# Quantized Ramblings

## By Chetan Pandey

We like to listen to each other talk about physics. We will recklessly extrapolate and assume that you like to listen to us ramble too. Welcome to Quantized Ramblings

### Quantized RamblingsSep 04, 2020

#### 8.5 Part 3: String theory and (other) science fiction

Chetan begins by reviewing the eikonal approximation, and factorization theorems for amplitudes. Amartya then discusses this in context of quantum gravity, causality constraints and regge behaviour. This brings us to Vasiliev gravity the origins of string theory, and Chetan makes interesting remarks about string worldsheets, Ricci flows, the a-theorem, and the Poincare conjecture. We briefly discuss Weyl anomalies and the a-theorem in 6 dimensions. Santhosh then rambles about things such as advanced civilizations, lost knowledge, alien worlds and other fascinating plots for science fiction. Amartya concludes by describing about the recent developments in the anomalous (g-2) of muons, and tension between proposed models and data.

#### 8.5 Part 2

Santhosh begins this episode with a discussion about transverse field Ising chains and dualities, anyon algebras, and systems with known spectra but unknown states. Amartya then talks about the relation between the emergence proposal in EFTs and the weak gravity conjecture, the graviton forward pole, and string theory motivated regge-behavior of amplitudes. Chetan then rambles about the limitations of string theoretic models, SIMPs, and Strominger's work on asymptotic symmetries.

#### 8.5 Part 1: Impromptu over chai

We reunite in person after nearly 2 years. Chetan begins this episode with a discussion about Witten's recent work on the deep connection between gauge-gravity amplitudes and geometry in twistor space, and how this suggests a more fundamental language underlying gauge theories and gravity; with many sacred principles of QFTs coming out as emergent. Amartya then elaborates upon signatures of violations of these sacred principles, the IR-UV correspondences used to constrain physics beyond the standard model, extra dimensions, swampland conjectures and the S-matrix bootstrap. Santhosh then rambles about an array of related topics in condensed matter, from density functional theory, percolation theory, equilibrium, thermalization and Anderson Localization, to stochastic thermodynamics and non-hermitian hamiltonians. We discuss how Supersymmetry seems to be the common conceptual bridge between these topics. We close with an array of questions to be discussed subsequently and ramble about how nice it is to be back.

#### Positivity bounds and gravity

In this episode, we begin by reviewing the weak gravity conjecture. We then discuss such "swampland conjectures" from the EFT perspective- in the form of positivity bounds, and discuss in detail the UV completion of dimension 6 operators. We then discuss Witten's classic work on the ADM mass positivity; seeing how all these ideas are elegantly related. We ramble about the status of global symmetries in quantum gravity, and we conclude with a rant about linearly designed curricula.

#### CPT and the neutrino story

In this episode, we discuss aspects of hermiticity and unitarity, in the context of PT-symmetric Hamiltonians. Then, we take a detour towards discussing the fascinating story of neutrinos in the standard model, the big problem of neutrino masses, and the hierarchy problem; and reminisce about the good ol' days.

#### Thoughts on Academia

In this episode, we discuss what has our experience doing physics been so far-how it's different from what we thought it'd be, what lies ahead. We express (some very strongly) our thoughts about the general nature of the academic institution, what we think its shortcomings are, and what we think its future looks like. Quite unlike other episodes, a disclaimer; the thoughts and opinions expressed in this episode are solely those of the person expressing them.

#### 2D magnetism with Rohan Maniar

In this episode, our friend and today's guest on the podcast, Rohan Maniar, talks about his area of research- 2D magnetic systems. We discuss long-range order in 2D systems and the Mermin-Wagner theorem. We then ramble about stochastic thermodynamics, concluding with brief insights from quantum field theory and the subtleties involved.

#### "Chai pe charcha"

We start by briefly discussing axions and inflation. Amartya then rambles about the structure of vacua in compactified theories. Chetan discusses an interesting relationship between moduli stabilization and compactification. We then finally move onto actually relevant things like Santhosh's literary excursions, Spotify ads, and everything but physics, reminding us of our "good ol' days" at the MDP tea stall.

#### Integrability

In this episode, we discuss ideas of integrability in physics, ranging from classical mechanics to classical and quantum field theories. Amartya discusses some ideas about positivity bounds and the swampland, and with a brief existential discussion about the future, we wrap up.

#### From Parafermions to the Swampland

In this episode, Santhosh describes some features of 1D interacting systems, exploring Bethe ansatz, parafermions, dualities, etc. and Amartya rambles about unitarity bounds, 'ghosts', etc; distinguishing 'healthy' field theories from those in the "swampland".

#### Cosmological collider physics

In this episode, Amartya rambles about an interesting idea of studying inflationary correlators, and we discuss the unreasonable effectiveness of physics in math.

#### An operator for time?

In this episode, we discuss the consequences of having a "time" operator in physical theories and ramble about related ideas.

#### Bose-Einstein condensates with Gautam Hegde

In this episode, we have our first guest, our good friend Gautam, who rambles about cool stuff from granular gases to superfluids.

#### Spontaneous Symmetry Breaking

In this episode, we talk about an idea central to both condensed matter and particle physics-spontaneous symmetry breaking. Starting from the instructive example of a ferromagnet, we move to the famous Higgs mechanism in the context of gauge theories. We discuss the question of why the Higgs is so light, how the same problem shows up in inflationary cosmology, and the can of worms this 'naturalness' problem opens up- as a reminder of how little are QFTs understood.

#### But, what is Time?

In this episode, we discuss the idea of time in physics, inspired by the concept in the movie, Arrival. We ramble about general covariance in relativity, choosing space-like hypersurfaces in cosmology, the metric signature and how despite its supposed arbitrariness, the time co-ordinate stands out.

#### From Compactifications to Topological Insulators

In this episode, we discuss the interesting ideas of spontaneous compactification of higher dimensions in theories like string theory, the Kaluza-Klein picture, etc. We then ramble about aspects of bulk-boundary correspondence and topological invariants in condensed matter physics.

#### Starts with a bang: story of the Universe

#### Hot stuff: From Temperature to Black holes

In this episode, we discuss various ideas to understand what "temperature" is. Usually a statistical parameter describing equilibrium systems, we try to look for a more general description, which leads to a discussion of black holes and quantum field theory.

#### RG flows and all that

In this episode, we (Chetan, Amartya, and Santhosh) discuss some random ideas about quantum field theories, which range from hidden structures/symmetries, RG flows, anomalies to ideas about condensed matter physics.