10,073 research outputs found
Non-equilibrium Transport in the Anderson model of a biased Quantum Dot: Scattering Bethe Ansatz Phenomenology
We derive the transport properties of a quantum dot subject to a source-drain
bias voltage at zero temperature and magnetic field. Using the Scattering Bethe
Anstaz, a generalization of the traditional Thermodynamic Bethe Ansatz to open
systems out of equilibrium, we derive exact results for the quantum dot
occupation out of equilibrium and, by introducing phenomenological spin- and
charge-fluctuation distribution functions in the computation of the current,
obtain the differential conductance for large U/\Gamma. The Hamiltonian to
describe the quantum dot system is the Anderson impurity Hamiltonian and the
current and dot occupation as a function of voltage are obtained numerically.
We also vary the gate voltage and study the transition from the mixed valence
to the Kondo regime in the presence of a non-equilibrium current. We conclude
with the difficulty we encounter in this model and possible way to solve them
without resorting to a phenomenological method.Comment: 20 pages, 20 figures, published versio
A Supersymmetric U(1)' Model with Multiple Dark Matters
We consider a scenario where a supersymmetric model has multiple dark matter
particles. Adding a U(1)' gauge symmetry is a well-motivated extension of the
Minimal Supersymmetric Standard Model (MSSM). It can cure the problems of the
MSSM such as the mu-problem or the proton decay problem with high-dimensional
lepton number and baryon number violating operators which R-parity allows. An
extra parity (U-parity) may arise as a residual discrete symmetry after U(1)'
gauge symmetry is spontaneously broken. The Lightest U-parity Particle (LUP) is
stable under the new parity becoming a new dark matter candidate. Up to three
massive particles can be stable in the presence of the R-parity and the
U-parity. We numerically illustrate that multiple stable particles in our model
can satisfy both constraints from the relic density and the direct detection,
thus providing a specific scenario where a supersymmetric model has
well-motivated multiple dark matters consistent with experimental constraints.
The scenario provides new possibilities in the present and upcoming dark matter
searches in the direct detection and collider experiments.Comment: 25 pages, 5 figure
Coarse-graining the dynamics of coupled oscillators
We present an equation-free computational approach to the study of the
coarse-grained dynamics of {\it finite} assemblies of {\it non-identical}
coupled oscillators at and near full synchronization. We use coarse-grained
observables which account for the (rapidly developing) correlations between
phase angles and oscillator natural frequencies. Exploiting short bursts of
appropriately initialized detailed simulations, we circumvent the derivation of
closures for the long-term dynamics of the assembly statistics.Comment: accepted for publication in Phys. Rev. Let
"Dark" Z implications for Parity Violation, Rare Meson Decays, and Higgs Physics
General consequences of mass mixing between the ordinary Z boson and a
relatively light Z_d boson, the "dark" Z, arising from a U(1)_d gauge symmetry,
associated with a hidden sector such as dark matter, are examined. New effects
beyond kinetic mixing are emphasized. Z-Z_d mixing introduces a new source of
low energy parity violation well explored by possible future atomic parity
violation and planned polarized electron scattering experiments. Rare K (B)
meson decays into pi (K) l^+ l^- (l = e, mu) and pi (K) nu anti-nu are found to
already place tight constraints on the size of Z-Z_d mixing. Those
sensitivities can be further improved with future dedicated searches at K and B
factories as well as binned studies of existing data. Z-Z_d mixing can also
lead to the Higgs decay H -> Z Z_d, followed by Z -> l_1^+ l_1^- and Z_d ->
l_2^+ l_2^- or "missing energy", providing a potential hidden sector discovery
channel at the LHC. An illustrative realization of these effects in a 2 Higgs
doublet model is presented.Comment: Version to appear in PR
Coarse-grained computations of demixing in dense gas-fluidized beds
We use an "equation-free", coarse-grained computational approach to
accelerate molecular dynamics-based computations of demixing (segregation) of
dissimilar particles subject to an upward gas flow (gas-fluidized beds). We
explore the coarse-grained dynamics of these phenomena in gently fluidized beds
of solid mixtures of different densities, typically a slow process for which
reasonable continuum models are currently unavailable
U(1)' solution to the mu-problem and the proton decay problem in supersymmetry without R-parity
The Minimal Supersymmetric Standard Model (MSSM) is plagued by two major
fine-tuning problems: the mu-problem and the proton decay problem. We present a
simultaneous solution to both problems within the framework of a U(1)'-extended
MSSM (UMSSM), without requiring R-parity conservation. We identify several
classes of phenomenologically viable models and provide specific examples of
U(1)' charge assignments. Our models generically contain either lepton number
violating or baryon number violating renormalizable interactions, whose
coexistence is nevertheless automatically forbidden by the new U(1)' gauge
symmetry. The U(1)' symmetry also prohibits the potentially dangerous and often
ignored higher-dimensional proton decay operators such as QQQL and UUDE which
are still allowed by R-parity. Thus, under minimal assumptions, we show that
once the mu-problem is solved, the proton is sufficiently stable, even in the
presence of a minimum set of exotics fields, as required for anomaly
cancellation. Our models provide impetus for pursuing the collider
phenomenology of R-parity violation within the UMSSM framework.Comment: Version published in Phys. Rev.
