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. X

    A good book on QFT for an undergrad

    Im still in 2year college, and studyin QM alone, would like to know a good book for QFT that I can understand. I have some questions that seems can only be answered with QFT, right now, I am half way through the Griffith's QM book..! thx a lot guys..!
  2. N

    QFT Recipe: Outlining the Formal Structure

    I understand that the formal structure of QFT has resisted axiomatization (so far) and that what formal structure presently exists is really a set of recipes. Can somebody outline the recipe please.
  3. G

    Particle physics & QFT, A conceptual question

    Hi In Halzen's "Quarks & Leptons" all discussed particle interactions conserve particle number in some sense (Actually particle number is not conserved but if you count the particles minus the antiparticles before the reaction you get the same "particles minus the antiparticles" number after...
  4. I

    Interpretation of Interaction in Boosts in QFT

    Question concerns the existence of the interaction in boost operator in the instant form of relativistic dynamics. (referring to "Relativistic quantum dynamics" after E.V.Stefanovich, http://arxiv.org/abs/physics/0504062) From the existence of interactions in boosts (e.g., in instant form...
  5. H

    Mathematical pre-requisites for Relativistic QFT

    Hello, I plan on continuing to study physics, mathematics and Earth science. (independently) What are the mathematical pre-requisites for learning relativistic quantum field theory as smoothly as possible. On MIT's opencourseware, it indicates that a class on advanced ODEs is enough, but we...
  6. maverick280857

    Correlation Functions in Path Integral Formulation of QFT

    Hi, I was going through section 9.2 of Peskin and Schroeder, and came across equation 9.16 which reads \int\mathcal{D}\phi(x) = \int \mathcal{D}\phi_{1}({{\bf{x}}}) = \int \mathcal{D}\phi_{2}({{\bf{x}}}\)int_{\phi(x_{1}^{0},{\bf{x}})\\\phi(x_{1}^{0},{\bf{x}})}\mathcal{D}\phi(x) What does the...
  7. LarryS

    Best Intro to QFT Book for Mathematicians?

    Can anybody recommend a good introduction to QFT book? I'm looking for something that just barely classifies as a textbook, with lots of tutorial verbiage between the equations. Thanks in advance.
  8. R

    Transition from QFT to Classical Physics using Path Integrals?

    I have a question in Srednicki's book regarding path integrals, but first I'll set it up so that no familiarity of the book is required to answer the question. The vacuum to vacuum transition amplitude for the photon field in the presence of a source is given by: <0|0>_J=\int \mathcal D A...
  9. haushofer

    Genereral:Questions about Srednicki's QFT

    ********************** Hi, I did some searching and found quite some questions about the Srednicki book on QFT, so apparently there are more people working with it. I thought maybe it would be a nice idea to have some sort of "questions about QFT encountered while reading Srednicki's...
  10. maverick280857

    Exploring the Concept of Classical Limit in Quantum Field Theory

    Hi, Is it meaningful to inquire about the classical limit of a quantum field theory? Specifically, is it possible to formally recover NRQM and RQM from quantum field theory? I am told this is a wrong/ill-posed question, so I wanted to get a clearer idea about it...after all, in a QM course...
  11. I

    What is Gauge Invariance in QFT?

    According to Steven Weinberg ('The quantum theory of fields', vol.1), the principle of gauge invariance stems from the fact, that one cannot build the 4-vector field from the creation/annihilation operators of massless bosons with spin >= 1. This '4-vector field' ('vector potential'), if we...
  12. MathematicalPhysicist

    What preliminary knowledge of QM should I know before learning QFT

    What preliminary knowledge of QM should I know before learning QFT, or should I learn QFT in parallel with me learning QM?
  13. maverick280857

    Path Integral Propagator Normalization in Lewis Ryder's QFT book

    Hi, In Lewis Ryder's QFT book on page 160, the propagator for the case when the Lagrangian can be written as L = \frac{p^2}{2m} + V(q) is given as \langle q_f t_f|q_i t_i \rangle = \lim_{n\rightarrow\infty}\left(\frac{m}{i\hbar\tau}\right)^{(n+1)/2}\int...
  14. T

    QFT theory book by Eberhard Zeidler

    Has anyone read the book (at least the first volume) by Eberhard Zeidler called "Quantum Field Theory: A Bridge Between Mathematicians and Physicists"? I started reading it last year and thought it was amazing. It's so ambitiously comprehensive! But no-one ever mentions it, and it's not in...
  15. MathematicalPhysicist

    Synthesis between Quantum Chaos and QFT.

