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    I Lorenz gauge, derivative of field tensor

    Fμν = ∂μAν- ∂νAμ ∂μFμν = ∂2μAν - ∂ν(∂μAμ) = ∂2μAν Why ∂ν(∂μAμ) and not ∂μ∂νAμ ? And why does ∂ν(∂μAμ) drop out? thank you
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    I Reading suggestions about the "nature of time"

    There are quite some pop-sci books (by Greene, Smolin, Carroll and others) that deal with the "nature of time". Why does time appear to flow? Why is there a special moment, the "now"? Does simultaneity in SR imply a block universe? Why time-symmetric laws but a time-unsymmetric universe? Does...
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    I Equation of motion Chern-Simons

    The Lagrangian (Maxwell Chern-Simons in Zee QFT Nutshell, p.318) has as equation of motion: Where does the 2 in front come from? Thank you very much
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    I Particles more fundamental than fields

    In this Nima Arkani-Hamed paper on page 5 I found the sentence: These constraints are an artifact of using fields as auxiliary objects to describe the interactions of the more fundamental particles. In Schwartz's QFT book I also get away with the impression that the Poincaré irreps (i.e...
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    I Transforming a matrix

    I want to transform the first matrix below into the second one. The book ( Neutsch, "Coordinates") says this can be done by elementary transformation. I guess he means by some Gaussian elimination. But the entries of the matrix are from the finite field 2, so I can not multiply rows, that would...
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    I Fermions Bosons vertices in SM - but no SUSY

    In the Standard Model fermions interact via exchanges of massless (virtual) spin-1 particles. Fermions are turned into a boson. How is that different from the SUSY transformation that turns fermions into bosons?
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    B Rindler - uniform acceleration

    So a light signal is sent off some space behind me. At the same time I start accelerating extremely quickly. Even though the light signal will always be faster than me it will never catch up with me. I have difficulties to understand that something that is always faster than you can still never...
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    I Havil's book "Gamma" page 57, formula

    Where does the 1 in the last line come from? Thank you!
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    I Dimensionless and dimensioned fundamental constants

    There are 25 or so dimensionless constants in the standard models, such as the masses of the fundamental particles (that can be divided by Planck mass or some other mass to become dimensionless). And there are the three dimensionful constants c, h, G (speed of light, Planck's constant, Newton...
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    I Rényi entropy becomes von Neumann entropy

    In holographic entanglement entropy notes like here, they let alpha go to one in (2.41) and get (2.42). But (2.41) goes towards infinity, when doing that! Can someone explain how alpha --> 1 will make (2.41) into (2.42)? Thank you!
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    I Off-shell on-shell

    Here they say that if you add two momentum vectors of two on-shell particles, you get an off-shell particle. Two questions: 1. Since on-shell solutions are solutions to the free equation of motion, should no adding two solutions also give a solution? 2. Why should adding two on-shell...
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    I BCFW recursion relation

    Below is a snipet from http://file:///C:/Users/Christian.Hollersen/Downloads/Britto_2011_2%20(1).pdf [Broken] of Britto. Similar explanation can be found in the QFT books of Zee, Schwarz or the Scattering Amplitude text of Huang. Or any other text that covers BCFW recursion. My dumb question...
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    I Degrees of freedom of elementary particles

    The EM wave and the photon have two degrees of freedom. Their polarization directions and spin states, respectively. But they move in space, too. I mean light has the freedom to go in all directions in space. Like a macroscopic ball in 3-D space, which can go all three directions, if there are...
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    I Points of a finite projective line

    I found in Thompson "From Error-Correcting to Sphere Packing and Simple Groups" this on page 131 How do you compute m/n in a finite field? Take the equivalence class 5 given above. Why does 2/5 and 18/22 give 5? thanks
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    A Imaginary parts of amplitues (Schwartz QFT text)

    From Schwartz qft notes p. 257 or his qft book p. 455 1. Why and how does the integral in (24.24) go imaginary, when M > 2m? Is it because the logarithms can not take negative real numbers, thus we have to switch to complex numbers? 2. (24.25) is the principal value equation, right? 3. How...
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    I Early opaque universe - why little proton-photon scattering?

    I read many times that the early universe was opaque foremost because of the scattering of photons off free electrons (Thomson scattering). Why is the scattering off free protons not equally important? Btw, the same they say about stars. Photons within stars need a very long time to get out of...
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    I Conformal geometry vs. projective geometry

    How are those two geometries realeted? Conformal geometry is a metric geometry. Projective geometry is not. But the stereographic projection is related to the conformal geometry. Or does someone know a book/ notes where the individual geometries (affine, projective, euclidean, hyperbolic...
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    Good compact chemistry overview for scientists

    Can someone recommend a good chemistry overview/ review? Some pdf document perhaps, not more than 200 pages or so. Notes that do not assume you are complete beginner, but you have a science (physics) background. That gives brief summaries and the highlights of all the topics that are dealt with...
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    I Particle horizon rewritten

    Here, I find on page 31 in (2.1.5) I assume that it is childish calculus that connects both sides of this equation. But still, can someone help me why the integral can be rewritten like that? thanks!
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    A Zee, QFT Nut, III.6, p. 194

    ..where can be found: What in the whole wide world does Zee mean with ?? Thank you
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    I Inverse Square Law and various space dimensions

    I am interested in the derivation of the inverse square law in various dimensions via Green's functions. I think the trick is to imagine a sphere and then to integrate over it. Does anyone know a book or notes where this is explained? I found this below from here, but could not really...
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    I Tangent plane in Zee text

    In Zee "Einstei gravity in a nutshell" section I.6, page 83, the author says about the approxiamtion of the south pole of sphere How is the first equation approximated by the second? One page later he does this expansion again. Is this thecalculus Leibnitz rule? Or some clever trick...
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    Klein's quartic

    Can someone tell me how I have to glue together the hyperbolic plane so that I get the surface (Klein's quartic) shown to the left. I found this picture on the net, but without a desription how to glue. thanks!
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    An elementary equation manipulation in CFT

    A presumably basic introductory equation manipulation in 2-d conformal field theory. How does from (when the metric is Euclidean) follow The right equation is clear (the metric is zero for different indices). But how do i get to the first equation on the left? thank you
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    Functional equation Riemann Zeta function

    There are two forms of Riemann functional equation. One is more symmetric and follows from the other and the duplication theorem of the Gamma function. At least, that's been claimed here...
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    Add the Hermetian conjugate to make Lagrangian real

    How does adding a h.c. term make a Lagrangian real? Like here on page 99 (11.51)? thanks in advance
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    QM notes with entanglement, Bell, decoherence, etc.

    Does anyone know of QM notes (or a review article) that covers entanglement, the measurement problem, Bell inequalities, decoherence, or the delayed choice experiment (or the more recent mesoscopic experiments). So to speak the more modern and the exciting aspects of QM. I think closest to that...
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    Why complex reps of gauge group for chiral theory?

    Why must the gauge group be in a complex representation so that chirality of the fermions is respected? thanks
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    Why decaying false-vacuum necessary for inflation?

    According to inflation theory, there first was a scalar quantum field in a false-vacuum (the inflaton). The whole inflationary expansion only got started when the inflaton decayed to its true vacuum. But then people say that the dark energy that causes the universe to expand today, could be...
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    Su(2), so(3) and their representations

    I try to understand the statement "Every representation of SO(3) is also a representation of SU(2)". Does that mean that all the matrices of an integer-spin rep of SU(2) are identical to the matrices of the corresponding spin rep of SO(3)? Say, the j=1 rep of SU(2) has three 3x3 matrices, so...