48,522 research outputs found
Presymmetry beyond the Standard Model
We go beyond the Standard Model guided by presymmetry, the discrete
electroweak quark-lepton symmetry hidden by topological effects which explain
quark fractional charges as in condense matter physics. Partners of the
particles of the Standard Model and the discrete symmetry associated with this
partnership appear as manifestations of a residual presymmetry and its
extension from matter to forces. This duplication of the spectrum of the
Standard Model keeps spin and comes nondegenerated about the TeV scale.Comment: 6 pages, 11 figures. To be published in the proceedings of DPF-2009,
Detroit, MI, July 2009, eConf C09072
Experimental and analytical tools for evaluation of Stirling engine rod seal behavior
The first year of a two year experimental and analytical program is reported. The program is directed at the elastohydrodynamic behavior of sliding elastomeric rod seals for the Stirling engine. During the year, experimental and analytical tools were developed for evaluating seal leakage, seal friction, and the fluid film thickness at the seal/cylinder interface
On the Casimir effect for parallel plates in the spacetime with one extra compactified dimension
In this paper, the Casimir effect for parallel plates in the presence of one
compactified universal extra dimension is reexamined in detail. Having
regularized the expressions of Casimir force, we show that the nature of
Casimir force is repulsive if the distance between the plates is large enough,
which is disagree with the experimental phenomena.Comment: 7 pages, 3 figure
Modulation Doping near Mott-Insulator Heterojunctions
We argue that interesting strongly correlated two-dimensional electron
systems can be created by modulation doping near a heterojunction between Mott
insulators. Because the dopant atoms are remote from the carrier system, the
electronic system will be weakly disordered. We argue that the competition
between different ordered states can be engineered by choosing appropriate
values for the dopant density and the setback distance of the doping layer. In
particular larger setback distances favor two-dimensional antiferromagnetism
over ferromagnetism. We estimate some key properties of modulation-doped Mott
insulator heterojunctions by combining insights from Hartree-Fock-Theory and
Dynamical-Mean-Field-Theory descriptions and discuss potentially attractive
material combinations.Comment: 9 pages, 9 figures, submitte
Colossal negative magnetoresistance in dilute fluorinated graphene
Adatoms offer an effective route to modify and engineer the properties of
graphene. In this work, we create dilute fluorinated graphene using a clean,
controlled and reversible approach. At low carrier densities, the system is
strongly localized and exhibits an unexpected, colossal negative
magnetoresistance. The zero-field resistance is reduced by a factor of 40 at
the highest field of 9 T and shows no sign of saturation. Unusual "staircase"
field dependence is observed below 5 K. The magnetoresistance is highly
anisotropic. We discuss possible origins, considering quantum interference
effects and adatom-induced magnetism in graphene.Comment: 21 pages, 4 figures, including supplementary informatio
Phenomenological Analysis of D Meson Lifetimes
The QCD-based operator-product-expansion technique is systematically applied
to the study of charmed meson lifetimes. We stress that it is crucial to take
into account the momentum of the spectator light quark of charmed mesons,
otherwise the destructive Pauli-interference effect in decays will lead
to a negative decay width for the . We have applied the QCD sum rule
approach to estimate the hadronic matrix elements of color-singlet and
color-octet 4-quark operators relevant to nonleptonic inclusive decays. The
lifetime of is found to be longer than that of because the latter
receives a constructive -exchange contribution, whereas the hadronic
annihilation and leptonic contributions to the former are compensated by the
Pauli interference. We obtain the lifetime ratio
, which is larger than some earlier theoretical
estimates, but still smaller than the recent measurements by CLEO and E791.Comment: 14 pages, 3 figure
Analyticity and crossing symmetry of the eikonal amplitudes in gauge theories
After a brief review and a more refined analysis of some relevant analyticity
properties (when going from Minkowskian to Euclidean theory) of the high-energy
parton-parton and hadron-hadron scattering amplitudes in gauge theories,
described nonperturbatively, in the eikonal approximation, by certain
correlation functions of two Wilson lines or two Wilson loops near the light
cone, we shall see how these same properties lead to a nice geometrical
interpretation of the crossing symmetry between quark-quark and quark-antiquark
eikonal amplitudes and also between loop-loop eikonal amplitudes. This relation
between Minkowskian-to-Euclidean analyticity properties and crossing symmetry
is discussed in detail and explicitly tested in the first orders of
perturbation theory. Some nonperturbative examples existing in the literature
are also discussed.Comment: Completely revised version with new comments, new references and new
figures; 37 pages + 5 figure
SU(2) Non-Abelian Holonomy and Dissipationless Spin Current in Semiconductors
Following our previous work [S. Murakami, N. Nagaosa, S. C. Zhang, Science
301, 1348 (2003)] on the dissipationless quantum spin current, we present an
exact quantum mechanical calculation of this novel effect based on the linear
response theory and the Kubo formula. We show that it is possibxle to define an
exactly conserved spin current, even in the presence of the spin-orbit coupling
in the Luttinger Hamiltonian of p-type semiconductors. The light- and the
heavy-hole bands form two Kramers doublets, and an SU(2) non-abelian gauge
field acts naturally on each of the doublets. This quantum holonomy gives rise
to a monopole structure in momentum space, whose curvature tensor directly
leads to the novel dissipationless spin Hall effect, i.e., a transverse spin
current is generated by an electric field. The result obtained in the current
work gives a quantum correction to the spin current obtained in the previous
semiclassical approximation.Comment: 14 pages, 2 figures, added some discussions, to appear in Phys. Rev.
Local electronic structure near oxygen dopants in BSCCO-2212: a window on the high-Tc pair mechanism?
The cuprate material BSCCO-2212 is believed to be doped by a combination of
cation switching and excess oxygen. The interstitial oxygen dopants are of
particular interest because scanning tunnelling microscopy (STM) experiments
have shown that they are positively correlated with the local value of the
superconducting gap, and calculations suggest that the fundamental attraction
between electrons is modulated locally. In this work, we use density functional
theory to try to ascertain which locations in the crystal are energetically
most favorable for the O dopant atoms, and how the surrounding cage of atoms
deforms. Our results provide support for the identification of STM resonances
at -1eV with dopant interstitial O atoms, and show how the local electronic
structure is modified nearby.Comment: 5 pages, 3 figure
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