Scientific Series

I present an overview of how inspiral-merger-ringdown (IMR) waveforms are currently being used within LIGO and Virgo search efforts. I'll discuss search strategies from the two major astrophysics working groups within t he LIGO/Virgo collaboration searching for transient gravitational-wave signals - the Compact Binary Coalescence group and the Burst Group. For masses where the inspiral, merger and ring-down phases are prominent in the LIGO/Virgo band both working groups have developed pipelines that are sensitive to these systems and are now trying to work together to make a joint statement about LIGO and Virgo's sensitivity to IMR systems.

A recent breakthrough in quantum computing has been the realization that quantum computation can proceed solely through single-qubit measurements on an appropriate quantum state. One exciting prospect is that the ground or low-temperature thermal state of an interacting quantum many-body system can serve as such a resource state for quantum computation. The system would simply need to be cooled sufficiently and then subjected to local measurements. It would be unfortunate, however, if the usefulness of a ground or low-temperature thermal state for quantum computation was critically dependent on the details of the system's Hamiltonian; if so, engineering such systems would be difficult or even impossible. A much more powerful result would be the existence of a robust ordered phase which is characterized by the ability to perform measurement-based quantum computation. I’ll discuss some recent results on the existence of such a computational phase of matter. I’ll first outline some positive results on a phase of a toy model that contains the cluster state. Then, in a realistic model of coupled spin-1 particles, I’ll demonstrate the existence of a computational phase. This result is obtained by using a local measurement sequence to “renormalize” the state to a computationally-universal fixed point. Together, these results reveal that the characterization of computational phases of matter has a rich, complex structure – one which is still poorly understood. Joint work with Gavin Brennen, Akimasa Miyake, and Joseph Renes.

Gravitational waves provide a unique way to study the Universe. From 2005 to 2007, the Laser Interferometer Gravitational-wave Observatory (LIGO) took data at design sensitivity. After describing gravitational waves and how LIGO works, I will discuss the status of searches for those waves and current astronomical constraints imposed by those searches. Data taking resumed in summer 2009 with enhanced LIGO detectors and the European Virgo detectors. I will discuss plans for combined electromagnetic and gravitational observing campaigns. Finally, I will highlight the prospects for gravitational-wave astronomy with Advanced LIGO over the next decade.

Underlying the standard cosmological model is the assumption that it is possible to coarse-grain the energy density of the Universe, and that the dynamical and optical properies of space-time should be well modelled by the result. However, even if the average coarse-grained geometry does have the same dynamical properties as the fine-grained system it is intended to imitate, there are good reasons to suspect that the optical properties may be different. To investigate this we consider a simple model of the Universe in which the matter content is in the form of uniformly distributed discrete islands, rather than a continuous fluid. It is found that in the appropriate limits the resulting large-scale dynamics of the model approach those of an FRW universe, while the optical properties do not. We find the angular diameter distance, luminosity distance and redshifts that would be measured by observers inside such a space-time, and use preliminary results to show that the effect on estimates of the cosmological constant can be of the order of 10%.

Ultrarelativistic heavy-ion collisions are one of the most difficult problems for theoretical physicists: they probe non-abelian dynamics deep in the non-perturbative (strong coupling) regime in a many-body system, are highly dynamical (strong gradients), exhibit collective behavior, and involve phase transitions. Fluid dynamics with input from holography is surprisingly good at describing some aspects of experimental data in heavy-ion collisions. I will review some of this successful description, its limitations, and point out open problems that one may be able to understand using gauge/gravity duality.

A closer look at some proposed Gedanken-experiments on BECs promises to shed light on several aspects of reduction and emergence in physics. These include the relations between classical descriptions and different quantum treatments of macroscopic systems, and the emergence of new properties and even new objects as a result of spontaneous symmetry breaking.

Weak gravitational lensing is a powerful probe of modifications of General Relativity on cosmological scales, since such modifications can affect both how matter produces gravitational potential wells and how photons move within these wells. I will discuss alternative theories of gravitation and how we may constrain such theories using weak lensing observables, including those that could be obtained with the balloon-borne High Altitude Lensing Observatory (HALO). I will also discuss the "parametrized-post-Friedmannian" approach for obtaining model-independent constraints, in which new parameters are introduced to characterize the departure from General Relativity on large scales.

We utilize the tools of the gauge/gravity correspondence in order to investigate electroweak symmetry breaking (EWSB). For quite some time now, a walking technicolor sector has been viewed by phenomenologists as a very promising alternative to the Higgs boson. Unfortunately however, no precise computations have been possible since in the technicolor gauge theory EWSB is due to strong-coupling dynamics. Using recent developments in the gauge/gravity duality, we construct a gravity dual of a walking technicolor model and aim to compute the Peskin-Takeuchi S-parameter, which is an observable that can distinguish between a Higgs and a technicolor sector.

Recently there has been great interest in calculating transport coefficients for field theories at large coupling, using AdS/CFT. In this talk I will discuss recent work showing how to use the membrane paradigm to easily compute the shear viscosity and conductivity in arbitrary gravity theories. In a certain sense these can be thought of as effective couplings at the black hole horizon dual to the field theory plasma. An explicit Wald-like formula for these couplings is given for a large class of generalized gravity theories.

In generalized models of gauge-mediated supersymmetry breaking, a standard model-like Higgs boson can decay to pairs of neutralino superpartners. If the energy scale of supersymmetry breaking is very low, each of these neutralinos will subsequently decay promptly to a photon and a gravitino. This process gives rise to a collider signal consisting of a pair of photons and missing energy. In this talk I will describe scenarios of supersymmetry breaking that can give rise this signature and other non-standard Higgs decay modes, and discuss how it might be discovered with upcoming data from the Tevatron and the LHC.

The idea behind an intersection between loop quantum gravity and noncommutative geometry is to combine elements of unification with a setup of canonical quantum gravity. In my talk I will first review the construction of a semi-finite spectral triple build over an algebra of holonomy loops. Here, the loop algebra is a noncommutative algebra of functions over a configurations space of connections, and the interaction between the Dirac type operator and the loop algebra captures information of the kinematical part of canonical quantum gravity. Next, I will show how certain normalizable, semi-classical states are build which connects the spectral triple construction to the Dirac Hamiltonian in 3+1 dimensions. Thus, these states can be interpreted as one-particle fermion states in an ambient gravitational field. This analysis indicates that the spectral triple construction involves matter degrees of freedom.

Physicists have been working for banks and hedge funds on applied problems in finance for more than two decades, and recently have doing academic research as well. This talk will survey academic research by physicists and contrast it with mainstream economics. I will argue that the difference comes not from the application of alternative techniques or new mathematics, but rather from fundamental differences in what questions are considered interesting and how one should go about solving them. This will be illustrated with a simple model for how systemic risks and extreme price movements are generated by the use of leverage (buying with credit). The current financial crisis illustrates that the economy is indeed a complex system, and that new approaches are needed that properly take this into account.