Gauge Definition and 641 Threads

If you follow QG research you will remember that in September 2009 there was a mainly Loop QG school/workshop on Corfu at which several people presented minicourses (John Baez, Carlo Rovelli, Abhay Ashtekar, Vincent Rivasseau, John Barrett...) Each minicourses was a series of 5 onehour lectures...

I have been trying to teach myself Lagrangian mechanics from a textbook “Lagrangian and Hamiltonian Mechanics” by MC Calkin. It has covered virtual displacements, generalised coordinates, d’Alembert’s principle, the definition of the Lagrangian, the Euler-Lagrange differential equation and how...

First of all, let me remind about an older thread on this topic: https://www.physicsforums.com/showthread.php?t=330517 Here I'd like to thank again to everybody, who participated in that discussion. However, I still find myself at a deadlock with some questions about Gauge Invariance (GI)...

Hello, It's well known that the action for a relativistic point particle is: S=-m\int d\tau\left(-\dot{x}^2\right)^{1/2} the canonical momentum is p_{\mu}= \frac{m\dot{x}_{\mu}}{\left(-\dot{x}^2\right)^{1/2}}. This action is invariant under reparametrizations of \tau, then its...

Question on Witten's paper: "Perturbative Gauge Theory As A String Theory..." Hi guys, I have a question regarding formula 2.12 of Witten's paper hep-th/0312171 "Perturbative Gauge Theory As A String Theory In Twistor Space". He just states this formula but i don't really understand his...

As we know, the number of physical degrees of freedom(DoF) for a photon is 2. I can understand this by gauging away redundant DoF's by gauge fixing. For example, in QED, by fixing the Lorentz gauge \partial_\mu A^\mu = 0 , we could get rid of one DoF, moreover, the residual gauge...

Basic question, but nevertheless. In a non-Abelian gauge theory, the fermions transform in the fundamental representation, i.e. doublets for SU(2), triplets for SU(3), while the gauge fields transform in the adjoint representation, which can be taken straight from the structure constants of...

Short intro.: I'm a 2nd year M.Sc. student in particle physics, with basic quantum field theory and knowledge of the SM and perhaps a bit more. I've read the forums before and tried to find questions/answers that were similar to my own until I decided, "why not just join so I can ask exactly...

I am going to be pulsing a laser diode at around 2 Watt (room temperature) with a frequency of around 1-10 MHz. Right now I'm planning on using 26 AWG wire. Anyone have any thoughts on whether this is okay? Is the gauge okay? Since it's pulsed I assume I don't have to worry as much about heat...

I'm applying to grad school this year and I'm thinking I might be interested in exploring lattice gauge theory. Honestly, I don't know very much about the subject but it sounds very interesting to me. Does anybody know which schools have lattice gauge theory and which schools are really good...

Hi, I'm currently reading "Supersymmetry demystifed" by Patrick Labelle, chapter 10, about SUSY non-Abelian gauge theories. We have a Lagrangian with SU(N)-gauge fields, and gaugino's. What puzzles me are the following claims of Labelle about the representations. In the...

Two decades ago, Gribov copies arising in the Lorentz- or Coulomb gauge were considered problematic in non-perturbative calculations, e.g. due to potential failure of cluster decomposition (are there other reasons?) In the meantime this bug turned into a feature, as IR properties, especially...

I know little about these issues, so my questions may be dumb. 1. Do exact solutions exist for non-Abelian gauge theory without matter fields? 2. Do exact solutions exist for Abelian/Non-Abelian theory with matter fields (scalar or spinor)? 2. Are solutions well-behaved? I'm asking because no...

Can LSS unification (gravity, gauge, Higgs) be quantized à la "new LQG"? This came out in April. We had it on our second quarter MIP ("most important paper") poll. https://www.physicsforums.com/showthread.php?t=413838 So far, this is a classical treatment. And it uses a spacetime manifold...

Peter Woit ("Not Even Wrong" blog) reported today on two recent talks by Edward Witten which are available video online. Here is the link to Woit's blog, which gives an brief overview of what the talks are about. http://www.math.columbia.edu/~woit/wordpress/?p=3107 In case anyone is...

Got a quick question on gauge particles: why are they always spin-1? Is it because they are introduced into theories in the form \partial_mu +cA^mu, and hence must be vectors (given that the derivative they have to compensate is a vector?)

