Symmetry Definition and 907 Threads

I would like to hear an original explanation of gauge symmetry. What gauge symmetry really means and why it is needed to describe nature. I am more or less familiar with the standard treatment of electromagnetism and Yang Mills theories from QFT texts, but feel still unsatisfied since I have...

I was going through Le Bellac's Quantum Physics book.In the "symmetry" chapter 1st page(Classical physics), he makes the following comments a part of which look a bit weired to me...Each statement starts with "Invariance of the potential energy".Do you think this is meaningful? *Invariance...

Hello, I would be grateful if someone could comment on my problem. I am trying to simulate diffraction of optical wavelength on a sub-wavelength aperture (aperture diameter/wavelength < 0.1). What I want to achieve is: - simulate a geometrical model with an aperture of 15um diameter -...

Hi, There are some points I really want to clear up in this topic...I promise to finish my chain of doubts as quicly as possible! I'll put in my first questions... 1. Rotoinversion is a combination of inversion and rotation-- often it ends up as having the same effect on the crystal as...

It is well known, that a point charge q\delta^3(\boldsymbol{x}-\boldsymbol{x}') creates the same electric field \boldsymbol{E}(\boldsymbol{x}) as any spherically symmetric charge density \rho(\boldsymbol{x}) around the point \boldsymbol{x}', with the right total charge, for the points...

This is pretty much like the twin paradox question: if person A and person B were moving with a velocity v relative to each other and away from each other, then person B would observe a time dilation in person A's reference frame while person A would observe a time dilation in person B's...

When I take the fft of a set of data and plot it, there is a reflection around the nyquist. Everybody knows this, but I would like to know what the physical meaning of the second half (the reflected half) is. The real component is the same as the first half, and the imaginary component has...

Hi, I was wondering how would i determine if <p,q> = p(0)q(0)+ p(1)q(1) is an inner product for P2. I know, we have to check for non-negativity, symmetry and linearity. Just not sure how. thanks!

If you have a 3d shape how do you simplify the problem using symmetry. eg with a sphere is symmetric along any axis therefore the centroid must be in the middle of it eg2 A cone sitting on the xy plane, where the pointy bit is points up the z axis. -nb it is sitting on point (0,0,0) where the...

In standard, old-fashioned, Kaluza Klein theory we have new dimensionful parameters, the size of the compact dimensions, but they become dimensionless after quotient against the Plank size, so they become the adimensional coupling constants of the gauge groups associated to the symmetry of the...

In Weinberg's book, Quantum theory of fields-II, he talks about a chair in the chapter on spontaneous symmetry breaking. He says that, for a chair, a state with a definite l value is not stable but a state with a definite orientation is. I do not understand what he means. An l state can...

If you model the quarks as massless, there should be no flavor mixing, because flavor mixing is achieved through the CKM matrix, which is a mass matrix. However, if quarks are massless, there ought to be an axial flavor symmetry, but there isn't. So to reconcile this, we must spontaneously...

There's an interesting series of papers by Bahr and Dittrich, and a related video talk by Dittrich at the Planck Scale site. The papers bear on issues discussed in the Lewandowski thread. The first in the series is a good introduction to the rest. Here are some links and abstracts to show what...

hello, i am trying to get familiar with magnetic dichroism, first question on that is, why bands of same symmetry are not allowd to cross each other and why as a consequence hybridization gaps are formed. thanks for help

"It's the planet that really shouldn't exist – or at least not for long. It is 10 times the size of Jupiter, orbits its own star in under 24 hours and should soon be spiralling into the surface of its searingly-hot sun..." Full story...

Hi, I'm reading the article "Galilean Conformal Algebra's and AdS/CFT", 0902.1385v2, and have a quick question about the Schrodinger symmetry group. The symmetry group consists of the usual Galilean group G(d,1) with rotations, boosts and (space and time) translations. On top of that we have...

