# What is Srednicki: Definition and 56 Discussions

Henryk Średnicki (17 January 1955 – 10 April 2016) was a Polish amateur boxer who represented his native country twice at the Summer Olympics, starting in 1976.
Średnicki was best known for winning the world title at the second World Amateur Boxing Championships in 1978, beating Cuba's Héctor Ramírez in the final.

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1. ### Quantum Srednicki QFT draft vs printed versions

There is a draft of Srednicki's QFT book available for free online (here: https://web.physics.ucsb.edu/~mark/ms-qft-DRAFT.pdf). I have a book voucher and, since I couldn't find it in the library, was thinking of buying it so long as the content of the book was sufficiently better (i.e...
2. ### A Getting particle/antiparticle solutions from the Dirac Equation

Hi! I am studying Dirac's equation and I already have understood the derivation. Following Griffiths, from factoring Einstein's energy relation with the gamma matrices: ## (\gamma^\mu p_\mu + m)(\gamma^\mu p_\mu - m) = 0 ## You take any of the two factors, apply quantization and you arrive to...
3. ### A QFT Srednicki Chap 6: Weyl Ordering

In Srednicki’s QFT Chapter 6 (intro to path integrals), he introduces Weyl ordering of the quantum Hamiltonian: $$H(P,Q)=\int{\frac{dx}{2\pi}\frac{dk}{2\pi} e^{ixP+ikQ}}\int{dp \text{ }dq\text{ }e^{-ixp-ikq}H(p,q)}$$ where ##P,Q## are momentum and position operators and ##H(p,q)## is the...
4. ### 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...
5. ### A Effective field theory in Srednicki's book

Hi! I'm currently learning for my QFT exam with the book from srednicki (here as pdf: http://web.physics.ucsb.edu/~mark/ms-qft-DRAFT.pdf) and I am trying to understand the chapter "Effective field theory" (p. 185 in the pdf above) He first introduces an ultraviolet cutoff Λ and then computes...

9. ### Decay into electron-positron pair in Yukawa theory

Homework Statement I have a question regarding exercise 48.4-b in Srednicki's QFT book (the chapter is related to Yukawa theories). I have the official solution + explanation to the problem but I still do not fully understand the reasoning used in it, so perhaps you can help me. In the...
10. ### Error in Srednicki renormalization?

On page 164-165 of srednicki's printed version (chapter 27) on other renormalization schemes, he arrives at the equation $$m_{ph}^{2} = m^2 \left [1 \left ( +\frac{5}{12}\alpha(ln \frac{\mu^2}{m^2}) +c' \right ) + O(\alpha^2)\right]$$ But after taking a log and dividing by 2 he arrives at...
11. ### Ward Identity in Srednicki QFT book

Hello guys, I am working on Ch22 "Continuous symmetries and conserved currents" of Srednicki QFT book. I am trying to understand how to prove the Ward-Takahashi identity using path integral method, done in page 136 of Srednicki. I understood everything up to Equation 22.22, which is 0 =...
12. ### Srednicki 58: EM current conservation & Gauge Symmetry

Hi I am re-reading Srednicki's QFT. In chapter 58, he points out that the Noether current $$j^\mu=e\bar{\Psi}\gamma^\mu\Psi$$ is only conserved when the fields are stationary, which is obvious from the derivation of the conservation law. Meanwhile he assumes that \partial _\mu...
13. ### [Srednicki] Charge Conjugation of Dirac Spinor

Homework Statement I am reading Srednicki's QFT up to CPT symmetries of Spinors In eq. 40.42 of http://web.physics.ucsb.edu/~mark/ms-qft-DRAFT.pdf I attempted to get the 2nd equation: C^{-1}\bar{\Psi}C=\Psi^{T}C from the first one: C^{-1}\Psi C=\bar{\Psi}^{T}C Homework Equations...
14. ### Understanding the Symmetry of SU(N) Subgroups in Srednicki's Notation

Homework Statement (a) For SU(N), we have: N ⊗ N = A_A + S_S where A corresponds to a field with two antisymetric fundamental SU(N) in- dices φij = −φji, and S corresponds to a field with two symmetric fundamental SU(N) indices φij = φji. By considering an SU(2) subgroup of SU(N), compute...
15. ### Solve Srednicki Problem 3.3: Show U(\Lambda) Invariance

