Gauge Definition and 641 Threads

such as the "Lorentz gauge"

Hi guys! I'll go straight to my question.. how come the lorentz group is not the gauge group of general relativity but it is instead the two sheet SL(2,\mathbb{C}) covering of it?? Thanks!

What is the meaning of the local gauge transformation exactly?? These days I'm studying. [D.J. Griffiths, Introduction to Elementary Particles 2nd Edition, Chapter 10. Gauge Theories] Here the Section 3. Local Gauge Invariance, the author gives the Dirac Lagrangian, \mathcal{L}=i \hbar c...

Hi everyone! Two question for you (): 1) I know that General relativity may also be seen as a gauge theory, but which kind of gauge group is used there?? 2) In the gauge theory wiew the Christoffel symbols \Gamma^{\alpha}_{\mu\kappa} in the covariant derivative...

As you may guess from the title this question is about the covariant derivatives, more precisely about the difference between the usual covariant derivative, the one used in General Relativity defined by:\nabla_{e_{\mu}}=\left(\frac{\partial v^{\beta}} {\partial...

How to choose the "symmetrical gauge" for 2D triangular lattice under uniform magnetic field and staggered magnetic field?

10 moles of an ideal gas has a gauge pressure of 2 atm what is new T?? no clue [b]1. Homework Statement [/b 10 moles of an ideal gas has a gauge pressure of 2 atm and a temperature of 200 K. If the volume of the gas is doubled and the pressure dropped to 1 atm., what is the new temperature...

Homework Statement A large cylinder is filled with an equal volume of two immiscible fluids. A balloon is submerged in the first fluid; the gauge pressure in the balloon at the deepest point in the first fluid is found to be 3 atm. Next, the balloon is lowered all the way to the bottom of the...

Though I've learned gauge transformation for a while, I can't figure out why it is significance in describing fields? For example, why electromagnetic tensor has to be gauge invariant? What does it physically mean?

I am trying to understand the derivation of the covariant derivative in Peskin/Schroeder (chapter 15.1, page 483). This is the important stuff: n^\mu\partial_\mu\psi=\lim_{\epsilon \rightarrow 0} \frac{1}{\epsilon}\left[\psi(x+\epsilon n)-\psi(x)\right] Scalar quantity: U(y,x): U(y,x)...

It is well know that massless spin-1 gauge bosons have two spin states s³=+1 and s³=-1. There are two independent approaches how this can be shown: 1) via the representations of the Lorentz group for p²=0 2) via fixing / eliminating unphysical gauge d.o.f., e.g. via elimination of the...

Hi all, (Also - if anybody could tell me how to get the latex to work on this page that'd be very handy!) While not technically homework this is a problem I've found I'm stuck on during my revision. Any help would be greatly appreciated. Homework Statement "By demanding that the covariant...

Hi, first post here so be nice! I'd be interested to hear any input on a fairly minor point that I've come across with gauge fixing. Specifically, for a U(N) gauge group, how to show it is possible to fix A_\mu=0 for some coordinate (the specific example I'm using is lightcone gauge in...

This is exact copy from Griffiths Introduction to Electrodynamics 3rd edition page 421. This is regarding to information travel in space. In time varying situation, E depend not only on V, but on A also.

I 've been reading about Homotopy , homology and abstract lie groups and diff.forms and I would like to see those beautiful ideas applied on a Nonabelian Gauge Theory . Any recommendations for a textbook that apply these ideas to gauge theory ? Text books on particle Physics and QFT do not...

http://online.kitp.ucsb.edu/online/qcdscat11/ You can see it happening in these talks. For now it's just d=4 N=4 super-Yang-Mills and d=4 N=8 supergravity, but there is every reason to think that the relationships being discovered there will be extended (in more complex forms) to other gauge...

Design a circuit that uses a stain gauge to create a voltage related to the strain experienced by the gauge. The strain gauge should remain electrically isolated from the ground. The DC common mode voltage should be minimized. Only stain-related signal to be measured does not have any...

