Gauge Definition and 685 Threads

Homework Statement The human sneeze can reach speeds of 150km/hr. Calculate the gauge pressure in the lungs required to generate a flow with this speed at atmospheric pressure. Assume the density of the air is constant at 1.3 kg/m^3. Homework Equations The Attempt at a Solution I...

Do the $\mathrm{SU(2)}$ gauge fields takes the same value in the Lie subalgebra spanned by the $\mathrm{SU(2)}$ field strength tensor? I will try to clarify my questions. Define the Lie algebra as: \begin{equation} [t^a,t^b] = \varepsilon_{abc}t^c \end{equation} where $\varepsilon$ is the...

Homework Statement In a system to regulate speed, a speed gauge is connected to the following circuit What's the purpose of this circuit? What's the difference between Uout and U*out? The Attempt at a Solution I assume that the purpose of this circuit is to help prevent...

Hi! I have to prove that the amplitude of the process \gamma \gamma \to W^+ W^- does not depend on the gauge we will choose, R_{\xi}. So I use the most general expressions for the propagators and vertices. I find 5 diagrams. One that involves only the 4 fields and a vertex, 1 t and...

i am searching the physical significance of lorenz and coloumb gauge but can't find anything besides that coloumb gauge is used for finding time independent potentials while lorenz is for finding time dependent potentials. and i'll be really grateful if u give me applications of then in any field.

The formula for absolute pressure is absolute P=gauge P+atmospheric pressure. So when the gauge is at 0 it's actually 1 atm. So using the gas law if I were to half the volume the pressure would increase to 2 atm. So would the gauge read 1 atm when this happens? So how does the mechanism...

Homework Statement In a plane onset flow of 4 m/s, a source of strength 13 m2/s per metre is located at the origin (x=0, y=0) and another source of strength 18 m2/s per metre is located at (x=3m, y=0). Calculate the gauge pressure at the point (0, 2m), Take ρ =1.2kg/m3 Homework...

Hi. I'm reading about non-abelian theories and have thus far an understanding that a gauge invariant Lagrangian is something to strive for. I previously thought that the Yang-Mills gauge boson free field term ##-1/4 F^2 ## was gauge invariant, but now after realizing that the field strength...

I'm trying to measure and regulate gauge pressure in a pipe that has water flowing through it, but I need the pressure to be about .75psi (1.8 ft H2O). Most dial gauge ranges are too high and not accurate enough. Pressure transducers I've had no luck with as far as finding one that's inexpensive...

Homework Statement A gauge transformation is defined so as to leave the fields invariant. The gauge transformations are such that \vec{A}=\vec{A'}+\nabla\Lambda and \Phi=\Phi'-\frac{\partial\Lambda}{\partial t}. Consider the Coulomb Gauge \nabla\cdot\vec{A}=0. Find out what properties the...

what is physical meaning of Lorentz gauge condition in classical electrodynamics??

Hey all, I am trying to see that in linearized gravity, choosing the transverse-traceless gauge is actually a valid choice to make. More specifically, I am trying to explicitly show what most textbooks just mention in passing, e.g. Maggiore: Where the \xi^\mu encode the gauge...

I understand that writing the E-H action in terms of tetrads makes evident GR is a gauge theory. IOW general covariance/diffeomorphism invariance in GR is a form of gauge invariance. However unlike other gauge theories(for instance EM dependence on Minkowski spacetime), this gauge invariance in...

Say Alice gives Bob the wave-function, a momentum eigenstate, of a charged particle. Bob then makes a local gauge transformation on the wave-function, ψ --> exp[iqθ(X,t)]ψ. Can Alice now undo the local gauge transformation with the right addition (or subtraction?) of electromagnetic...

Whether traveling at c in the form of radiation and carrying energy in the process or to exert the force propagated by force fields, the mass-less gauge bosons cannot go faster than c and even the gravitational force which is caused by the space-time curvature or hypothetically gravitons cannot...

HAI I am SYED , i am doing my project using strain gauges. Problem description: I have 4 strain gauges bonded to an octagonal ring. The strain gauge i am using is METAL FOIL TYPE , GF(gauge factor) -2 and 320ohm resistance. The strain gauge has two terminals ,my question is (1) Can anyone...

