Scientific Series

In holographic duality an eternal AdS black hole is described by two copies of the boundary CFT in the thermofield double state. We provide explicit constructions in the boundary theory of infalling time evolutions which can take bulk observers behind the horizon. The constructions also help to illuminate the boundary emergence of the black hole horizons, the interiors, and the associated causal structure. A key element is the emergence, in the large N limit of the boundary theory, of a type III1 von Neumann algebraic structure and the half-sided modular translation structure associated with it.

Zoom Link: https://pitp.zoom.us/j/99458239757?pwd=YTBRdXdwTjltMkdZc0Q4WW1jQjA3QT09

I will describe an approach to extracting the physical consequences of S-duality of four-dimensional N = 4 super Yang-Mills (SYM) and its string theory dual based on SL(2,Z) spectral theory. I will show that processing S-duality in this way leads to strong consequences for the CFT data, both perturbatively and non-perturbatively in all parameters. In large-N limits, I will argue for the existence and scaling of non-perturbative effects, both at large N and at strong 't Hooft coupling. An elegant benchmark for these techniques is a certain integrated stress-tensor multiplet four-point function, whose form I will elucidate. I will explain how the ensemble average of CFT observables over the N = 4 supersymmetric conformal manifold with respect to the Zamolodchikov measure is cleanly isolated by the spectral decomposition, and will show that the large-N limit of the ensemble average is equal to the strong-coupling limit of the observable in the planar theory, which is its value in type IIB supergravity on AdS_5 x S^5. This embeds an emergent averaged holographic duality within the conventional holographic paradigm.

Zoom link:  https://pitp.zoom.us/j/95197874062?pwd=QU4vbXNNeFVmS0hNbTVLL24wdDBndz09

In this talk, we first introduce the basic idea of asymptotic safety and discuss its application to quantum gravity. We compute non-perturbative flow equations for the couplings of quantum gravity in fourth order of a derivative expansion. It is shown that the beta functions admit two possible fixed points: One is the asymptotically safe fixed point, and the other is the asymptotically free one. The corresponding critical exponents to these fixed points are evaluated.

Next, we argue that asymptotically safe gravity could be an effective theory emerging from the spontaneous symmetry breaking in an ultraviolet (UV) theory. We consider a UV theory invariant under SO(4) local Lorentz symmetry and diffeomorphism. In particular, we impose the degenerate limit (zero eigenvalues of vierbein) on the action and then show that only spinor fields can be dynamical. We will discuss prospects whether or not this UV theory could be a fundamental theory underlying asymptotically safe gravity.

Zoom Link: https://pitp.zoom.us/j/94422371986?pwd=a25pS3cyUmJkNWJHL3hic1NhNlozQT09

By considering the photon-graviton scattering amplitude at low-energy including loops from the Standard Model, I will argue how we can infer constraints on the Regge behaviour of the gravitational scattering amplitude. I will also comment on implications to other gauge fields in four and higher dimensions and application to the Weak Gravity Conjecture and connections with causality considerations.

Zoom Link: https://pitp.zoom.us/j/91414100213?pwd=Z3g5SmRPb2xjUXEweGtjUC83WCtKdz09

We discuss the minimal coupling of gauge fields to the dual graph lattice of Causal Dynamical Triangulations (CDT) as a preliminary step towards the investigation of more realistic systems of gravity coupled to bosonic and fermionic matter. We first introduce the CDT approach and how the gravity and gauge fields are discretized, for general dimensions and gauge groups, focusing on some of the algorithmic complications which arise. Next, we discuss some results from 2D simulations of CDT coupled to U(1) and SU(2) gauge groups, where we studied both gravity and gauge-related observables and the ones related to gauge fields, comparing them to analogous simulations in the flat case.

I will present an argument that if a theory of quantum gravity is physically discrete at the Planck scale and the theory recovers General Relativity as an approximation, then, at the current stage of our knowledge, causal sets must arise within the theory, even if they are not its basis. I will argue in particular that an apparent alternative to causal sets, viz. a certain sort of discrete Lorentzian simplicial complex, cannot recover General Relativistic spacetimes in the appropriately unique way. For it cannot discriminate between Minkowski spacetime and a spacetime with a certain sort of gravitational wave burst.

Zoom Link: https://pitp.zoom.us/j/96897602807?pwd=VkJ3VTAwYjhaTnJ3Z2ZVclZFYXErZz09

Cosmic inflation is an important paradigm of the early Universe which is so far developed in two equivalent ways, either by geometrical modification of Einstein's general relativity (GR) or by introducing new forms of matter beyond the standard model of particle physics. Starobinsky's R+R^2 inflation based on a geometric modification of GR is one of the most observationally favorable models of cosmic inflation based on a geometric modification of GR. In this talk, I will discuss in detail the fundamental motivations for Starobinsky inflation and present how certain logical steps in the view of its UV completion lead to the emergence of a gravity theory that is non-local in nature. Then I will establish how one can perform studies of the early Universe in the context of non-local gravity and what are the observational consequences in the scope of future CMB and gravitational waves. I will discuss in detail how non-local R^2-like inflation can be observationally distinguishable from the local effective field theories of inflation. 

