During the semester we have a high energy seminar and a lunch seminar. In addition to these two seminars we participate in a joint theoretical high energy theory seminar in Newe Shalom. The joint seminar takes place on Tuesdays from 10:30 until 13:30 and includes two talks and lunch. This seminar is attended by the high energy groups of all the Israeli institutions and usually attracts a crowd of roughly twenty participants.
Title: The structure of the initial conditions of the universe
Abstract: I will review what we know about the initial conditions of the universe from observations. Then, I will explain how they arise within the framework of inflation, and describe recent progress in classifying (or “bootstrapping”) the possible correlation functions between primordial fluctuations. Finally, time permitting, I will touch upon work in progress trying to apply the bootstrap philosophy to more general cosmologies.
Title: Holography of Chronology Protection
Abstract: After an introduction to time-machine spacetimes and simple models of them, I will discuss recent work with M. Tomasevic where we use holography to study quantum effects when closed timelike curves (CTCs) are developed. We address the question of whether it is possible to send a signal across the chronology horizon, passing into the region where CTCs are present. We find that the self-interaction of quantum fields manages to banish the passage of field excitations into the non-chronal region. Going further, we compute the gravitational backreaction of the quantum fields, and show that the null chronology horizon turns into a strong, spacelike curvature singularity. This is one of the few controlled, explicit examples where we can see quantum effects change a Cauchy horizon into a spacelike singularity.
Title: Mastering bounds on correlators
Abstract: We discuss a new viewpoint onto the CFT landscape: bounds on values of CFT correlators. We show that such bounds can be obtained by constructing suitable ‘master functionals’. We present both numerical results for 3d CFTs as well as exact results for correlators on the line. The latter follow from crossing symmetric dispersion relations. We briefly discuss how these may be used to study the Regge and flat space limits of CFT correlators.
Title: Multi-trace correlators in the SYK model and Non-geometric wormholes
Abstract: We consider the global fluctuations in the density of states of the SYK model, which are much larger than the standard RMT correlations. We provide a diagrammatic description of their leading and subleading behavior. In either case, the new set of correlations are not associated with (and are much larger than) the ones given by topological wormholes, and hint towards the dual of a single realization. In particular, we suggest that incorporating them in the gravity description requires the introduction of new, lighter and lighter, fields in the bulk with fluctuating boundary couplings.
Title: Bootstrapping N = 4 super-Yang-Mills on the conformal manifold
Abstract: We study the N = 4 SYM stress tensor multiplet 4-point function for any value of the complexified coupling tau, and in principle any gauge group (we focus on SU(2) and SU(3) for simplicity). By combining non-perturbative constraints from the numerical bootstrap with two exact constraints from supersymmetric localization, we are able to compute upper bounds on low-lying CFT data (e.g. the Konishi) for any value of tau. These upper bounds are very close to the 4-loop weak coupling predictions in the appropriate regime. We also give preliminary evidence that these upper bounds become small islands under reasonable assumptions, in which case our method would provide a numerical solution to N = 4 SYM for any gauge group and tau.