26,141 research outputs found
From yeV to TeV: Search for the neutron electric dipole moment
The existence of electric dipole moments (EDM) for fundamental particles signals time-reversal symmetry (T) violation accompanied by violation of parity (P); only upper limits have been established to date. Time-reversal violation in turn implies CP violation under the assumption that CPT is a good symmetry. The neutron is an attractive system for an EDM search, both because it is neutral and because a neutron EDM would be relatively easier to interpret than the comparable quantity for a nucleus or even an atom. We introduce briefly the key experimental requirements for such search and describe some aspects of the neutron EDM experiment planned for the Spallation Neutron Source at the US Oak Ridge National Laboratory
A dynamical model for the heavily ram pressure stripped Virgo spiral galaxy NGC 4522
A dynamical model including ram pressure stripping is applied to the strongly
HI deficient Virgo spiral galaxy NGC 4522. A carefully chosen model snapshot is
compared with existing VLA HI observations. The model successfully reproduces
the large-scale gas distribution and the velocity field. However it fails to
reproduce the large observed HI linewidths in the extraplanar component, for
which we give possible explanations. In a second step, we solve the induction
equation on the velocity fields of the dynamical model and calculate the large
scale magnetic field. Assuming a Gaussian distribution of relativistic
electrons we obtain the distribution of polarized radio continuum emission
which is also compared with our VLA observations at 6 cm. The observed maximum
of the polarized radio continuum emission is successfully reproduced. Our model
suggests that the ram pressure maximum occurred only ~50 Myr ago. Since NGC
4522 is located far away from the cluster center (~1 Mpc) where the
intracluster medium density is too low to cause the observed stripping if the
intracluster medium is static and smooth, two scenarios are envisaged: (i) the
galaxy moves very rapidly within the intracluster medium and is not even bound
to the cluster; in this case the galaxy has just passed the region of highest
intracluster medium density; (ii) the intracluster medium is not static but
moving due to the infall of the M49 group of galaxies. In this case the galaxy
has just passed the region of highest intracluster medium velocity. This study
shows the strength of combining high resolution HI and polarized radio
continuum emission with detailed numerical modeling of the evolution of the gas
and the large-scale magnetic field.Comment: 15 pages, 11 figures, accepted for publication in A&
Charge order and phase segregation in overdoped bilayer manganites
There have been recent reports of charge ordering around in the
bilayer manganites. At , there appears to be a coexistence region of
layered A-type antiferromagnetc and charge order. There are also reports of
orbital order in this region without any Jahn-Teller effect. Based on physical
grounds, this region is investigated from a model that incorporates the two
orbitals at each Mn site and a near-neighbour Coulomb repulsion. It is
shown that there indeed is both charge and orbital order close to the
half-doped region coincident with a layered magnetic structure. Although the
orbital order is known to drive the magnetic order, the layered magnetic
structure is also favoured in this system by the lack of coherent transport
across the planes and the reduced dimensionality of the lattice. The
anisotropic hopping across the orbitals and the underlying layered
structure largely determine the orbital arrangements in this region, while the
charge order is primarily due to the long range interactions.Comment: 6 pages, 6 figure
Measurement of transparency ratios for protons from short-range correlated pairs
Nuclear transparency, Tp(A), is a measure of the average probability for a
struck proton to escape the nucleus without significant re-interaction.
Previously, nuclear transparencies were extructed for quasi-elastic A(e,e'p)
knockout of protons with momentum below the Fermi momentum, where the spectral
functions are well known. In this paper we extract a novel observable, the
transparency ratio, Tp(A)/T_p(12C), for knockout of high-missing-momentum
protons from the breakup of short range correlated pairs (2N-SRC) in Al, Fe and
Pb nuclei relative to C. The ratios were measured at momentum transfer Q^2 >
1.5 (GeV/c)^2 and x_B > 1.2 where the reaction is expected to be dominated by
electron scattering from 2N-SRC. The transparency ratios of the knocked-out
protons coming from 2N-SRC breakup are 20 - 30% lower than those of previous
results for low missing momentum. They agree with Glauber calculations and
agree with renormalization of the previously published transparencies as
proposed by recent theoretical investigations. The new transparencies scale as
A^-1/3, which is consistent with dominance of scattering from nucleons at the
nuclear surface.Comment: 6 pages, 4 figure
Entrance-channel Mass-asymmetry Dependence of Compound-nucleus Formation Time in Light Heavy-ion Reactions
The entrance-channel mass-asymmetry dependence of the compound nucleus
formation time in light heavy-ion reactions has been investigated within the
framework of semiclassical dissipative collision models. the model calculations
have been succesfully applied to the formation of the Ar compound
nucleus as populated via the Be+Si, B+Al,
C+Mg and F+F entrance channels. The shape evolution
of several other light composite systems appears to be consistent with the
so-called "Fusion Inhibition Factor" which has been experimentally observed. As
found previously in more massive systems for the fusion-evaporation process,
the entrance-channel mass-asymmetry degree of freedom appears to determine the
competition between the different mechanisms as well as the time scales
involved.Comment: 12 pages, 3 Figures available upon request, Submitted at Phys. Rev.
Spin-wave propagation in a microstructured magnonic crystal
Transmission of microwave spin waves through a microstructured magnonic
crystal in the form of a permalloy waveguide of a periodically varying width
was studied experimentally and theoretically. The spin wave characteristics
were measured by spatially-resolved Brillouin light scattering microscopy. A
rejection frequency band was clearly observed. The band gap frequency was
controlled by the applied magnetic field. The measured spin-wave intensity as a
function of frequency and propagation distance is in good agreement with a
model calculation.Comment: 4 pages, 3 figure
Cataclysmic Variables and Other Compact Binaries in the Globular Cluster NGC 362: Candidates from Chandra and HST
Highly sensitive and precise X-ray imaging from Chandra, combined with the
superb spatial resolution of HST optical images, dramatically enhances our
empirical understanding of compact binaries such as cataclysmic variables and
low mass X-ray binaries, their progeny, and other stellar X-ray source
populations deep into the cores of globular clusters. Our Chandra X-ray images
of the globular cluster NGC 362 reveal 100 X-ray sources, the bulk of which are
likely cluster members. Using HST color-magnitude and color-color diagrams, we
quantitatively consider the optical content of the NGC 362 Chandra X-ray error
circles, especially to assess and identify the compact binary population in
this condensed-core globular cluster. Despite residual significant crowding in
both X-rays and optical, we identify an excess population of H{\alpha}-emitting
objects that is statistically associated with the Chandra X-ray sources. The
X-ray and optical characteristics suggest that these are mainly cataclysmic
variables, but we also identify a candidate quiescent low mass X-ray binary. A
potentially interesting and largely unanticipated use of observations such as
these may be to help constrain the macroscopic dynamic state of globular
clusters.Comment: 6 pages, 6 figures, to appear in the proceedings of the conference
"Binary Star Evolution: Mass Loss, Accretion, and Mergers," Mykonos, Greece,
June 22-25, 201
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