## Colloquium

Thursday, September 18, 2014

**Thomas Gregor,** Princeton University

**Title: "Precision and reproducibility in development"**

**Bill Bialek**, Department of Physics, Princeton University

Thursday, October 2, 2014

**David Huse,** Princeton University

**"Quantum thermalization, many-body Anderson localization, and the entanglment frontier"**

Host:

**Duncan Haldane**, Department of Physics, Princeton University

Thursday, October 9, 2014

**Leslie Rosenberg**, University of Washington

**Title: "Searching for Dark-Matter Axions"**

The axion is a hypothetical elementary particle whose existence would explain the baffling absence of CP violation in strong interactions. Axions also happen to be a compelling dark-matter candidate. Even if dark-matter axions were to comprise the overwhelming majority of mass in the universe, they would be extraordinarily difficult to detect. However, several experiments, either under construction or taking data, would be sensitive to even the more pessimistically coupled axions. This talk describes the current state of these searches.

Host:** Cristiano Galbiati**, Department of Physics, Princeton University

Thursday, October 16, 2014

**Michael Gordin**, Department of History, Princeton University

**Title: "Einstein in Bohemia: Not-So-General Relativity, 1911-1912"**

In the spring of 1911, Albert Einstein moved from Zurich to the German University in Prague, taking up his first appointment as a full professor. Heavily on his mind was a project to extend the special theory of relativity (1905) to a general theory of relativity, building from his 1907 inspiration on the equivalence of inertial and gravitational mass. It was only after his arrival in the Bohemian capital — then the third city of Austria-Hungary and torn between nationalist Czechs and the dwindling German-speaking minority — that Einstein’s attention could shift almost entirely to gravitation. His progress, however, was limited and frustrating, yielding in the end a static theory that has been typically dismissed as a wrong turn on the path to his famous field equations of 1915. Prague was equally vexing: both Einstein and his family disliked it, and they moved back to Zurich in 1912. This talk focuses on Einstein’s overlooked Prague year to argue for the centrality of both the context and the static theory in the future of Einstein’s scientific career.

Host: **Igor Klebanov**, Department of Physics, Princeton University

Thursday, October 23, 2014

There will be **no colloquium event **as the PCTS public lecture is scheduled at 8 p.m.

Thursday, November 6, 2014

**Slava Rychkov**, CERN (Theory Division), and ENS-Paris (Laboratoire de Physique Théorique de l'Ecole Normale Supérieure)

**Title:** **“Non-Hamiltonian approach to conformal quantum field theory – 40 years later”**

Most takes on quantum field theory start from microscopics, fundamental degrees of freedom, a Lagrangian. Conformal field theory is an exception—it focuses on the algebra of local operators and avoids any reference to the Lagrangian. This leads to a method for doing practical CFT calculations—the conformal bootstrap. The method is 40 years old, though it seemed limited to D=1+1 dimensions where the conformal group is infinite. Recent work shows how to set it up for any D. Applications are rapidly expanding, and the method will become a standard QFT tool next to the RG, the epsilon-expansion, and the 1/N expansion. We will highlight the world-record determination of the 3D Ising critical exponents obtained by the conformal bootstrap.

Host: **Igor Klebanov**, Department of Physics, Princeton University

Thursday, November 13, 2014

**Eva Halkiadakis, **Rutgers University

**Title: "Searching for Supersymmetry with the CMS Experiment at the LHC"**

**Dan Marlow**, Department of Physics, Princeton University

Thursday, November 20, 2014

**E.K.U. Gross**, Max-Planck Institute of Microstructure Physics, Germany

**Title: " How to make the Born-Oppenheimer approximation exact: A fresh look at potential energy surfaces and Berry phases in the vicinity of strong non-adiabatic couplings"**

The Born-Oppenheimer approximation is among the most fundamental ingredients of modern condensed matter physics. This approximation not only makes calculations feasible, it also provides us with an intuitive picture of electronic and nuclear motion. Yet it is an approximation, and some of the most fascinating phenomena such as the process of vision or photovoltaic dynamics occur in the regime where the Born-Oppenheimer approximation breaks down. To tackle such situations one has to face the Hamiltonian of the complete system of interacting electrons and nuclei. We deduce an exact factorization of the full electron-nuclear wavefunction into a purely nuclear part and a many-electron wavefunction which parametrically depends on the nuclear configuration. From this we derive equations of motion for the nuclear and electronic wavefunctions which lead to a unique definition of *exact* potential energy surfaces as well as *exact* geometric phases, both in the time-dependent and in the static case. We show an example where the geometric phase associated with the conical intersection of Born-Oppenheimer surfaces has no counterpart in the true electron-nuclear wavefunction. In the time-domain, whenever there is a splitting of the nuclear wavepacket in the vicinity of an avoided crossing, the exact time-dependent surface shows a nearly discontinuous step. This makes the classical force on the nuclei jump from one to another adiabatic surface, reminiscent of Tully’s surface hopping algorithms. Based on this observation we propose novel mixed-quantum-classical algorithms.

Host: **David Limmer**, Princteton Center for Theoretical Science

Thursday, December 4, 2014

**Yifang Wang**, Institute of High Energy Physics (Beijing)

**Title: "Daya Bay neutrino experiment and the future"**

Recently reactor neutrino experiments have made important contributions to the neutrino oscillation. I will introduce the Daya Bay experiment which observed for the first time the neutrino mixing angle θ13 with a statistical significance of 5.2 σ. The concept of the experiment, the detector construction and data analysis will be described. The next generation reactor neutrino experiment, JUNO, is about to start the construction in China. This experiment can determine the neutrino mass hierarchy and improve the precision of neutrino mixing parameters by one order of magnitude. It is also sensitive to supernova neutrinos, geoneutrinos and many others. I will also describe a new idea of neutrino beam for CP phase determination.

Host: **Chris Tully**, Department of Physics, Princeton University