Hello, Two copper cables have the same Impedance and Voltage but different Gauge. Will they act differently? Application: copper cable assemblies used for internet. Both with 100 Ohms impedance and 3.3 Volts but they have different Gauges (24, 26, 28 and 30). Thank you in advance...

Hi! I have a process with multiple feynman diagrams where gluon propagators occur. When I use an axial gauge for the gluon propagator, do I have to use the same n-vector for every propagator? Following this I wonder whether I can use the same n-vector for every polarization sum in axial gauge...

Hello Friends, Kindly tell me the formula/values for the following: 1. Gauge Factor in the primary winding of a transformer with voltage 5 MVA 2. Voltage Drop in the Secondary Side of a Current Transformer with 100:5 Please help Thanks

I'm just beginning to learn about Feynman diagrams and wanted to make sure I've got the correct basic understanding of QED. This is what I believe to be true right now: QED allows us to describe the interaction between an EM field and light/matter. The QED vertex is composed of a photon and...

Please teach me this: For gauge symmetry fields,only one of any elementary subconfiguration of the whole configuration covers the all physics of the field.So we need to cut off the redundant configuration.It seem to me,in a loose sense,there is only one way to cut off the redundancy(the gauge...

Hi, Hope some one can help me with a problem I am working on: It involves working out: \frac{\delta L}{\delta A_\nu} of the following Lagrangian: L=\frac{1}{4}F_{\mu\nu}F^{\mu\nu} + \frac{1}{2} (D_{\mu} \Psi)^{*} D^{\mu}\Psi The solutions show that this is equal to: \frac{\delta...

Hi everybody, i have a question concerning potential energy (in all its forms, which basically means all forms of energy except the kinetic one). The kinetic energy of a system is always well defined: in the rest frame it is m² (convention c=1), in a frame moving at a relative speed v compared...

A rectangular fish tank measuring .75 x .50 m is filled with water to a height of 65 cm. What is the gauge pressure on the bottom of the tank? So I'm pretty sure I use the equation P=densityxgravityxheight I know gravity is 9.8, but I'm not sure what height I should use considering it is...

Is the following formula correct? Suppose we work in a 4D Euclidean space for a certain gauge theory, \int d^4x~ \text{tr}\Big(D_i(\phi X_i )\Big) = \oint d^3S_i~ \text{tr}(\phi X_i) and, \int d^4x~\partial_j \text{tr}(\phi F_{mn}\epsilon_{mnij}) = \oint d^2S_j~ \text{tr}(\phi...

Why is there no gauge symmetry for spin-1/2 fields? Has gauge symmetry to be related to spin-1 fields/ particles? thanks

Hello, if someone could enlighten me I'd be most grateful. Also, if anybody could point me in the direction of some really good free resources that would be great too. Thanks.

Hello, I don't understand two steps in solution to the problem: I. Homework Statement Show that QED action is invariant under gauge transformation. II. Relevant equations QED action: S= \int{d^{4} x \left[\overline{\Psi}\left(i\gamma^{\mu} D_{\mu} -m \right)\Psi...

What does it mean by "independent"(in gauge fixing of EM field) In my textbook, it gives the Coulomb gauge \phi = 0,\nabla A = 0 and says they will kill two degrees of freedom of the four potential and leave two independent components. I understand \phi = 0 will kill one degree of freedom...

Hi, I'm designing a wire harness for class 8 heavy duty trucks. I need to size the wires. Everything is 12V DC. I have designed a first draft of a wiring harness and I have all of the currents and voltage drops over each wire mapped out. All the wires are in a bundle that will be run along...

Is it possible to produce massive composite particles from a non abelian gauge theory of massless fermions? I know that if the quarks were massless, the pions will be massless too (goldstone bosons). But what about baryons? Will they be also massless? If so, can we make a general statement that...

Just to review a little bit: In general, for a gauge field with Yang-Mills Lagrangian \mathcal L=-\frac{1}{4}F^{c}_{\mu \nu}F^{c \mu \nu} for each c it is impossible to find the resulting free Green's function G(k) in momentum space: (g^{\mu \nu}k^2-k^{\mu}k^{\nu})G_{\nu...

