Colloquium

The universe has turned out to be simpler than expected on both very small and very large scales. We propose a minimal, highly predictive framework connecting particle physics to cosmology. Instead of introducing an ``attractor” phase such as inflation we extrapolate the observed universe all the way back to the initial singularity where we impose a CPT symmetric boundary condition via a generalization of the method of images. If the hot plasma in the early universe is perfectly conformal, so is the singularity. The cosmos may then be analytically extended to a ``mirror image” universe prior to the bang. Using this new boundary condition we calculate the gravitational entropy for cosmologies with radiation, matter, Lambda and space curvature, finding it favours spatially flat, homogeneous and isotropic universes with a small positive cosmological constant in accord with observation. To maintain conformal symmetry, we include unusual Dim-0 (dimension zero) fields. They improve the SM’s coupling to gravity, cancelling the vacuum energy and two local “Weyl” anomalies, without introducing additional propagating modes. They also cancel pathologies introduced into the graviton propagator by loops of SM particles. Cancellation requires precisely 3 generations of SM fermions, each with a RH neutrino. It also requires a composite Higgs, presumably built with the Dim-0 fields. One of the RH neutrinos, if stable, is a viable candidate for the dark matter which will be tested soon. The Dim-0 fields source scale-invariant curvature perturbations in the early universe. Subject to two simple but crucial theoretical assumptions, the amplitude and spectral tilt match the observations with remarkable accuracy. (See arXiv:2302.00344 and references therein).

Zoom Link: https://pitp.zoom.us/j/95784600151?pwd=dkppa2s3ZDM4NG5yb0ZVV2w5SXErdz09

Complementing the spectacular breakthroughs in gravitational wave and multi-messenger astronomy, advancements in our theoretical understanding and modelling of the strong gravity are essential to apprehending the nonlinear dynamics of spacetime, and to unlocking the full potential of the observations. I will illustrate the scope of new physics that might be probed by black holes, neutron stars, and other such systems, including testing general relativity and strong gravity signatures of new particles, and describe some recent developments that allow for uncovering novel phenomena and making detailed predictions in this regime.

Zoom Link: https://pitp.zoom.us/j/96180256322?pwd=LzEyd3ZBWGdZeDR6MjB1dGpLWFRpUT09

There are fascinating new insights we could achieve if we succeeded in connecting quantum gravity to particle physics in the visible and the dark universe. However, making such a connection is challenging, because the typical scale of quantum gravity is believed to be far from the typical scales in particle physics. I will exploit lever arms that could make it possible to bridge this gap in scales.  To provide concrete examples for these ideas, I will review recent results on the proton lifetime in quantum gravity, the effects of asymptotically safe quantum gravity on properties of Standard Model matter and the effects of asymptotically safe quantum gravity on simple models of dark energy and dark matter.

Zoom Link: https://pitp.zoom.us/j/96545839038?pwd=UG1IVzJPWUZGa2ovOFhzdHBhOFhOdz09

Schrodinger's thought experiment famously illustrates the dramatic effect of measuring a quantum state. The resulting wave function collapse is often thought to make states more classical and familiar. However, in this colloquium, we explore how measurements can be used as a chisel to efficiently build exotic forms of quantum entanglement. We focus on topological states of matter, whose quasiparticles exhibit generalized 'anyonic' exchange statistics with potential relevance to quantum computation. We use these ideas to experimentally realize the first controlled realization of non-Abelian anyons, which can remember the sequence in which they are exchanged. The smoking gun signature of this experiment is inspired by the coat of arms of the House of Borromeo.

Zoom Link: https://pitp.zoom.us/j/98167813390?pwd=aG5vcklVZzBWT1BRSjI4RVRtbDhBUT09

The classical spacetime manifold of general relativity disappears in quantum gravity, with different research programs suggesting a variety of alternatives in its place. As an illustration of how philosophers might contribute to an interdisciplinary project in quantum gravity, I will give an overview of recent philosophical debates regarding how classical spacetime "emerges."  I will criticize some philosophers as granting too much weight to the intuition that a coherent physical theory must describe objects as located in space and time.  I will further argue, based in part on historical episodes, that an account of emergence needs to recover the structural features of classical GR responsible for its empirical success.  This is more demanding than it might at first appear, although the details of recovery will differ significantly among different approaches to quantum gravity.

Zoom link:  https://pitp.zoom.us/j/98331676824?pwd=VTNOakMxWWUzT2ZFZFYwYzBRdWxBUT09

The aim of the presentation is to review the beautiful geometry underlying the standard model of particle physics, as captured by the framework of "SO(10) grand unification." Some new observations related to how the Standard Model (SM) gauge group sits inside SO(10) will also be described. 

