Gauge Definition and 685 Threads

I need to build a table saw miter gauge at about 1/4/-1/8 scale. The center axis of rotation seems pretty straightforward - I have many old rollerblade bearings - but I have no idea how to do the handle assembly (the cylindrical screw arrangement that locks and unlocks the angle) and the sliding...

Hey gang, I'm re-working my way through gauge theory, and I've what may be a silly question. Promotion of global to local symmetries in order to 'reveal' gauge fields (i.e. local phase invariance + Dirac equation -> EM gauge field) is, as far as i can tell, always done on the Lagrangian...

A gauge field W_\mu is known to transform as W_\mu\to W'_\mu=UW_\mu U^{-1} +(\partial_\mu U)U^{-1} under a gauge transformation U, where the first term UW_\mu U^{-1} means it transforms under the adjoint representation. Can anyone explain to me why it means a transformation under the adjoint...

Hi, I have a question in Srednicki's QFT textbook. In p.460 section 75(about Chiral gauge theory), it says "In spinor electrodynamics, the fact that the vector potential is odd under charge conjugation implies that the sum of these diagrams(exact 3photon vertex at one-loop) must vanish."...

I always thought that magnetism was the exact same thing as electricity because of SR. That's probably why I am confused about the search for a magnetic monopole, as well as the classical view of light being perpendicular magnetic and electric fields. So I have a few questions. 1. What is the...

It is possible to introduce the gauge field in a QFT purely on geometric arguments. For simplicity, consider QED, only starting with fermions, and seeing how the gauge field naturally emerges. The observation is that the derivative of the Dirac field doesn't have a well-defined transformation...

I am not a (real) engineer, but have undertaken an ambitious project which contains some technical intricacies I have to learn on the fly. My first question (of many to come no doubt) is about strain gauge load cell technology - specifically powering the device. My project requires a battery...

Definition/Summary Gauge invariance is a form of symmetry. An experiment here today will work the same way over there tomorrow and with the apparatus pointing in a different direction. This is called "global invariance" … the laws of physics are invariant under translations, both in...

Definition/Summary A particular choice of "gauge fields" in which the vector potential has no divergence. Equations \nabla\cdot\vec A=0 Extended explanation As explained elsewhere, one introduces "gauge fields" in order to identically solve two of the four Maxwell equations...

Agreed. The misunderstanding comes from the ambiguity of the word "pushing". I interpreted it as "applying a force", so a helicopter is pushing the air that it accelerates. [mod note: split from here: https://www.physicsforums.com/showthread.php?t=762789 ]

In the Dirac equation, the only thing about the gamma matrices that is "fixed" is the anticommutation rule: \gamma^\mu \gamma^\nu + \gamma^\nu \gamma^\mu = 2 \eta^{\mu \nu} We can get an equivalent equation by taking a unitary matrix U and defining new spinors and gamma-matrices via...

Could anyone give a really quick explanation for gauge theory to me? Or a link, or a book is perfectly fine. I just completely don't understand SU symmetry breaking and etc. etc. I also have a question, is everyone who lurks around here a college professor on quantum physics or something...

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...

Hi, while I'm going deeper in my SR/GR knowledge, having LQG unrderstanding as main goal ( my QM background and maths is a bit stronger than GR's one, til now ) I came across some interesting youtube lectures about Gauge theory of Gravitation...

Hello, Brief context to this question: I'm an economics student and I've recently seen a lecture by phycisist-turned-economist Eric Weinstein, who says that "neoclassical economics is a naturally occurring gauge theory". In response to this, I tried to find out about group theory and gauge...

From the first moments that I read about gauge theories, till now, after years, They are still a mystery to me.Maybe that's because I never had someone explaining them to me or never actually seen any real calculation regarding them, but I think I should be able to understand them now. Anyway...

There are quite subtle gauge anomaly cancellations in the standard model. Does anybody know a good summary about the algebraic constraints for number of fermions per generation, value of electroweak charges, etc.?

Hi all, I have the following exercise about the The electroweak gauge bosons commutations relations: Homework Statement If ## [ \tau_i ,\tau_k] = 2 i \epsilon_{ikl} \tau_l ## and ## \{ \tau_i ,\tau_k\} = 2 \delta_{ik} ## where ## \bar{\tau} ## are the Pauli matrices, Then...

