Bulletin of the American Physical Society
2005 7th Annual Meeting of the Northwest Section
Friday–Saturday, May 13–14, 2005; Victoria, BC, Canada
Session B4: Astrophysics and Gravity |
Hide Abstracts |
Chair: Chris Pritchet, University of Victoria Room: MacLaurin D114 |
Friday, May 13, 2005 2:00PM - 2:36PM |
B4.00001: ZEN and the search for high-redshift galaxies Invited Speaker: The study of the most distant objects in the universe places unique constraints upon the nature of the early cosmos. Over the past 80 years the known universe has expanded dramatically with advances in telescope and detector technology, and has been accompanied by a growing insight into the formation of the first galaxies and quasars. Current observations of the most distant galaxies and quasars extend to when the universe was only 13\%\ of its current size (a redshift $z = 6.6$ - equivalent to a look-back time of 12.6 Billion years) and place unique constraints upon the formation and distribution of the first stars together with the physical state of the high-redshift inter-galactic medium. In addition to providing an overview of the field, I will present the initial results of an ambitious observational programme which aims to extend studies of distant galaxies to a redshift $z = 9$ (Z Equals Nine - ZEN). The programme employs some of the deepest astronomical images currently in existence and places important constraints upon high-redshift star-formation and the role of neutral gas in the early universe. [Preview Abstract] |
Friday, May 13, 2005 2:36PM - 3:12PM |
B4.00002: Measuring Dark Energy with the Supernova Legacy Survey Invited Speaker: The Supernova Legacy Survey was brought about in response to the discovery, at the close of the last millennium, that the expansion of the universe is accelerating. The implied dark energy driving this acceleration is completely unknown at this point and poses a significant challenge to the standard model of physics. Dark energy theories abound and include a vitiation of Einstein's ``biggest blunder'': the Cosmological Constant, quintessence theories which model dark energy as a scalar field, and radical models that require new physics. The implications for fundamental physics that a confirmation of any of these theories would bring are far-reaching and demand a measurement of the universal expansion at an unprecedented accuracy in order to select between these theories. The Supernova Legacy Survey is a five year, multi-observatory project that is on track to characterize 700 Type Ia supernovae, the 'standard candles' that provided the original measurement of the acceleration. Already the most successful high-redshift supernova study in history after only 18 months of operation, the survey will not only measure dark energy at a higher statistical significance by increasing the number of measurements by an order of magnitude over previous studies, but will also offer improved control of systematic effects by repeated observing of 4 one-square-degree areas of the sky and by using the largest telescopes in the world to acquire the spectra of the distant suprenovae. The resulting measurement of the equation of state of the universe has the potential to eliminate broad categories of dark energy theories. The survey database characterizing this large sample of Type Ia supernovae will provide the cornerstone for third generation surveys already being designed and due to take the stage in the middle of the next decade. [Preview Abstract] |
Friday, May 13, 2005 3:12PM - 3:37PM |
B4.00003: COFFEE BREAK
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Friday, May 13, 2005 3:37PM - 3:49PM |
B4.00004: Solar dynamo and the effects of magnetic diffusivity E.J. Zita, Night Song, Eric McDonald, Mausumi Dikpati We are closer to understanding how the Sun's magnetic field flips polarity every 11 years. Dikpati's kinematic dynamo model shows that in addition to the two familiar Babcock-Leighton effects (convection and differential rotation), a third mechanism is required. Meridional circulation was discovered by helioseismology, and its inclusion enables our model to accurately reproduce major features of the solar cycle. However, fundamental questions about the solar dynamo remain unanswered. How does magnetic reconnection release magnetic energy and change topology? How do magnetic fields diffuse in the convection zone, where the solar dynamo operates? How do resistivity and turbulence in the solar plasma determine the magnetic diffusivity? We explore some of these questions with our kinematic dynamo model. Our simulations show how meridional circulation carries evolving magnetic flux up from the base of the convection zone at the equator, poleward along the surface, and back down inside the Sun. Our tests give new clues about how magnetic diffusivity varies across the convection zone, and can lead to improved predictions of future solar cycles. [Preview Abstract] |
Friday, May 13, 2005 3:49PM - 4:01PM |
B4.00005: A Lab-scale Test of the Inverse-Square Law of Gravity Ricco Bonicalzi Many attempts to quantize gravity entail a violation of the inverse-square law. Our null torsion-pendulum experiment, soon to become operational, is expected to lower by as much as two orders-of-magnitude the upper bound on the strength of any putative inverse-square law violating interaction. A unique feature central to this improvement is the configuration of the mass distribution of both the pendulum and source mass to provide high-sensitivity to the horizontal derivative of the Laplacian of the gravitational potential (a signature of a non-Newtonian force), while simultaneously strongly suppressing the coupling through Newtonian gravity. In this way systematic gravitational effects due to fabrication errors arise only in second-order, so no extraordinary metrology or fabrication measures are necessary to achieve this stronger test. [Preview Abstract] |
Friday, May 13, 2005 4:01PM - 4:13PM |
B4.00006: Measuring Negative Energy Dilaton Particles George Soli Measured dilaton particles have negative energy because they support one-way ``superluminal'' group velocity data. Dilaton particles are modeled as negative energy excitations of a dark energy field. These excitations saturate the Ford-Roman Quantum Inequality (QI) below the cutoff energy value required to stabilize the vacuum aginst decay through a negative energy channel. The QI saturates near the dark energy density value required to drive the observed accelerated expansion rate of the universe. [Preview Abstract] |
Friday, May 13, 2005 4:13PM - 4:25PM |
B4.00007: Report on LIGO Science Run S4 Frederick Raab Following a year of detector commissioning advances, the Laser Interferometer Gravitational-Wave Observatory (LIGO) conducted a search for gravitational wave sources from Feb 22 to Mar 23, 2005. The run included LIGO's 4-km and 2-km interferometers at Hanford, Washington and the 4-km interferometer at Livingston, Louisiana. The GEO600 interferometer in Hannover, Germany and the Allegro and Auriga resonant bar detectors in Baton Rouge, Louisiana and Padova, Italy also took data overlapping this run. Improvements to wave-front sensing and alignment control of mirrors, implementation of thermal lensing controls and implementation of active vibration isolation allowed operation of the LIGO interferometers with duty cycles exceeding 74{\%} and with strain-equivalent noise of order 10$^{-22}$ Hz$^{-1/2}$. [Preview Abstract] |
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