Qft Definition and 980 Threads

In particle physics, the history of quantum field theory starts with its creation by Paul Dirac, when he attempted to quantize the electromagnetic field in the late 1920s. Major advances in the theory were made in the 1940s and 1950s, and led to the introduction of renormalized quantum electrodynamics (QED). QED was so successful and accurately predictive that efforts were made to apply the same basic concepts for the other forces of nature. By the late 1970s, these efforts successfully utilized gauge theory in the strong nuclear force and weak nuclear force, producing the modern standard model of particle physics.
Efforts to describe gravity using the same techniques have, to date, failed. The study of quantum field theory is still flourishing, as are applications of its methods to many physical problems. It remains one of the most vital areas of theoretical physics today, providing a common language to several different branches of physics.

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  1. Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 25: Feynman Rules in QED 1

    Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 25: Feynman Rules in QED 1

    Copyright reserved to Prof. Tripathy and NPTEL, Govt. of India. Duplication prohibited. Lectures: http://nptel.ac.in/courses/115106065/ Syllabus: http://nptel.ac.in/syllabus/syllabus.php?subjectId=115106065
  2. Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 26: Feynman Rules in QED 2

    Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 26: Feynman Rules in QED 2

    Copyright reserved to Prof. Tripathy and NPTEL, Govt. of India. Duplication prohibited. Lectures: http://nptel.ac.in/courses/115106065/ Syllabus: http://nptel.ac.in/syllabus/syllabus.php?subjectId=115106065
  3. Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 27: Compton Scattering 1

    Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 27: Compton Scattering 1

    Copyright reserved to Prof. Tripathy and NPTEL, Govt. of India. Duplication prohibited. Lectures: http://nptel.ac.in/courses/115106065/ Syllabus: http://nptel.ac.in/syllabus/syllabus.php?subjectId=115106065
  4. Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 28: Compton Scattering 2

    Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 28: Compton Scattering 2

    Copyright reserved to Prof. Tripathy and NPTEL, Govt. of India. Duplication prohibited. Lectures: http://nptel.ac.in/courses/115106065/ Syllabus: http://nptel.ac.in/syllabus/syllabus.php?subjectId=115106065
  5. Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 30: Moller Scattering 1

    Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 30: Moller Scattering 1

    Copyright reserved to Prof. Tripathy and NPTEL, Govt. of India. Duplication prohibited. Lectures: http://nptel.ac.in/courses/115106065/ Syllabus: http://nptel.ac.in/syllabus/syllabus.php?subjectId=115106065
  6. Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 31: Moller Scattering 2

    Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 31: Moller Scattering 2

    Copyright reserved to Prof. Tripathy and NPTEL, Govt. of India. Duplication prohibited. Lectures: http://nptel.ac.in/courses/115106065/ Syllabus: http://nptel.ac.in/syllabus/syllabus.php?subjectId=115106065
  7. Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 32: Vertex Correction 1

    Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 32: Vertex Correction 1

    Copyright reserved to Prof. Tripathy and NPTEL, Govt. of India. Duplication prohibited. Lectures: http://nptel.ac.in/courses/115106065/ Syllabus: http://nptel.ac.in/syllabus/syllabus.php?subjectId=115106065
  8. Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 33: Vertex Correction 2

    Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 33: Vertex Correction 2

    Copyright reserved to Prof. Tripathy and NPTEL, Govt. of India. Duplication prohibited. Lectures: http://nptel.ac.in/courses/115106065/ Syllabus: http://nptel.ac.in/syllabus/syllabus.php?subjectId=115106065
  9. Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 34: Vertex Correction 3

    Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 34: Vertex Correction 3

    Copyright reserved to Prof. Tripathy and NPTEL, Govt. of India. Duplication prohibited. Lectures: http://nptel.ac.in/courses/115106065/ Syllabus: http://nptel.ac.in/syllabus/syllabus.php?subjectId=115106065
  10. Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 35: Vertex Correction 4

    Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 35: Vertex Correction 4

    Copyright reserved to Prof. Tripathy and NPTEL, Govt. of India. Duplication prohibited. Lectures: http://nptel.ac.in/courses/115106065/ Syllabus: http://nptel.ac.in/syllabus/syllabus.php?subjectId=115106065
  11. Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 36: Electron Self-energy

    Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 36: Electron Self-energy

    Copyright reserved to Prof. Tripathy and NPTEL, Govt. of India. Duplication prohibited. Lectures: http://nptel.ac.in/courses/115106065/ Syllabus: http://nptel.ac.in/syllabus/syllabus.php?subjectId=115106065
  12. Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 37: Photon Self-energy 1

    Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 37: Photon Self-energy 1

    Copyright reserved to Prof. Tripathy and NPTEL, Govt. of India. Duplication prohibited. Lectures: http://nptel.ac.in/courses/115106065/ Syllabus: http://nptel.ac.in/syllabus/syllabus.php?subjectId=115106065
  13. Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 38: Photon Self-energy 2

    Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 38: Photon Self-energy 2

    Copyright reserved to Prof. Tripathy and NPTEL, Govt. of India. Duplication prohibited. Lectures: http://nptel.ac.in/courses/115106065/ Syllabus: http://nptel.ac.in/syllabus/syllabus.php?subjectId=115106065
  14. Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 29: Compton Scattering 3

    Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 29: Compton Scattering 3

    Copyright reserved to Prof. Tripathy and NPTEL, Govt. of India. Duplication prohibited. Lectures: http://nptel.ac.in/courses/115106065/ Syllabus: http://nptel.ac.in/syllabus/syllabus.php?subjectId=115106065
  15. K

    A Vacuum in QFT: Fock space or effective potential?

    There seem to be two ways of defning what a vacuum is in QFT: 1. It is state $|0\rangle$ such that $$a_k|0\rangle = 0$$ for all anihilation operators $$a_k$$, with creation operators $$a_k^{\dagger}$$. Thus, it is defined in Fock space. 2. It is state $$|0\rangle$$ such that derivative...
  16. Ramil

    QFT on the lattice and Green's functions

    Homework Statement [/B] I'm trying to write a program for caclulating Green's function using Monte Carlo method (Metropolis algorithm) in scalar field theory with a potential λφ4 in 4D. I'm writing it in python. N_t, N_x, N_y, N_z - total number of lattice sites in each directions. Field...
  17. binbagsss

    QFT, Noether and Invariance, Complex fields, Equal mass

    Homework Statement Question attached: Hi I am pretty stuck on part d. I've broken the fields into real and imaginary parts as asked to and tried to compare where they previously canceled to the situation now- see below. However I can't really see this giving me a hint of any sort unless...
  18. Peter Morgan

    A Generalized free fields as dark matter?

    @vanhees71 reminds us that which suggests something I've wondered about for a while, whether dark matter might be adequately modeled by generalized free fields, which do not have asymptotic free states. Ray Streater, in Rep. Prog. Phys. 1975 38 771-846, "Outline of axiomatic relativistic...
  19. binbagsss

    QFT, more a QM Question, Hamiltonian relation time evolution

    Homework Statement Question attached here: I am just stuck on the first bit. I have done the second bit and that is fine. This is a quantum field theory course question but from what I can see this is a question solely based on QM knowledge, which I've probably forgot some of. Homework...
  20. Dyatlov

    Studying Which QFT Lecture Series Includes Unitary IR of Poincare Group?

    Hello. I self-studied and have a good grasp on QM, statistical mechanics and Group theory. Next step is QFT. There are several sets of video lectures on Youtube about this subject and I am asking for a recommendation (I would like a set of videos which involves the unitary IR of the Poincare...
  21. Jianphys17

    I Relation between statistics and theoretical physics

    Hi at all, maybe it's a bit trivial. However, the question that i ask myself is ; that relation there is between statistics-probab theory & theoretical physics. What role does it play in theoretical research ? (apart from the probabilistic amplitudes encountered in qm) Thanks for the answers
  22. D

    A Renormalisation: what are the physical observables?

    I'm trying to understand renormalisation properly, however, I've run into a few stumbling blocks. To set the scene, I've been reading Matthew Schwartz's "Quantum Field Theory & the Standard Model", in particular the section on mass renormalisation in QED. As I understand it, in order to tame the...
  23. M

    A How to construct a spin-3/2 theory from the ground up

    I'll start by saying I'm posting this in Beyond the SM just because we have no elementary spin-3/2 particles in the SM as far as we know, though I was also considering posting it elsewhere. If you feel it's more appropriate in another area just let me know. As for the question itself, I'd like...
  24. LarryS

    I Is Dirac's Equation Sufficient for Modeling a System of Electrons Without QFT?