¿Is there an unique wavefunction for a system if we know the distribution probability function for variables from the system and first derivatives from these variables and we have the gauge fixed (by external impositions not related with the wavefunction knowledge obviously? (Nothing about...

Hi, I haven't done many problems of this nature so there are a few steps in my working that i'd like to check are acceptable/agree with what the question implies. Homework Statement A water tower is a familiar sight in many towns. The purpose of such a tower is to provide storage...

If gauge symmetries are really just redundancies in our description accounting for nonphysical degrees of freedom, then how does one explain the deep and powerful fact that if one begins with, say, just fermions and no gauge field in one's theory (and no interactions & essentially no dynamics)...

What would happen to the accuracy of a float gauge if the fluid it is measuring is heated?

Hello, I am currently studying spontaneous symmetry breaking in qft. Several textbooks I've read prove Goldstone's theorem under supposing that 1) There exists a continuous global symmetry under which the Lagrangian is invariant. 2) The vacuum state is not annihilated by the conserved...

I'm trying to make a fixture measure how much force it takes to deform various items. However, digital force gauges costs upwards from while simple scales don't cost much at all. What's the difference between using a fancy force gauge and placing a digital scale underneath an item that's...

From supersymmetry, gauge particles have superpartners, gauginos. Supersymmetry breaking will make all the gauginos massive, since none have been observed. But that has certain problems. A gauge field is a multiplet in its gauge group where each member corresponds to a generator of that...

Hi folks -- I was reading some (non-technical) work by Frank Wilczek, in which he stated that any fundamental theory -- that is, well behaved in the E →∞ limit -- must be a local gauge theory. Does anyone know of the reasons for why this is thought to be the case? Even sketchy remarks...

Hello, This thread is about the two books by Naber: https://www.amazon.com/dp/1461426820/?tag=pfamazon01-20 https://www.amazon.com/dp/0387989471/?tag=pfamazon01-20 The topics in this book seem excellent. They are standard mathematical topics such as homotopy, homology, bundles...

I've come across countless sources that gauge fix SU(N) Yang-Mills fields using the typical U(1) gauges (e.g. Lorenz gauge, coulomb gauge, temporal gauge, etc). However, I can't find a single one where they prove that this gauge fixing is valid for all field configurations... I've tried to...

I was first considering to post this in the GR section on the forum, but as I've understood it, compactification is essential in string theory, so I thought that perhaps you guys know the subject better also in Kaluza-Klein theory. Compactification in Kaluza-Klein theory as I understand it is...

Homework Statement We study the free electromagnetic field in a charge and current free cubic box with with edge length L and volume V. The vector potential in such a system is given via Fourier series: Homework Equations \vec{A}(\vec{r}, t) = \sum\limits_{k} \vec{A}_k(t) e^{i...

Hi, I am working on this water pressure problem, given: v_A = 2.0 \frac{m}{s} gauge pressure_A = 50 kPa the view is from above, no height changes find: gauge pressure @ B so, A_Av_A=2(A_Bv_B) 1.5*10^{-2}m^2(2.0\frac{m}{s})=2(5*10^{-3}m^2v_B) v_B=9.0\frac{m}{s} Bernoulli's equation (w/o...

Photons are referred to as the field quanta for the electromagnetic field. I would like to understand how the exchange of field quanta such as photons can create an attractive force. For example, I can see that an electron could repel another electron by hitting it with photons...

Hi All, I'm working through the theory of the strong interaction and I roughly follow it. However I have some questions about the meaning of the terms. The book I use gives the gauge transformation as: \psi \rightarrow e^{i \lambda . a(x)} \psi First question ... What are the a(x)...

I need some help with a derivation in GR. The linearized field equation in GR is: G_{ab}^{(1)} = - \frac{1}{2}{\partial ^c}{\partial _c}{{\bar \gamma }_{ab}} + {\partial ^c}{\partial _{(b}}{{\bar \gamma }_{a)c}} - \frac{1}{2}{\eta _{ab}}{\partial ^c}{\partial ^d}{{\bar \gamma }_{cd}} = 8\pi...