Higgs Sector in Extensions of the MSSM
Extensions of the Minimal Supersymmetric Standard Model (MSSM) with
additional singlet scalar fields solve the important mu-parameter fine tuning
problem of the MSSM. We compute and compare the neutral Higgs boson mass
spectra, including one-loop corrections, of the following MSSM extensions:
Next-to-Minimal Supersymmetric Standard Model (NMSSM), the nearly-Minimal
Supersymmetric Standard Model (nMSSM), and the U(1)'-extended Minimal
Supersymmetric Standard Model (UMSSM) by performing scans over model
parameters. We find that the Secluded U(1)'-extended Minimal Supersymmetric
Standard Model (sMSSM) is identical to the nMSSM if three of the additional
scalars decouple. The dominant part of the one-loop corrections are
model-independent since the singlet field does not couple to MSSM particles
other than the Higgs doublets. Thus, model-dependent parameters enter the
masses only at tree-level. We apply constraints from LEP bounds on the Standard
Model and MSSM Higgs boson masses and the MSSM chargino mass, the invisible Z
decay width, and the Z-Z' mixing angle. Some extended models permit a Higgs
boson with mass substantially below the SM LEP limit or above theoretical
limits in the MSSM. Ways to differentiate the models via masses, couplings,
decays and production of the Higgs bosons are discussed.Comment: 65 pages, 15 figures. Figure replaced and typos corrected. Version to
appear in Phys. Rev.
Effects of intra-animal nephron heterogeneity on studies of glomerular dynamics
Effects of intra-animal nephron heterogeneity on studies of glomerular dynamics. Quintuplicate determinations of the parameters measured in studies of glomerular dynamics revealed that the intra-animal coefficients of variation for Bowman's space and star vessel pressures, nephron filtration rate, and filtration fractions were 54 to 72% larger than the corresponding interanimal coefficients of variation; those for glomerular capillary pressure were more nearly equal. With a net efferent filtration pressure (ΔPE) of 10.6 ± SEM 1.92mm Hg, the rats were far from filtration pressure equilibrium and the calculated ultrafiltration coefficient (Kf) of 2.1 ± SEM 0.2 nl/min ·2mm Hg was lower than in many other studies. Statistical analysis revealed that the precision of estimates of both the measured and the derived parameters in glomerular dynamic studies is affected appreciably by ignoring the intra-animal effect. The importance of the intra-animal variance in glomerular dynamic studies is greatest when only one or two samples of each measured parameter are obtained in every rat (k = 1 or 2) and least when k is large. Triplicate sampling provides combined SEMS that are not greatly larger than those obtained with k = 5, however, and offers the greatest economy in studies of glomerular dynamics. The number of animals required to provide values with ΔPE and Kf that are within ± 20% of the “true” values is rather large.Effets de l'hétérogénéité néphronique intra-animale sur les études de la dynamique glomérulaire. Des déterminations en quintuple des paramètres mesurés dans les études de la dynamique glomérulaire ont révélé que les coefficients de variation intra-animale pour les pressions dans l'espace de Bowman et les vaisseaux étoilés, le débit de filtration glomérulaire et les fractions de filtration étaient 54 à 74% plus grandes que les coefficients de variation inter-animale correspondants; ceux de la pression capillaire glomérulaire étaient plus proches. Avec une pression de filtration effèrente nette (ΔPE) de 10,6 ± SEM 1,92mm Hg, les rats étaient loin d'une pression de filtration en équilibre, et le coefficient d'ultrafiltration calculé (Kf) de 2,1 ± SEM 0,2 nl/min ·2mm Hg était plus faible que lors de nombreuses autres études. L'analyse statistique a révélé que la précision des paramètres mesurés et déduits des études de la dynamique glomérulaire est affectée de façon appréciable en ignorant l'effet intra-animal. L'importance de la variance intra-animale dans les études de la dynamique glomérulaire est très grande lorsque seulement un ou deux échantillons de chaque paramètre mesuré sont obtenus chez chaque rat (k = 1 ou 2), et moindre lorsque k est élevé. Un échantillon-age triple offre cependant des SEM combinés qui ne sont pas beaucoup plus grands que ceux obtenus pour k = 5, cependant, et offre la plus forte économie lors des mesures de la dynamique glomérulaire. Le nombre d'animaux nécessaires pour obtenir des valeurs avec ΔE et Kf entre ± 20% des valeurs “vraies” est assez grand
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