10 research outputs found
Heavy Operators and Hydrodynamic Tails
The late time physics of interacting QFTs at finite temperature is controlled
by hydrodynamics. For CFTs this implies that heavy operators -- which are
generically expected to create thermal states -- can be studied
semiclassically. We show that hydrodynamics universally fixes the OPE
coefficients , on average, of all neutral light operators with two
non-identical heavy ones, as a function of the scaling dimension and spin of
the operators. These methods can be straightforwardly extended to CFTs with
global symmetries, and generalize recent EFT results on large charge operators
away from the case of minimal dimension at fixed charge. We also revisit
certain aspects of late time thermal correlators in QFT and other diffusive
systems.Comment: 60 pages, 9 figures; v2: published versio
Bound on Thermalization from Diffusive Fluctuations
The local equilibration time of quantum many-body systems has been
conjectured to satisfy a "Planckian bound", . We provide a sharp and universal definition of this time
scale, and show that it is bounded below by the strong coupling scale of
diffusive fluctuations, which can be expressed in terms of familiar transport
parameters. When applied to conformal field theories at finite temperature,
this fluctuation bound implies the Planckian bound. The fluctuation bound
moreover applies to any local thermalizing system, and we study its implication
for correlated insulators, metals, as well as disordered fixed points, where it
can be used to establish a lower bound on the diffusivity in terms of the
specific heat . Finally, we discuss how
the local equilibration time can be directly measured in experiments
(Re-)Inventing the Relativistic Wheel: Gravity, Cosets, and Spinning Objects
Space-time symmetries are a crucial ingredient of any theoretical model in
physics. Unlike internal symmetries, which may or may not be gauged and/or
spontaneously broken, space-time symmetries do not admit any ambiguity: they
are gauged by gravity, and any conceivable physical system (other than the
vacuum) is bound to break at least some of them. Motivated by this observation,
we study how to couple gravity with the Goldstone fields that non-linearly
realize spontaneously broken space-time symmetries. This can be done in
complete generality by weakly gauging the Poincare symmetry group in the
context of the coset construction. To illustrate the power of this method, we
consider three kinds of physical systems coupled to gravity: superfluids,
relativistic membranes embedded in a higher dimensional space, and rotating
point-like objects. This last system is of particular importance as it can be
used to model spinning astrophysical objects like neutron stars and black
holes. Our approach provides a systematic and unambiguous parametrization of
the degrees of freedom of these systems.Comment: 30 page
Thermalization and chaos in a 1+1d QFT
We study aspects of chaos and thermodynamics at strong coupling in a scalar
model using LCT numerical methods. We find that our eigenstate spectrum
satisfies Wigner-Dyson statistics and that the coefficients describing
eigenstates in our basis satisfy Random Matrix Theory (RMT) statistics. At weak
coupling, though the bulk of states satisfy RMT statistics, we find several
scar states as well. We then use these chaotic states to compute the equation
of state of the model, obtaining results consistent with Conformal Field Theory
(CFT) expectations at temperatures above the scale of relevant interactions. We
also test the Eigenstate Thermalization Hypothesis by computing the expectation
value of local operators in eigenstates, and check that their behavior is
consistent with thermal CFT values at high temperatures. Finally, we compute
the Spectral Form Factor (SFF), which has the expected behavior associated with
the equation of state at short times and chaos at long times. We also propose a
new technique for extracting the connected part of the SFF without the need of
disorder averaging by using different symmetry sectors.Comment: 16 pages, 17 figure
Thermalization and Hydrodynamics of Two-Dimensional Quantum Field Theories
We consider 2d QFTs as relevant deformations of CFTs in the thermodynamic
limit. Using causality and KPZ universality, we place a lower bound on the
timescale characterizing the onset of hydrodynamics. The bound is determined
parametrically in terms of the temperature and the scale associated with the
relevant deformation. This bound is typically much stronger than ,
the expected quantum equilibration time. Subluminality of sound further allows
us to define a thermodynamic -function, and constrain the sign of the
term in EFTs.Comment: 33 pages, 7 figures; v2: published version; v3: Sec. 5.4 updated,
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