10,026 research outputs found
Holographic Estimate of Oblique Corrections for Technicolor
We study the oblique corrections to the electroweak interaction in the
holographic model of technicolor theories. The oblique S parameter is expressed
in terms of a solution to the equations of motion for the AdS bulk gauge
fields. By analyzing the solution, we establish a rigorous proof that the S
parameter is positive and is reduced by walking. We also present the precise
numerical values for the S parameter of various technicolor models by solving
the equations numerically.Comment: 10 pages, 1 figure, RevTeX 4.0: published version. references adde
Unexpected Structures for Intercalation of Sodium in Epitaxial Graphene-SiC Interfaces
We show using scanning tunneling microscopy, spectroscopy, and ab initio
calculations that several intercalation structures exist for Na in epitaxial
graphene on SiC(0001). Intercalation takes place at room temperature and Na
electron-dopes the graphene. It intercalates in-between single-layer graphene
and the carbon-rich interfacial layer. It also penetrates beneath the
interfacial layer and decouples it to form a second graphene layer. This
decoupling is accelerated by annealing and is verified by direct Na deposition
onto the interface layer. Our observations show that intercalation in graphene
is fundamentally different than in graphite and is a versatile means of
electronic control.Comment: 10 pages text, 2 pages, references, and 4 figure page
LFV in semileptonic decays and conversion in nuclei in SUSY-seesaw
Here we review the main results of LFV in the semileptonic tau decays (), (), and () as well as in conversion in nuclei within SUSY-seesaw scenarios,
and compare our predictions with the present experimental boundsComment: Talk given by M. J. Herrero in SUSY08 conference, Seou
Micro-resonator soliton generated directly with a diode laser
An external-cavity diode laser is reported with ultralow noise, high power
coupled to a fiber, and fast tunability. These characteristics enable the
generation of an optical frequency comb in a silica micro-resonator with a
single-soliton state. Neither an optical modulator nor an amplifier was used in
the experiment. This demonstration greatly simplifies the soliton generation
setup and represents a significant step forward to a fully integrated soliton
comb system.Comment: 7 pages, 5 figure
A criterion for the nature of the superconducting transition in strongly interacting field theories : Holographic approach
It is beyond the present techniques based on perturbation theory to reveal
the nature of phase transitions in strongly interacting field theories.
Recently, the holographic approach has provided us with an effective dual
description, mapping strongly coupled conformal field theories to classical
gravity theories. Resorting to the holographic superconductor model, we propose
a general criterion for the nature of the superconducting phase transition
based on effective interactions between vortices. We find "tricritical" points
in terms of the chemical potential for U(1) charges and an effective
Ginzburg-Landau parameter, where vortices do not interact to separate the
second order (repulsive) from the first order (attractive) transitions. We
interpret the first order transition as the Coleman-Weinberg mechanism, arguing
that it is relevant to superconducting instabilities around quantum
criticality.Comment: 7 pages, 7 figure
Quantum Number Density Asymmetries Within QCD Jets Correlated With Lambda Polarization
The observation of jets in a variety of hard-scattering processes has allowed
the quantitative study of perturbative quantum chromodynamics (PQCD) by
comparing detailed theoretical predictions with a wide range of experimental
data. This paper examines how some important, nonperturbative, facets of QCD
involving the internal dynamical structure of jets can be studied by measuring
the spin orientation of Lambda particles produced in these jets. The
measurement of the transverse polarization for an individual Lambda within a
QCD jet permits the definition of spin-directed asymmetries in local quantum
number densities in rapidity space (such as charge, strangeness and baryon
number densities) involving neighboring hadrons in the jet. These asymmetries
can only be generated by soft, nonperturbative dynamical mechanisms and such
measurements can provide insight not otherwise accessible into the color
rearrangement that occurs during the hadronization stage of the fragmentation
process.Comment: The replacement manuscript contains a new abstract, five pages of
additional material and a revised version of Fig.
Antiferromagnetic metal to heavy-fermion metal quantum phase transition in the Kondo lattice model: A strong coupling approach
We study the quantum phase transition from an antiferromagnetic metal to a
heavy fermion metal in the Kondo lattice model. Based on the strong coupling
approach we {\it first} diagonalize the Kondo coupling term. Since this strong
coupling approach makes the resulting Kondo term {\it relevant}, the Kondo
hybridization persists even in the antiferromagnetic metal, indicating that
fluctuations of Kondo singlets are not critical in the phase transition. We
find that the quantum transition in our strong coupling approach results from
{\it softening of antiferromagnetic spin fluctuations of localized spins},
driven by the Kondo interaction. Thus, the volume change of Fermi surface
becomes continuous across the transition. .....
Janus and Multifaced Supersymmetric Theories
We investigate the various properties Janus supersymmetric Yang-Mills
theories. A novel vacuum structure is found and BPS monopoles and dyons are
studied. Less supersymmetric Janus theories found before are derived by a
simpler method. In addition, we find the supersymmetric theories when the
coupling constant depends on two and three spatial coordinates.Comment: 20 pages, no figures, typos, equations corrected. Additional comment
Perspectives: Quantum Mechanics on Phase Space
The basic ideas in the theory of quantum mechanics on phase space are
illustrated through an introduction of generalities, which seem to underlie
most if not all such formulations and follow with examples taken primarily from
kinematical particle model descriptions exhibiting either Galileian or
Lorentzian symmetry. The structures of fundamental importance are the relevant
(Lie) groups of symmetries and their homogeneous (and associated) spaces that,
in the situations of interest, also possess Hamiltonian structures. Comments
are made on the relation between the theory outlined and a recent paper by
Carmeli, Cassinelli, Toigo, and Vacchini.Comment: "Quantum Structures 2004" - Meeting of the International Quantum
Structures Association; Denver, Colorado; 17-22 July, 200
Neutrino reactions via neutral and charged current by Quasi-particle Random Phase Approximation(QRPA)
We developed the quasi-particle random phase approximation (QRPA) for the
neutrino scattering off even-even nuclei via neutral current (NC) and charged
cur- rent (CC). The QRPA has been successfully applied for the \beta and
\beta\beta decay of relevant nuclei. To describe neutrino scattering, general
multipole transitions by weak interactions with a finite momentum transfer are
calculated for NC and CC reaction with detailed formalism. Since we consider
neutron-proton (np) pairing as well as neutron-neutron (nn) and proton-proton
(pp) pairing correlations, the nn + pp QRPA and np QRPA are combined in a
framework, which enables to describe both NC and CC reactions in a consistent
way. Numerical results for \nu-^{12}C, -^{56}Fe and -^{56}Ni reactions are
shown to comply with other theoretical calculations and reproduce well
available experimental data
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