8,281 research outputs found
Gauge-Fermion Unification and Flavour Symmetry
After we study the 6-dimensional supersymmetry breaking
and symmetry breaking on , we construct two supersymmetric models on where is
broken down to by orbifold projection. In Model I, three
families of the Standard Model fermions arise from the zero modes of bulk
vector multiplet, and the symmetry
can be considered as flavour symmetry. This may explain why there are three
families of fermions in the nature. In Model II, the first two families come
from the zero modes of bulk vector multiplet, and the flavour symmetry is
similar. In these models, the anomalies can be cancelled, and we have very good
fits to the SM fermion masses and mixings. We also comment on the supersymmetric models on and ,
SU(9) models on , and SU(8) models on orbifolds.Comment: Latex, 33 pages, minor change
Inflationary Cosmology with Five Dimensional SO(10)
We discuss inflationary cosmology in a five dimensional SO(10) model
compactified on , which yields below the compactification scale. The gauge
symmetry is preserved on one of the fixed points, while
``flipped'' is on the other fixed point. Inflation is
associated with breaking, and is implemented through -term scalar
potentials on the two fixed points. A brane-localized Einstein-Hilbert term
allows both branes to have positive tensions during inflation. The scale of
breaking is fixed from measurements to be around
GeV, and the scalar spectral index . The inflaton field
decays into right-handed neutrinos whose subsequent out of equilibrium decay
yield the observed baryon asymmetry via leptogenesis.Comment: 1+19 pages, improved discussion of 5D cosmology, Version to appear in
PR
Neutrino Democracy, Fermion Mass Hierarchies And Proton Decay From 5D SU(5)
The explanation of various observed phenomena such as large angle neutrino
oscillations, hierarchies of charged fermion masses and CKM mixings, and
apparent baryon number conservation may have a common origin. We show how this
could occur in 5D SUSY SU(5) supplemented by a flavor symmetry
and additional matter supermultiplets called 'copies'. In addition, the proton
decays into , with an estimated lifetime of order
yrs. Other decay channels include and with comparable rates. We
also expect that BRBR
Model Building with Gauge-Yukawa Unification
In supersymmetric theories with extra dimensions, the Higgs and matter fields
can be part of the gauge multiplet, so that the Yukawa interactions can arise
from the gauge interactions. This leads to the possibility of gauge-Yukawa
coupling unification, g_i=y_f, in the effective four dimensional theory after
the initial gauge symmetry and the supersymmetry are broken upon orbifold
compactification. We consider gauge-Yukawa unified models based on a variety of
four dimensional symmetries, including SO(10), SU(5), Pati-Salam symmetry,
trinification, and the Standard Model. Only in the case of Pati-Salam and the
Standard Model symmetry, we do obtain gauge-Yukawa unification. Partial
gauge-Yukawa unification is also briefly discussed.Comment: 23 page
Crystal Structure and Magnetism of the Linear-Chain Copper Oxides Sr5Pb3-xBixCuO12
The title quasi-1D copper oxides (0=< x =<0.4) were investigated by neutron
diffraction and magnetic susceptibility studies. Polyhedral CuO4 units in the
compounds were found to comprise linear-chains at inter-chain distance of
approximately 10 A. The parent chain compound (x = 0), however, shows less
anisotropic magnetic behavior above 2 K, although it is of substantially
antiferromagnetic (mu_{eff}= 1.85 mu_{B} and Theta_{W} = -46.4 K) spin-chain
system. A magnetic cusp gradually appears at about 100 K in T vs chi with the
Bi substitution. The cusp (x = 0.4) is fairly characterized by and therefore
suggests the spin gap nature at Delta/k_{B} ~ 80 K. The chain compounds hold
electrically insulating in the composition range.Comment: To be published in PR
SU(4)_c x SU(2)_L x SU(2)_R model from 5D SUSY SU(4)_c x SU(4)_{L+R}
We investigate supersymmetric theory in 5
dimensions whose compactification on a orbifold yields N=1
supersymmetric supplemented by a
\tl{U}(1) gauge symmetry. We discuss how the problem is resolved, a
realistic Yukawa sector achieved, and a stable proton realized. Neutrino masses
