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Satellite Dynamics in Dark Matter HalosKamiab, Farbod January 2010 (has links)
I have used an analytic model of tidal interactions to predict the evolution of a substructure in a static dark matter halo. Given the initial conditions of the satellite and background halo, the model predicts with high accuracy the mass loss of the satellite and also its density evolution. The main phenomena taken into account in the model are tidal truncation at the tidal radius of the satellite and heating due to tidal shocks at the pericenter of its orbit. To calibrate and test the model, it has been compared with numerical simulations of a satellite orbiting in a static dark matter halo. The model predicts a set of tidal radii for the satellite in different stages of its evolution. The mass of the satellite is accurately calculated at each stage by truncating an NFW (Navarro, Frenk and White)
profile at the tidal radius. The mass lost beyond the tidal limit is scaled by half the instantaneous orbital period of the satellite. The model can also be used to predict analytically the new density profile of the satellite. This new profile is given by a modification of the NFW density profile as a function of radius. The tidal radius is the only parameter going into this modification. The effect of numerical relaxation has been studied and quantified
by performing the same simulations in lower resolutions. I find that substructures with
less than 1000 particles are artificially relaxed and this process affects their mass loss and results in their premature disruptions. This underlines the utility of an analytic model predicting the evolution of substructures in minor mergers.
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Dark matter detection with polarized detectorsChiang, Chi-Ting 29 October 2012 (has links)
We consider the prospects to use polarized dark-matter detectors to discriminate between various dark-matter models. If WIMPs are fermions and participate in parity-violating interactions with ordinary matter, then the recoil-direction and recoil-energy distributions of nuclei in detectors will depend on the orientation of the initial nuclear spin with respect to the velocity of the detector through the Galactic halo. If, however, WIMPS are scalars, the only possible polarization-dependent interactions are extremely velocity-suppressed and, therefore, unobservable. Since the amplitude of this polarization modulation is fixed by the detector
speed through the halo, in units of the speed of light, exposures several times larger than those of current experiments will be required to be probe this effect. / text
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Cosmology with Bose-Einstein-condensed scalar field dark matterLi, Bohua 24 September 2013 (has links)
Despite the great successes of the Cold Dark Matter (CDM) model in
explaining a wide range of observations of the global evolution and the formation of galaxies and large-scale structure in the universe, the origin and microscopic nature of this dark matter is still unknown. The most common form of CDM considered to-date is that of Weakly Interacting Massive Particles (WIMPs), but some of the cosmological predictions for this kind of CDM are in apparent conflict with observations (e.g. cuspy-cored halos and an overabundance of satellite dwarf galaxies). For these reasons, it is important to consider the consequences of different forms
of CDM. We focus here on the hypothesis that the dark matter is comprised, instead, of ultralight bosons that form a Bose-Einstein Condensate (BEC),
described by a complex scalar field.
We start from the Klein-Gordon and Einstein field equations to describe
the evolution of the Friedmann-Robertson-Walker (FRW) universe in the presence of this kind of dark matter. We find that, in addition to the
phases of radiation-domination (RD), matter-domination (MD) and
Lambda-domination (LD) familiar from the standard CDM model, there is an
earlier phase of scalar-field-domination (SFD) which is special to this model. In addition, while WIMP CDM is non-relativistic at all times after
it decouples, the equation of state of BEC-SFDM is found to be relativistic at early times, evolving from incompressible ($\bar{p} = \bar{\rho}$)
to radiation-like ($\bar{p} = \bar{\rho}/3$), before it becomes non-relativistic and CDM-like at late times. The timing of the transitions between these
phases and regimes is shown to yield fundamental constraints on the particle
mass and self-interaction coupling strength. We also discuss progress
on the description of structure formation in this model, which includes
additional constraints on these parameters. / text
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Galactic dark halos陳家強, Chan, Ka-keung, Kurt. January 1992 (has links)
published_or_final_version / Physics / Master / Master of Philosophy
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Observing dark in the galactic spectrum?Lawson, Kyle 05 1900 (has links)
Observations from a broad range of astrophysical scales have forced us to the realization that the well understood matter comprising the stars and galaxies we see around us accounts for only a small fraction of the total mass of the Universe. An amount roughly five times larger exist in the form of dark matter about which we have virtually no direct evidence apart from its large scale gravitational effects. It is also known that the largest contribution to the energy density of the universe is the dark energy, a negative pressure form of energy which will not be dealt with here.
I will present a candidate for the dark matter which is based completely in known physics and which presents several possible observational signatures. In this model the dark matter is composed of dense nuggets of baryonic matter and antimatter in a colour superconducting state. If these object are sufficiently massive their low number density will make them effectively dark in the sense that collisions with visible matter become infrequent. This work presents the basics of dark matter as a colour superconductor and then uses the physical properties of the quark nuggets to extract observational consequences.
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Satellite Dynamics in Dark Matter HalosKamiab, Farbod January 2010 (has links)
I have used an analytic model of tidal interactions to predict the evolution of a substructure in a static dark matter halo. Given the initial conditions of the satellite and background halo, the model predicts with high accuracy the mass loss of the satellite and also its density evolution. The main phenomena taken into account in the model are tidal truncation at the tidal radius of the satellite and heating due to tidal shocks at the pericenter of its orbit. To calibrate and test the model, it has been compared with numerical simulations of a satellite orbiting in a static dark matter halo. The model predicts a set of tidal radii for the satellite in different stages of its evolution. The mass of the satellite is accurately calculated at each stage by truncating an NFW (Navarro, Frenk and White)
profile at the tidal radius. The mass lost beyond the tidal limit is scaled by half the instantaneous orbital period of the satellite. The model can also be used to predict analytically the new density profile of the satellite. This new profile is given by a modification of the NFW density profile as a function of radius. The tidal radius is the only parameter going into this modification. The effect of numerical relaxation has been studied and quantified
by performing the same simulations in lower resolutions. I find that substructures with
less than 1000 particles are artificially relaxed and this process affects their mass loss and results in their premature disruptions. This underlines the utility of an analytic model predicting the evolution of substructures in minor mergers.
