Time: 10am - 6:30pm

Location: 4N12

Webpage: https://web.sas.upenn.edu/penn-jcppm/

# Events

Time: 2pm

Location: 2N36

TITLE: The re-emergance of spontaneously broken space-time symmetries without Goldstones or Inverse Higgs

ABSTRACT: In this talk I will discuss how broken space-time symmetries can emerge in the IRafter being spontaneously broken in the UV, even though there may be no Goldstonebosons. Given that there has been a large body of work on trying to get space-timesymmetry (e.g. Lorentz) to be emergent in the IR via an RG attractive basin, this may seemlike a very surprising and non-generic result. However, I will show that in the context ofFermi liquid theory it is quite natural, and even required to preserve Fermi liquid behavioras the existence of Goldstone bosons (in this case they would be non-derivative coupled) would lead to shortened life-times for quasi-particles. I will also consider the spontaneous breaking of Schrodingersymmetry whose emergence (with no dilaton) in the IR leads to very strong constraintson Fermi liquids at unitarity.

Time: 2pm

Location: 2N36

Title: Entanglement Entropy in Chern-Simons Theory and Link Invariants

Abstract: We will study the entanglement structure of states in Chern-Simons (CS) theory obtained by performing the Euclidean path-integral on certain highly non-trivial 3-manifolds, namely link complements in S^3. The corresponding entanglement entropies in fact provide framing independent link-invariants. In U(1) CS theory, we will give a general formula for the entanglement entropy across a bi-partition of a generic n-link into sub-links. In the non-Abelian case, we study various interesting 2 & 3-links including the Whitehead link & Borromean rings, both of which have non-trivial entanglement structures. If time permits, we will mention connections with gravity and hyperbolic geometry.

Time: 2pm

Location: 2N36

Title: Large N Tensor Models

Abstract: We review the double line notation for the Feynman diagram expansion of N by N matrix models. In the ‘t Hooft large N limit only the planar diagrams survive, and the dual graphs may be thought of as discretized random surfaces. We proceed to theories where the dynamical degrees of freedom are rank-3 tensors with distinguishable indices, each of which takes N values. Their Feynman diagrams may be drawn using colored triple lines (red, blue, green), while the dual graphs are made out of tetrahedra glued along their triangular faces. Such theories possess a special solvable large N limit dominated by the “melon” diagrams. We discuss quantum mechanical models of fermionic rank-3 tensors and their similarity with the Sachdev-Ye- Kitaev disordered model. We then use the large N Schwinger-Dyson equations to study the conformal dimensions of certain composite operators. Gauging the global symmetry in the quantum mechanical models removes the non-singlet states; therefore, one can search for their well-defined gravity duals. We note that the models possess a vast number of gauge-invariant operators involving higher powers of the tensor field. Finally, we discuss similar models of a commuting rank-3 tensor in dimension d. While the quartic interaction is not positive definite, we study the large N Schwinger-Dyson equations and show that their solution is consistent with conformal invariance.

Time: 12pm (Special Seminar)

Location: 2N36

Title: Black Holes in Massive Gravity: Time-Dependent Solutions

Abstract: When starting with a static, spherically-symmetric ansatz, there are two types of black hole solutions in massive gravity: (i) exact Schwarzschild solutions which exhibit no Yukawa suppression at large distances and (ii) solutions which contain coordinate-invariant singularities at the horizon. In this talk, I will present new black hole solutions which have a nonsingular horizon and can potentially be matched to Yukawa asymptotics at large distances. These solutions recover Schwarzschild black holes in the limit of zero graviton mass and are thus observationally viable. At finite mass they depend explicitly on time. However, the location of the apparent horizon is time-independent indicating that these black holes are neither accreting or evaporating (classically).

Time: 2pm

Location: 2N36

Title: Modular spacetime and Metastring theory

Abstract: In this talk we review our recent work on metastring theory and its habitat, a new form of quantum spacetime, called modular spacetime. We emphasize that the geometry underlying modular spacetime, i.e. the background geometry of metastring theory, is also the geometry underlying generic representations of quantum theory as formulated in terms of Aharonov's modular variables. Thus the metastring sheds light on the foundations of quantum theory, and it represents a new formulation of string theory and quantum gravity based on the principle of relative locality. (This work is done in collaboration with Laurent Freidel (Perimeter Institute) and Rob Leigh (Urbana).)

Time: 11am

Location: 4N12 (Special Seminar)

Title: Monopole-antimonopole creation and other numerical studies.

Abstract: I will describe magnetic monopoles, their properties, and recent numerical work on their creation from particles.

Time: 2pm

Location: 2N36

Title:

Causality and Universality at Strong Coupling

Abstract:

Causality imposes constraints on the coupling constants in perturbative effective field theory, which have played a role in understanding scattering amplitudes, the a-theorem for renormalization group flows, and higher curvature corrections in quantum gravity. I will describe similar constraints on strongly interacting theories, then use them to derive the averaged null energy condition, and discuss the connection to emergent geometry at large N.