Homework Statement Use ##U(\Lambda)^{-1}\varphi(x)U(\Lambda) = \varphi(\Lambda^{-1}x)## to show that ##U(\Lambda)^{-1}a(\mathbf{k})U(\Lambda) = a(\Lambda^{-1}\mathbf{k})## and ##U(\Lambda)^{-1}a^{\dagger}(\mathbf{k})U(\Lambda) = a^{\dagger}(\Lambda^{-1}\mathbf{k})## and hence that...
16. ### Srednicki Problem 3.4: Deriving the Klein-Gordon Equation

Homework Statement Recall that ##T(a)^{-1}\varphi(x)T(a) = \varphi(x - a)## where ##T(a) = e^{-iP^{\mu}a_{\mu}}## is the space-time translation operator and ##P^{\mu}## is the 4-momentum operator. (a) Let ##a^{\mu}## be infinitesimal and derive an expression for ##[P^{\mu},\varphi]##...
17. ### Srednicki Ch5 creation operator time dependence

Hi folks, originally I read Peskin & Schroeder but then I realized it was too concise for me. So I switched to Srednicki and am reading up to Chapter 5. (referring to the textbook online edition on Srednicki's website) Two questions: 1. In the free real scalar field theory, the creation...
18. ### Deriving Srednicki eqn. (9.19)

can anybody help me to derive eqn. (9.19) of Srednicki's QFT book?
19. ### Discovering Alternative References for Studying Srednicki's QFT

I am studying Srednicki' QFT. What I have found is that this book is very terse. And the author often leaves out most of the calculations. Most importantly, this book is written using phi-cubed theory. Can you suggest me another references written using the phi-cubed theory as I can use it as a...
20. ### Srednicki QFT chapter 67, LSZ formula

Homework Statement I would like to know how to get from eq. (67.3) to (67.4) in Srednicki's book on QFT. The problem is the following: Given the LSZ formula for scalar fields \langle f|i \rangle = i \int d^{4}x_1e^{ik_1x_1}(\partial^{2}+m^{2})\ldots \langle 0|T\phi(x_1)\ldots|0\rangle This...
21. ### Field-strength renormalization problem (13.1) in Srednicki

Hi- I've just completed problem 13.1 in Srednicki in which he tells us to relate the field-strength renormalization $Z_{\phi}$ to the spectral density $\rho(s)$ that appears in the Lehmann representation of the exact propagator. It seems straightforward-- I follow the hint, insert unity using...
22. ### Srednicki Ch90: How to Identify Electromagnetic Gauge Field

Does anyone know exactly how Srednicki identitifies the electromagnetic gauge field with his l,r,b fields. I know he is trying to match covariant derivatives, i.e. D_{\mu} p=(\partial_{\mu}-il_{\mu})p with D_{\mu} p=(\partial_{\mu}-ieA_{\mu})p and that he has set l_{\mu}=l_{\mu}^a...
23. ### Exploring the Dirac Fields in Srednicki (Ch88)

Hi, In srednicki (ch88) he starts off considering the electron and associated neutrino, by introducing the left handed Weyl fields l, \bar{e} in the representations (2,-1/2), (1,+1) of SU(2)XU(1). The covariant derivaties are thus...
24. ### Propagator for matrix fields (based on Srednicki ch80, p490)

Hi, If I have a matrix valued field B(x)_i^{..j}=B^a (x) (T^a)_i^{..j} and the relevant part of my Lagrangian is L=Tr(-\tfrac{1}{2}\partial^{\mu}B\partial_{\mu}B+..) then how can I see that the propagator for the matrix field is...
25. ### Assorted questions about Srednicki ch78

Hi, I have a few questions about ch78 of Srednicki's QFT: background field gauge. I'll just post a couple to see if anyone can help and so this post isn't huge, then maybe some more later. 1) If the background field transforms as \delta_G \bar{A^a_{\mu}}(x)=0 and \delta_{BG}...
26. ### Anyone familiar with Srednicki ch72?