Homework Statement The Variation of the density with depth h in a muddy lake is given by ρ=ρ0+kh, where ρ0= 1000kg/m^3 is the density at the surface and k=100kg/m^4 Calculate the gauge pressure at a depth of 10m.

I've left particle physics after my diploma a few years ago so I am not familiar with all of the slang, anymore. My question is pretty simple: How common is it to call the W and the Z boson "gauge bosons" in professional physics. Is it pretty much not used and seen as a sign of the person...

Hi, I have a short question about gauge theories and constraints. Imagine I have a symmetry algebra, and I gauge it. With N generators in the algebra I get N gauge fields and N gauge curvatures. In realizing the algebra on the gauge fields I assume the gauge parameters are independent and...

Alright, I understand that there are redundant degrees of freedom in the Lagrangian, and because transformations between these possible "gauges" can be parametrized by a continuous variable, we can form a Lie Group. What I am not so firm upon is how Lie Algebras, specifically, the Lie Algebra...

I've recently been researching how to measure strain using strain gauges. I came upon the subject of shunt calibration and hit a mental roadblock. From what I understand, shunt calibration simulates a strain across a strain gauge using a comparatively large resistor placed in parallel with...

I have learned not long ago that JTBell loves streetcars - so here is something he may find amusing - narrow gauge railway in Piaseczno. Piaseczno is a city bordering Warsaw (partially flooded lately :frown:). Pictures are almost three years old, but from what I hear not much have changed. This...

Hi there, I'm studying the interaction of one electron atom with an electromagnetic field. In every textbook the starting point is the hamiltonian of the system containing the scalar potential and the vector potential. But then the scalar potential is ignored and I don't understand why. I've...

Recently I hear there's lots of research on higher spin gauge theories. I know nothing about it, so I'll ask some naive questions. How is Weinberg-Witten no-go theorem which forbids spins greater than 1 bypassed in these theories? Is the topic related to string theory? Thanks for answer.

Does someone know something about this theory? Is it popular, or just accepted by very few people? What is the flaw or defect of this theory? Has it been ruled out by some observations or experiments? Thx.

Hello, Could somebody please point me out introductory online book/paper with which I can start understanding gauge theory and how to find out about the progress in the areas Thx

After the first explanation of superconductivity by Bardeen, Cooper and Schrieffer, it was for several years a matter of concern to render the theory charge conserving and gauge invariant. I have been reading the article by Y. Nambu, Phys. Rev. Vol. 117, p. 648 (1960) who uses Ward identities to...

Hello all quantum nerds! :D I have a question regarding the "classical" limit of quantum fields, and in particular gauge fields. When we for instance do a surface integration in QFT, we let phi -> 0 as V->oo why? this is said in textbooks to correspond to the "classical limit", and...

http://arxiv.org/abs/1004.4866 Unification of gravity, gauge fields, and Higgs bosons A. Garrett Lisi, Lee Smolin, Simone Speziale (Submitted on 27 Apr 2010) We consider a diffeomorphism invariant theory of a gauge field valued in a Lie algebra that breaks spontaneously to the direct sum...

Hello folks. I have a sangamo weston temperature gauge. Back of this gauge there is 2 screws and a small wire(5cm) connecting the 2 wires. I want to taking measurement in 1m distance from the gauge so I tried to replace this wire with a copper one but the gauge doesn't work with copper wire. I...

Hello, I have read an interesting paper from the Proceedings of the American Philosophical Society about the use of the V-2 rocket at White Sands, New Mexico for high-altitude research. In it the different gauges for atmospheric pressure measurement were mentioned, as well as the difficulty to...

Hello, suppose you start with Yang Mills theory with some gauge group G, for example SU(5). Then you turn on a gauge bundle, say a U(1) bundle, and the group breaks down. I know that from hearsay but I wonder how would you describe that explicitly in formulas? meha

http://arxiv.org/abs/1004.0693 Gravity as the Square of Gauge Theory Zvi Bern, Tristan Dennen, Yu-tin Huang, Michael Kiermaier (Submitted on 5 Apr 2010) We explore consequences of the recently discovered duality between color and kinematics, which states that kinematic numerators in a...