Homework Statement (x_1 - x_2)(x_3 - x_4) Find permutations of subscripts that leave value unchanged Homework Equations The Attempt at a Solution Okay so I know that it's asking how I should rearrange things and still not change the value. Switching 1 with 2 or 3 with 4 would work but I know...

Hello: The gauge symmetry of the standard model is written in authoritative places like wikipedia :-) as U(1)xSU(2)xSU(3). This would have 12 elements in its Lie algebra corresponding to one photon, W+, W- and W0 or Z, and the 8 gluons. I recall reading discussions that such a...

I would like some tips about what book I should read if I want to properly understand the relation between local symmetry and forces in gauge theories. And with properly uinderstand I mean a combination of mathematics and intuition/visualization. On the topic of QFT I have the books by Zee (...

Book: Maggiore-A modern Introduction to QFT Section:11.1 He says that if a symmetry transformation multiplies the vacuum state by a constant phase factor only, the symmetry is not broken.. Section:11.2 U(1) symmetry is spontaneously broken...multiplication by exp(i theta) takes the...

I was interrested in the general solutions to the wave equation depending on only one spatial coordinate. For one linear coordinate, the general solution is: a f(x-ct) + b g(x+ct) For one radial spherical coordinate, the general solution is: a f(r-ct)/r + b g(r+ct)/r I thought that...

I have just read a book. It said that: "if symmetry is exact, interaction is a long range". Could you explain me more detailed? Thanks!

Why in QCD chiral symmetry breaking study only the light quarks are taken into account? And why are their masses usually set to zero, Goldstone bosons are found, and then their masses are corrected by letting the quarks have non-zero mass? What happens if one study this symmetry breaking with...

I have 2 questions: 1. When there are no fermion mass terms, the Dirac part of the Lagrangian posseses an SU(N) left X SU(N) right flavour symmetry for N flavours of fermions. This can be "re-arranged" as an SU(N) vector X SU(N) axial symmetry. The axial part is spontaneously broken by the...

It is common knowledge in Physics that eigenstates share the symmetries of the Hamiltonian. And it is trivial to show that this is true for the eigenspaces. Let g be an element of a symmetry group of Hamiltonian H, M_g its representation, \left| \phi \right> an eigenvector and \lambda the...

I'm trying to derive the lie algebra for the conformal symmetry group and was curious if anyone could help? I'll go through what I have and highlight the parts I"m unsure of ds^2 = \bar g_{\alpha \beta } (\bar x)d\bar x^\alpha d\bar x^\beta = g_{\alpha \beta } (x)dx^\alpha dx^\beta...

I've been following along with Lenny Susskinds lectures on modern classical mechanics on youtube. at 34:30 he writes a few translation formulas on the board: delta X = - epsilon Y delta Y = epsilon X It's not obvious to me why these equations are true. I can't seem to find a...

Hello I am trying to learn more about NMSSM, and in the Lecture Notes by Jack Gunion, held at SUSY08 conference in Seoul 2008 ( http://susy08.kias.re.kr/slide/pl/Gunion.pdf ) there is in slide #20 arguments for a Z_3 symmetry of the NMSSM superpotential. My questions are what/which is this...

I have of late been reflecting on something. Generally as a rough approximation we may divide physics into classical mechanics, quantum mechanics, classical field theory (like E/M, fluid mechanics...), quantum field theory, and then statistical mechanics. All the classical and quantum...

I don't see it. Can someone explain? The Wikipedia article (http://en.wikipedia.org/wiki/Rotational_symmetry) defines an object with rotational symmetry as an object that looks the same after a certain amount of rotation. But this seems vacuous; doesn't *everything* look the same after a...

Hello I'm currently studying the reaction of anisole with hexacarbonylchromium, and experiment shows the displacement of 2 of the carbonyl ligands with the anisole group, forming a 2-η ligand with the chromium ion. After refluxing to obtain the crystals, IR and nmr spectra of the sample...

anyone know what research is being done in CP symmetry violations and Matter Antimatter Asymmetry currently?