I'm currently attempting to explain the concept of Gauge Symmetry to a friend. Copied and pasted pretty much directly from MathIM, (And the same applies for any other potential field, such as gravitational potential.) Would this be correct? I've tried explaining Gauge Symmetry multiple...

Hey there guys! So we know that in linearized GR we work with small perturbations \gamma _{ab} of the background flat minkowski metric. In deriving the linearized field equations the quantity \bar{\gamma _{ab}} = \gamma _{ab} - \frac{1}{2}\eta _{ab}\gamma is usually defined, where \gamma =...

http://arxiv.org/abs/1204.3672 Gauge Theory of Gravity and Spacetime Friedrich W. Hehl (U Cologne and U of Missouri, Columbia) (Submitted on 17 Apr 2012) The advent of general relativity settled it once and for all that a theory of spacetime is inextricably linked to the theory of gravity...

Hello, just had a quick silly question about the coulomb gauge here, though I guess it applies for gauge transformations in general. The problem is, I'm concerned about my gauge choice not being consistent with the equations of motion. For example, suppose I'm working with a nonrelativistic...

I've been reading up on gauge theory and it isn't easy. Can someone give me an easy summary of its fundamental scope and postulates without too much math. It seems really important insofar as it defines itself as something of a "parent" theory to most of the leading cosmological models of the...

These are notes I made when I was studying the subject 20 years ago. They seem fine considering that I was student then. I believe they can be useful for those who are studying Yang-Mills and other related material. Sam

Homework Statement Consider a massivegauge field in AdS_{d+1} space given by the action S=\int_{AdS} d^{d+1}x\sqrt{g}\left(\frac{1}{4}F_{\mu\nu}F^{\mu \nu}+\frac{m^2}{2}A_\mu A^\mu \right) a) Derive the equations of motion for A_\mu in the Poincaré patch of AdS_{d+1}. The metric is...

This is an exciting development in LQG. They have a proposal for how to generalize the ideas of spin network and spin foam so that the network vertices are made of chunks of noncommutative space instead of ordinary space. I'd be glad if anybody who's looked at the paper and wants to volunteer...

It is said that : electrodynamics is a gauge theory for U(1) gauge group . what is its physical concept? Mathematically it mean that the field is invariant under transformation under components of U(1) group, that we can show them with e^{i\theta} and we can consider them as a phase angle . so...

I've read that gauge invariance leads to a fundamental phenomenon.What is that? Thanks

I have a motor that I am using, and I need to know what gauge wire to use to connect to the motor. I've looked all over online, but haven't found anything that can tell me a formula or anything to use to figure this out. The motor is 24VDC and draws 50A max, and would be running about 15...

For free EM field: L=-\frac{1}{4}FabFab Then the stress-energy tensor is given by: Tmn=-Fml∂vAl+\frac{1}{4}gmnFabFab The author then redefines Tmn - he adds ∂lΩlmn to it, where Ωlmn=-Ωmln. The redefined tensor is: Tmn=-FmlFvl+gmv\frac{1}{4}FabFab It is gauge invariant and still satisfies...

I'm curious if anybody else has felt this/ what they did to deal with it. I starting going to school with the intention of working in very theoretical physics, something along the lines of M-Theory possibly. I'm in my third year double majoring in physics and mathematics. Unfortunately, I've...

I have a question about gauges in gravity. Symmetric tensor field in four dimensions has 10 independet components, when we want to describe massless spin-two field (graviton) we impose harmonic gauge which reduces 10 independet components to 6 and afterwards we use diff invariance and...

Hi, my question is, if there is an interpretation for electromagnetic gauge fields, whose components are imaginary. This would lead to an imaginary magnetic field... Does anything like this exist? Or is it forbidden ny some first principal arguments? Thank you in advance for every input! Melvin

Hi all, I'm taking graduate level QM I and trying to wrap my head around the notion of gauge symmetry. For some reason I've struggled with this concept more than others. I don't really have a specific question; I'm more looking to see if someone has a succinct explanation of the relevant...

Homework Statement Homework Equations I am learning QFT, and I am confused of such transformations. For example, first, in these equations, especially the one that defines the transformation of A(x), whether should the partial derivative acts on U(or U-1), or just take U as a constant...