    I’m attempting to learn QFT on my own and would like to get an idea of just how much I still do not know. Consider a system consisting only of electrons and for the purpose of this question, pretend that particle creation and annihilation never occur. QUESTION: Would Dirac’s famous...
  25. K

    Gamma matrices in higher (even) dimensions

    Homework Statement I define the gamma matrices in this following representation: \begin{align*} \gamma^{0}=\begin{pmatrix} \,\,0 & \mathbb{1}_{2}\,\,\\ \,\,\mathbb{1}_{2} & 0\,\, \end{pmatrix},\qquad \gamma^{i}=\begin{pmatrix} \,\,0 &\sigma^{i}\,\,\\ \,\,-\sigma^{i}...
  26. J

    A Time independence of a Noether charge in QFT?

    In classical field theories, I believe I understood how to derive a Noether charge that corresponds to a symmetry of action. And there is no problem in understanding its time independence. But in quantum field theory, it looks like the two different approaches, 1) Canonical quantization...
  27. TeethWhitener

    I Srednicki QFT Chapter 4 time-evolved operator

    In chapter 4 of Srednicki's QFT book (introducing the spin-statistics theorem for spin-0 particles), he introduces nonhermitian field operators (just taking one as an example): $$\varphi^+(\mathbf{x},0) = \int \tilde{dk}\text{ }e^{i \mathbf{k}\cdot\mathbf{x}}a(\mathbf{k})$$ and time-evolves them...
  28. A

    Quantum Field Theory, Momentum Space Commutation Relations

    Homework Statement Derive, using the canonical commutation relation of the position space representation of the fields φ(x) and π(y), the corresponding commutation relation in momentum space.Homework Equations [φ(x), π(y)] = iδ3(x-y) My Fourier transforms are defined by: $$ φ^*(\vec p)=\int...
  29. F

    I Exploring Oscillations & Interference in Particle Physics

    I will soon start with the course introduction to QFT and are hence an amateur on the subject. However I could not help but wonder, If particles are describes by oschlliations in a field, how can a "bigger body" be made up of several such oscillation? (A bigger particle is made out of several...
  30. F

    I Thought experiment about wave functions

    Suppose we have a particle, let's say an electron, in a box of size D. And we add another one next to it at some distance L center to center. How do we solve for the wavefunctions of the electron. Can it be solved in normal QM or do we need QFT. Thanks.
  31. F

    Which courses before GR and QFT?

    Hi! I will soon begin my third year at the theoretical physics program. I have done a bunch of classical & Lagrangian mechanics, SP, atomic physics, electromagnetism, and basic particle physics. Is it a good idea to study general relativity and quantum field theory with this knowledge, what...
  32. hilbert2

    A Coupling constants with fractional dimensions

    Most QFT texts, such as Peskin&Schroeder and D. Tong's lecture notes, contain a mention that the renormalizability of an interacting theory requires the coupling constants to have correct dimensions, making scalar fields with ##\phi^5 , \phi^6, \dots## interactions uninteresting. Maybe there are...
  33. J

    A QFT Field Expansion: Explaining (2.72) - Schwartz

    The attached pic is from Schwartz. Can someone explain the second equality sign in (2.72)?
  34. smodak

    Quantum QFT Book by Ticciati: Reviews & Readability

    Anyone read this book? Is it good? Is it readable compared to other begineer's QFT books? https://www.amazon.com/dp/0521060257/?tag=pfamazon01-20
  35. D

    Gauge invariance of lagrangian density

    The problem: $$\mathcal{L} = F^{\mu \nu} F_{\mu \nu} + m^2 /2 \ A_{\mu} A^{\mu} $$ with: $$ F_{\mu \nu} = \partial_{\nu}A_{\mu} - \partial_{\mu}A_{\nu} $$ 1. Show that this lagrangian density is not gauge invariance 2.Derive the equations of motion, why is the Lorentzcondition still...
  36. G

    A Rigorous interacting effective QFT in d=4?

    Sometimes one can read that constructive QFT has become somewhat superfluous with the advent of effective QFT, so there is no need anylonger to define a QFT on arbitrary small distances. But is there a rigorous interacting effective QFT in d=4 at all? If so, how is it constructed?
  37. binbagsss

    EoM from action, indices confused, (QFT)

    Homework Statement Using the E-L equations to get the EoM from the action. Homework Equations I am using E-L equations in the form: ## \frac{\partial}{\partial_u} \frac{\partial L}{\partial_u \phi}-\frac{\partial L}{\partial \phi} ## where ##L ## is the Lagrangian The Attempt at a...
  38. J

    Quantum What is the level of Klauber's Student Friendly QFT?

