Events at Physics |
Events on Friday, April 11th, 2008
- Seminar
- Temporal resolution and bandwidth of human hearing
- Time: 8:30 am
- Place: MSC Room 281
- Speaker: Milind N. Kunchur, Department of Physics and Astronomy, University of South Carolina
- Abstract: Experiments were conducted to assess the bandwidth and temporal resolution of human hearing using special ultrahigh-fidelity equipment. The experiments demonstrated discernment at a ~5 microsecond timescale, which is much shorter than found previously and falls below the nominal 9 microseconds (=1/[2 pi 18kHz]) threshold expected for a linear system. Analysis of the stimuli suggests that the discernment does not arise solely from direct spectral-amplitude differences but may involve additional non-linear and/or temporal mechanisms. Possible mechanisms, which are quantitatively consistent with the findings, are discussed. The present work also shows that typical instrumentation used in psychoacoustic research has insufficient temporal speed and fidelity for properly assessing all aspects of human hearing and that digital sampling rates used in consumer audio are insufficient for fully preserving transparency. [This work was partially supported by the University of South Carolina Office of Research and Health Sciences Research Funding Program.]
- Host: Donata Oertel (Physiology)
- NPAC (Nuclear/Particle/Astro/Cosmo) Forum
- Joint NPAC and Pheno Seminar
- Dark-matter sterile neutrinos from decays of a gauge-singlet Higgs
- Time: 2:30 pm - 3:30 pm
- Place: 5280 Chamberlin
- Speaker: Kalliopi Petraki, UCLA
- Abstract: Sterile neutrinos are usually introduced to explain the masses of active neutrinos. If one of these fermions has mass of several keV, it can also account for the cosmological dark matter. The same particle can explain the observed velocities of pulsars, speed up the formation of the first stars and stir up supernova explosions. I will describe a mechanism for sterile neutrino production that involves a minimal extension of the Higgs sector by a gauge-singlet scalar. The relic abundance of sterile neutrinos is produced from decays of the singlet Higgs and does not depend on their mixing angle. The resulting dark matter is colder than the warm dark matter produced in neutrino oscillations. I will discuss the small-scale structure formation properties of these neutrinos and show that they comply with current observations. The presence of the gauge singlet in the Higgs sector has important implications for the electroweak phase transition, baryogenesis, and the upcoming experiments at the LHC.
- Physics Department Colloquium
- Trapping and Counting Photons without Destroying Them: A New Way to Look at Light
- Time: 4:00 pm
- Place: 2241 Chamberlin Hall (coffee at 3:30 pm)
- Speaker: Serge Haroche, Ecole Normale Superieure
- Abstract: An experiment realizing a quantum non-demolition measurement of a microwave field trapped in a cavity will be described. While usual photo-detection destroys light quanta, we have developed a new way to count photons without absorbing them, making it possible to measure the same field repeatedly. We use as detectors atoms prepared in a superposition of Rydberg states which cross the cavity one at a time and behave as microscopic clocks whose ticking rate is affected by light. By measuring the clocks' delay, information is extracted without energy absorption and the field progressively collapses into a well-defined photon number state. Quantum jumps between decreasing photon numbers are recorded as the cavity field subsequently relaxes towards vacuum. This new way to "look" at light also generates coherent superpositions of photonic states with different phases called "Schroedinger cats". By monitoring the evolution of these states, we directly observe the process of decohere once in experiments opening new avenues for the exploration of the boundary between the quantum and classical worlds.
- Host: Yavuz