Homework Statement Glue two dodecahedra together along a pentagonal face and find the rotational symmetry group of this solid. What is its full symmetry group? Homework Equations The Attempt at a Solution Since this clearly is a finite subgroup of SO3, it must be isomorphic to a...

Homework Statement Past exam question: Briefly explain the roles of symmetry, uniqueness and superposition in solving electrostatics problems. Homework Equations N/A The Attempt at a Solution I know the definition of these words and could cobble together an answer from that - but...

Homework Statement I would like to find the number of distinct elements in S17 that are made up of two 4-cycles and three 3-cycles. Homework Equations The Attempt at a Solution This seems like a very simple question but since the group is so huge it's hard to figure out. I have...

In the Electric field of a Continuous Charge Distribution, what is "conti.." exactly? -I know its the "distribution"! but I`m asking about, like, how would the "distribution" be continuous? -I think the word "symmetry" should be used? -why is the word "continuous" used?

Hello, im a first year phd student, and I am reading http://arxiv.org/abs/0901.1847 right now in an attempt to figure out something cool to do with lie 3 algebras. In the paper they mention that turning on a B field in the 1,2 dimensions breaks the SO(4) symmetry the theory has to...

I have never really understood the approximate 'Custodial symmetry' in the Standard Model. I've seen it being described in many texts, but I can't seem to be able to put my finger on it. Would somebody please write down the transformation law for the Higgs fields under a 'custodial SU(2)...

Homework Statement Show that the solution u(r,theta) of Laplace's equation (nabla^2)*u=0 in the semi-circular region r<a, 0<theta<pi, which vanishes on theta=0 and takes the constant value A on theta=pi and on the curved boundary r=a, is u(r,theta)=(A/pi)[theta + 2*summation ((r/a)^n*((sin...

I am confused with the coordinates when using the symmetry argument for this graph. Is Mx=0 using the symmetry argument ?

I read a introductory book on symmetry of physics system. The author says symmetry of quantum mechanical system is VERY different from that of classical system. I just wonder what's the main difference?

I am having trouble understanding the concept of cylindrical symmetry in an infinitely long line. Please picture a finite Gaussian cylinder enclosing a portion of the length of the line, parallel to the line. My book states that there cannot be any component of E perpendicular to the...

Can someone explain what's Z2 symmetry ? Is it necessary to have it in a model, even SM ?

In any place of our universe we can define a 'preferred' or 'rest' frame based on the observation of the Cosmic Microwave Background. Of course, in different places of our universe these frames are different, but the idea is the same. If instead of the CMB we define this frame based on the an...

why does the spherical symmetry of the ground state orbital of hydrogen necessitate zero angular momentum? I really don't have any intuition for "quantum angular momentum"

ehim ehim...hello, I wonder if anyone knows about “group theory” [= approximation method] which is helpful in describing band gap structure of semiconductor oxides, my main problem is the high symmetry points i.e. gama point which occur at k=0 [the first Brillion zone], how it varies from gama...

I was wondering if anybody has any experience with Lie Symmetry Method for solving PDE and ODE's? I have heard that the method is very general/systematic, but rather tedious and useless in practice. But recently I've noticed that Maple and Mathematica contain very nice functions, for example...

Symmetry Arguments--a finite cylindrical can Homework Statement Consider a finite cylindrical can shape that has charge uniformly distributed on its surface. Symmetry does allow us to say some things about the electric field of this distribution A) at points along the can's central axis B) At...

In most of quantum textbook, they say strong magnetic field destroy the spherical symmetry of an atom in zeeman effect. Total angular moment is not conserved. Can anyone explain what physical meaning is? I cannot picture it in my mind. How does strong magnetic field cause spherical symmetry...

Homework Statement Three plastic sheets that are large, parallel and uniformly charged are placed side-by-side. The electric field strength between sheets 1 and 2 is 2x105; the electric field strength between sheets 2 and 3 is 6x105. What is the ratio of the charge density on sheet 3 to that on...