10,074 research outputs found
Glassy Dynamics in a Frustrated Spin System: Role of Defects
In an effort to understand the glass transition, the kinetics of a spin model
with frustration but no quenched randomness has been analyzed. The
phenomenology of the spin model is remarkably similiar to that of structural
glasses. Analysis of the model suggests that defects play a major role in
dictating the dynamics as the glass transition is approached.Comment: 9 pages, 5 figures, accepted in J. Phys.: Condensed Matter,
proceedings of the Trieste workshop on "Unifying Concepts in Glass Physics
Dirac Leptogenesis with a Non-anomalous Family Symmetry
We propose a model for Dirac leptogenesis based on a non-anomalous
gauged family symmetry. The anomaly cancellation conditions are
satisfied with no new chiral fermions other than the three right-handed
neutrinos, giving rise to stringent constraints among the charges. Realistic
masses and mixing angles are obtained for all fermions. The model predicts
neutrinos of the Dirac type with naturally suppressed masses. Dirac
leptogenesis is achieved through the decay of the flavon fields. The cascade
decays of the vector-like heavy fermions in the Froggatt-Nielsen mechanism play
a crucial role in the separation of the primodial lepton numbers. We find that
a large region of parameter space of the model gives rise to a sufficient
cosmological baryon number asymmetry through Dirac leptogenesis.Comment: 8 pages, 8 figures, version to appear in JHE
A New Approach to Testing Dark Energy Models by Observations
We propose a new approach to the consistency test of dark energy models with
observations. To test a category of dark energy models, we suggest introducing
a characteristic Q(z) that in general varies with the redshift z but in those
models plays the role of a (constant) distinct parameter. Then, by
reconstructing dQ(z)/dz from observational data and comparing it with zero we
can assess the consistency between data and the models under consideration. For
a category of models that passes the test, we can further constrain the
distinct parameter of those models by reconstructing Q(z) from data. For
demonstration, in this paper we concentrate on quintessence. In particular we
examine the exponential potential and the power-law potential via a widely used
parametrization of the dark energy equation of state, w(z) = w_0 + w_a z/(1+z),
for data analysis. This method of the consistency test is particularly
efficient because for all models we invoke the constraint of only a single
parameter space that by choice can be easily accessed. The general principle of
our approach is not limited to dark energy. It may also be applied to the
testing of various cosmological models and even the models in other fields
beyond the scope of cosmology.Comment: 19 pages, 5 figure
High energy pseudogap and its evolution with doping in Fe-based superconductors as revealed by optical spectroscopy
We report optical spectroscopic measurements on electron- and hole-doped
BaFe2As2. We show that the compounds in the normal state are not simple metals.
The optical conductivity spectra contain, in addition to the free carrier
response at low frequency, a temperature-dependent gap-like suppression at
rather high energy scale near 0.6 eV. This suppression evolves with the
As-Fe-As bond angle induced by electron- or hole-doping. Furthermore, the
feature becomes much weaker in the Fe-chalcogenide compounds. We elaborate that
the feature is caused by the strong Hund's rule coupling effect between the
itinerant electrons and localized electron moment arising from the multiple Fe
3d orbitals. Our experiments demonstrate the coexistence of itinerant and
localized electrons in iron-based compounds, which would then lead to a more
comprehensive picture about the metallic magnetism in the materials.Comment: 6 pages, 7 figure
Search for the Lepton-Number-Violating Decay
A sensitive search for the lepton-number-violating decay has been performed using a sample of hyperons
produced in 800 GeV/ -Cu collisions. We obtain at 90% confidence, improving on the best
previous limit by four orders of magnitude.Comment: 9 pages, 5 figures, to be published in Phys. Rev. Let
Static Charge Density Wave Order in the Superconducting State of La2-xBaxCuO4
Charge density wave (CDW) correlations feature prominently in the phase
diagram of the cuprates, motivating competing theories of whether fluctuating
CDW correlations aid superconductivity or whether static CDW order coexists
with superconductivity in inhomogeneous or spatially modulated states. Here we
report Cu -edge resonant x-ray photon correlation spectroscopy (XPCS)
measurements of CDW correlations in superconducting LaBaCuO
. Static CDW order is shown to exist in the superconducting state at
low temperatures and to persist up to at least 85\% of the CDW transition
temperature. We discuss the implications of our observations for how
\emph{nominally} competing order parameters can coexist in the cuprates.Comment: 6 pages, 5 figures, Accepted in Phys. Rev. B Rapid Communication
Measurement of the Alpha Asymmetry Parameter for the Omega- to Lambda K- Decay
We have measured the alpha parameter of the Omega- to Lambda K- decay using
data collected with the HyperCP spectrometer during the 1997 fixed-target run
at Fermilab. Analyzing a sample of 0.96 million Omega- to Lambda K^-, Lambda to
p pi- decays, we obtain alpha_Omega*alpha_Lambda =
[1.33+/-0.33(stat)+/-0.52(syst)] x 10^{-2}. With the accepted value of
alpha_Lambda, alpha_Omega is found to be [2.07+/-0.51(stat)+/-0.81(syst)] x
10^{-2}.Comment: 5 pages, 4 figures, to be appeared as a Rapid Communication in Phys.
Rev.
Multidimensional Conservation Laws: Overview, Problems, and Perspective
Some of recent important developments are overviewed, several longstanding
open problems are discussed, and a perspective is presented for the
mathematical theory of multidimensional conservation laws. Some basic features
and phenomena of multidimensional hyperbolic conservation laws are revealed,
and some samples of multidimensional systems/models and related important
problems are presented and analyzed with emphasis on the prototypes that have
been solved or may be expected to be solved rigorously at least for some cases.
In particular, multidimensional steady supersonic problems and transonic
problems, shock reflection-diffraction problems, and related effective
nonlinear approaches are analyzed. A theory of divergence-measure vector fields
and related analytical frameworks for the analysis of entropy solutions are
discussed.Comment: 43 pages, 3 figure
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