    Hi! I have studied about 70% of the textbook QFT for the Gifted Amateur by Lancaster and Blundell and I think that I am now ready to go to more advanced treatments. My thoughts were to go to Klauber's Student Friendly Quantum Field Theory as I have read that it is very pedagogical. Problem is...
  39. F

    I Is the Existence of Photons Proven by Modern Quantum Optics?

    from wiki "Although the photoelectric effect and Compton scattering strongly suggest the existence of the photon, it might alternatively be explained by a mere quantization of emission; more definitive evidence of the quantum nature of radiation is now taken up into modern quantum optics as in...
  40. F

    I Are Force carriers real or not

    from QFT wiki " In QED, the electromagnetic force between two electrons is caused by an exchange of photons. Similarly, intermediate vector bosons mediate the weak force and gluons mediate the strong force in QCD. The notion of a force-mediating particle comes from perturbation theory, and does...
  41. F

    I How does QFT handle particle creation and conversion?

    I was reading this thread by stevendaryl https://www.physicsforums.com/threads/second-quantization-vs-many-particle-qm.835472/ I have two questions 1. which QFT picture are those, Schrodinger, path integral or Heisenberg. 2.In QM the creation/annihilation operators raise and lower energies...
  42. L

    Books for overview of QM and/or QFT?

    I am not ready to learn the formalism for QM or QFT (maybe someday). Does anyone have any book suggestions for a beginner like myself that present the theories in accurate ways without going into all the mathematical formalism? Preferably something that is not tied to one interpretation of the...
  43. binbagsss

    QFT T-duality, Massless vector states

    Homework Statement Part C) Please: Homework Equations above,below The Attempt at a Solution so I think I understand the background of these expressions well enough, very briefly, changing the manifold from ## R^n ## to a cylindrical one- ##R^{(n-1)}^{+1}## we need to cater for winding...
  44. F

    I A question about Zee's book QFT in a nutshell

    I have read( even Peter Donis mentioned it) that the derivation of the potential between two particles is not a true QFT, why is that? if not, then what is it? Thanks in advance.
  45. Iliody

    I Doubt about partition functions in QFT and in stat Mechanics

    Hi, I was studying for my final exam on statistical physics and a doubt raised on my head that was truly strong and disturbing (at least, for me), and that I couldn't answer to myself by now. The doubt is: Given that we have in d dimensions a fermion non interacting gas, the statistical...
  46. MichPod

    I Self education: how to proceed from QM to QFT?

    I tried to start many books/video courses to learn QFT but this failed because of many factors, including my weak math/physics background, laziness, lack of time, lack of persistence, just to count some. The whole blame is on me, no doubt. Still, if I was able to learn QM to some extent...
  47. DeathbyGreen

    Trouble with Peskin QFT textbook

    I'm trying to work through a scattering calculation in the Peskin QFT textbook in chapter 5, specifically getting equation 5.10. They take two bracketed terms 4[p'^{\mu}p^{\nu}+p'^{\nu}p^{\mu}-g^{\mu\nu}(p \cdot p'+m_e^2)] and 4[k_{\mu}k'_{\nu}+k_{\nu}k'_{\mu}-g_{\mu\nu}(k \cdot...
  48. L

    Studying How to learn QFT on curved spacetimes by myself?

    I have a major in mathematical physics and mathematics and currently I'm on a graduate course in Physics working on a master's thesis. When I started the graduate course I was going to work on General Relativity and Quantum Field Theory on Curved Spacetimes (QFTCS). It turns out that by several...
  49. Milsomonk

    How to Express Charge Q Using Creation and Annihilation Operators in QFT?

    Homework Statement Express the charge Q in terms of the creation and annihilation operators. Homework Equations $$\phi_{(x)}=\int \dfrac {d^3 p} {(2\pi)^3} \dfrac {1} {2 \omega_p} (a_p e^{i x \cdot p} + b^{\dagger}_{p} e^{-i x \cdot p})$$ $$\pi_{(x)}=\dfrac {-i} {2}\int \dfrac {d^3 p}...
  50. A

    High Energy Recommended books in HEP, QFT, QM, GR

    Hi everyone! I'm trying to make a list of recommended books (introductory and advanced). So far, what I was able to search are the following: Particle Physics: - Griffiths: Introduction to Elementary Particles - Thomson: Modern Particle Physics - Nachtmann: Elementary Particle Physics -...
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