530 research outputs found
Radiation MHD modeling of a proposed dynamic hohlraum
In this paper we report 2D radiation magnetohydrodynamic simulations of a dynamic hohlraum target designed to be driven by the Z accelerator at Sandia National Laboratory, Albuquerque New Mexico. Z generates currents up 20 MA with a rise time of 100 ns and peak electrical power of 40 TW. In this design we attempt to reduce the effects of magneto-Rayleigh Taylor (RT) modes by using a distributed initial density profile. Earlier work showed that ``tailoring`` the initial density profile could reduce the sheath acceleration and the number of e-foldings that the RT instability grows during the implosion . As the sheath moves in radially, fresh material is swept up or ``snow plowed``, providing a back pressure that counters the J x B force. A special profile can be found in which the unstable outer surface of the sheath implodes at constant velocity, reducing the classical growth rate to zero, although residual Richtmeyer-Meshkov type instability (instability of the snow-plow shock front) may be present. In practice, it is hard to create tailored initial density profiles due to the difficulty of machining and otherwise manipulating very low density materials. It becomes easier to manufacture these complex targets as the current, energy and load mass increase with large drivers. Z is the first fast pulse power device with enough energy to consider loads of this type
On the modification of the Efimov spectrum in a finite cubic box
Three particles with large scattering length display a universal spectrum of
three-body bound states called "Efimov trimers''. We calculate the modification
of the Efimov trimers of three identical bosons in a finite cubic box and
compute the dependence of their energies on the box size using effective field
theory. Previous calculations for positive scattering length that were
perturbative in the finite volume energy shift are extended to arbitrarily
large shifts and negative scattering lengths. The renormalization of the
effective field theory in the finite volume is explicitly verified. Moreover,
we investigate the effects of partial wave mixing and study the behavior of
shallow trimers near the dimer energy. Finally, we provide numerical evidence
for universal scaling of the finite volume corrections.Comment: 21 pages, 8 figures, published versio
Universality in Four-Boson Systems
We report recent advances on the study of universal weakly bound four-boson
states from the solutions of the Faddeev-Yakubovsky equations with zero-range
two-body interactions. In particular, we present the correlation between the
energies of successive tetramers between two neighbor Efimov trimers and
compare it to recent finite range potential model calculations. We provide
further results on the large momentum structure of the tetramer wave function,
where the four-body scale, introduced in the regularization procedure of the
bound state equations in momentum space, is clearly manifested. The results we
are presenting confirm a previous conjecture on a four-body scaling behavior,
which is independent of the three-body one. We show that the correlation
between the positions of two successive resonant four-boson recombination peaks
are consistent with recent data, as well as with recent calculations close to
the unitary limit. Systematic deviations suggest the relevance of range
corrections.Comment: Accepted for publication in special issue of Few-Body Systems devoted
to the Sixth Workshop on the Critical Stability of Quantum Few-Body Systems,
October 2011, Erice, Sicily, Ital
Parity-violating neutron spin rotation in hydrogen and deuterium
We calculate the (parity-violating) spin rotation angle of a polarized
neutron beam through hydrogen and deuterium targets, using pionless effective
field theory up to next-to-leading order. Our result is part of a program to
obtain the five leading independent low-energy parameters that characterize
hadronic parity-violation from few-body observables in one systematic and
consistent framework. The two spin-rotation angles provide independent
constraints on these parameters. Using naive dimensional analysis to estimate
the typical size of the couplings, we expect the signal for standard target
densities to be 10^-7 to 10^-6 rad/m for both hydrogen and deuterium targets.
We find no indication that the nd observable is enhanced compared to the np
one. All results are properly renormalized. An estimate of the numerical and
systematic uncertainties of our calculations indicates excellent convergence.