    Are there any attempts to synthesize between these two theories? I mean are there methods from QFT being used in QC and vice versa? I asked one professor from my univ if I were to research under his belt in QC, would I need some QFT knowledge and he said not. So I wonder are they really...
  16. Hepth

    QFT : Why do tensors in lagrangian densities contract?

    What is the general rule behind why for any given lagrangian (QED/QCD show this) that any vectors or tensors contract indices? I know it must be something simple, but I just can't think of it offhand. QED : F_{\mu\nu}F^{\mu\nu} Proca (massive vector): A_\mu A^\mu QCD : G^{\alpha}_{\mu\nu}...
  17. P

    QFT: Exploring Connected Diagrams & Single Sources

    hi all, i have a question regarding page 81 in Srednicki's QFT book. He states there that the sum over all connected diagrams with a single source is zero. Then he says that if you replace this single source by an arbitrary subdiagram the sum will still be zero. Can somebody explain why this...
  18. F

    Is string theory an approximation to QFT?

    The historic roots of string theory are in an explanation of the strong force. Nowadays QCD is the accepted theory of strong force. But having heard several lectures on the large N limit (SU(N)) of gauge theories it seems these theories start to looklike string theories in this limit. I believe...
  19. malawi_glenn

    Questions on chapter 95 in Srednickis QFT book, Supersymmetry

    Hello all Since there seems that quite many here have followed Professor Srednickis QFT book, I want to ask a couple of question I have from his chapter on Supersymmetry. i) on page 617 he defines the kinetic term of the Chiral Superfields as: L_{\text{kin}} = \Phi^{\dagger} \exp(-2gV)...
  20. M

    Difficulties in Canonical Quantization and Tensor Relations in Elementary QFT

    Hi all, I'm trying to teach myself the basics of QFT. I'm using Peskin and Schroeder, and having a few difficulties reproducing a couple of the calculations. I don't think I've made careless algebraic slips, so before I show my working explicitly and beg for proof-reading I'd like to ask a...
  21. MTd2

    Going Beyond LQG: how to define QFT over Loops?

    Does anyone have any ideas? Marcus, do you have?
  22. T

    On equivalence of QFT and Quantum Statistical Physics

    Does fact that QFT in imaginary time is equivalent to QSP represents the proof that many-particle quantum physics is equivalent to quantum theory of fields? To elaborate a little, I had some discussion with some engineers, and when I was explaining them Standard Model I had to invoke concepts...
  23. N

    Can the Commutator of Charges in QFT be Calculated Using Different Times?

    Consider the SUSY charge Q= \int d^3y~ \sigma^\mu \chi~ ~\partial_\mu \phi^\dagger~ The SUSY transformation of fields, let's say of the scalar field, can be found using the commutator i [ \epsilon \cdot Q, \phi(x)] = \delta \phi(x) using the equal time commutator...
  24. F

    Can fermion fields in QFT have dimensions other than 3/2 and 1/2?

    I have a question about the dimensions of quantum fields. In natural units, the dimensions of bosonic fields (both scalar and vector) is 1. The dimension of spin=1/2 fermion fields is 3/2. This is all very good, but I have never read any explanation anywhere why we cannot have other types of...
  25. R

    QFT: Gauge Invariance, Ghosts, Symmetry & Lorentz Invariance

    When quantizing boson fields, ghosts and gauge-fixing terms seem to break gauge invariance. The unitary gauge (where there are no ghosts or gauge-fixing terms) respects gauge invariance however. So which is correct - is the Standard Model a gauge theory or not? Sometimes I hear people speak...
  26. O

    From String theory to QFT & SM: What does AdS/CFT theory can do and what cann't do?