Hi, so I'm trying to derive the charge conservation law for a general SU(N) gauge field theory by using gauge invariance. For U(1) this is trivial, but for the more general SU(N) I seem to be stuck... So if anyone sees any flaws in my logic below please help! Starting with the Lagrangian...

So, I have a basic/general question here. I understand that, for example, the QED Langrangian has U(1) gauge symmetry. I also understand that this means (when you have written the Lagrangian with the covariant derivative) that if you transform the wavefunction (\psi \rightarrow e^{i \theta (x)}...

Hi, I have a question to ask. On my notes that my teacher gave me, he said that there are some errors in the notes. He had not responded to me which are the errors yet but he said about zero errors in vernier calipers and micrometer screw gauge. The question is: On my notes, it says that...

Hi there, firstly I have to apologize if this is not the right section of the forum to post my question... Well, what I need is a more sophisticated Newton meter, to measure the force on the line. Let me describe the whole thing: I am a paragliding pilot and we use gliders that have lots...

Gauge Principle is successful in strong electroweak force modeling in the the form U(1), SU(2), SU(3) and in GR but it fails in SU(5) or attempted gauge symmetry between leptons and quarks, it fails in Supersymmetry, fails in Supergravity, and even fails in String Theory. Don't we even know...

gauge forces like electromagnetic, weak and strong forces have local gauge symmetry invariance in terms of u(1), su(2), su(3) because the em for example can't have the same global phase or global symmetry at all points of space. but is there no corresponding gauge forces for global symmetry?

The photon field has two physical degrees of freedom (dof): its two transverse polarization directions. But what about non-abelian gauge theories? What about N massless spin-1 particles that transfom under SU(N), how do I count their degrees of freedom? Gluons, for example, are massless spin-1...

Hello fellow physicsforumists. I am currently looking at the standard model and one of the key ingridients is to rotate the gauge eigenstates to the mass eigenstates by a transformation acting on their family index. The problem is that I can't really see what we are doing. The mass...

Homework Statement A village maintains a large tank with an open top, containing water for emergencies. The water can drain from the tank through a hose of diameter 6.60cm. the hose ends with a nozzle of diameter 2.20 cm. A rubber stopper is inserted into the nozzle. the water level in the...

Hello, I'm new here and that's because I've run into a problem I can't reliable find anywhere else. I guess I need some personal experience or input from someone. I'm designing a force sensor for a project of mine, it will be measuring force in three orthogonal directions. Now, I'm confident...

I have a 75w 2meter mobile transceiver (Yaesu FT-2900R – 13.8 volts DC, 15 Amp max draw, min draw is .3 A-.7 A ) that I would like to use in a camp type setup. The power source will be Two 12volt batteries (not dedicated) on a small enclosed utility trailer, which will be 20’-50’ away from the...

"Gauge" is normally understood as "mathematically redundant" Why are gauge theories so prevalent? Why do they always seem to win out in the contest to describe the world? In a theory with some group of gauge symmetries, only the gauge-invariant quantities are considered physically...

Can someone explained in simple language what is Lorent'z gauge or Lorent'z gauge condition, and can you give me example from practice or real life, can it maybe "carry" 2 different frequency at once let say.

This is Problem 10.6 in page 422 of "Introduction to Electrodynamics" Edition 2 by David Griffiths. The question is: Which of the potentials in the following is in the Coulomb gauge? Which is in Lorenz Gauge?( Notice that these gauges are not mutually exclusive.) This is what the solution...

I understand ##\vec A\rightarrow\vec A+\nabla \psi\;## as ##\;\nabla \times \nabla \psi=0##\Rightarrow\;\nabla\times(\vec A+\nabla \psi)=\nabla\times\vec A But what is the reason for V\;\rightarrow\;V+\frac{\partial \psi}{\partial t} What is the condition of ##\psi## so \nabla...

Hi everyone Homework Statement Give is a generall gauge transformation \Phi \rightarrow \Phi ' =\Phi -\frac {\partial \chi}{\partial t} and \vec A \rightarrow \vec A' = \vec A + \nabla \chi first task for now is the following: How do I have to choose Chi in order to fulfill the...