Hey, Just wondering if anyone is familiar with this chapter or the subject matter. I'm trying to understand why there are an additional 5 permutations of the the three gluon vertex making 6 terms in all (equation 72.5). I know you have to label external propagators with all different...
27. ### Understanding the Yukawa Term in Srednicki's Lepton Sector

Hi all, I am just reading Srednicki, chapter 88: The Standard Model: Lepton Sector and I'm not sure if I really understand it. There are left-handed Weyl fields l, \overline{e}, \varphi in the (SU(2), U(1)) representations (2, -1/2), (1,1), (2, -1/2) Now there is also a...
28. ### Srednicki 43.10: Minus Sign Explained

Trivial question... How exactly does the minus sign arise in eq. 43.10? The sentence below states because the functional derivative goes through one spinor, but I can't see how that works... book is online here http://www.physics.ucsb.edu/~mark/ms-qft-DRAFT.pdf equation 43.10 is on pdf...
29. ### LSZ reduction coeffs etc (Srednicki)

In free field theory one particle states can be created as: |k\rangle =a^{\dag}(\vec{k})|0\rangle . Just as we can expand the field operator in terms of the creation and annihilation operators it is possible to obtain an expression for the creation operator in terms of the field, it turns out...
30. ### Feynman rules for Majorana fields (based on Srednicki)

Hi, So if we have an interaction Lagrangian for a Majorana field: L_1=\tfrac{1}{2} g\phi\Psi^{T}C\Psi Now looking at the path integral, I believe this must go like: Z (\eta^{T},J) ~ \exp{[\tfrac{1}{2} ig \int\,\mathrm{d}^4x (\tfrac{1}{i}\tfrac{\delta}{\delta J(x)...
31. ### Symmetry factors (Srednicki, figure 9.11)

In Srednicki's QFT book on page 63, figure 9.11, the diagram in the middle of the second row is a Feynman diagram with four external lines, two vertices, one internal line and one loop placed on one external line. It has symmetry factor 4. Does the symmetry facor stand for the 4 possibilities...
32. ### Srednicki Bar Notation: Understanding (39.8)

Hi, Srednicki says in (38.14) that for any combination of gammas \bar{A}\equiv \beta A^{\dag}\beta. This is fine, and I can work at such relations as (38.15), like \bar{\gamma^{\mu}}=\gamma^{\mu} and so on. We also have for spinors \bar{u_s}\equiv u^{\dag}_s\beta, and for the Dirac...
33. ### Exploring Left & Right Spinor Fields in Srednicki

Hi, I'm just looking at the stuff on left and right handed spinor fields in Srednicki. Srednciki distinguishes fields in the left rep from those in the right rep by putting a dot over them. Since hermitian conjugation swaps the two SU(2) algebras, the hermitian conj of a left spinor is a right...
34. ### Continuous symmetries (Srednicki)

Hi, In ch22, Srednicki considers the path integral Z(J)=\int D\phi \exp{i[S+\int d^4y J_a\phi_a]} He says the value of Z(J) is unchanged if we make the change of var \phi_a(x)\rightarrow\phi_a(x)+\delta\phi_a(x), with \phi_a(x) an arbitrary infinitesimal shift that leaves the mesure...
35. ### Srednicki 2.8 / Inverse Lorentz Transformation

Homework Statement I need to demonstrate the relation [\varphi(x),M^{\mu\nu}]=\matchal{L}^{\mu\nu}\varphi(x) where \mathcal{L}^{\mu\nu}\equiv \frac{\hbar}{i}(x^\mu\partial^\nu-x^\nu\partial^\mu). Homework Equations U(\Lambda)^{-1}\varphi(x)U(\Lambda) = \varphi(\Lambda^{-1}x) \Lambda =...
36. ### Help with Understanding CH27 of Srednicki

Hi, I'm reading through CH27 of Srednicki at the moment, and struggling to understand a couple of concepts. 1) He states that in the MS (bar) scheme the location of the pole in exact propagator is no longer when k^2=-m^2 , where m is Lagrangian parameter usually thought of as mass. I...
37. ### Srednicki CH26 Explained: Solving Eqn 26.7

Hi, I was wondering if anyone could explain how Srednicki gets to his eqn 26.7: \tilde{dk_1}\tilde{dk_2} \sim (\omega^{d-3}_{1}d\omega_1) (\omega^{d-3}_{2}d\omega_2)(sin^{d-3}\theta d\theta) I thought this would be to do with transforming into some kind of d-dimensional polar coords...
38. ### Is this an error in Srednicki?

Hi, On p104 of Srednicki's QFT, he does an integral in closed form, equations 14.43 and 14.44. I just ran the calculations for this in Mathematica, and I get his answer exactly except for my constants c_1=4-\pi\sqrt{3} and c_2=4-2\pi\sqrt{3} . The mathematica code I used to generate...
39. ### Why is there no time dependent a_1^{\dagger}(t) in the Srednicki equation 5.10?

