Talks

A recent analysis of gamma rays from the centre of our galaxy has provided possible evidence for a dark matter annihilation signal, with the dark matter taking the form of low-mass WIMPs annihilating predominantly to taus. We study an extended Higgs model proposed to yield such a dark matter candidate. Scanning over parameter space in this model, we find suitable areas that feature fairly little fine-tuning. In favoured areas, the cross-sections for invisible decays of neutral Higgses are predicted to be too low for detection atcolliders. However, dark matter direct detection experiments are currently becoming relevant for constraining parameter space in the model.

This is a very informal talk about some of the issues associated with the notion of "macroscopic realism" (MR) and its relation to quantum mechanics (QM). After a brief discussion of the motivation for attempts to modify QM at some point between the level of the atom and that of our own direct experience, and a survey of some candidate experimental systems, I will discuss attempts to quantify the notion of "macroscopic distinctness", the use of temporal Bell inequalities to discriminate between the predictions of QM and those of MR, the related concept of "noninvasive measurement" and existing and possible ways to implement it. I will also comment briefly on the relation between Bell-EPR experiments and those on MR.

Magnetic fields of stars can provide insight on their structure and evolution. These magnetic fields can be detected by exploiting the Zeeman effect. The theory behind detection and the method of Lease Squares Deconvolution will be described and preliminary results will be presented.

Neutron stars are the collapsed cores of massive stars that went under supernova explosions. They are found with high surface magnetic fields, rapid but steady rotation and high density comparable to that inside an atomic nucleus. In the past 20 years, many different classes of neutron stars have been discovered. One of the most enigmatic classes of neutron stars is the compact central objects (CCOs). Only seven of them have been discovered and their emission process are still not well understood. Three of them have magnetic field estimates which are found to be significantly lower than those of the other neutron stars of comparable age. I will describe our project searching for more of these mysterious objects with NASA's Chandra X-ray Observatory. We compiled a list of eleven nearby weak-field neutron stars to look for CCO-like X-ray emission. Chandra carried short observations of six of them and no x-ray emission was found. The physical implications of the results will be discussed.

The large number of high-energy rotational lines of C18O, available via the Herschel Space Observatory, provides an unprecedented ability to model the total C18O column density in hot cores. Using the emission from all the observed lines (up to J=16-15) we use an automated algorithm to model all transitions simultaneously. Under Local Thermodynamic Equilibrium (LTE) assumptions and knowledge of source size, centroid velocity and line width, the model determines the values for total C18O column densities in 4 separate line-of-sight components of Orion KL known as the Extended Ridge, the Outflow/Plateau, the Compact Ridge, and the Hot Core. These values are determined to be: 2.5 X 10^16, 5.9 X 10^16, 1.8 X 10^16, and 6.0 X 10^16 cm^(-2) respectively. We also explain the difficulties in using the said algorithm to model optically thick molecules such as CO which require non-LTE modeling.

Neutron stars are collapsed remnants of massive stars. One form of neutron star, pulsars, produce clock-like radio pulses, a result of their rotation combined with a misalignment of their rotation and magnetic axes. These pulses can be used in a variety of experiments in fundamental physics, including tests of gravity theories, constraining the properties of supranuclear density matter, and gravitational wave detection. In this talk, I will describe pulsar properties and explain how the above experiments are carried out, as well as show interesting recent results.

Continuous-variable SICPOVMS seem unlikely to exist, for a variety of reasons. But that doesn't rule out the possibility of other 2-designs for the continuous-variable Hilbert space L2(R). In particular, it would be nice if the coherent states -- which form a rather nice 1-design -- could be generalized in some way to get a 2-design comprising *Gaussian* states. So the question is: "Can we build a 2-design out of Gaussian states?". The answer is "No, but in a very surprising way!" Like coherent states, Gaussian states have a natural transitive symmetry group. For coherent states, it's the Heisenberg group. For Gaussian states, it's the affine symplectic group -- the Heisenberg group plus squeezings and rotations. And this group acts irreducibly on the symmetric subspace of L2(R) x L2(R)... which, by Schur's Lemma, implies that the Gaussian states *should* be a 2-design. Yet a very simple explicit calculation shows that they are not! The resolution is fascinating -- it turns out that the "symplectic twirl" involves an integral that does not quite converge, and this provides a loophole out of Schur's Lemma. So, in the end, we: (1) Show that Gaussian 2-designs do not exist, (2) Demonstrate a major stumbling block to *any* symplectic-covariant 2-designs for L2(R), (3) Gain a pretty complete understanding of *one* of the [formerly] mysterious discrepancies between discrete and continuous Hilbert spaces.

If we imagine that the universe is truly eternal, special challenges arise for attempts to solve cosmological fine-tuning problems, especially the low entropy of the early universe. If the space of states is finite, the universe should spend most of its time near equilibrium. If the space of states is infinite, it becomes difficult to understand why our universe was in a particular low-entropy state. I will discuss approaches to addressing this problem in a model-independent fashion.

"A positive cosmological constant allows arbitrarily many different quantum states, but apparently only if there can be big bangs and/or big crunches. Without any big bang or big crunch, the entropy may be limited by the Gibbons-Hawking entropy of pure deSitter, and the matter entropy might even more limited by a value roughly the three-fourths power of the Gibbons-Hawking entropy. A classical analogue of an upper limit on the entropy is the finite canonical measure for nonsingular cosmologies. Inflation by itself does not explain the arrow of time and seems to require that not only a small region have suitable initial conditions. A special quantum state, such as the Symmetric-Bounce one, with a suitable measure, such as volume averaging and Agnesi weighting, appears possible to explain the arrow of time and other observations, such as high order that would not be expected for Boltzmann brain observations, distant stars that would not be expected if we were fluctuations of empty de Sitter spacetime, and positive cosmological constant that appears not to dominate many other measures."

Closed systems never evolve to lower entropy states -- except when they do, which is if one waits a time that is exponential in the entropy change. Thus macroscopic decreases in entropy are 'never' observed. Yet in cosmology there are eternal systems in which downward entropy fluctuations of any magnitude eventually happen. What is the nature of such fluctuations? I will argue that these can be understood in a simple and general way that sheds light on our understanding of various interesting cosmological processes such as bubble nucleation, black/white hole formation, eternal stochastic inflation, Boltzmann brain formation, and other processes.