Weak Definition and 473 Threads

In http://arxiv.org/abs/hep-th/9506035 the author said after writing this equation: $$\frac{1}{4}\eta^{\mu\nu\lambda\rho} F_{\mu\nu}F_{\lambda\rho} = \eta_{\sigma\tau\alpha\beta}\frac{\partial L}{\partial F_{\sigma\tau}} \frac{\partial L}{\partial F_{\alpha\beta} } + 2C$$ where C was arbitrary...

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...

Question: hypothesis Would it be possible to determine/ capture the total wave function of an ensemble using quantum tomography & weak measurement ? As seen in the following article.. Its been done on a photon.. My question is, could this same technique be done on an ensemble of particles...

The weak value of an observable A with pre-selected state ##\psi## and post-selected state ##\phi## is defined as: A_w =\langle \phi | A | \psi \rangle / \langle \phi | \psi \rangle References like Wikipedia then include a comment that the weak value is not bounded by the range of eigenvalues...

Recently it struck me that I'm not sure I understand the weak interaction at all. What causes it to happen? I know that its mediated by the W and Z bosons and has a short range as a result of the large mass these bosons posses, but what does that range refer to? Range from what?!

Homework Statement Given a strong form boundary value problem, derive the weak form using weighted residuals. Homework Equations ##(2-x)u''(x)-u'(x)+u(x)=f(x)## for ##x\in(0,1)## with $$u(0)=u(1)=0$$ The Attempt at a Solution I must multiply both sides of this equation by an arbitrary test...

Hi, I have problems figuring out what both c-coefficients means. Can someone explain this in a conceptual way? Also, Vg and V-g are the coefficients of the Fourier series if you expand V, but what does it mean physically? Thanks in advance.

I'm reading stuff about weak measurements with post selection and its likely ability to improve computational performance. What I'm curious about is whether weak measurement is a real thing or not. There are many papers showing how to do the measurements and the theory behind them, and then...

I have read online that light can produce a weak gravitational field (for example antiparallel beams should, in principle, attract weakly). This made me wonder if light can produce minute gravitational waves. Even if the waves were extremely weak (no disregarding of those high order terms in the...

Forgive me if this is a foolish question but, what caused the super force in the early universe to split into the weak and strong forces and obviously without them the universe as we know it wouldn't exsist.

Here I criticize the whole concept of weak measurements and weak values in quantum mechanics, first proposed by Aharonov, Albert and Vaidman: http://prola.aps.org/abstract/PRL/v60/i14/p1351_1 1. By a suitable choice of the post-selected state, the weak value can be made ARBITRARILY large. In...

Homework Statement "Describe what might happen to the particles in the accelerator if the magnetic field was too weak." Homework Equations N/A The Attempt at a Solution I am merely guessing here. I am looking on the internet for info regarding this but I can't find anything...

Hi, I have been getting a little confused; the textbook (and from what i can see on-line) are saying that Hadrons only interact through the strong interaction (along with the electromagnetic force if charged Q) and yet K Mesons decay through the weak interaction. If my understanding is correct...

Hi, I am numerically solving the 2D effective-mass Schrodinger equation \nabla \cdot (\frac{-\hbar^2}{2} c \nabla \psi) + (U - \epsilon) \psi = 0 where c is the effective mass matrix \left( \begin{array}{cc} 1/m^*_x & 1/m^*_{xy} \\ 1/m^*_{yx} & 1/m^*_y \\ \end{array} \right) I know that...

Why is that gravity is weak at the quantum level?

In SM, people say the ##SU(2)\otimes U(1)## theory unify the EM and weak interaction. I understand that the two interactions both originate from the electroweak theory in a mixed way. But does this mean they are unified? Since when we talk about unification like GUT, we require the couplings run...

How can we determine the ranges of strong interactions and weak interactions? Can calculations of relevant scattering cross sections do this? Thanks.

Hello, I have been working for a while in weak measurements and I have noticed that some physicists such as Aharonov, Vaidmenn or Popescu have suggested that weak measurements reveal some sort of retro causation phenomena. One of the things that confuse me is that they state that when we weakly...

Hi, I know the weak form of the Poisson problem \nabla^2 \phi = -f looks like \int \nabla \phi \cdot \nabla v = \int f v for all suitable v. Is there a similarly well-known form for the slightly more complicated poisson problem? \nabla (\psi \nabla \phi ) = -f I am writing some finite...

