Talks

Neutrino physics entered a new era in the last decade. With the discovery of a non-vanishing neutrino rest mass in oscillation experiments a variety of new questions showed up in the context of nuclear and particle physics. One of the crucial questions is the determination of the absolute neutrino mass, which cannot be measured in oscillation experiments. One option is neutrino-less double beta decay, the simultaneous conversion of two neutrons into two protons emitting two electrons. This total lepton number violating process requires that neutrinos are their own antiparticles and is considered to be gold plated. Furthermore, the measured half-life is directly linked with the neutrino mass. Currently, half-life measurements beyond 1025 years are discussed. This requires a large amount of the isotope of interest and a reduction of disturbing background to the smallest possible level. Indeed it is a search for the needle in a haystack. After a general introduction into double beta decay and the related physics, the talk will focus on the status of the experiments GERDA, COBRA and SNO+.

The Large Hadron Collider has been operating for more than a year and delivering exciting results. It has already excluded large parts of the parameter space for supersymmetry. If the hints of a Higgs boson at 125 GeV hold up, the implications for supersymmetry are even more profound. I will explain some of the consequences, including the failure of large classes of models like general gauge mediation to account for such a heavy Higgs. I will also discuss some ideas about how to look for scalar top quarks, which must be present in the low-energy spectrum for supersymmetry to be natural.

The LHC is offering our first glimpses of physics at energies above a TeV, allowing us an unprecedented chance to search for very heavy new particles from electroweak compositeness, new gauge forces, extra dimensions, and supersymmetry.  Some of the most interesting signals involve decays into Standard Model particles that we are used to thinking of as "heavy":  W/Z bosons, top quarks, and perhaps Higgs bosons.  However, at genuinely TeV-scale energies, these SM particles with O(100 GeV) mass are produced with relativistic velocities.  Consequently, their own decay products are Lorentz-boosted into very collimated configurations, and can look uncomfortably similar to the jets of particles that are copiously produced by QCD at hadron colliders.  The past several years have witnessed a surge of ideas for how to uncover these challenging signals by carefully organizing the patterns of radiation observed in the LHC detectors, an approach called Jet Substructure.  I will discuss some of these recent ideas, and show a handful of important applications to searches for new physics.

We introduce an exactly solvable model to test various proposals for the imposition of the spin foam simplicity constraints. This model is a three-dimensional Holst-Plebanski action for the gauge group SO(4), in which the simplicity constraints mimic the situation of the four-dimensional theory. In particular, the canonical analysis reveals the presence of secondary second class constraints conjugated to the primary ones. We perform the spin foam quantization of the theory in the spirit of the BC and EPRL models, and give arguments for modifying the measure over the holonomies in order to account for the presence of the secondary second class constraints.

Entropy plays a fundamental role in quantum information theory through applications ranging from communication theory to condensed matter physics.  These applications include finding the best possible communication rates over noisy channels and characterizing ground state entanglement in strongly-correlated quantum systems.  In the latter, localized entanglement is often characterized by an area law for entropy.  Long-range entanglement, on the other hand, can give rise to topologically ordered materials whose collective excitations are robust against local noise.  In this talk, I will present a property of quantum entropy for multipartite quantum systems that resolves several open questions in quantum information theory about entanglement measures, provides new algorithmic opportunities and makes nontrivial statements about the structure of states with vanishing - but nonzero - topological entropy.  I will also comment how extensions of this work could help our understanding of quantum communication over certain very noisy channels.

Supersymmetry is a popular candidate for the 'model beyond the Standard Model', however minimal versions of it are quite constrained by the first year of data from the LHC. In this talk I will focus on supersymmetry scenarios where the gaugino masses are Dirac rather than Majorana. This seemingly innocuous change has a profound impact on collider bounds -- reducing the bound on (1st and 2nd generation) squark masses by nearly a factor of two. In addition, Dirac gaugino scenarios have amazing flavor properties, smoking gun LHC signals, and cosmological implications.

This talk presents two results on the interplay between causality and quantum information flow. First I will discuss about the task of switching the connections among quantum gates in a network. In ordinary quantum circuits, gates are connected in a fixed causal sequence.  However, we can imagine a physical mechanism where the connections among gates are not fixed, but instead are controlled by the quantum state of a control system. Such a "quantum switch" mechanism is consistent with quantum theory but cannot be described with in the standard model of causally ordered circuits, where it would be equivalent to a deterministic time travel and hence would violate the causality principle. With respect to the standard circuit model, the quantum switch is a new primitive that enables new information-processing protocols, such as the perfect discrimination between two classes of channels that are not perfectly distinguishable in a single query by any ordinary quantum circuit. Second, I will discuss about the probabilistic simulation of impossible channels that take an input in the future and produce an output in the past. In this case, I will show that the maximum probability of success in such a simulation is determined by causality and is inversely proportional to the amount of information that the channel can transmit.