I'm currently working through Griffith's book Introduction to Elementary Particles, and studying the chapters on gauge theories. From classical E&M, I understand what we mean by a gauge transformation and why the Lagrangian must be invariant under such a transformation, but what I don't...

How to arrive at Lorenz gauge condition? http://en.wikipedia.org/wiki/Lorenz_gauge_condition I know it's used to simplify the 2 partial differential equations of the potentials, but why can we put such a restriction on the potentials? Doesn't that restriction restrict the possible electrical...

Homework Statement Confirm that the retarded potentials satisfy the Lorentz gauge condition. Homework Equations \vec{A}(\vec{r}, t) = \frac{\mu_{0}}{4\pi}\int\frac{\vec{J}(\vec{r'},t_{r})}{R}d\tau' V(\vec{r}, t) = \frac{1}{4\pi\epsilon_{0}}\int\frac{\rho(\vec{r'},t_{r})}{R}d\tau' Where...

1) Since Wigner it is well known that for massless particles of spin s the physical states are labelled by helicity h = ±s; other states are absent. So e.g. for photons the physical states are labelled by |kμ, h> with kμkμ = 0 and h = ±1 and we have two d.o.f. 2) For gauge theories with...

My book has introduced the idea of gauge invariance in terms of classical electrodynamics (attached file). However, I am not sure I completely understand how it works. On the one hand they use a lot of time on specifying how you can add to the vector potential the gradient of any scalar, whilst...

hi everyone, I have been trying to understand gauge theory. I am familiar with the Noether's theorem applied in the context of simpler textbook cases like poincare invariant Lagrangians. This is my question: Are there Noether currents corresponding to the local gauge symmetries too and would...

My understanding is that for electrons, there is a standard argument that the electromagnetic interaction between them is required, not optional. Since they're identical particles, we should be able to take the wavefunction of two electrons and mix up their identities by any amount we like, and...

Homework Statement I'm working on some things to do with linearized gravitational radiation and I'm trying to justify the claim that in the Lorenz gauge, where \partial_{\nu}\bar{h}^{\mu\nu}=0 (1.1), we are able to impose the additional conditions A_{\alpha}^{\alpha}=0 (1.2) and...

I'm reading wald page 85, and he defines a stress-energy tensor for the linearized gravitational field. he mentions that it not gauge invariant as a problem. but isn't that a general property of any tensor (except scalars). so any stress-energy tensor will not be gauge invariant (change of...

Could someone explain what a gauge theory is, both in general and how it applies to physics? Please try to keep definitions relatively simple, even though the topic is exceedingly complicated. Examples are also greatly appreciated. Thanks!

I have a few strain gauges that are going onto the suspension of a race bike. I've never installed these things before. While I have found a lot of information on installing them, I am having a hard time finding many adhesive and chemical options. It seems a lot of them are non-permanent, or...

Hello everyone, I read on Wikipedia that a lot of the properties of photons are explained by them being the quanta of an abelian gauge field (link). Does anyone happen to have a good source on this? I haven't learned anything about gauge theories yet, so I'm looking for an introductory text...

I have read 2 arguments that a gauge symmetry cannot be spontaneously broken. 1. Wen's textbook says a gauge symmetry is a by definition a "do nothing" transformation, so it cannot be broken. 2. Elitzur's theorem, eg.http://arxiv.org/abs/hep-ph/9810302v1 The first argument seems sound...

Internal symmetries of the SM -U(1), SU(2), SU(3)- are usually said to belong to abstract spaces unrelated to spacetime symmetries, have there been many attempts to relate internal symmetries to spacetime symmetries, and if so how far have they gotten?

Once I've asked here why you physicist use Gauge theories with such confidence and the overall answer was "because it works". This probably is true but perhaps is also a bit disappointing to me because I was looking something more fundamental. I've recently thought of something that may be the...

What is means that unintegrated parton distributions and matrix elements are supposed to be gauge invariant??

I know what gauge invariance is, but I'm not sure what gauge covariance is. Is it that a given field has a gauge covariant derivative? And under which circumstances do we get a field that is gauge invariant but not gauge covariant? And I would appreciate an example (other than the one...