and oscillations are also briefly discussed.Comment: Version to appear in Physical Review
SUSY GUT Model Building
I discuss an evolution of SUSY GUT model building, starting with the
construction of 4d GUTs, to orbifold GUTs and finally to orbifold GUTs within
the heterotic string. This evolution is an attempt to obtain realistic string
models, perhaps relevant for the LHC. This review is in memory of the sudden
loss of Julius Wess, a leader in the field, who will be sorely missed.Comment: 24 pages, 14 figures, lectures given at PiTP 2008, Institute for
Advanced Study, Princeton, to be published in the European Physical Journal
Transfer RNA-derived small RNAs in the cancer transcriptome
The cellular lifetime includes stages such as differentiation, proliferation, division, senescence and apoptosis.These stages are driven by a strictly ordered process of transcription dynamics. Molecular disruption to RNA polymerase assembly, chromatin remodelling and transcription factor binding through to RNA editing, splicing, post-transcriptional regulation and ribosome scanning can result in significant costs arising from genome instability. Cancer development is one example of when such disruption takes place. RNA silencing is a term used to describe the effects of post-transcriptional gene silencing mediated by a diverse set of small RNA molecules. Small RNAs are crucial for regulating gene expression and microguarding genome integrity.RNA silencing studies predominantly focus on small RNAs such as microRNAs, short-interfering RNAs and piwi-interacting RNAs. We describe an emerging renewal of inter-est in aâlargerâsmall RNA, the transfer RNA (tRNA).Precisely generated tRNA-derived small RNAs, named tRNA halves (tiRNAs) and tRNA fragments (tRFs), have been reported to be abundant with dysregulation associated with cancer. Transfection of tiRNAs inhibits protein translation by displacing eukaryotic initiation factors from messenger RNA (mRNA) and inaugurating stress granule formation.Knockdown of an overexpressed tRF inhibits cancer cell proliferation. Recovery of lacking tRFs prevents cancer metastasis. The dual oncogenic and tumour-suppressive role is typical of functional small RNAs. We review recent reports on tiRNA and tRF discovery and biogenesis, identification and analysis from next-generation sequencing data and a mechanistic animal study to demonstrate their physiological role in cancer biology. We propose tRNA-derived small RNA-mediated RNA silencing is an innate defence mechanism to prevent oncogenic translation. We expect that cancer cells are percipient to their ablated control of transcription and attempt to prevent loss of genome control through RNA silencing
The strong coupling, unification, and recent data
The prediction of the strong coupling assuming (supersymmetric) coupling
constant unification is reexamined. We find, using the new electroweak data,
. The implications of the large
value are discussed. The role played by the beauty width is
stressed. It is also emphasized that high-energy (but not low-energy)
corrections could significantly diminish the prediction. However, unless
higher-dimension operators are assumed to be suppressed, at present one cannot
place strong constraints on the super-heavy spectrum. Non-leading electroweak
threshold corrections are also discussed.Comment: 12 pages, LaTex + RevTex, uuencoded postscript file (including 13
figures) is attached. Also available at ftp://dept.physics.upenn.edu/pub/Ni
Dynamical relaxation of the CP phases in next-to-minimal supersymmetry
After promoting the phases of the soft masses to dynamical fields
corresponding to Goldstone bosons of spontaneously broken global symmetries in
the supersymmetry breaking sector, the next-to-minimal supersymmetric model is
found to solve the problem and the strong CP problem simultaneously with
an invisible axion. The domain wall problem persists in the form of axionic
domain formation. Relaxation dynamics of the physical CP-violating phases is
determined only by the short-distance physics and their relaxation values are
not necessarily close to the CP-conserving points. Having observable
supersymmetric CP violation and avoiding the axionic domain walls both require
nonminimal flavor structures.Comment: 13 pp, 3 figs, published versio
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