Theoretical Physics Seminar - Grigory Tarnopolsky, Harvard - “Spontaneous symmetry breaking in Sachdev-Ye-Kitaev and Tensor models” (virtual)

Event time: 
Thursday, March 26, 2020 - 1:00pm to 2:00pm
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217 Prospect Street
New Haven, CT 06511
Event description: 

“Spontaneous symmetry breaking in Sachdev-Ye-Kitaev and Tensor models”
A Majorana fermion is the most elemental quantum degree of freedom—a pair of them has only two quantum states. Despite this simplicity, these fermions can exhibit complex and fascinating quantum dynamics in large ensembles where interactions couple four of them at a time. Models that describe this scenario include the Sachdev-Ye-Kitaev model, where the interaction coefficients are randomly distributed, and the tensor models, where the coefficients respect continuous symmetries.
We find that two coupled SYK or Tensor models exhibit dynamical phenomena characteristic of higher-dimensional quantum field theories. These include a continuous set of scale-invariant theories, sometimes called a conformal window, with critical exponents varying along the window and formally acquiring imaginary parts outside it. For one sign of the coupling constant, the approximate scale invariance continues to hold. For the other, a gap opens in the energy spectrum, resulting in an exponential falloff of the correlation functions; this is indicative of a second-order phase transition associated with breaking of a discrete symmetry.
Host: Leonid Glazman
This talk will be given via Zoom: