239 research outputs found
Lepton Masses and Flavor Violation in Randall Sundrum Model
Lepton masses and mixing angles via localization of 5D fields in the bulk are
revisited in the context of Randall-Sundrum models. The Higgs is assumed to be
localized on the IR brane. Three cases for neutrino masses are considered: (a)
The higher dimensional LH.LH operator (b) Dirac masses (c) Type I see-saw with
bulk Majorana mass terms. Neutrino masses and mixing as well as charged lepton
masses are fit in the first two cases using minimisation for the bulk
mass parameters, while varying the Yukawa couplings between
0.1 and 4. Lepton flavour violation is studied for all the three cases. It is
shown that large negative bulk mass parameters are required for the right
handed fields to fit the data in the LH LH case. This case is characterized by
a very large Kaluza-Klein (KK) spectrum and relatively weak flavour violating
constraints at leading order. The zero modes for the charged singlets are
composite in this case and their corresponding effective 4-D Yukawa couplings
to the KK modes could be large. For the Dirac case, good fits can be obtained
for the bulk mass parameters, , lying between 0 and 1. However, most of
the `best fit regions' are ruled out from flavour violating constraints. In the
bulk Majorana terms case, we have solved the profile equations numerically. We
give example points for inverted hierarchy and normal hierarchy of neutrino
masses. Lepton flavor violating rates are large for these points. We then
discuss various minimal flavor violation (MFV) schemes for Dirac and bulk
Majorana cases. In the Dirac case with MFV hypothesis, it is possible to
simultaneously fit leptonic masses and mixing angles and alleviate lepton
flavor violating constraints for Kaluza-Klein modes with masses of around 3
TeV. Similar examples are also provided in the Majorana case.Comment: 43 pages, 20 figures, Revtex; version 2:a few clarified comments,
added references, Published in PRD versio
Dynamic imaging of the delay- and tilt-free motion of Néel domain walls in perpendicularly magnetized superlattices
We report on the time-resolved investigation of current- and field-induced domain wall motion in the flow regime in perpendicularly magnetized microwires exhibiting anti-symmetric exchange interaction by means of scanning transmission x-ray microscopy using a time step of 200 ps. The sub-ns time step of the dynamical images allowed us to observe the absence of incubation times for the motion of the domain wall within an uncertainty of 200 ps, together with indications for a negligible inertia of the domain wall. Furthermore, we observed that, for short current and magnetic field pulses, the magnetic domain walls do not exhibit a tilting during its motion, providing a mechanism for the fast, tilt-free, current-induced motion of magnetic domain walls
Straightening of Thermal Fluctuations in Semi-Flexible Polymers by Applied Tension
We investigate the propagation of a suddenly applied tension along a
thermally excited semi-flexible polymer using analytical approximations,
scaling arguments and numerical simulation. This problem is inherently
non-linear. We find sub-diffusive propagation with a dynamical exponent of 1/4.
By generalizing the internal elasticity, we show that tense strings exhibit
qualitatively different tension profiles and propagation with an exponent of
1/2.Comment: Latex file; with three postscript figures; .ps available at
http://dept.physics.upenn.edu/~nelson/pull.p
High precision measurement of the associated strangeness production in proton proton interactions
A new high precision measurement of the reaction pp -> pK+Lambda at a beam
momentum of 2.95 GeV/c with more than 200,000 analyzed events allows a detailed
analysis of differential observables and their inter-dependencies. Correlations
of the angular distributions with momenta are examined. The invariant mass
distributions are compared for different regions in the Dalitz plots. The cusp
structure at the N Sigma threshold is described with the Flatt\'e formalism and
its variation in the Dalitz plot is analyzed.Comment: accepted for publication in Eur. Phys. J.
First Model-Independent Measurement of the Spin Triplet Scattering Length from Final State Interaction in the Reaction
The reaction has been measured with the
COSY-TOF detector at a beam momentum of . The polarized
proton beam enables the measurement of the beam analyzing power by the
asymmetry of the produced kaon (). This observable allows the
spin triplet scattering length to be extracted for the first time
model independently from the final-state interaction in the reaction. The
obtained value is . This value is
compatible with theoretical predictions and results from model-dependent
analyses.Comment: Revised version as accepted for publication in PR
The Straw Tube Trackers of the PANDA Experiment
The PANDA experiment will be built at the FAIR facility at Darmstadt
(Germany) to perform accurate tests of the strong interaction through bar pp
and bar pA annihilation's studies. To track charged particles, two systems
consisting of a set of planar, closed-packed, self-supporting straw tube layers
are under construction. The PANDA straw tubes will have also unique
characteristics in term of material budget and performance. They consist of
very thin mylar-aluminized cathodes which are made self-supporting by means of
the operation gas-mixture over-pressure. This solution allows to reduce at
maximum the weight of the mechanical support frame and hence the detector
material budget. The PANDA straw tube central tracker will not only reconstruct
charged particle trajectories, but also will help in low momentum (< 1 GeV)
particle identification via dE/dx measurements. This is a quite new approach
that PANDA tracking group has first tested with detailed Monte Carlo
simulations, and then with experimental tests of detector prototypes. This
paper addresses the design issues of the PANDA straw tube trackers and the
performance obtained in prototype tests.Comment: 7 pages,16 figure
Deterministic Field-Free Skyrmion Nucleation at a Nanoengineered Injector Device
Magnetic skyrmions are topological solitons promising for applications as encoders for digital information. A number of different skyrmion-based memory devices have been recently proposed. In order to demonstrate a viable skyrmion-based memory device, it is necessary to reliably and reproducibly nucleate, displace, detect, and delete the magnetic skyrmions, possibly in the absence of external applied magnetic fields, which would needlessly complicate the device design. While the skyrmion displacement and detection have both been thoroughly investigated, much less attention has been dedicated to the study of the skyrmion nucleation process and its sub-nanosecond dynamics. In this study, we investigate the nucleation of magnetic skyrmions from a dedicated nanoengineered injector, demonstrating the reliable magnetic skyrmion nucleation at the remnant state. The sub-nanosecond dynamics of the skyrmion nucleation process were also investigated, allowing us to shine light on the physical processes driving the nucleation
History-dependent domain and skyrmion formation in 2D van der Waals magnet Fe3GeTe2
The discovery of two-dimensional magnets has initiated a new field of research, exploring both fundamental low-dimensional magnetism, and prospective spintronic applications. Recently, observations of magnetic skyrmions in the 2D ferromagnet Fe3GeTe2 (FGT) have been reported, introducing further application possibilities. However, controlling the exhibited magnetic state requires systematic knowledge of the history-dependence of the spin textures, which remains largely unexplored in 2D magnets. In this work, we utilise real-space imaging, and complementary simulations, to determine and explain the thickness-dependent magnetic phase diagrams of an exfoliated FGT flake, revealing a complex, history-dependent emergence of the uniformly magnetised, stripe domain and skyrmion states. The results show that the interplay of the dominant dipolar interaction and strongly temperature dependent out-of-plane anisotropy energy terms enables the selective stabilisation of all three states at zero field, and at a single temperature, while the Dzyaloshinksii-Moriya interaction must be present to realise the observed Néel-type domain walls. The findings open perspectives for 2D devices incorporating topological spin textures
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