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Characterization of Pulse–Shape Discrimination for Background Reduction in the DEAP-1 DetectorPasuthip, PARADORN 02 February 2009 (has links)
DEAP (Dark Matter Experiment with Argon and Pulse Shape Discrimination) is
an experiment that aims to directly detect dark matter particles via nuclear recoils
in liquid argon. The experiment uses the scintillation property of liquid argon as a
means to discriminate the γ and β backgrounds from the expected signal. DEAP-1
is a 7 kg single phase liquid argon detector. It was constructed to demonstrate the
scalability for a larger (3600 kg) detector. The detector was originally operated at
Queen’s University, where the background rejection level achieved was 6.3×10−8 for
the recoil detection efficiency of 97.1%. The detector was relocated to SNOLAB,
where the background in the energy region of interest was reduced by a factor of
7.7 (from 4.61±0.17 mHz to 0.60±0.05 mHz.). The background rejection level of
9.64×10−9 (10.4 part per billion) was achieved from the combined data set (Queen’s
University and SNOLAB) for a recoil detection efficiency of 35.5 ± 1.3 %. With
the current background rate, the background rejection level required for the 3600 kg
detector (1.8×10−9 ) is projected to be achieved in 382 days at the neutron efficiency
of 9.1±0.6 %. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2009-01-26 09:28:25.432
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Gamma Calibration Using A New Test Apparatus At Queen’s University And Optimization Analyses For The PICASSO ExperimentLEVY, CECILIA 26 September 2009 (has links)
The PICASSO experiment located 2 km underground in SNOLAB is directly
searching for dark matter signals by looking for interactions between dark matter
particles and an active target made of superheated droplets of freon C4F10. During
the interaction, energy is deposited to the freon triggering a phase transition,
inducing pressure waves which are detected by piezo-electric sensors.
A temperature dependent analysis of the amplitudes of the signals for detector
71 showed that, above 25 ◦C, between 20 and 80 % of the events were saturated
implying that the preamplifiers had too high a gain. Decreasing this gain by a fixed
factor was not found to be a suitable solution to the problem. Ideally, a temperature
dependent gain should be established. In addition, some channels have intrinsic
problems and should be repaired.
A threshold analysis was used to establish the trigger efficiency which was found
to be 90% above 25 ◦C but only 50% at lower temperatures with the current setting
of the threshold. A temperature dependent threshold setting has been proposed.
A new setup at Queen’s University has been built and a gamma calibration using
three different radioactive sources (22Na,137Cs,57Co) was undertaken leading to a
new detector response curve for gammas. For a proper analysis, new and more
appropriate cuts were implemented. The analysis confirmed the expectation that
the PICASSO detectors are mostly blind to gammas below 50 ◦C. However, the
detectors appear to be more sensitive to 122 keV gammas than to 622 keV gammas
by a factor of about 10. The sensitivity for 22Na also differs by a large factor from
what was expected from old calibrations on detectors with much smaller bubbles.
The rate plots exhibit a strong exponential increase in rate above 40 ◦C which is not
due to any of the gamma sources used, but could be due to neutrons or low energy
x-rays. This remains under investigation. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2009-09-24 18:28:21.308
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Detector Development and Test Facility Commissioning for SuperCDMSFox, Joseph 06 June 2011 (has links)
SuperCDMS, the next stage of the Cryogenic Dark Matter Search (CDMS), uses cylindrical germa-
nium crystals as particle detectors to measure phonon and ionization signals resulting from particle
interactions. The aim of CDMS is to identify and measure interactions from dark matter particles
(WIMPs). Phonons produced during a particle interaction are absorbed by sensors on the detector
surface and are measured through the change in the sensors' temperature dependent resistance.
Electrodes on the detector surface create an electric eld causing charges released during an inter-
action to drift through the detector and produce an ionization signal. Surface events, which are
interactions that occur within a few m from the electrodes, cause a reduced ionization signal due
to di usion of some of the initially hot charge carriers into the electrode. Because the ability of
CDMS to discriminate between a WIMP interaction and background radiation is based on the ratio
of phonon to ionization energies, surface events cause a signal similar to a WIMP interaction and
are currently the largest source of background.
A detector test facility at Queen's University has been commissioned to characterize detectors
and test new detector technology. Multiple detectors have been characterized and many tungsten
samples have been measured. Two sets of experiments were performed to test new detector designs.
To possibly reduce surface events, an insulating layer was deposited on a germanium detector be-
neath the electrode to prevent back di usion of charge into the electrode. To possibly simplify the
phonon sensor production process, di erent cryogenic glues were used to attach silicon wafers with
a tungsten lm to the crystal surface and phonon propagation through these glues was measured.
The most e ective cryogenic glue for coupling tungsten samples to CDMS detectors was found to
be Araldite epoxy. Both experiments were successful at measuring interactions. Energy calibrations
were performed on both charge and phonon sensors. Further research is required to determine the
success of reducing surface events with an insulating layer. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2011-05-30 10:39:02.976
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Structure of dark matter in galaxies /Trott, Cathryn Margaret. January 2004 (has links)
Thesis (Ph.D.)--University of Melbourne, School of Physics, 2005. / Typescript (photocopy). Includes bibliographical references (leaves [171]-185).
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