In equation 5.10, second line srednicki uses the same definition as eq 5.6, while 5.6 is time independent a_1^{\dagger}(k) and in 5.10 we have to use the new time dependent a_1^{\dagger}(t) . Why don't we have a new a_1^{\dagger}(t), which say explicitly depends on t ? I will be glad if...
40. ### Why is counterm included in both orders of correction in Srednicki chapter 14

Hi, I think maybe my last question was too much of an essay for anybody to bother going through, so I thought I would ask something more modest: In Srednicki chapter 14 fig 14.1, we have the counterm correction from A and B contributing to O(g^2), I understand it being here since A,B...
41. ### Srednicki Equation 7.7: Explained

Hello everyone, I will be glad if someone can explain how equation 7.7 \tilde{x}(E) = \tilde{q}(E) + \frac{\tilde{f}(E)}{E^2-\omega^2+i\epsilon} is a shift by constant, here's the link for the book http://www.physics.ucsb.edu/~mark/ms-qft-DRAFT.pdf thanks
42. ### Srednicki 2.17. How does metric act on Levi Cevita symbol?

Sorry to be asking again so soon, the help yesterday was great. I'm now trying to reach 2.17 from the generator commutation relation: [M^{\mu\nu}, M^{\rho\sigma}]=i\hbar(g^{\mu\rho}M^{\nu\sigma}-g^{\nu\rho}M^{\mu\sigma})+... 2.16 J is defined by its components as...
43. ### How can I solve for Equation 2.16 in Srednicki?

Hi, I'm having a little troubling reaching this equation. I'm starting with 2.14 which is: U(\Lambda)^{-1} M^{\mu\nu} U(\Lambda)=\Lambda^\mu{}_{\rho}\Lambda^\nu{}_{\sigma} M^{\rho\sigma} Now letting \Lambda=1+\delta\omega and using U(1+\delta\omega)=I+\frac{i}{2\hbar}...
44. ### Srednicki QFT chapter 8 question

Hi, In chapter 8 Srednicki employs the 1-i \epsilon trick. He multiplies the Hamiltonian desity, H=\frac{1}{2} \Pi^2+\frac{1}{2}(\nabla\phi)^2+\frac{1}{2}m^2\phi^2 by this 1-i \epsilon , and says it's equivalent to if we replaced m^2 with m^2-i \epsilon . I can't see how this is...
45. ### Srednicki 34.15 - Notation Question

Homework Statement Is the index notation in Srednicki's 34.16 correct given what he does in 35.29. Essentially, in going from 34.15 to 34.16, when taking the hermitian conjugate, he does not remove the dots. In going from 35.27 to 35.29, he has done so (the dot on 'a' has moved over onto...
46. ### MS renormalization scheme /RG & Srednicki ch 27,28

Hi all, I have two questions regarding chapter 27 and 28 in Srednicki's book. On page 163 he states: But this would mean that |<k|\phi |0>|^2 = R I can not see why this is? I would expect that the result is R^2 because there is a factor of k^2 + m^2 in the LRZ formula... My second...
47. ### Srednicki 9.17, 9.18: Sum of Diagrams with Single Source Removed

Why is the expression 9.17 the sum of all diagrams with a single source removed? I thought diagrams stand for terms in double taylor expansion of Z_1(J).
48. ### Srednicki Path Integrals eq 6.22

Hi everyone, I was reading through the section on path integrals in Srednicki's QFT book. I came across equation 6.22 \langle 0|0\rangle_{f,h} = \int\mathcal{D}p\mathcal{D}q\exp{\left[i\int_{-\infty}^{\infty}dt\left(p\dot{q}-H_{0}(p,q)-H_{1}(p,q)+fq+hp\right)\right]} =...
49. ### Lorentz Generators, Srednicki eq. 2.13

Hello, I am trying to prove eq 2.13 in srednicki: \delta \omega _{\mu\nu}U(\Lambda)^{-1}M^{\mu\nu}U(\Lambda) = \delta \omega _{\mu\nu}\Lambda^\mu{}_{\rho}\Lambda^\nu{}_{\sigma}M^{\rho\sigma} where we have expanded the following and comparing the linear term...
50. ### Understanding Counterterms: Demystifying Srednicki's Equation 9.25

Hi, I was wonder what mr. Srednicki is meaning on page 68 (page 82 in his pre-print), where he writes that "Eq. 9.25" results in a new vertex where two lines meet" Now I have a hard time to figure it out how it would look like diagrammatically and was wondering if anyone had a more hands-on...