Quantum Fields and Strings

Anomaly cancellation conditions place strong constraints on many physical theories. In the traditional framework, local and global anomalies are detected by computing an eta invariant of a certain Dirac operator on a mapping torus. Recent research has uncovered the existence of finer anomaly cancellation conditions, not visible in these traditional settings. I will review the traditional and refined anomalies, and apply them to various symmetries of interest in particle physics. Examples include the (various global forms of) the Standard Model, GUT's, and discrete gauge symmetries of physical interest such as proton triality and a certain Z4 symmetry in the (MS)SM.

In many-body chaotic systems, the size of an operator generically grows in Heisenberg evolution, which can be measured by certain out-of-time-ordered four-point functions. However, these only provide a coarse probe of the full underlying operator growth structure. We develop a methodology to derive the full growth structure of fermionic systems, that also naturally introduces the effect of finite temperature. We then apply our methodology to the SYK model, which features all-to-all q-body interactions. We derive the full operator growth structure in the large q limit at all temperatures. We see that its temperature dependence has a remarkably simple form consistent with the slowing down of scrambling as temperature is decreased. Furthermore, our finite-temperature scrambling results can be modeled by a modified epidemic model, where the thermal state serves as a vaccinated population, thereby slowing the overall rate of infection.

Motivated by the problem of defining the entanglement entropy of the graviton, we study the division of the phase space of general relativity across subregions. Our key requirement is demanding that the separation into subregions is imaginary---i.e., that entangling surfaces are not physical. This translates into a certain condition on the symplectic form. We find that gravitational subregions that satisfy this condition are bounded by surfaces of extremal area. We characterise the 'centre variables' of the phase space of the graviton in such subsystems, which can be taken to be the conformal class of the induced metric in the boundary, subject to a constraint involving the traceless part of the extrinsic curvature. We argue that this condition works to discard local deformations of the boundary surface to infinitesimally nearby extremal surfaces, that are otherwise available for generic codimension-2 extremal surfaces of dimension ≥ 2.

I will discuss how holographic and effective field theory methods could shed light on important open questions in low energy condensed matter systems. I will focus on the study of the vibrational degrees of freedom, i.e. ''phonons'', in liquids, solids and disordered systems like glasses. Building intuition from the holographic systems I will tackle the problem of the low frequency elastic response in liquids and the universal emergence of the boson peak in ordered crystals and amorphous solids.

Part 1 is about anomalies and how they can deform generalized global symmetry into 2-group global symmetry.  This is illustrated with simple QFT examples in 4d.  Part 2 is about 6d.

6d theories with 2-group symmetry exist, but cannot be conformal.  6d superconformal theories (SCFTs) cannot have 2-group or higher-form, generalized global symmetries.  This requires cancellation of mixed gauge and global terms in the anomaly polynomial.   SCFT relations between conformal and ’t Hooft anomalies will also be discussed.   Based on papers with Cordova and Dumitrescu.

Bulk coherent states produced by Euclidean CFT sources can be used to study how geometry arises from entanglement: when these states obey the Ryu-Takayanagi formula, the linearized Einstein equations hold in the bulk without assuming the complete AdS/CFT correspondence.  However, the Faulkner-Lewkowycz-Maldacena bulk entanglement term that corrects the RT formula does not play a role in these previous studies, since to leading order coherent states have the same entanglement entropy as the vacuum.  We study states CFT states created by Euclidean, bilocal, double trace sources, which produce bulk squeezed states.  We consider possible modifications to RT and study divergences in the perturbative expansion that occur for certain choices of source.  We work towards determining constraints on the bulk geometry and state that arise from requiring FLM, akin to the linearized Einstein equations that arose for coherent states.

We review the color memory effect which is the non-abelian gauge theory analog of the gravitational memory effect, in which the passage of color radiation induces a net relative SU(3) color rotation of a pair of nearby quarks. Then, we show how the color memory effect arises in Regge limit scattering processes and propose that this effect can be measured in the Regge limit of deeply inelastic scattering at electron-ion colliders.

In this talk I will consider the S-matrix bootstrap of four dimensional scattering amplitudes with O(3) symmetry and no bound states and apply the formalism to pion physics. I will discuss the remarkable location where QCD seems to lie in the multi-dimensional space of zeros, scattering length and resonance mass values, based on various experimental and theoretical expectations.

We consider implications of superrotations as an asymptotic symmetry of asymptotically flat spacetimes.  Beginning with a review of the rich structure of interconnections between soft theorems, asymptotic symmetries, and                 memory effects, we describe the superrotation iteration.  The subleading soft graviton theorem can be cast as a Ward identity for this asymptotic symmetry in 4D, and also as one for the stress tensor of a putative CFT2.  We detail the change of scattering basis motivated by this asymptotic symmetry and discuss recent progress.

In gauge theories, there is an inherent tension between locality and gauge invariance.   This is precisely expressed by the failure to factorize the physical Hilbert space into local tensor products.   The extended Hilbert space offers a resolution to this problem by embedding physical states into a larger Hilbert space containing gauge variant degrees of freedom.  For two dimensional TQFT's, we show how this extension fits inside the framework of extended quantum field theory, as described by the Moore-Segal axioms.  These are sewing axioms that impose a sort of spacetime covariance for the extended Hilbert space.   For the case of two-dimensional Yang Mills and it's string theory dual, we show how this framework leads to exact calculations of multi-interval modular flow,  ,negativity, and entanglement entropy.  Moreover, we given an axiomatic formulation of the "entanglement brane", which nicely compliments the worldsheet description given in previous work.

The two-point functions <O^n(x) Obar^n(y)> for generator O of Coulomb branch chiral rings in D=4 N=2 SCFT will be determined universally to all orders in 1/n by the theory's a-anomaly.
The calculation will be done using the method of large-charge expansion presented in [1706.05743]; the absence of F-terms in the (R-charge)^(-1) expansion of the effective action ensures this universality.
I will also comment on the non-universal and non-perturbative corrections to the two-point functions whose leading piece was numerically shown to go as O(exp(-sqrt(n))).