1,036 research outputs found
Anomaly-Mediated Supersymmetry Breaking with Axion
We construct hadronic axion models in the framework of the anomaly-mediated
supersymmetry breaking scenario. If the Peccei-Quinn symmetry breaking is
related to the supersymmetry breaking, mass spectrum of the minimal
anomaly-mediated scenario is modified, which may solve the negative slepton
mass problem in the minimal anomaly-mediated model. We find several classes of
phenomenologically viable models of axion within the framework of the anomaly
mediation and, in particular, we point out a new mechanism of stabilizing the
axion potential. In this class of models, the Peccei-Quinn scale is related to
the messenger scale. We also study phenomenological aspects of this class of
models. We will see that, in some case, the lightest particle among the
superpartners of the standard-model particles is stau while the lightest
superparticle becomes the axino, the superpartner of the axion. With such a
unique mass spectrum, conventional studies of the collider physics and
cosmology for supersymmetric models should be altered.Comment: 20 pages, 5 figures, added footnotes and references for section
Relaxing Constraints on Inflation Models with Curvaton
We consider the effects of the curvaton, late-decaying scalar condensation,
to observational constraints on inflation models. From current observations of
cosmic density fluctuations, severe constraints on some class of inflation
models are obtained, in particular, on the chaotic inflation with higher-power
monomials, the natural inflation, and the new inflation. We study how the
curvaton scenario changes (and relaxes) the constraints on these models.Comment: 18 pages, 6 figure
Akt and mitogen-activated protein kinase enhance C-type lectin-like receptor 2-mediated platelet activation by inhibition of glycogen synthase kinase 3α/ÎČ
BACKGROUND: The Câtype lectinâlike receptor 2 (CLECâ2) and the collagen receptor glycoprotein (GP)VI activate platelets through Src and Syk tyrosine kinases, and phospholipase CÎł2. The initial events in the two signaling cascades, however, are distinct, and there are quantitative differences in the roles of proteins downstream of Syk activation. The activation of Akt and mitogenâactivated protein kinases (MAPKs) has been shown to enhance platelet activation by GPVI, but their role in CLECâ2 signaling is not known. OBJECTIVES: We sought to investigate the role of the Akt and MAPK pathways in platelet activation by CLECâ2. RESULTS: The CLECâ2 agonist rhodocytin stimulated phosphorylation of Akt and p38 and extracellular signalârelated kinase (ERK) MAPKs, but with a delay relative to Syk. Phosphorylation of these proteins was markedly inhibited in the combined presence of apyrase and indomethacin, consistent with the reported feedback action of ADP and thromboxane A(2) in CLECâ2 signaling. Phosphorylation of Akt and phosphorylation of ERK were blocked by the phosphoinositide 3âkinase (PI3K) inhibitor wortmannin and the protein kinase C (PKC) inhibitor Ro31â8220, respectively, whereas Syk phosphorylation was not altered. On the other hand, both inhibitors reduced phosphorylation of the Akt substrate glycogen synthase kinase 3α/ÎČ (GSK3α/ÎČ). Phosphorylation of GSK3α/ÎČ was also blocked by the Akt inhibitor MK2206, and reduced at late, but not early, times by the MEK inhibitor PD0325901. MK2206 and PD0325901 inhibited aggregation and secretion in response to a low concentration of rhodocytin, which was restored by GSK3α/ÎČ inhibitors. CONCLUSIONS: These results demonstrate that CLECâ2 regulates Akt and MAPK downstream of PI3K and PKC, leading to phosphorylation and inhibition of GSK3α/ÎČ, and enhanced platelet aggregation and secretion
Cosmological gravitino problem confronts electroweak physics
A generic feature of gauge-mediated supersymmetry breaking models is that the
gravitino is the lightest supersymmetric particle (LSP). In order not to
overclose the universe, the gravitino LSP should be light enough (~ 1 keV), or
appropriately heavy (~ 1 GeV). We study further constraints on the mass of the
gravitino imposed by electroweak experiments, i.e., muon g-2 measurements,
electroweak precision measurements, and direct searches for supersymmetric
particles at LEP2. We find that the heavy gravitino is strongly disfavored from
the lower mass bound on the next-to-LSP. The sufficiently light gravitino, on
the other hand, has rather sizable allowed regions in the model parameter
space.Comment: 11 pages, 8 figures, version to appear in PR
Higher-Dimensional Origin of Heavy Sneutrino Domination and Low-Scale Leptogenesis
If the expectation value of the right-handed (rhd) sneutrino comes to
dominate the universe, its decay naturally leads to successful leptogenesis, as
well as significant dilution of dangerous inflationary relics, such as the
gravitino. The resulting baryon asymmetry is independent of other cosmological