Hello, I'm trying to understand the standard model, and I'm confused in a few places. Correct me please, if I seem confused somewhere. I'll give my understanding first, and then a few questions. I'm certain I have a couple of things not straight in my head. Alright, so the standard model has...

I am in the process of building an human sized electric race car, and am wondering what gauge wire would best benefit me. The car will be powered by 5 HR22-12, data sheet attached, batteries in series running at 12 V 20AH each for a total of 60V 20AH. This is an endurance race lasting one...

How does the electromagnetic gauge field lead to charge superselection and why does this fail when the symmetry is broken as e.g. in superconductors?

I'm hoping there will be some comment on this new paper of Kirill Krasnov http://arxiv.org/abs/1101.4788 Gravity as a diffeomorphism invariant gauge theory Kirill Krasnov 24 pages (Submitted on 25 Jan 2011) "A general diffeomorphism invariant SU(2) gauge theory is a gravity theory with two...

Hello I have been having trouble understanding equation 14.25 in Bjorken and Drell "Relativistic Quantum Fields" and how exactly it gets to it. Also I would like to explicitly find/derive what the operator gauge function is. Can anyone help please?

what is american wire gauge with relation to resistivity and circular mils??

I was reading in a paper for Chamseddine the following: "In the past many attempts were made to construct gravity as a gauge theory of the Lorentz or Poincar6 groups in four dimensions . It later became clear that if both the vierbein and the spin connection are to be viewed as gauge...

I am studying strain gauges at uni and was wondering if you could clarify for me how they may be used to measure mechanical strains in structures like towers, houses etc.. I know that it is possible to use a mechnical gauge that measures the development of a crack (see wiki)but I can't work...

Hi all, Just a question i was wondering about. We know that in electrodynamics the Lagrangian is invariant under a gauge transformation of the potential, and this is equivalent to the law of conservation of charge. Concerning relativity, what is the quantity that is conserved and are the...

Basically, the title says it all. I've never heard of Noether charge corresponding to gauge symmetry of the Lagrangian. Is it because gauge symmetry isn't the "right type" of symmetry (one parameter continuous symmetry) so the Noether theorem doesn't apply to it?

Homework Statement A 4.0 m^3 container of oxygen gas has a gauge pressure of 8x10^5 Pa at 25 degrees c. a) how many moles of oxy are present in the containe?r ANS: 1292 moles b)how many oxy molecules are present? ANS: 7.78E26 oxy (yes, i have the answers but i don't know how to get to them...

Hi, I have a question about gravity. I think most of you know that we can obtain Einstein gravity by gauging the Poincaré algebra and imposing constraints. The Poincaré algebra consists of {P,M}. P describes translations, and M describes Lorentz rotations. Gauging M gives us the so-called...

Are Lattice Gauge Theories still considered an area of active physics research? (i.e., are people still producing PhDs in this subject?) Or has this research area become passe?

I have received a pr. gauge for calibration. It's graduations are in bar and kN. The gauge is to be calibrated using kN readings and result should be given along with the uncertainty in measurements. The diameter of the piston used in the system (provided by the customer) is 5.4cm. Can anybody...

Gauge Pressure of Tires -- find car mass Homework Statement The gauge pressure in each of the four tires of an automobile is 240 kPa. If each tire has a "footprint" of 22.0 cm-squared, estimate mass of the car. P=240 kPa A=22.0 cm-squared g=9.8 m/s^2 Homework Equations P=F/A 1 atm =...

Homework Statement This is a two part problem: a) A reservoir behind a dam is 56 m deep. What is the gauge pressure at the base of the dam? The acceleration of gravity is 9.8 m/s 2 and atmospheric pressure is 10100 Pa . Answer in units of kPa. b) What is the gauge pressure 19 m from...

Homework Statement A test tube standing vertically in a test tube rack contains 3.8 cm of oil, whose density is 0.81 g/cm3 and 6.4 cm of water. What is the gauge pressure on the bottom of the tube? The acceleration of gravity is 9.8 m/s2. Answer in units of Pa Homework Equations...