6,085 research outputs found
Decaying dark matter with heavy axino
A TeV scale decaying dark matter chiral multiplet N is introduced in addition
to the minimal supersymmetric standard model(MSSM). For a calculable abundance
of N, we introduce heavy axino decaying to N and MSSM particles including the
lightest supersymmetric particle(LSP). In the scenario that heavy axino, once
dominating the energy density of the universe, decays after the LSP decouples,
it is possible to estimate the relative cosmic abundances of N and the LSP.
Dimension 6 interactions allow the lifetime of the fermionic or the bosonic
superpartner of N in the 10^{27} s range to be compatible with the recent
astrophysical bounds. A diagrammatic strategy obtaining a suppression factor
1/M^2 is also given.Comment: 5 pages with 2 figure
Renormalization group theory of nematic ordering in d-wave superconductors
We examine the quantum theory of the spontaneous breaking of lattice rotation
symmetry in d-wave superconductors on the square lattice. This is described by
a field theory of an Ising nematic order parameter coupled to the gapless
fermionic quasiparticles. We determine the structure of the renormalization
group to all orders in a 1/N_f expansion, where N_f is the number of fermion
spin components. Asymptotically exact results are obtained for the quantum
critical theory in which, as in the large N_f theory, the nematic order has a
large anomalous dimension, and the fermion spectral functions are highly
anisotropic.Comment: 17 pages, 8 figure
Simulation of Electrospray Emission Processes for Highly Conductive Liquids
An electrohydrodynamic numerical model is used to explore the electrospray
emission behavior of both moderate and high electrical conductivity liquids
under electrospray conditions. The Volume-of-Fluid method, incorporating a
leaky-dielectric model with a charge relaxation consideration, is used to
conserve charge to accurately model cone-jet formation and droplet breakup. The
model is validated against experiments and agrees well with both droplet
diameters and charge-to-mass ratio of emitted progeny droplets. The model
examines operating conditions such as flow rate and voltage, with fluid
properties also considered, such as surface tension, electrical conductivity,
and viscosity for both moderate and high conductivity. For high conductivity
and surface tension, the results show that high charge concentration along with
the meniscus and convex cone shape results in a higher charge-to-mass ratio of
the emitted droplets while lower conductivity and surface tension tend towards
concave cone shapes and lower charge-to-mass droplets. Recirculation flows
inside the bulk liquid are investigated across a range of non-dimensional flow
rates, and electric Reynolds numbers. For high conductivity liquid emission at
the minimum stable flow rate, additional recirculation cells develop near the
cone tip suggesting the onset of the axisymmetric instability.Comment: submitted to Journal of Fluid Mechanic
Data-Discriminants of Likelihood Equations
Maximum likelihood estimation (MLE) is a fundamental computational problem in
statistics. The problem is to maximize the likelihood function with respect to
given data on a statistical model. An algebraic approach to this problem is to
solve a very structured parameterized polynomial system called likelihood
equations. For general choices of data, the number of complex solutions to the
likelihood equations is finite and called the ML-degree of the model. The only
solutions to the likelihood equations that are statistically meaningful are the
real/positive solutions. However, the number of real/positive solutions is not
characterized by the ML-degree. We use discriminants to classify data according
to the number of real/positive solutions of the likelihood equations. We call
these discriminants data-discriminants (DD). We develop a probabilistic
algorithm for computing DDs. Experimental results show that, for the benchmarks
we have tried, the probabilistic algorithm is more efficient than the standard
elimination algorithm. Based on the computational results, we discuss the real
root classification problem for the 3 by 3 symmetric matrix~model.Comment: 2 table
511 keV -ray emission from the galactic bulge by MeV millicharged dark matter
We propose a possible explanation for the recently observed anomalous 511 keV
line with a new "millicharged" fermion. This new fermion is light []. Nevertheless, it has never been observed by any collider
experiments by virtue of its tiny electromagnetic charge . In
particular, we constrain parameters of this millicharged particle if the 511
keV cosmic -ray emission from the galactic bulge is due to positron
production from this new particle.Comment: 3 pages, 1 figure, A talk given by J.C.Park at the 16th International
Conference on Supersymmetry and the Unification of Fundamental Interactions
(SUSY08), Seoul, Korea, June 16-21, 200
Photoinduced Magnetization in a Thin Fe-CN-Co Film
The magnetization of a thin Fe-Co cyanide film has been investigated from 5 K
to 300 K and in fields up to 500 G. Upon illumination with visible light, the
magnetization of the film rapidly increases. The original cluster glass
behavior is further developed in the photoinduced state and shows substantial
changes in critical temperature and freezing temperature.Comment: 2 pages, 2 figures, 1 table, International Conference on Magnetism
200
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