    Can anyone please comment on this? Any new progress in extending String theory to QFT & SM other than AdS/CFT?
  27. W

    Is it valid to pull out the -\nabla^2 \phi(x') in this commutator calculation?

    Homework Statement When calculating this commutator, [ \pi(x), \int d^3x' { \frac{1}{2} \pi^2(x') + \frac{1}{2} \phi(x')(-\nabla^2 + m^2) \phi(x') }] I almost get the right answer, but not sure if this is valid, or if there is an identity The Attempt at a Solution when I get to this...
  28. marcus

    A contrasting variant of QFT (J. Math. Phys 48, 2007)

    I do a regular check through the new papers on arxiv and today I came across this http://arxiv.org/abs/0903.3176 which is a continuation of a paper which Peter Morgan published in the Journal of Mathematical Physics a couple of years ago. http://arXiv.org/abs/0704.3420 This is not something I...
  29. malawi_glenn

    Problem Books in Quantum Field Theory Discussion

    Hello, as a new student of OFT and theoretical particle physics, I thought there might be good to create a thread where discussion on "Problems and solutions"-books in QFT are devoted. There is already discussion going on about "which book is best for QFT" and also thread where McMahons book...
  30. N

    QFT question about algebra of charges

    If a Lagrangian has some symmetry leaving the action invariant, we can introduce the corrsponding currents and charges. Now, the transformation can also be implemented as a unitary transformation of the fields in the form (let's consider a scalar field) \phi \rightarrow \phi' = U \phi...
  31. W

    [qft] Srednicki 2.3 Lorentz group generator commutator

    Homework Statement Verify that (2.16) follows from (2.14). Here \Lambda is a Lorentz transformation matrix, U is a unitary operator, M is a generator of the Lorentz group. Homework Equations 2.8: \delta\omega_{\rho\sigma}=-\delta\omega_{\sigma\rho} M^{\mu\nu}=-M^{\nu\mu} 2.14...
  32. pellman

    Req: A conceptual QFT example

    I need someone to point me towards an instance of a relatively simple QFT problem which illustrates what can be calculated from QFT, how it is calculated, and its physical significance. (Note the qualification "relative". I realize there are likely no simple problems in QFT.) If someone...
  33. X

    QFT, QED for condensed matter physics

    I don't have the time now to study QFT in depth but I need some basic knowledge about QED and quantum forces (like casimir). I want to study the role of casimir force to solid state devices (photonic and plasmonic devices). Which part of QFT is needed to study for now and which books are...
  34. A

    Solve Peskin's QFT Eqn 2.54 with Hints

    QFT Peskin p.30 eqn 2.54 Homework Statement i am perplexed with eqn 2.54 peskins introductory qft. just can't make out how to arrive at it from the previous step. i think that there are dirac delta funtions involved but simply can't make it out. can somebody help? provide some hint? thanks...
  35. A

    QFT: Is a^+_{-p}\ a_{-p} = a^+_{p}\ a_{p}?

    Homework Statement Hi I was trying to get the expression for H ,eqn 2.31 on page 21 peskins introductory QFT Homework Equations I get the final expression only if a^+_{-p}\ a_{-p} = a^+_{p}\ a_{p} so pls tell me if a^+_{-p}\ a_{-p} = a^+_{p}\ a_{p} (+ stands for dagger) thanks in advance
  36. H

    Martin Kober: The relation of a unified QFT of spinors to the structure of GR

    As suggested by Marcus, I have read the whole paper and decided to start a discussion of Kober's paper by asking a few questions. The paper certaintly presents a very interesting view. Part of it is an extension of Heisenberg's work on unified QFT, that the mass originates from self-interaction...
  37. J

    Interaction picture (Is there a mistake in QFT books?)

