Quanfum field theory Definition and 20 Threads

This is probably a stupid question but, I want to show that a Lagrangian written in field theory is Lorentz invariant WITHOUT using the Lorentz transformation representation / generators. I know we know that a Lorentz scalar is automatically Lorentz invariant, but, I want to show this by...

Until recently, I was not seriously interested in physics. But while working on my project called Enland, I became interested in the quantum universe, if I may say so. The Enland project is an attempt to begin simulating the Third Reality. That's what I call the world in which everything is...

I am highly interested in Topological Quantum Field Theory (TQFT) and am currently planning on doing a project on this topic this year. Some of my relevant background: Algebra (Groups, Rings, Fields, basics of Categories and Modules), Topology (Munkres), Smooth Manifolds (John Lee's book, first...

So QFT treats particles as excitations of their underlying quantum field, meaning that fields are more fundamental than particles. Then String theory comes in and says that actually strings are the fundamental building block of the universe and that the different particles are vibrating strings...

from what I understand it is believed that information is preserved but we are still working out how exactly, is this the case?

Hi everyone How can i prove that the propagator is And then

My Progress: I tried to perform the coordinate transformation by considering a general function ##f(\mathbf{k},\omega,\mathbf{R},T)## and see how its derivatives with respect all variable ##(\mathbf{k},\omega,\mathbf{R},T)## change: $$ \frac{\partial}{\partial\omega} f =...

I have taken a Quantum Field Theory course recently in which we first derived the Callan-Symanzik equation and then discussed Wilson's Renormalization. However, I don't think I have a clear understanding of the procedures and how they relate to each other. For the sake of this question, let's...

Hello! I'm starting to study curved QFT and am slightly confused about the invariance of the Klein Gordon Lagrangian under a linear diffeomorphism. This is $$L=\sqrt{-g}\left(g^{\mu\nu}\partial_\mu \phi \partial_\nu \phi-\frac{m^2}{2}\phi^2\right),$$ I don't see how ##g^{\mu\nu}\to...

Hi there. I'm trying to solve the problem mentioned above, the thing is I'm truly lost and I don't know how to start solving this problem. Sorry if I don't have a concrete attempt at a solution. How do I derive the Feynman rules for this Lagrangian? What I think happens is that in momentum...

Hello all! Here is a brief description of myself. In 2015, I completed my Ph.D. in theoretical physics at NYU and subsequently spent two years as a postdoc researcher at YU. My research was on many-body quantum systems out of equilibrium, a subject that permeates multiple fields, including...

For a real scalar field, I have the following expression for the field operator in momentum space. $$\tilde{\phi}(t,\vec{k})=\frac{1}{\sqrt{2\omega}}\left(a_{\vec{k}}e^{-i\omega t}+a^{\dagger}_{-\vec{k}}e^{i\omega t}\right)$$ Why is it that I can discard the phase factors to produce the time...

Hi! My name's Logan Knox and I'm aspiring to eventually understand the physics and nature of the quantum world in its totality, and I have a LONG way to go, but I have to get there by asking the right questions, and I think this is the first step to finding the right question to ask for this...

I have one request, I hope you could answer it…. I saw this article that makes heavy assumptions based on Quantum Electrodynamics, like something like formation of an energy domain or sorts, and it connects it with brain activity which is super weird, I did ask a neuroscientist and he said he...

Here is the Code File in an txt. I can on request provied the whole Program, which includes the PSE, AtomFunctions and many useful but not all implemented Funtions to solve the Many Worlds Problem in C#. Please feel free to ask questions via here or email [e-mail address deleted by Mentors] I...

Hi all, One more virtual particle question (sorry all!): for individuals who would take virtual particles as being 'real' (but unobservable), what is their understanding then of the content of the vacuum? For example, if I place a electron all by itself in the vacuum (thus making it no longer...

Hi all, I've been looking at de Broglie-Bohm theory and more recent attempts at Bohm-like models that are relativistic and attempt to reproduce QFT. What I'm not clear on (non-expert) is how the vacuum is modeled in these cases? If we have a set of infinite quantum harmonic oscillators...

Folks, I'm back to reading Muller's paper (https://arxiv.org/pdf/1606.07975.pdf) about the flow of time. He postulates that time is expanding similar the way space is expanding (ok... so if you can swallow that). He asks: "why are the new nows created at the end of time, rather than uniformly...

When defining quantum fields as a sum of creation and annihilation operators for each momenta, we do it in analogy with the simple example of the harmonic oscillator in quantum mechanics. But why do we assume that the coefficients in the expansion can be interpreted in the same way as in the...

I'm working through Lahiri & Pal's book A First Book of Quantum Field Theory, Second Edition and I'm stuck on their explanation of the polarization vector in quantum electrodynamics in Chapters 8 and 9. In section 8.8, they derive a formula for the sum over the transverse polarization modes of...