Talks

Visible matter consists mostly of hydrogen and helium, only a small fraction
of which is in stars. Until recently, the bulk of the gas in the local
universe was in fact not seen. In the largest structures, massive galaxy
clusters, the gas is seen via its x-ray emission, but in the much more
numerous groups and isolated galaxies, it has not been possible to detect
it. I will describe how, in the last year or so, the situation has changed,
with the detection of a cross-correlation between the thermal SZ effect and
lensing maps, and through the stacking of SZ images at the locations of
galaxies. These and similar techniques will tell us about the physics by
which stars and massive black holes heat and move gas in and around the
halos of galaxies and cluster, and will allow for tighter constraints on the
value of the primordial power spectrum (sigma_8).

The interplay of quantum mechanics and inter-particle interactions leads to enormously rich tapestry of quantum phases of matter. In this talk I will illustrate the unique synthesis offered by quantum entanglement on the landscape of quantum phases. I will especially discuss phases which do not show any kind of ordering even at the absolute zero temperature, two prime examples being spin liquids and quantum Hall phases. These phases are fascinating because they can exhibit extraordinary properties such as emergent fermions in a system composed only of bosons, or systems where the elementary excitations are neither fermions, nor bosons (“anyons”). I will discuss how quantum entanglement not only plays a crucial role in characterizing and diagnosing such quantum disordered phases, but in fact it also sheds light on their stability.

The Kerr metric of vacuum general relativity is expected to describe astrophysical black holes. Boson stars, on the other hand, are one of the simplest gravitating solitons, suggested as astrophysical compact objects, black holes mimickers and as dark matter candidates. Kerr black holes with scalar hair, found in [1], continuously interpolate between these two types of, per se, physically interesting solutions. I will describe the construction of these solutions and discuss theoretical, astrophysical and high energy physics aspects and challenges for Kerr black holes with scalar hair.

References:

[1] Kerr black holes with scalar hair, Carlos A. R. Herdeiro, Eugen Radu, Phys. Rev. Lett. 112 (2014) 221101; e-Print: arXiv:1403.2757

[2] A new spin on black hole hair, C. Herdeiro, E. Radu, International Journal of Modern Physics D 23 (2014) 1442014; e-Print: arXiv: 1405.3696;

[3] Construction and physical properties of Kerr black holes with scalar hair, C. Herdeiro and E. Radu, arXiv:1501.04319 [gr-qc]; Focus Issue on "Black holes and fundamental fields" to appear in Classical and Quantum Gravity

Water Stress:
Seeking Solutions in the
Unusual Properties of Water

Water is ubiquitous, but the availability of fresh water is limited. Today, one in six people is under “water stress,” meaning that they have no access to clean water. It is one of the many paradoxes of water. This essential liquid, which in many ways is so commonplace, is also very peculiar. Water behaves differently than other materials in more than 70 ways. These anomalies not only keep our bodies in balance, but secure the thermal stability of our planet as well. Whereas most liquids contract when cooled, water does the opposite – it expands as temperature drops, which, among other effects, allows fish to survive the winter. What’s more, water diffuses more quickly as a system becomes denser – the opposite behaviour to most other fluids.

In her Perimeter Institute Public Lecture, physicist Dr. Marcia C. Barbosa will examine how we can better understand this precious resource that is both incredibly abundant on Earth, yet dangerously scarce to millions of people. Decoding the strange properties of water, Barbosa argues, may be essential to resolving the widespread problem of water stress.

We study the separability of quantum states in bosonic system. Our main tool here is the "separability witnesses", and a connection between "separability witnesses" and a new kind of positivity of matrices--- "Power Positive Matrices" is drawn. Such connection is employed to demonstrate that multi-qubit quantum states with Dicke states being its eigenvectors is separable if and only if two related Hankel matrices are positive semidefinite. By employing this criterion, we are able to show that such state is separable if and only if it's partial transpose is non-negative, which confirms the conjecture in [Wolfe, Yelin, Phys. Rev. Lett. (2014)]. Then, we present a class of bosonic states in d⊗d system such that for general d, determine its separabilityNP-hard although verifiable conditions for separability is easily derived in case d=3,4.