733,616 research outputs found
Model Dependence of the 2H Electric Dipole Moment
Background: Direct measurement of the electric dipole moment (EDM) of the
neutron lies in the future; measurement of a nuclear EDM may well come first.
The deuteron is one nucleus for which exact model calculations are feasible.
Purpose: We explore the model dependence of deuteron EDM calculations. Methods:
Using a separable potential formulation of the Hamiltonian, we examine the
sensitivity of the deuteron EDM to variation in the nucleon-nucleon
interaction. We write the EDM as the sum of two terms, the first depending on
the target wave function with plane-wave intermediate states, and the second
depending on intermediate multiple scattering in the 3P1 channel, the latter
being sensitive to the off-shell behavior of the 3P1 amplitude. Results: We
compare the full calculation with the plane-wave approximation result, examine
the tensor force contribution to the model results, and explore the effect of
short range repulsion found in realistic, contemporary potential models of the
deuteron. Conclusions: Because one-pion exchange dominates the EDM calculation,
separable potential model calculations will provide an adequate description of
the 2H EDM until such time as a better than 10% measurement is obtained.Comment: 21 pages, 2 figures, submitted to Physical Review
The quenching of star formation in accretion-driven clumpy turbulent tori of active galactic nuclei
Galactic gas-gas collisions involving a turbulent multiphase ISM share common
ISM properties: dense extraplanar gas visible in CO, large linewidths (>= 50
km/s), strong mid-infrared H_2 line emission, low star formation activity, and
strong radio continuum emission. Gas-gas collisions can occur in the form of
ICM ram pressure stripping, galaxy head-on collisions, compression of the
intragroup gas and/or galaxy ISM by an intruder galaxy which flies through the
galaxy group at a high velocity, or external gas accretion on an existing gas
torus in a galactic center. We suggest that the common theme of all these
gas-gas interactions is adiabatic compression of the ISM leading to an increase
of the turbulent velocity dispersion of the gas. The turbulent gas clouds are
then overpressured and star formation is quenched. Within this scenario we
developed a model for turbulent clumpy gas disks where the energy to drive
turbulence is supplied by external infall or the gain of potential energy by
radial gas accretion within the disk. The cloud size is determined by the size
of a C-type shock propagating in dense molecular clouds with a low ionization
fraction at a given velocity dispersion. We give expressions for the expected
volume and area filling factors, mass, density, column density, and velocity
dispersion of the clouds. The latter is based on scaling relations of
intermittent turbulence whose open parameters are estimated for the CND in the
Galactic Center. The properties of the model gas clouds and the external mass
accretion rate necessary for the quenching of the star formation rate due to
adiabatic compression are consistent with those derived from high-resolution
H_2 line observations. Based on these findings, a scenario for the evolution of
gas tori in galactic centers is proposed and the implications for star
formation in the Galactic Center are discussed.Comment: 13 pages, 1 figure, accepted for publication by A&
Thermally-driven Neutron Star Glitches
We examine the thermal and dynamical response of a neutron star to a sudden
perturbation of the inner crust temperature. During the star's evolution,
starquakes and other processes may deposit \gap 10^{42} ergs, causing
significant internal heating and increased frictional coupling between the
crust and the more rapidly rotating neutron superfluid the star is expected to
contain. Through numerical simulation we study the propagation of the thermal
wave created by the energy deposition, the induced motion of the interior
superfluid, and the resulting spin evolution of the crust. We find that energy
depositions of ergs produce gradual spin-ups above the timing
noise level, while larger energy depositions produce sudden spin jumps
resembling pulsar glitches. For a star with a temperature in the observed range
of the Vela pulsar, an energy deposition of ergs produces a
large spin-up taking place over minutes, similar to the Vela ``Christmas''
glitch. Comparable energy deposition in a younger and hotter ``Crab-like'' star
produces a smaller spin-up taking place over day, similar to that seen
during the partially time-resolved Crab glitch of 1989.Comment: 21 pages plus 17 figures, uuencode compressed Postscript. Accepted
for publication in the Astrophysical Journa
The Z^0-tagged jet event asymmetry in heavy-ion collisions at the CERN Large Hadron Collider
Tagged jet measurements provide a promising experimental channel to quantify
the similarities and differences in the mechanisms of jet production in
proton-proton and nucleus-nucleus collisions. We present the first calculation
of the transverse momentum asymmetry of Z^0/gamma^*-tagged jet events in
sqrt{s}=2.76$ TeV reactions at the LHC. Our results combine the
O(G_F\alpha_s^2) perturbative cross sections with the radiative and collisional
processes that modify parton showers in the presence of dense QCD matter. We
find that a strong asymmetry is generated in central lead-lead reactions that
has little sensitivity to the fluctuations of the underlying soft hadronic
background. We present theoretical model predictions for its shape and
magnitude.Comment: 4 pages, 4 figures, as published in PR
Bott - Borel - Weil Construction For Quantum Supergroup Uq(gl(m|n))
The finite dimensional irreducible representations of the quantum supergroup
are constructed geometrically using techniques from the Bott -
Borel - Weil theory and vector coherent states.Comment: Latex, 22 page
Spin-fluctuation theory beyond Gaussian approximation
A characteristic feature of the Gaussian approximation in the
functional-integral approach to the spin-fluctuation theory is the jump phase
transition to the paramagnetic state. We eliminate the jump and obtain a
continuous second-order phase transition by taking into account high-order
terms in the expansion of the free energy in powers of the fluctuating exchange
field. The third-order term of the free energy renormalizes the mean field, and
fourth-order term, responsible for the interaction of the fluctuations,
renormalizes the spin susceptibility. The extended theory is applied to the
calculation of magnetic properties of Fe-Ni Invar.Comment: 20 pages, 4 figure
Third Harmonic Cavity Modal Analysis
Third harmonic cavities have been designed and fabricated by FNAL to be used
at the FLASH/XFEL facility at DESY to minimise the energy spread along the
bunches. Modes in these cavities are analysed and the sensitivity to frequency
errors are assessed. A circuit model is employed to model the monopole bands.
The monopole circuit model is enhanced to include successive cell coupling, in
addition to the usual nearest neighbour coupling. A mode matching code is used
to facilitate rapid simulations, incorporating fabrication errors. Curves
surfaces are approximated by a series of abrupt transitions and the validity of
this approach is examinedComment: Proceedings of 14th International Conference on RF Superconductivity
(SRF 2009), 2009, Berlin, German
- …