I will start by reviewing the SM fermion content, organising the description in terms of 2-component spinors, which give the cleanest picture. 

I will then explain a simple and concrete way to understand how spinors work in 2n dimensions, based on the algebra of differential forms in n dimensions.

This will be followed by an explanation of how a single generation of standard model fermions (including the right-handed neutrino) is perfectly described by a spinor in a 10 ("internal") dimensions. 

I will review how the two other most famous "unification" groups -- the SU(5) of Georgi-Glashow and the SO(6)xSO(4) of Pati-Salam -- sit inside SO(10), and how the SM symmetry group arises as the intersection of these two groups, when they are suitably aligned.

I will end by explaining the more recent observation that the choice of this alignment, and thus the choice of the SM symmetry group inside SO(10), is basically the choice of two Georgi-Glashow SU(5) such that the associated complex structures in R^{10} commute. This means that the SM gauge group arises from SO(10) once a "bihermitian" geometry in R^{10} is chosen. I will end with speculations as to what this geometric picture may be pointing to. 

Zoom link:  https://pitp.zoom.us/j/95984379422?pwd=SE1ybktzQzcreWREblhEUkZWWElMUT09

In this colloquium, I will review how the notion of quantum error-correction has transformed our understanding of quantum gravity in the past decade.

Zoom link:  https://pitp.zoom.us/j/94349082665?pwd=OFdJdkpHU1NEcmlNeW5pWlg4WmNBZz09

In quantum many-body physics, we aim to understand and predict the exciting phenomena emerging from the interactions of many quantum particles. In this talk I will use the paradigmatic Fermi-Hubbard model, a conceptually simple model of interacting fermionic particles, as an example to highlight different approaches to gain insights into quantum many-body problems. I will describe a semi-analytical theory, established numerical methods, machine learning techniques, as well as quantum simulation experiments, which provide detailed information about the quantum state of the system. A particular focus will be on how to combine these different approaches to learn as much as possible about the system of interest, for example through new observables and modified microscopic models.

Zoom link:  https://pitp.zoom.us/j/94368447256?pwd=clhQcUJNaTR0UjVydnBHelo4N3JIQT09

In 2008 Masahiro Hotta proposed a protocol for transporting energy between two localized observers A and B without any energy propagating from A to B. When this protocol is applied to the vacuum state of a quantum field, the local energy density in the field achieves negative values, violating energy conditions

We will explore the protocol of quantum energy teleportation and show how quantum information techniques can be used to activate thermodynamically passive states. We will review the first experiment showcasing the local activation of ground state energy (carried out in 2022), and we will discuss the potential of this relativistic quantum information protocol to create exotic distributions of stress-energy density in a quantum field theory, and how spacetime might react to them.

Zoom link:  https://pitp.zoom.us/j/98393523926?pwd=LzI4N1UyLzR4QVVGcENEbjBycjJwUT09

In this talk, I will discuss our work on using models inspired by natural language processing in the realm of many-body physics. Specifically, I will demonstrate their utility in reconstructing quantum states and simulating the real-time dynamics of closed and open quantum systems. Finally, I will show the efficacy of using these models for combinatorial optimization, yielding solutions of exceptional accuracy compared to traditional simulated and simulated quantum annealing methods.

Zoom link:  https://pitp.zoom.us/j/99042603813?pwd=eWl2eC90bXFXVHdJeG9zb3lIQVZKUT09

The importance of the tenfold way in physics was only recognized in this century. Simply put, it implies that there are ten fundamentally different kinds of matter. But it goes back to 1964, when the topologist C. T. C. Wall classified the associative real super division algebras and found ten of them. The three 'purely even' examples were already familiar: the real numbers, complex numbers and quaternions. The rest become important when we classify representations of groups on Z/2-graded Hilbert spaces. We explain this classification, its connection to Clifford algebras, and some of its implications.

Zoom Link: https://pitp.zoom.us/j/96451287888?pwd=dlp2eVhKVTU0L2hqN2UxMy95V21SQT09

I will introduce asymptotically safe quantum gravity, which is based on the quantum realization of scale invariance, as one candidate theory to describe nature at all scales. I will discuss the concept of an asymptotically safe fixed point, and how the realization of scale invariance at high energies might provide a predictive and UV-complete description of nature. In particular, I will focus on the interplay of gravity and matter, and highlight mechanisms how this interplay might lead to constraints and predictions of asymptotically safe gravity-matter systems.

Zoom Link: https://pitp.zoom.us/j/99056179498?pwd=SzlXK1R5dExNckFMM1pMS3IvS1VyQT09