Tag: symmetry
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Quintessence: The basic idea
Following the recent results announced by DESI, the interest in quintessence models may increase dramatically. So, this is a good time to write a small post on the basic ideas behind quintessence. Basics of GR and QFT are assumed for this post. Firstly, let’s review the basic idea of a cosmological constant. The Einstein equation…
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What are conformal field theories? (Part 1)
In this series of posts, I will explain what conformal field theories (CFTs) are. Basic familiarity with Quantum Field Theories (QFTs) is assumed. In usual relativistic QFTs have some spacetime symmetries. These symmetries are rotations (one about every space direction), boosts (one along every space direction) and translations (one along every spacetime direction). The set…
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What are RG flows?
In this post, I will explain what Renormalization Group (RG) flow is. I will assume the knowledge of the basics of QFT for this post. The idea of an RG flow is intimately related to the idea of effective field theories (EFTs). An EFT is a theory that makes predictions upto some energy scale (called…
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How to make the Standard Model?
This is a post to describe how we construct the standard model lagrangian and generate the masses for gauge bosons and fermions. I will assume basic familiarity with QFT, lagrangians, gauge transformations and gauge groups (like U(1), SU(2)). Recall that the mass term of a scalar field φ is simply proportional to φ2. Vector fields…
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How to derive the Schwarzchild metric?
In this post, we will go through the reasoning that gives us the Schwarzchild solution of Einstein field equations. Prerequisites for this post include familiarity with Einstein field equations. We start with the Einstein field equation (EFE) and convert it to a form that is used to solve this equation. This form is called the…
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First corrections to GR
In this small post, I will show why the first few possible corrections to the Einstein-Hilbert action are the way they are. Basic familiarity with General Relativity is assumed. I will use the natural units (units used in high energy physics) in this article. In these units, the unit of length is the inverse of…
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What is supersymmetry?
This post summarizes the main ideas behind supersymmetry. Pre-requisites to read this post include some familiarity with Poincare algebra and basics of quantum field theory (especially the basics of fermions) In relativistic quantum field theory, we have a certain amount of spacetime symmetries. These symmetries include 3 rotational symmetries (along three space directions), 3 boost…
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AdS3/CFT2 correspondence (Part 2: WZW models)
This is second of my series of posts on AdS3/CFT2 correspondence (for the first post, click here). In this post, I will describe what WZW (Wess-Zumino-Witten) models are. They are relevant here because a WZW model is used to decribe string theory on AdS3 . Basics of field theory, little familiarity with Lie groups and…
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AdS3/CFT2 correspondence (Part 1: AdS3 space)
This is first in a series of posts on duality between strings moving on AdS3 x S3 x T4 spacetime (don’t get intimidated by this) and a conformal field theory living on the boundary of the AdS3 spacetime (which is two dimensional). I will try to explain the basics required to understand this duality. In…
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What are generalized symmetries?
This is a post about the generalization of the concept of global symmetries. This area has been a very active area of research for the last 8 years or so. A basic understanding of global symmetries unitary operators (acting on quantum states and operators) and local operators is required to read this post. This topic…
Hassaan Saleem 