1,779 research outputs found
In vitro reactivation of spindle elongation in fission yeast nuc2 mutant cells.
To investigate the mechanisms of spindle elongation and chromosome separation in the fission yeast Schizosaccharomyces pombe, we have developed an in vitro assay using a temperature-sensitive mutant strain, nuc2. At the restrictive temperature, nuc2 cells are arrested at a metaphase-like stage with short spindles and condensed chromosomes. After permeabilization of spheroplasts of the arrested cells, spindle elongation was reactivated by addition of ATP and neurotubulin both at the restrictive and the permissive temperatures, but chromosome separation was not. This suggests that the nuc2 cells are impaired in function at a stage before sister chromatid disjunction. Spindle elongation required both ATP and exogenous tubulin and was inhibited by adenylyl imidodiphosphate (AMPPNP) or vanadate. The ends of yeast half-spindle microtubules pulse-labeled with biotinylated tubulin moved past each other during spindle elongation and a gap formed between the original half-spindles. These results suggest that the primary mechanochemical event responsible for spindle elongation is the sliding apart of antiparallel microtubules of the two half-spindles
Inverted Hybrid Inflation as a solution to gravitino problems in Gravity Mediation
It was recently found that the decay of inflaton and the SUSY breaking field
produces many gravitinos in the gravity mediation scenario. These discoveries
led to an exclusion of many inflation models such as chaotic, (smooth) hybrid,
topological and new inflation models. Under these circumstances we searched for
a successful inflation model and found that the ``inverted'' hybrid inflation
models can solve the gravitino overproduction problem by their distinctive
shape of the potential. Furthermore, we found that this inflation model
simultaneously can explain the observed baryon asymmetry through the
non-thermal leptogenesis and is consistent with the WMAP results, that is,
and the negligible tensor to scalar ratio.Comment: 23 pages, 2 figures in
Probing Variant Axion Models at LHC
We study collider implications of variant axion models which naturally avoid
the cosmological domain wall problem. We find that in such models the branching
ratio of can be enhanced by a factor of 5 up to 30 as
compared with the standard model prediction. The process
is therefore a promising channel to discover a light Higgs boson at the LHC and
to probe the Peccei-Quinn charge assignment of the standard model fields from
Yukawa interactions.Comment: 16 pages, 4 figure
Constraints on leptogenesis from a symmetry viewpoint
It is shown that type I seesaw models based on the standard model Lagrangian
extended with three heavy Majorana right-handed fields do not have leptogenesis
in leading order, if the symmetries of mass matrices are also the residual
symmetry of the Lagrangian. In particular, flavor models that lead to a
mass-independent leptonic mixing have a vanishing leptogenesis CP asymmetry.
Based on symmetry arguments, we prove that in these models the Dirac-neutrino
Yukawa coupling combinations relevant for leptogenesis are diagonal in the
physical basis where the charged leptons and heavy Majorana neutrinos are
diagonal.Comment: 5 pages; a few comments added; final version to appear in Phys. Rev.
Duality in Left-Right Symmetric Seesaw Mechanism
We consider type I+II seesaw mechanism, where the exchanges of both
right-handed neutrinos and isotriplet Higgs bosons contribute to the neutrino
mass. Working in the left-right symmetric framework and assuming the mass
matrix of light neutrinos and the Dirac-type Yukawa couplings to be
known, we find the triplet Yukawa coupling matrix , which carries the
information about the masses and mixing of the right-handed neutrinos. We show
that in this case there exists a duality: for any solution , there is a dual
solution , where is the VEV of the triplet Higgs.
Thus, unlike in pure type I (II) seesaw, there is no unique allowed structure
for the matrix . For lepton generations the number of solutions is
. We develop an exact analytic method of solving the seesaw non-linear
matrix equation for .Comment: 4 pages, revtex, small clarifications added, title changed to match
published versio
New signals of a R-parity violating model of neutrino mass at the Tevatron
In a variety models of neutrino masses and mixings the lighter top squark
decays into competing R - parity violating and R - parity conserving channels.
Using Pythia we have estimated in a model independent way the minimum value of
P BR()
BR(), where and , corresponding
to an observable signal involving the final state
1 + jets +\met (carried by the neutrinos from the
decay) at Tevatron Run II. For the kinematical cuts designed in this paper P
depends on only. We then compute P for representative
choices of the model parameters constrained by the oscillation data and find
that over a significant region of the allowed parameter space P is indeed
larger than . This signal is complementary to the dilepton + dijet
signal studied in several earlier experimental and phenomenological analyses
and may be observed even if BR() is an order of
magnitude smaller than BR(). The
invariant mass distribution of the hardest lepton and the hardest jet may
determine and reveal the lepton number violating nature of
the underlying interaction. The invariant mass distribution of the two lowest
energy jets may determine .Comment: Some minor changes in language are made at pages 1,2,8 and 18
respectivel
Probing R-parity violating models of neutrino mass at the LHC via top squark decays
It is shown that the R-parity violating decays of the lighter top squarks
() triggered by the lepton number violating couplings
, where the lepton family index i = 1-3, can be
observed at the LHC via the dilepton di-jet channel even if the coupling is as
small as 10 or 10, which is the case in several models of
neutrino mass, provided it is the next lightest supersymmetric particle(NLSP)
the lightest neutralino being the lightest supersymmetric particle(LSP). We
have first obtained a fairly model independent estimate of the minimum
observable value of the parameter ()) at the LHC for an integrated
luminosity of 10fb as a function of \mlstop by a standard Pythia based
analysis. We have then computed the parameter in several
representative models of neutrino mass constrained by the neutrino oscillation
data and have found that the theoretical predictions are above the estimated
minimum observable levels for a wide region of the parameter space.Comment: 19 pages, 1 Figure and 11 Table
Dark matter in the classically conformal B-L model
When the classically conformal invariance is imposed on the minimal gauged
B-L extended Standard Model (SM), the B-L gauge symmetry is broken by the
Coleman-Weinberg mechanism naturally at the TeV scale. Introducing a new Z_2
parity in the model, we investigate phenomenology of a right-handed neutrino
dark matter whose stability is ensured by the parity. We find that the relic
abundance of the dark matter particle can be consistent with the observations
through annihilation processes enhanced by resonances of either the SM Higgs
boson, the B-L Higgs boson or the B-L gauge boson (Z' boson). Therefore, the
dark matter mass is close to half of one of these boson masses. Due to the
classically conformal invariance and the B-L gauge symmetry breaking via the
Coleman-Weinberg mechanism, Higgs boson masses, Z' boson mass and the dark
matter mass are all related, and we identify the mass region to be consistent
with experimental results. We also calculate the spin-independent cross section
of the dark matter particle off with nucleon and discuss implications for
future direct dark matter search experiments.Comment: 13 pages, 4 figure
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