    It is often stated that the transition amplitude between eigenstates of the free-field Hamiltonian H_0 is encoded by the S-matrix, defined by \langle \mathrm{f} | U{_\mathrm{I}} (\infty,-\infty)|\mathrm{i} \rangle. where U_{\mathrm{I}} is the time-evolution operator in the interaction...
  38. A

    Evaluating Feynman diagram in QFT without external fermion lines

    ...like in Photon-Photon-scattering. I know this doesn't make sense physically but the value for the diagram should still be computeable. If I want to put the expression for the matrix element together, I get a matrix, but it should be a scalar, right? Since the spinor bi-product is missing...
  39. I

    [QFT] Feynman rules for self-interacting scalar field with source terms

    I'm not sure if this is the right place to post a graduate level course material, but I have a question about perturbative expansion of the 2n-point function of a scalar field theory. Homework Statement First, the question: In which space (position or momentum) is the topological distinctness...
  40. E

    Does the calculated large cosmological constant in falsify QFT?

    QFT it is possible to calculate the energy density of empty space. It is known to be around 10^50 orders to large. Does the calculated large cosmological constant in falsify QFT? Or does GR have to be re-done with a higher energy density
  41. J

    Conservation of momentum in QFT

    Can conservation of momentum be directly derived from quantum field theory (e.g. QED). My feeling is this should be true since the Dirac equation reduces to Schrodinger's wave equation in the nonrelativistic limit which is a reflection of Newton's second law, thereby implying conservation of...
  42. M

    Learning QFT: Scanning Mandl & Shaw for Highlights

    I am starting to learn QFT and I am scanning my text (Mandl and Shaw) for the highlights. Would some please confirm whether these are the highlights. (1) The states are Fock states where the states are distinguished by occupation numbers for various single particle or single photon states...
  43. T

    Discrete energy states (explanations in QFT?)

    I've been thinking about one of the postulates about one particle quantum mechanics, it says that whenever we measure an energy value, we get one of those eigenvalues. Firstly, pretty much 99% of the stuffs I know in nonrelativistic QM applies in the realm of electromagnetism. I just don't...
  44. M

    Divergences in the sense of QFT

    if we consider the propagators and other Fourier integrals in the sense of 'distribution' then are all the divergences that appear in QFT (quantum field theory) due to the divergent quantities \delta ^{k} (0) that is my idea, all the divergences appear because in the commutation...
  45. N

    QFT Overview for Soon-to-be Students

    Hello Forum Does anybody know of a good summary article or webpage that concisely and accurately outlines QFT (wikipedia's page is pretty bad)? I am not looking for a layman's guide but rather something suitable for a soon-to-be-student of QFT - something that can be read and understood in a...
  46. G

    Exploring Peskin & Schroeder's QFT Propositions on p. 166

    It would be nice if someone commented a couple of propositions by Peskin and Schroeder in their QFT book in p.166. There they say that when the helicity is conserved in the high energy Compton scattering, one unit of spin angular momentum is converted to one unit of orbital angular momentum...
  47. T

    How to get QFT operator expectation values?

    I am having some great difficulty getting intuition out of the standard quantization of the Klein-Gordon Lagrangian. consider the H operator. In QM, the expectation values for H in any eigenstates |n> is just <n|H|n> now, in QFT, suppose I have a state |p> in the universe, what do I get if I...
  48. I

    Verifying a simple QFT derivation in Peskin's

    Hiya, just stumbled upon this forum searching out 'Peskin errata' when trying to figure out a simple QFT calculation in the textbook. Apparently, there is no mention of the simple derivation that I'm struggling with, so there must be something wrong with my own working. I would really...
  49. haushofer

    Exploring Imaginary Shifts in QFT: A Necessary Tool for Convergence?

    Hi, I'm studying QFT (quantum field theory) again, with the help of Peskin&Schroeder. Altough the book is much better to read for a second time, there are some things that keep me wondering. It's about shifting physical quantities by a small imaginary constant in order to be sure that...
  50. W

    Is Mark Srednicki's QFT Textbook Worth the Download?

    According to the https://www.amazon.com/review/product/0521864496/ref=dp_top_cm_cr_acr_img?_encoding=UTF8&showViewpoints=1"&tag=pfamazon01-20 on Amazon, it's pretty good. Download it http://www.physics.ucsb.edu/~mark/qft.html".
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