Time: 2pm

Location: 2N36

Title: Constraining QFT with Relative Entropy

Time: 2pm

Location: 2N36

Title: Physics and geometry of F-theory compactifications

Abstract: I will give a basic introduction to F-theory — a non-perturbative formulation of type IIB string theory. After going through some of the mathematical details of the subject, I will focus on the interplay between 4D anomaly cancellations and the geometry of Calabi—Yau fourfolds.

Time: 2pm

Location: 2N36

Title: The Fate of the Higgs Vacuum

Abstract: Now that the Higgs boson has finally been detected, its mass suggests that we are in a region of "metastability", with various claims being made about the lifetime of the vacuum. However, the new minimum lies in a Planckian regime, and we would expect gravity to be relevant in any decay process. The decay of a false vacuum is always described by a tunneling process, the Coleman-de Luccia instanton, however, this assumes our universe is featureless. Just as impurities can act as nucleation sites of a phase transition, gravitational impurities, in the guise of black holes, can act as bubble nucleation sites for false vacuum decay. I will describe how a black hole can significantly enhance the probability of vacuum decay, and discuss implications for the Higgs vacuum.

Time: 2pm

Location: 2N36

Title: Entanglement, Gravity, and Quantum Error Correction

Abstract: Over the last few years it has become increasingly clear that there is a deep connection between quantum gravity and quantum information. The connection goes back to the discovery that black hole entropy is given by the horizon area. I will present evidence that this is only the tip of the iceberg, and prove that a similar area law applies to more general Renyi entanglement entropies. Furthermore, I will provide quantum corrections to the area law and use it to address a longstanding problem in quantum gravity: what region of the dual spacetime is described by a subregion in a holographic theory? The answer to this question lies in a new perspective that I will advocate: holography is a quantum error correcting code.

Time: 2pm

Location: 2N36

Title: TBA

Time: 2pm

Location: 2N36

Title: **Shaving off Black Hole Soft Hair**

Abstract: After recalling a definition of a black hole "hair" we explain why the only interesting hairs are those that are also remnants. Next, we will examine a recent proposal by Hawking, Perry and Strominger, who suggest that soft photons and soft gravitons can be regarded as black hole hairs that may be relevant to the black hole information paradox. We will make use of factorization theorems for infrared divergences of the S-matrix to argue that, by appropriately dressing in and out hard states, the soft-quanta-dependent part of the S-matrix becomes essentially trivial, in the sense that the information paradox can be fully formulated in terms of dressed hard states, which do not depend on soft quanta.

Time: 2pm

Location: 2N36

Title: Reinventing the wheel: an effective theory approach to dissipative spinning objects.

Abstract: In this talk, I will show how effective field theory techniques can be used to shed a new light on the dissipative dynamics of spinning astrophysical objects. After introducing the basic formalism, I will discuss two different applications. The first one is a modern description of superradiance — a phenomenon by which a spinning object can loose angular momentum by amplifying the intensity of scattered radiation, or by producing particles in a bound state. Along the way, I will also provide a simple derivation of vacuum friction — a “quantum torque” that acts on spinning objects in empty space. The second application I will discuss (if time will allow it) is to tides and the role they play in the dynamics of moons, planets and other “Newtonian” objects. I will argue in particular that the time scales over which orbit circularization and tidal locking take place satisfy a hierarchy which follows exclusively from symmetry and is thus a model independent prediction of the effective theory.

Time: 2pm

Location: 2N36

Title: TBA

Time: 2pm

Location: 2N36

Title: Relative entropy of excited states in conformal field theories

Abstract:We study the relative entropy between the reduced density matrices obtained from globally excited states in conformal field theories of arbitrary dimensions. We find a general formula in the small subsystem size limit. When one of the states is the vacuum of the CFT, our result matches with the holographic entanglement entropy computations in the corresponding bulk geometries, including AdS black branes. We also discuss the first asymmetric part of the relative entropy and comment on some implications of the results on the distinguishability of black hole microstates in AdS/CFT.

Time: 2pm

Location: 2N36

**Title**: Recent developments in 3-D dualities

**Abstract**: This summer has seen a flurry of activity in particle-vortex duality and, more generally, in non-supersymmetric dualities in three spacetime dimensions. Much of this work has been directly related to the properties of so-called topological quantum matter and gapped phases of matter. In this talk, I will give a more-or-less pedagogical introduction to these ideas, beginning with the sine-Gordon/massive Thirring correspondence and building toward our current understanding of the 3-dimensional web of dualities.

Time: 2pm

Location: 2N36

Title: No-go results and promising directions in the space of causal diamonds

Abstract: The space of causal diamonds recently brought to attention by de Boer et al. and Czech et al. provides an organizing principle for the dependence of entanglement entropy in conformal field theories on the spatial subregion considered. I will show that the inclusion relation of causal diamonds does not give rise to a consistent notion of a causal structure and thus does not provide an alternate metric on this space. I will also show that the entanglement entropy of ball shaped regions is not enough to reconstruct the areas of higher dimensional bulk surfaces in a static geometry. Instead, I will provide a new direction for the reconstruction of the areas of bulk surfaces from boundary data in holography, using the shape derivatives of the entanglement entropy of nearly ball shaped regions.

Time: 2pm

Location: 2N36

Title: New forms of quantum entanglement in discretely gauged theories