Gauge Definition and 641 Threads

Gauge transformation can be written as: ##\psi(\vec{r},t)\rightarrow e^{-i \frac{e}{\hbar c}f(\vec{r},t)}\psi(\vec{r},t)## http://quantummechanics.ucsd.edu/ph130a/130_notes/node296.html Does it have any sense that we choose such function ##f##, that all right side is constant in time. Is this...

Why is ##\bar{\psi}=e^{i\theta}\psi##, where ##\theta## is a real number, used as the global gauge transformation? Why ##e^{i \theta}##; what's the physical significance or benefit? Why is ##\bar{\psi} = e^{i \theta(x)} \psi## the local gauge transformation? What does ##\theta## being a...

Hello All May i ask a question? Could anyone give me a paper or a book that allows me to understand Gauge formalism from A-Z? I already have some ideas but i want more details. Thank you

It's well known when if we are working on problems related to particles in presence of an electromanetic field, the way we state the problem can be done using the next Hamiltonian: H=\dfrac{(p-\frac{e}{c}A)^2}{2m} +e \phi where the only condition for A is: \vec{\nabla } \times \vec{A} =\vec{B}...

It's well known when if we are working on problems related to particles in presence of an electromanetic field, the way we state the problem can be done using the next Hamiltonian: H=\dfrac{(p-\frac{e}{c}A)^2}{2m} +e \phi where the only condition for A is: \vec{\nabla } \times \vec{A} =\vec{B}...

Hello everyone, I'm trying to write down a Lagrangian invariant under local ISO(3) (rotations+shifts) transformations. I'm working at classical level and there will be no quantization of any kind so the theory shouldn't have any ghost pathology. However, I found that, out of the 6 gauge fields...

Hello everyone. Does anyone know if it is possible to build a gauge theory with a local ISO(3) symmetry (say a Yang-Mills theory)? By ISO(3) I mean the group composed by three-dimensional rotations and translations, i.e. if ##\phi^I## are three scalars, I'm looking for a symmetry under: $$...

Hello, I was wondering if anyone can help me out with this one. I am installing a 350 ohm strain gauge as shown in attached figure. I am expecting to see 350ohm value between terminal 1 and 2. I have checked the values for the following terminals. 1) 5 & 6 = 350ohm (PASS) 2) 3 & 4= 350ohm...

Using R = ρL/A, I am trying to get this formula, which is the change in resistance due to change in length, area, and resistivity. ΔR = (∂R/∂L)ΔL + (∂R/∂A)ΔA + (∂R/∂ρ)Δρ I understand the above conceptually, but I am confused about why we are multiplying by terms ΔL, ΔA, and Δρ. Intuitively, I...

Why must the gauge group be in a complex representation so that chirality of the fermions is respected? thanks

Do all forces of nature have to support gauge symmetry? Are there none gauge forces? Or what if there is a force but it is not gauge.. then what do you call it? For example. The quantum vacuum are very complex thing and can act like medium where other forces may propagate, what principles...

Hey guys, So I have a question about the gauge invariance of the weak field approximation. So if I write the approximation as \Box h^{\mu\nu} -\partial_{\alpha}(\partial^{\mu}h^{\nu\alpha}+\partial^{\nu}h^{\mu\alpha})+\partial^{\mu}\partial^{\nu}h=0 then this is invariant under the gauge...

Refering to this paper "Theoretical Aspects of Massive Gravity" (http://arxiv.org/abs/1105.3735) about the spin-2 boson field and GR. The author uses the Fierz-Pauli action ( I quote the massless part) ##-\frac{1}{2}\partial_\lambda h_{\mu\nu}\partial^\lambda h^{\mu\nu} + \partial_\mu...

My book says that in this case $$e^+e^- \rightarrow \gamma \gamma $$ gauge invariance requires that $$k_{1\nu}(A^{\mu\nu} + \tilde{A}^{\mu\nu})=0=k_{2\mu}(A^{\mu\nu} + \tilde{A}^{\mu\nu})$$ Please see attachment. My question is how does this statement hold?

Homework Statement Given your average Wheatstone Bridge with R1 R2 and R3 unknown resistor values and R4=RG= strain gauge, how to solve for the resistor values given only input voltage and the value of the resistances between the resistors?[/B]Homework Equations Not Sure[/B]The Attempt at a...

Homework Statement I want to built a simple ultrasonic thickness gauge for my final project. I have already search in google about that simple electronic circuit but i can't found it and also i have already looking for tutorial video in youtube about how to built simple ultrasonic...

Homework Statement Approximately how deep into water must a diver dive to reach the point where the gauge pressure is 1 atm. (1 atm = 1.013 x 10^5 N/m^2) (assume fresh water) Homework Equations gauge pressure = pgd density of fresh water p = 1 kg/m^3 The Attempt at a Solution pgd = (1...

