healthy individuals were enrolled into the study. PCR amplification followed by restriction enzyme digestion of D310 region was performed for RFLP analysis. Digestion products were analysed by agarose gel electrophoresis. Sequencing was also applied to samples in order to confirm the RFLP data. RESULTS: Samples containing 7-C at first stretch of D310 region were successfully determined by the BsaXI RFLP method. Heteroplasmy and homoplasmy for 7-C content was also determined as evidenced by direct sequencing. Forty-one percent of the studied samples were found to be BsaXI positive. Furthermore, BsaXI status of colorectal cancer samples were significantly different from that of healthy individuals. CONCLUSION: In conclusion, BsaXI RFLP analysis is a simple and rapid approach for the single step determination of D310 polymorphism of mitochondrial DNA. This method allows the evaluation of a significant proportion of samples without the need for sequencing- and/or radioactivity-based techniques
Evolution of the Scale Factor with a Variable Cosmological Term
Evolution of the scale factor a(t) in Friedmann models (those with zero
pressure and a constant cosmological term Lambda) is well understood, and
elegantly summarized in the review of Felten and Isaacman [Rev. Mod. Phys. 58,
689 (1986)]. Developments in particle physics and inflationary theory, however,
increasingly indicate that Lambda ought to be treated as a dynamical quantity.
We revisit the evolution of the scale factor with a variable Lambda-term, and
also generalize the treatment to include nonzero pressure. New solutions are
obtained and evaluated using a variety of observational criteria. Existing
arguments for the inevitability of a big bang (ie., an initial state with a=0)
are substantially weakened, and can be evaded in some cases with Lambda_0 (the
present value of Lambda) well below current experimental limits.Comment: 29 pages, 12 figures (not included), LaTeX, uses Phys Rev D style
files (revtex.cls, revtex.sty, aps.sty, aps10.sty, prabib.sty). To appear in
Phys Rev
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