Physics Department, Princeton University

Biophysics Seminar Series - Sergey Kryazhimskiy, Harvard
“Epistasis and adaptation in yeast”

Populations adapt when they encounter new environments, but our ability to predict the course and rate of adaptation are quite limited. A major complication is that we do not know how one mutation might influence the fitness effects of other mutations. In other words, we do not know the structure of epistasis among beneficial mutations. I will describe an experiment that reveals an interesting statistical structure in how adaptive mutations affect each other and discuss the implications of these findings for our ability to predict evolutionary outcomes.
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Joseph Henry Room  ·  11:45 a.m.– 1:00 p.m.

Condensed Matter Seminar - Ganpathy Murthy, University of KY - Hamiltonian Theory of Fractionally Filled Chern Bands
Abstract: When a band of noninteracting electrons has a nontrivial Chern number, it is called a Chern band. When such a band is fully filled, the dimensionless Hall conductance is the Chern number. There is considerable numerical evidence that in the presence of suitable interactions, when a Chern band is fractionally filled, the electrons form insulating states which have many of the properties of fractional quantum Hall states. In the continuum, we know that incompressible FQH states can be understood in terms of Composite Fermions, which can be formed by "flux attachment". In this talk I will present work that demonstrates that one can construct a Hamiltonian theory of the fractional Chern insulators in terms of Composite Fermion variables which can be used to compute gaps, collective excitations etc.

PCTS Seminar Room  ·  1:15 p.m.– 2:30 p.m.

High Energy Theory Seminar - IAS - Joe Polchinski, KITP, University of California, Santa Barbara - “Black Holes: Complementarity or Firewalls?”
I argue that the following three widely believed statements cannot all be true: (i) Hawking radiation is in a pure state, (ii) the information carried by the radiation is emitted from the region near the horizon, with low energy effective field theory valid beyond some microscopic distance from the horizon, and (iii) the infalling observer encounters nothing unusual at the horizon. Perhaps the most conservative resolution is that the infalling observer burns up at the horizon. Alternatives would seem to require novel dynamics that nevertheless cause notable violations of semiclassical physics at macroscopic distances from the horizon.


Bloomberg Lecture Hall  ·  2:30 p.m.– 3:30 p.m.

Condensed Matter Physics with Ultracold Atoms: from Mott Insulators to Topological Superfluids - Waseem Bakr - MIT
Abstract: Recent advances in probing and controlling ultracold atomic gases have allowed access to rich physics from the realm of condensed matter. In the first part of this talk, I will describe quantum gas microscopy, a new tool for imaging and manipulating strongly interacting quantum gases containing thousands of atoms at the single atom level. I will describe its application to studying quantum phase transitions of Mott insulators and quantum magnets in bosonic systems of atoms. In the second part of the talk, I will shift focus to fermionic systems. I will discuss experiments that probe fermion pairing in lower dimensional systems and engineer spin-orbit coupling in Fermi gases by dressing them with Raman light fields. These ingredients are building blocks for the realization of topological matter, including topological insulators and perhaps even topological superfluids.
Joseph Henry Room  ·  2:30 p.m.– 3:30 p.m.

High Energy Theory Informal Seminar - IAS- Joe Polchinski, KITP, University of CA, Santa Barbara-“Scale and Conformal Invariance in Quantum Field"

Bloomberg Lecture Hall  ·  1:30 p.m.– 2:30 p.m.

Math Phys Seminar: Jean-Pierre Eckman (University of Geneva) 'Atoms, Nuclei, and 3d Triangulations'
Based on the work of Durhuus-Jonsson and Benedetti-Ziegler, we revisit the question of the number of triangulations of the 3-ball.  We introduce a notion of nucleus (a triangulation of the 3-ball without internal nodes, and with each internal face having at most 1 external  edge).  We show that every triangulation can be built from trees of nuclei. This leads to a new reformulation  of Gromov's question: We show that if the  number of rooted nuclei with N tetrahedra is exponentially bounded in N, then the number of rooted triangulations with N tetrahedra is also exponentially bounded.  This is joint work with Pierre Collet and Maher Younan.
Jadwin A06  ·  3:30 p.m.– 5:00 p.m.

High Energy Theory Seminar - Daniel Jafferis, Harvard University - "Exact results in 5d superconformal theories with gravity duals"
I will explain how the S^5 partition function of 5d superconformal field theories with gravity duals may be computed in the large N limit. This involves applying the techniques of localization to non-renormalizable 5d Yang-Mills theories obtained by deformation of these SCFTs by a relevant operator. The result matches exactly the leading supergravity behavior of the holographic entanglement entropy in the dual AdS6 geometry in massive IIA.
PCTS Seminar Room  ·  2:30 p.m.– 4:00 p.m.

New prospects for cold molecular physics - Kang-Kuen Ni - JILA
The role of molecular spectroscopy in the broader interests of physics has evolved over the years. It was traditionally the study of molecular structure and its underlying quantum mechanics. Later, it led to various applications including the first “atomic clock” that was actually based on molecular vibrations and to the observation of star light redshifts that reveal the expansion of the universe. More recent advances in techniques for quantum manipulation bring new directions to molecular physics where molecules serve as test systems to study a variety of phenomena. In this talk, I will discuss two examples. First, we make use of the extreme electric fields found within a molecular bond in an experiment that aims to improve our knowledge of the electron's electric dipole moment (eEDM), which will be sensitive to physics beyond the standard model. In the second example, quantum control of molecular internal and external states enables the study of ultra-cold chemistry, and may yield undiscovered quantum phases of matter.
Joseph Henry Room  ·  1:30 p.m.– 2:30 p.m.

High Energy Theory Seminar - IAS - David Simmons-Duffin, IAS - “Projectors, Shadows, and Conformal Blocks”

Bloomberg Lecture Hall  ·  1:30 p.m.– 2:30 p.m.