I was trying to prove all those little things you spend long as the local invariance in the free Lagrangian of electroweak interaction. Taking into account the appropriate SU(2) transformations (without covariant derivatives), came to the following expression \mathcal{L}_{\text{ferm.}} =...

Hi folks -- it is my understanding that only non-Abelian gauge theories can be asymptotically free. But can anyone provide me with a canonical reference showing that such symmetries can be dynamically broken and still retain that status? I gather that this is the case (from reading the...

A twisted cylindrial rod has the cross sectional symmetry so that it's not posible to tell whether it is twisted or not without knowing if there is any torsional energy. now drawing a line on the surface of it can tell us whether or not it's twisted. It might not be a straight line.. there are...

Is there any significance to the fact that: The electromagnetic and strong interactions have gauge bosons with no electric charge that are massless; and The weak interaction has two massive gauge bosons which do have electric charge. If there is a significance to this 'observation' then where...

Lets take QED just to simplify. When we are doing Path Integrals and we want to "fix the Gauge": 1 we add in the integral a delta(F) -meaning that we are going to integrate only in one representative of each class of equivalent configuration- 2 We take some factors out because they are constant...

Homework Statement Demonstrate the equivalence between the gauge fields A1=(0,bx,0) and A2=)-yB/2,xB/2,0) and find the scalar field Φ for which A1= A2 + ∇ΦHomework Equations B = ∇XA The Attempt at a Solution The first part is fine, you just plug it into the above relevant equation and you get...

I was walking around at work today to find an AC amp Gauge on a DC breaker (1000KW, 250 VDC), Which made me scratch my head if there is any difference between the two gauges for this application? Any idea? Thanks.

See the passage attached below. Consider the 1-loop vertex correction (c.f. p.2 of http://bolvan.ph.utexas.edu/~vadim/classes/2012f/vertex.pdf) and vacuum polarization diagrams in QED. A very simple UV regulator that makes the integrals for the amplitude very simple is the prescription that we...

I've seen explanations that when a neutrino with a W+ Boson comes near a neutron, it affects one of the bottom quarks and changes it to a up quark which effectively turns the neutron into a proton. The neutrino then turns into an electron. Source: (2:20 onwards) I've seen other explanations...

Can some one explain what are the so called "large gauge transformations" and where do they play important role in physics? Explanations with less mathematical rigor will be greatly appreciated.

Hello Community! I can't find a good answer(if there is) to my question. When in statistical mechanics we can define the order parameter for to study some phase transition. we need to define a order parameter. Now, I want to know if we can to define/find some "order parameter" for to...

Anyone can help me how to argue that interaction lagrangian is invariant under gauge transformation?

Hello, I'm trying to design a strain gauge load cell for force measurments. I have few questions regarding that. Q1: how to calculate the minimum froce that my load cell can detect? Q2: how to calculate the FSO(full scale output) of my load cell? Q3: Is there any way to measure the...

Hello, I would like to know, how to calculate the number of grid lines( or loops) in a strain gauge. I'm trying to calculate the output form the each grid lines. Thanks in advance

In the presence of a magnetic field with vector potential \vec A and an electric field, the Schrodinger equation for a charged particle with charge q and mass m becomes: \frac{1}{2m} (\frac{\hbar}{i} \vec \nabla-q\vec A)^2 \psi =(E-q \phi)\psi Another fact is that, Schrodinger equation...

Hi folks -- does anyone know of a good survey article on the topic of whether local gauge invariance is a requirement of a fundamental theory within QFT -- hence of an asymptotically safe theory? I only have a few scattered remarks to this effect (by F. Wilczek mostly), so any good...

I have a question about this classical invariance problem I'm working on. I'm almost done, and I understand the theory I think, so my question may seem a bit more math-oriented (it's been a few years since crunching equations). I have found that under a gauge transformation for a single particle...

Well I'm trying to understand the difference between these propagators: \frac{g_{\mu \nu}}{k^{2} - m^2 + i \epsilon} and \frac{g_{\mu \nu}+ \frac{ k_{\mu} k_{\nu}}{m^{2}}}{k^{2} - m^2 + i \epsilon} My professor told me that they are different gauges, and the from the second you rule out...

Do gauge fields work the same way as the Higgs field? Are gauge fields all encompassing too, like the Higgs field? What are the differences between the functioning of gauge fields and Higgs field?

I have a problem concerning gauge invariance in QM. QM should be invariant of electromagnetic gauge. However, the following two physically equivalent vector potential: 1. A = (-\frac{1}{2}By, \frac{1}{2}Bx, 0 ) 2. A = (-By, 0 , 0 ) generates the following hamitonian: 1. H =...

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...

[SIZE="4"]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...

[SIZE="4"]Definition/Summary A particular choice of "gauge fields" in which the vector potential has no divergence. [SIZE="4"]Equations \nabla\cdot\vec A=0 [SIZE="4"]Extended explanation As explained elsewhere, one introduces "gauge fields" in order to identically solve two of...

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...