initial conditions. This attractive variant of leptogenesis requires at least
one of the rhd neutrinos to have small Yukawa coupling and to have mass ~ 10^6
GeV, much smaller than the grand unified (GUT) scale. We show that these
features naturally arise in the context of independently motivated and
successful 5d orbifold GUTs with inverse-GUT-scale-sized extra dimensions. Rhd
neutrinos are realized as bulk fields N_i with 5d bulk masses, while Yukawa
couplings and lepton-number-violating masses for the N_i are localized at the
SM boundary. The exponential suppression of the would-be N_i zero-modes leads
to the desired small 4d Yukawa couplings and small masses for the rhd neutrino
states. The see-saw prediction for the lhd neutrino mass scale is automatically
maintained. We show that this realization of rhd neutrinos is nicely
accommodated within an attractive orbifold-GUT flavour model, where all flavour
hierarchies have a geometrical origin.Comment: LaTeX, 10 pages, clarifying comments adde
The non-adiabatic pressure in general scalar field systems
We discuss the non-adiabatic or entropy perturbation, which controls the
evolution of the curvature perturbation in the uniform density gauge, for a
scalar field system minimally coupled to gravity with non-canonical action. We
highlight the differences between the sound and the phase speed in these
systems, and show that the non-adiabatic pressure perturbation vanishes in the
single field case, resulting in the conservation of the curvature perturbation
on large scales.Comment: 6 pages, revtex4; v2: typos corrected, results clarified, version
being submitted; v3: version accepted for publicatio
QCD Correction to Neutralino Annihilation Process and Dark Matter Density in Supersymmetric Models
We calculate QCD correction to the neutralino annihilation cross section into
quark anti-quark final state and discuss its implications to the calculation of
neutralino relic density. We see that the QCD correction enhances the
pair-annihilation cross section by O(10 %) when final-state quarks are
non-relativistic. Consequently, when the lightest neutralinos dominantly
annihilate into a t\bar{t} pair, the relic density of the lightest neutralino
is significantly affected by the QCD correction, in particular when the
lightest-neutralino mass is close to the top-quark mass.Comment: 19 pages, 5 figure
Adiabatic Modes in Cosmology
We show that the field equations for cosmological perturbations in Newtonian
gauge always have an adiabatic solution, for which a quantity is
non-zero and constant in all eras in the limit of large wavelength, so that it
can be used to connect observed cosmological fluctuations in this mode with
those at very early times. There is also a second adiabatic mode, for which
vanishes for large wavelength, and in general there may be
non-adiabatic modes as well. These conclusions apply in all eras and whatever
the constituents of the universe, under only a mild technical assumption about
the wavelength dependence of the field equations for large wave length. In the
absence of anisotropic inertia, the perturbations in the adiabatic modes are
given for large wavelength by universal formulas in terms of the
Robertson--Walker scale factor. We discuss an apparent discrepancy between
these results and what appears to be a conservation law in all modes found for
large wavelength in synchronous gauge: it turns out that, although equivalent,
synchronous and Newtonian gauges suggest inequivalent assumptions about the
behavior of the perturbations for large wavelength.Comment: 24 pages, Latex, no special macro
Implications of the Curvaton on Inflationary Cosmology
We study implications of the curvaton, a late-decaying light scalar field, on
inflationary cosmology, paying particular attentions to modifications of
observable quantities such as the scalar spectral index of the primordial power
spectrum and the tensor-to-scalar ratio. We consider this issue from a general
viewpoint and discuss how the observable quantities are affected by the
existence of the curvaton. It is shown that the modification owing to the
curvaton depends on class of inflation models. We also study the effects of the
curvaton on inflation models generated by the inflationary flow equation.Comment: 21 pages, 9 figure
Curvaton Scenario with Affleck-Dine Baryogenesis
We discuss the curvaton scenario with the Affleck-Dine baryogenesis. In this
scenario, non-vanishing baryonic entropy fluctuation may be generated even
without primordial fluctuation of the Affleck-Dine field. Too large entropy
fluctuation is inconsistent with the observations and hence constraints on the
curvaton scenario with the Affleck-Dine baryogenesis are obtained. We calculate
the baryonic entropy fluctuation (as well as other cosmological density
fluctuations) in this case and derive constraints. Implications to some of the
models of the curvaton are also discussed.Comment: 16 pages,2 figure
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