An appendix contains the relevant partial-wave projectors of the three-nucleon
system.Comment: 44 pages, 17 figures; minor corrections; to be published in EPJ
Trapped electron coupled to superconducting devices
We propose to couple a trapped single electron to superconducting structures
located at a variable distance from the electron. The electron is captured in a
cryogenic Penning trap using electric fields and a static magnetic field in the
Tesla range. Measurements on the electron will allow investigating the
properties of the superconductor such as vortex structure, damping and
decoherence. We propose to couple a superconducting microwave resonator to the
electron in order to realize a circuit QED-like experiment, as well as to
couple superconducting Josephson junctions or superconducting quantum
interferometers (SQUIDs) to the electron. The electron may also be coupled to a
vortex which is situated in a double well potential, realized by nearby pinning
centers in the superconductor, acting as a quantum mechanical two level system
that can be controlled by a transport current tilting the double well
potential. When the vortex is trapped in the interferometer arms of a SQUID,
this would allow its detection both by the SQUID and by the electron.Comment: 13 pages, 5 figure
Efimov physics from the functional renormalization group
Few-body physics related to the Efimov effect is discussed using the
functional renormalization group method. After a short review of
renormalization in its modern formulation we apply this formalism to the
description of scattering and bound states in few-body systems of identical
bosons and distinguishable fermions with two and three components. The Efimov
effect leads to a limit cycle in the renormalization group flow. Recently
measured three-body loss rates in an ultracold Fermi gas Li atoms are
explained within this framework. We also discuss briefly the relation to the
many-body physics of the BCS-BEC crossover for two-component fermions and the
formation of a trion phase for the case of three species.Comment: 28 pages, 13 figures, invited contribution to a special issue of
"Few-Body Systems" devoted to Efimov physics, published versio
Proton-proton scattering above 3 GeV/c
A large set of data on proton-proton differential cross sections, analyzing
powers and the double polarization parameter A_NN is analyzed employing the
Regge formalism. We find that the data available at proton beam momenta from 3
GeV/c to 50 GeV/c exhibit features that are very well in line with the general
characteristics of Regge phenomenology and can be described with a model that
includes the rho, omega, f_2, and a_2 trajectories and single Pomeron exchange.
Additional data, specifically for spin-dependent observables at forward angles,
would be very helpful for testing and refining our Regge model.Comment: 16 pages, 19 figures; revised version accepted for publication in
EPJ
Origins of the Ambient Solar Wind: Implications for Space Weather
The Sun's outer atmosphere is heated to temperatures of millions of degrees,
and solar plasma flows out into interplanetary space at supersonic speeds. This
paper reviews our current understanding of these interrelated problems: coronal
heating and the acceleration of the ambient solar wind. We also discuss where
the community stands in its ability to forecast how variations in the solar
wind (i.e., fast and slow wind streams) impact the Earth. Although the last few
decades have seen significant progress in observations and modeling, we still
do not have a complete understanding of the relevant physical processes, nor do
we have a quantitatively precise census of which coronal structures contribute
to specific types of solar wind. Fast streams are known to be connected to the
central regions of large coronal holes. Slow streams, however, appear to come
from a wide range of sources, including streamers, pseudostreamers, coronal
loops, active regions, and coronal hole boundaries. Complicating our
understanding even more is the fact that processes such as turbulence,
stream-stream interactions, and Coulomb collisions can make it difficult to
unambiguously map a parcel measured at 1 AU back down to its coronal source. We
also review recent progress -- in theoretical modeling, observational data
analysis, and forecasting techniques that sit at the interface between data and
theory -- that gives us hope that the above problems are indeed solvable.Comment: Accepted for publication in Space Science Reviews. Special issue
connected with a 2016 ISSI workshop on "The Scientific Foundations of Space
Weather." 44 pages, 9 figure
Search for a W' boson decaying to a bottom quark and a top quark in pp collisions at sqrt(s) = 7 TeV
Results are presented from a search for a W' boson using a dataset
corresponding to 5.0 inverse femtobarns of integrated luminosity collected
during 2011 by the CMS experiment at the LHC in pp collisions at sqrt(s)=7 TeV.
The W' boson is modeled as a heavy W boson, but different scenarios for the
couplings to fermions are considered, involving both left-handed and
right-handed chiral projections of the fermions, as well as an arbitrary
mixture of the two. The search is performed in the decay channel W' to t b,
leading to a final state signature with a single lepton (e, mu), missing
transverse energy, and jets, at least one of which is tagged as a b-jet. A W'
boson that couples to fermions with the same coupling constant as the W, but to
the right-handed rather than left-handed chiral projections, is excluded for
masses below 1.85 TeV at the 95% confidence level. For the first time using LHC
data, constraints on the W' gauge coupling for a set of left- and right-handed
coupling combinations have been placed. These results represent a significant
improvement over previously published limits.Comment: Submitted to Physics Letters B. Replaced with version publishe
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