Talks

Causal dynamical triangulations (CDT) define a nonperturbative path integral for quantum gravity as a sum over triangulations. Causality is enforced on the kinematical level by means of a preferred
foliation.

In this talk I present a new model of dynamical triangulations based on Lorentzian building blocks, where the triangulations in general do not have such a preferred foliation. The essential ingredients of the new model are a local causality constraint and a consistency condition on the global flow of time. After a compact review on CDT I discuss the theoretical aspects of the new model in 1+1 and 2+1 dimensions, followed by a presentation of numerical results in 2+1 dimensions. These results show that the new model and CDT have similar long-distance properties in 2+1 dimensions.

The fuzzball proposal makes a conjecture about the nature of black hole
microstates. Now, more than a decade old and including several different
philosophies and perspectives, it is especially relevant after the recent
firewall argument and ensuing debate. Over three lectures, I plan to start
with a very general discussion of the general ideas and motivations, then
review the theoretical evidence from string theory, and finally close by
discussing open questions, including the fate of a freely falling observer

as he/she passes through the black hole horizon.

The decomposition of the magnetic moments in spin ice into freely moving magnetic monopoles has added a new dimension to the concept of fractionalization, showing that geometrical frustration, even in the absence of quantum fluctuations, can lead to the apparent reduction of fundamental objects into quasi particles of reduced dimension [1]. The resulting quasi-particles map onto a Coulomb gas in the grand canonical ensemble [2]. By varying the chemical potential one can drive the ground state from a vacuum to a monopole crystal with the Zinc blend structure [3].

The condensation of monopoles into the crystallized state leads to a new level of fractionalization:
the magnetic moments appear to collectively break into two distinct parts; the crystal of magnetic charge and a magnetic fluid showing correlations characteristic of an emergent Coulomb phase [4].

The ordered magnetic charge is synonymous with magnetic order, while the Coulomb phase space is equivalent to that of hard core dimers close packed onto a diamond lattice [5]. The relevance of these results to experimental systems will be discussed.

[1] C. Castelnovo, R. Moessner, and S. L. Sondhi, Nature 451, 42 (2008).
[2] L. D. C. Jaubert and P. C. W. Holdsworth, Nature Physics 5, 258 (2009).
[3] M. Brooks-Bartlett, A. Harman-Clarke, S. Banks, L. D. C. Jaubert and P. C. W. Holdsworth, In Preparation, (2013).
[4] C. L. Henley, Annual Review of Condensed Matter Physics 1, 179 (2010).
[5] D. A. Huse, W. Krauth, R. Moessner, and S. L. Sondhi, Phys. Rev. Lett. 91, 167004 (2003).