65,824 research outputs found
An investigation of pulsar searching techniques with the Fast Folding Algorithm
Here we present an in-depth study of the behaviour of the Fast Folding
Algorithm, an alternative pulsar searching technique to the Fast Fourier
Transform. Weaknesses in the Fast Fourier Transform, including a susceptibility
to red noise, leave it insensitive to pulsars with long rotational periods (P >
1 s). This sensitivity gap has the potential to bias our understanding of the
period distribution of the pulsar population. The Fast Folding Algorithm, a
time-domain based pulsar searching technique, has the potential to overcome
some of these biases. Modern distributed-computing frameworks now allow for the
application of this algorithm to all-sky blind pulsar surveys for the first
time. However, many aspects of the behaviour of this search technique remain
poorly understood, including its responsiveness to variations in pulse shape
and the presence of red noise. Using a custom CPU-based implementation of the
Fast Folding Algorithm, ffancy, we have conducted an in-depth study into the
behaviour of the Fast Folding Algorithm in both an ideal, white noise regime as
well as a trial on observational data from the HTRU-S Low Latitude pulsar
survey, including a comparison to the behaviour of the Fast Fourier Transform.
We are able to both confirm and expand upon earlier studies that demonstrate
the ability of the Fast Folding Algorithm to outperform the Fast Fourier
Transform under ideal white noise conditions, and demonstrate a significant
improvement in sensitivity to long-period pulsars in real observational data
through the use of the Fast Folding Algorithm.Comment: 19 pages, 15 figures, 3 table
Spontaneous electro-weak symmetry breaking and cold dark matter
In the standard model, the weak gauge bosons and fermions obtain mass after
spontaneous electro-weak symmetry breaking, which is realized through one
fundamental scalar field, namely Higgs field. In this paper we study the
simplest scalar cold dark matter model in which the scalar cold dark matter
also obtains mass through interaction with the weak-doublet Higgs field, the
same way as those of weak gauge bosons and fermions. Our study shows that the
correct cold dark matter relic abundance within uncertainty () and experimentally allowed Higgs boson mass
( GeV) constrain the scalar dark matter mass within GeV. This result is in excellent agreement with that of W. de
Boer et.al. ( GeV). Such kind of dark matter annihilation can
account for the observed gamma rays excess () at EGRET for energies
above 1 GeV in comparison with the expectations from conventional Galactic
models. We also investigate other phenomenological consequences of this model.
For example, the Higgs boson decays dominantly into scalar cold dark matter if
its mass lies within GeV.Comment: 4 Revtex4 pages, refs adde
Neutrino Constraints on Inelastic Dark Matter after CDMS II
We discuss the neutrino constraints from solar and terrestrial dark matter
(DM) annihilations in the inelastic dark matter (iDM) scenario after the recent
CDMS II results. To reconcile the DAMA/LIBRA data with constraints from all
other direct experiments, the iDM needs to be light ( GeV) and
have a large DM-nucleon cross section ( 10 pb in the
spin-independent (SI) scattering and 10 pb in the
spin-dependent (SD) scattering). The dominant contribution to the iDM capture
in the Sun is from scattering off Fe/Al in the SI/SD case. Current bounds from
Super-Kamiokande exclude the hard DM annihilation channels, such as ,
, and . For soft channels such as and
, the limits are loose, but could be tested or further constrained
by future IceCube plus DeepCore. For neutrino constraints from the DM
annihilation in the Earth, due to the weaker gravitational effect of the Earth
and inelastic capture condition, the constraint exists only for small mass
splitting 40 keV and GeV even in the channel.Comment: 11 pages, 8 figure
Loss of control in pattern-directed nucleation: a theoretical study
The properties of template-directed nucleation are studied close to the
transition where full nucleation control is lost and additional nucleation
occurs beyond the pre-patterned regions. First, kinetic Monte Carlo simulations
are performed to obtain information on a microscopic level. Here the
experimentally relevant cases of 1D stripe patterns and 2D square lattice
symmetry are considered. The nucleation properties in the transition region
depend in a complex way on the parameters of the system, i.e. the flux, the
surface diffusion constant, the geometric properties of the pattern and the
desorption rate. Second, the properties of the stationary concentration field
in the fully controlled case are studied to derive the remaining nucleation
probability and thus to characterize the loss of nucleation control. Using the
analytically accessible solution of a model system with purely radial symmetry,
some of the observed properties can be rationalized. A detailed comparison to
the Monte Carlo data is included
Observation of dressed intra-cavity dark states
Cavity electromagnetically induced transparency in a coherently prepared
cavity-atom system is manifested as a narrow transmission peak of a weak probe
laser coupled into the cavity mode. We show that with a resonant pump laser
coupling the cavity-confined four-level atoms from free space, the narrow
transmission peak of the cavity EIT is split into two peaks. The two peaks
represent the dressed intra-cavity dark states and have a frequency separation
approximately equal to the Rabi frequency of the free-space pump laser. We
observed experimentally the dressed intra-cavity dark states in cold Rb atoms
confined in a cavity and the experimental results agree with theoretical
calculations based on a semiclassical analysis.Comment: 10 pages, 6 figure
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