Suppose I have a gauge potential A_{\mu\nu}, which is totally antisymmetric, if, say, the theory is in 6 dimensions, so that there are 6\times5/2 = 15 degrees of freedom. For the action S = \int d^6x F_{\mu\nu\rho}F^{\mu\nu\rho} , where F_{\mu\nu\rho}\equiv \partial_\mu A_{\nu\rho} +...

Homework Statement Take the Schrodinger equation for a point particle in a field: i\hbar \frac{\partial \Psi}{\partial t} = \frac{1}{2m}(-i\hbar\nabla - q\vec{A})^2\Psi + q\phi\Psi I'm supposed to determine what the transformation for Psi is that corresponds to the gauge transformation...

Suppose I have a manifold. I say that it can support a certain configuration of gravity field described by metric tensor \gamma. I do not write \gamma_{\mu\nu}, because that would immediately imply a reference to a particular chart. A tensor field, however, exists on a manifold unrelated to this...

Homework Statement The weight of a 1142-kg car is supported equally by the four tires, which are inflated to the same gauge pressure. What gauge pressure is required so the area of contact of each tire with the road is 96.5 cm^2? W = 1142 kg A = 96.5 cm^2 Homework Equations No idea...

Homework Statement I recently did a bending lab with a WB Strain Gauge in a bunch of different configurations. One measurement in particular is bothering me. Referring to the figure below, there are four strain gauges, Yellow, Orange, Black and Red mounted to a cantilevered beam with an...

Hello i am trying to convert the strain gauge readings i took in a lab from an I beam that was subjected to torsion. I am trying to convert the microstrain readings to stress and shear stress. I have the following information the Yield strength of the I beam and the youngs modulus but not the...

Homework Statement Water flows through a .259m radius pipe at the rate of .125m^3/s. The pressure in the pipe is atmospheric. The pipe slants downhill and feeds into a second pipe with a radius of .190m, positioned .796m lower. What is the gauge pressure in the lower pipe? The acceleration of...

http://golem.ph.utexas.edu/category/2010/03/an_invitation_to_higher_gauge.html#c032039

Ok, so what I am looking for, as the title suggests, is a strain gauge data acquisition board. Currently, we have been using all sorts of National Instruments stuff to obtain our goals. To this point they have worked fine, but now we need to seriously downsize for a new lab device we are...

Hi there! Few weeks ago I came upon the following problem: Let B be a vector field derivable from a vector potential A (on a simply connected topological space, smooth enough and everything well established so that mathematicians do not have to care about), i.e. \vec B=rot \vec...

Homework Statement So I was doing a problem out of Merzbacher 3rd edition (end of chapter 4 problem 3); the homework set has already been turned in but I wanted to run this by you all and see what you thought. I am essentially working with a particle in a 1-d ring constrained to the x-y plane...

Consider a one dimensional gauge theory where the field has mass. The term, m^{2}A^{\mu}A_{\mu} is the conventional mass term. What if you find terms in your Unified Field Theory lagrangian of the form M_{\mu\nu}A^{\mu}A^{\nu} [SIZE="4"]? In this case M_{\mu\nu} is constant...

Homework Statement Show that it is always possible to pick a gauge so V' = 0. Homework Equations We weren't given any, but I've been working with: (a)\vec{E} + \frac{\partial\vec{A}}{\partial{t}} = -\nabla{V} (b)\vec{A'} = \vec{A} + \nabla{\psi} (where \psi is a scalar function) (c)V' =...

Hi... Would you please advise me what does gauge fixing term do (physical point of view) ? Does it eliminate unnecessary spin components from lagrangian for example: Vector particle has two (massless case) or three (massive case) degrees of freedom. Vector itself has four, and a vector...

just some dilemma I ran into I have an experimental setup with a pressure transducer output connections (wires)...I deemed now that a pressure gauge alone will suffice. How do I connect the wires to a pressure gauge? Or do I need to re-do everything?

hi, Zee in QFT in nut shell says "The most unsatisfying feature of field theory is the present formulation of gauge theories. Gauge symmetry does not relate 2 different physical states but the same physical state. We have this strange language with redundancy which we cannot live without" He...

What is meant by the term "gauge singlet"? Can anybody please explain what is meant by the term "gauge singlet"? To be more specific, I got the term in a discussion on wess-zumino lagrangian where the superpotential contains the term:a_i \phi_i . The author claims that in order the theory to...