Scientific Series

Quasars are highly biased tracers of the large-scale structure and therefore powerful probes of the initial conditions and the evolution of the universe. However, current spectroscopic catalogues are relatively small for studying the clustering of quasars on large-scales and over extended redshift ranges. Hence one must resort to photometric catalogues, which include large numbers of quasars identified using imaging data but suffer from significant stellar contamination and systematic uncertainties. I will present a detailed analysis of the photometric quasars from the Sloan Digital Sky Survey, and the resulting constraints on the quasar bias and primordial non-Gaussianity. The constraints on $f_{rm NL}$, its spectral index, and $g_{rm NL}$, are the tightest ever obtained from a single population of quasars or galaxies, and are competitive with the results obtained with WMAP, demonstrating the potential of quasars to complement CMB experiments. These results take advantage of a novel technique, 'extended mode projection', to mitigate the complex spatially-varying systematics present in the survey in a blind and robust fashion. This work is a new step towards the exploitation of data from the Dark Energy Survey, Euclid and LSST, which will require a careful mitigation of systematics in order to robustly constrain new physics.

I present a proposal for a worldline action for discretized gravity with the same field content as loop quantum gravity. The proposal is defined through its action, which is a one-dimensional integral over the edges of the discretization. Every edge carries a finite-dimensional phase space, and the evolution equations are generated by a Hamiltonian, which is a sum over the constraints of the theory. I will explain the relevance of the model, and close with possible relations to other approaches of quantum gravity, including: relative locality, causal sets and twistor theory.

Quantum information theory has taught us that quantum theory is just one possible probabilistic theory among many others. In the talk, I will argue that this "bird's-eye" perspective does not only allow us to derive the quantum formalism from simple physical principles, but also reveals surprising connections between the structures of spacetime and probability which can be phrased as mathematical theorems about information-theoretic scenarios.

I will discuss the violation of spin-charge separation in generic Luttinger liquids and investigate its effect on the relaxation, thermal and electrical transport of genuine spin-1/2 electron liquids in ballistic quantum wires. We will identify basic scattering processes compatible with the symmetry of the problem and conservation laws that lead to the decay of plasmons into the spin modes and also discuss Brownian backscattering of spin excitations. I will present a closed set of coupled kinetic equations for the spin-charge excitations and solve the problem of electrical and thermal conductance of interacting electrons for an arbitrary relation between the quantum wire length and spin-charge thermalization length.

Interferometers capture a basic mystery of quantum mechanics: a single particle can exhibit wave behavior, yet that wave behavior disappears when one tries to determine the particle's path inside the interferometer. This idea has been formulated quantitatively as an inequality, e.g., by Englert and Jaeger, Shimony, and Vaidman, which upper bounds the sum of the interference visibility and the path distinguishability. Such wave-particle duality relations (WPDRs) are often thought to be conceptually inequivalent to Heisenberg's uncertainty principle, although this has been debated. Here we show that WPDRs correspond precisely to a modern formulation of the uncertainty principle in terms of entropies, namely the min- and max-entropies. This observation unifies two fundamental concepts in quantum mechanics. Furthermore, it leads to a robust framework for deriving novel WPDRs by applying entropic uncertainty relations to interferometric models (arXiv reference: 1403.4687).

We discuss a topological description of the confining phase of (Super-)Yang-Mills theories with gauge group SU(N) which encodes all the Aharonov-Bohm phases of configurations of non-local operators. This topological action shows an additional 1-form gauge symmetry. After the introduction of domain walls, this 1-form gauge symmetry demands the appearance of new fields on the worldvolume of the wall. These new fields have a topological Chern-Simons action at level N, also suggested by string theory constructions.