Physics Department, Princeton University

High Energy Theory Seminar - Sheer El-Showk, CEA Saclay - New Skins for an Old Ceremony The Conformal Bootstrap and the Ising Model
The existence of a positive linear functional acting on the space of (differences between) conformal blocks has been shown to rule out regions in the parameter space of conformal field theories (CFTs). We argue that at the boundary of the allowed region the extremal functional contains, in principle, enough information to determine the dimensions and OPE coefficients of an infinite number of operators appearing in the correlator under analysis. Based on this idea we develop the Extremal Functional Method (EFM), a numerical procedure for deriving the spectrum and OPE coefficients of CFTs lying on the boundary (of solution space). We test the EFM by using it to rederive the low lying spectrum and OPE coefficients of the 2d Ising model based solely on the dimension of a single scalar quasi-primary – no Virasoro algebra required. Our work serves as a benchmark for applications to more interesting, less known CFTs (such as the 3d Ising model) in the near future.


Jadwin A08  ·  2:30 p.m.– 3:30 p.m.

High Energy Theory Seminar - Tigran Kalaydzhyan - DESY & ITEP - "Holography and chiral superfluidity for the quark-gluon plasma"
I would like to present our recent progress in understanding the local parity violating effects in QCD, and particularly in the strongly coupled quark-gluon plasma (sQGP).
First, I will describe a fluid-gravity (holographic) approach, predicting the strength of the chiral magnetic and vortical effects
(CME/CVE) and their dependence on the elliptic flow of the QGP, as well as on thermodynamic variables. For this purpose we build a gravity dual of an anisotropic fluid with multiple U(1) charges in presence of external vector fields and the chiral anomaly. The elliptic flow dependence allows us to separate P-/CP-odd effects from a purely hydrodynamic background in heavy-ion collisions.
Second, I will focus on a novel "chiral superfluid" effective theory of QCD in the deconfinement phase. The main idea of the model is the presence of a light axion-like dynamic degree of freedom within QCD, which one can obtain by a 4D bosonization of the near-zero fermionic
(Dirac) modes. This new axion-like field accommodates the essential chiral properties of QGP and, together with thermalized quarks and gluons, forms a two-component fluid. The latter turns out to be an unconventional (chiral) superfluid, which, being polarized in electromagnetic fields, gives rise to CME and other potentially measurable physical phenomena. I will also comment on topological defects populating the QCD vacuum as a physical origin of the superfluidity.

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

Condensed Matter Seminar - Tomasz Durakiewicz, Los Alamos National Laboratory - Time-resolved ARPES of f-electron systems
The coherence temperature, T*, sets an important energy scale in correlated f-electron systems. In this scale the hybridization gap opens at or in the vicinity of the Fermi level and the gap magnitude scales with effective quasiparticle mass. The coherent part of the self-energy corresponding to the gap formation is reduced at high temperatures, and the incoherent part corresponds to quasiparticle scattering. The coherent term in the self-energy expresses the mixing of f and d bands and is directly responsible for repulsion, producing the hybridization gap. In this talk I will show examples of time-resolved ARPES measurements of f-electron systems, providing valuable information about the evolution of coherence and the dynamics of the related quasiparticle states.


Jadwin 475  ·  2:00 p.m.– 3:30 p.m.

Physics Colloquium - Elizabeth Olson, Columbia University - "Amplification of Sound in the Mammalian Cochlea"
The snail-shaped mammalian cochlea houses a narrow strip of sensory tissue that separates compartments of salty water. Sound stimulation launches a mechanical traveling wave down the cochlea that peaks in a tonotopic manner: high/low frequencies peak in the cochlear base/apex. Sensory hair cells respond to the motion with intracellular current and voltage. In outer hair cells the electrical response elicits mechanical forces, by means of piezoelectric “prestin” proteins in the cell membrane. These forces augment the motion of the sensory tissue, boosting and sharpening the mildly frequency-resolved pattern of motion that obtains in the passive (dead) cochlea. The motion is increased by a factor of 100 or more for low sound pressure level sounds and very little for high level sounds, thus active cochlear mechanics is compressively nonlinear. Our work explores the dynamics of cochlear amplification in-vivo, using micro-pressure and voltage sensors and laser interferometry. Our recent results detect power amplification in the cochlea and inform the mechanism that gives rise to the localized sharpening of cochlear responses that is fundamental to normal hearing.
Jadwin A10  ·  4:30 p.m.– 5:30 p.m.

High Energy Theory Seminar - IAS - Christoph Keller, Rutgers, The State University of NJ - “Modular Constraints on Calabi-Yau Compactifications”

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