Magic-angle (θ=1.05∘) twisted bilayer graphene (MATBG) has shown two seemingly contradictory characters: the localization and quantum-dot-like behavior in STM experiments, and delocalization in transport experiments. We construct a model, which naturally captures the two aspects, from the Bistritzer-MacDonald (BM) model in a first principle spirit. A set of local flat-band orbitals (f) centered at the AA-stacking regions are responsible to the localization. A set of extended topological conduction bands (c), which are at small energetic separation from the local orbitals, are responsible to the delocalization and transport. The topological flat bands of the BM model appear as a result of the hybridization of f- and c-electrons. This model then provides a new perspective for the strong correlation physics, which is now described as strongly correlated f-electrons coupled to nearly free topological semimetallic c-electrons - we hence name our model as the topological heavy fermion model. Using this model, we obtain the U(4) and U(4)×U(4) symmetries as well as the correlated insulator phases and their energies. Simple rules for the ground states and their Chern numbers are derived. Moreover, features such as the large dispersion of the charge ±1 excitations and the minima of the charge gap at the Γ point can now, for the first time, be understood both qualitatively and quantitatively in a simple physical picture. Our mapping opens the prospect of using heavy-fermion physics machinery to the superconducting physics of MATBG. All the model’s parameters are analytically derived.

In recent years, generalizations of the notion of symmetry have significantly broadened our view on states of matter. We will discuss some recent progress of understanding and realizing the "fractal symmetry", where the symmetric charge i.e. the generator of the symmetry is defined on a fractal subset of the system with a noninteger or more generally irrational Hausdorff dimension. We will introduce a series of models with exotic fractal symmetries, which can in general be deduced from a "Pascal Triangle" (also called Yang Hui Triangle in ancient China) symmetry. We will discuss their various features including quantum phase transitions. We will also discuss the potential realization of these phases and phase transitions in experimental systems, such as the highly tunable platform of Rydberg atoms.

Zoom Link: https://pitp.zoom.us/meeting/register/tJcqc-ihqzMvHdW-YBm7mYd_XP9Amhypv5vO

Twisted interfaces between stacked van der Waals Cuprate crystals enable tunable Josephson coupling, utilizing anisotropic superconducting order parameters. Employing a novel cryogenic assembly technique, we fabricate high-temperature Josephson junctions with an atomically sharp twisted interface between Bi_2Sr_2CaCu_2O_{8+x} crystals. The critical current density J_c sensitively depends on the twist angle. While near 0 degree twist, J_c nearly matches that of intrinsic junctions, it is suppressed almost 2-orders of magnitude but remained finite near 45 degree. J_c also exhibits non-monotonic behavior versus temperature due to competition between two supercurrent contributions from nodal and anti-nodal regions of the Fermi surface. Near 45 degree twist angle, we observe two-period Fraunhofer interference patterns and fractional Shapiro steps at half integer values, a signature of co-tunneling Cooper pairs necessary for high temperature topological superconductivity.

Zoom Link: https://pitp.zoom.us/meeting/register/tJcqc-ihqzMvHdW-YBm7mYd_XP9Amhypv5vO

The patent system is designed to help innovators protect their intellectual property. In this colloquium, we will discuss logistical and strategic aspects of the patent process, to help you better understand how to leverage the patent system. Topics will include the anatomy of a patent, deadlines and procedural steps for filing patent applications, and strategic considerations in developing the claims and other components of a patent application.

Zoom Link: https://pitp.zoom.us/j/91402107798?pwd=UDRQV0IvY3JEUkVJeC9QR3JXVjZSdz09

Thermodynamics has shed light on engines, efficiency, and time’s arrow since the Industrial Revolution. But the steam engines that powered the Industrial Revolution were large and classical. Much of today’s technology and experiments are small-scale, quantum, far from equilibrium, and processing information. Nineteenth-century thermodynamics needs re-envisioning for the 21st century. Guidance has come from the mathematical toolkit of quantum information theory. Applying quantum information theory to thermodynamics sheds light on fundamental questions (e.g., how does entanglement spread during quantum thermalization? How can we distinguish quantum heat from quantum work?) and practicalities (e.g., quantum engines and the thermodynamic value of coherences). I will overview how quantum information theory is being used to revolutionize thermodynamics in quantum steampunk, named for the steampunk genre of literature, art, and cinema that juxtaposes futuristic technologies with 19th-century settings.

Zoom Link: https://pitp.zoom.us/j/92454766615?pwd=QzZXMnYwN3ZZOTE5RzZEcHp6TkhMdz09