Hi. I need help please with a textbook illustration that has confused me. Is the caption a typo? Should be "neutrons into protons" instead? Thanks.

I seem to have a problem understanding this: If 1% of a weak acid dissociates in pure water. I would assume that 99% of it’s conjugate base would dissociate to form HA in pure water, but this is not the case: I tried to set up a situation below: Please help me understand what I’m...

Hello everyone. I have a rather unusual issue in which I do not seem to some know/understand basic concepts in prealgebra, but do rather well in something like calculus. By basic concepts, I don't mean something like solving equations, but I don't understand why certain things work the way they...

Hi, I was reviewing some of my notes and was wondering what the correct steps for this would be (assuming in aqueous solution). If you have ## H_2CO_3 ⇔ H^+ + HCO_3^- ## finding the final concentration of HCO3- is simple enough. Now, for ## HCO_3^- ⇔ H^+ + CO_3^{2-} ## this would change the...

Homework Statement The metric for a given particle traveling in the presence of a gravitational field is g_{\mu\nu}=\eta_{\mu\nu}+h_{\mu\nu}, where \eta_{\mu\nu} is the Minkowski metric, h_{00}=-2\phi (\phi the Newtonian gravitational potential); h_{i0}=0; and h_{ij}=-2\phi\delta_{ij}. Units...

I am just a student. I read that if the strength of weak nuclear force were stronger than current value, this would cause the rarity of neutrons. And, if the strength of weak nuclear force were weaker than current value, this would cause most of hydrogen to convert to helium. I can't understand...

Hey, I've found circuit analysis super difficult all my life. Just not one of my things I was born to do. However, now I am doing electronics engineering so that topic often in lectures. In class we have to do analysis of complex transistor cirucuit analysis using 2 port network and norton...

A very handwaving argument for weak localization is the following: In a conductor the electron can take many paths leading back to its origin. Consider two of these, being the time reversed of each other and denote them +,-. The classical return probability is: P_classical = A+2 + A_2 While...

Hello, on Zumdahl's Chemistry (9th edition), p.736: HCN, weak acid (Ka=6.2x10^-10), is dissolved in water. 50ml sample of 0.100M HCN is titrated with 0.100M NaOH. Calculate pH after 8.00 mL of 0.100M NaOH has been added. The steps are given. Then final answer is 8.49. That makes no sense to...

Hey, I was wondering if anybody could give me a brief overview (if possible) of how weak localization differs from strong localization, and any rigorous definitions of "disorder" and "localization" (if they exist) and perhaps recommend some good papers to read on the subject. Thanks

\:Homework Statement What is the pH when 10 ml of 0.1 M NaOH is added to 25 ml of 0.1 M H_{}C_{2}H_{3}O_{2}? Homework Equations pH = -log[H_{3}O] The Attempt at a Solution The main thing confusing me about this type of problem is that my teacher taught me a way which is different from the...

My textbook assumes that whenever K-constant of a weak acid is bigger than K-constant of water, the water should be a negligible source of H+ ions. However, how do we know that the concentration of weak acid could be too low and the H+ ions from water can actually have a significant effect?

I just came across the hydrolysis of the salts and the formula pH=7+1/2(pKa-pKb) What's bugging me about this is how can this be independent of Concentration? I mean if we dilute it why won't it affect the pH? That means that even a negligible amount of such a salt can affect the pH of a...

I read in my textbook that a decay process involving the strong interaction has a very short lifetime (10^-23s) whereas a decay process involving the weak interaction has a longer lifetime (10^-10s). Why is this?

what property of elementary particles is reason for weak interaction? what I mean is as color charge is reason for strong force ,as electric charge is reason for EM force and as mass is reason for gravitational force what is reason for weak force?

Hi everyone, I tried to study BCS theory but got stuck, here are my notes: I have a civil engineering degree but now I am doing a master course in physics. I know most of the undergraduate level physics including modern physics (base on Young and Freedman's book), although I cannot say...

Geodesic equation: m_{0}\frac{du^{\alpha}}{d\tau}+\Gamma^{\alpha}_{\mu\nu}u^{\mu}u^{\nu}= qF^{\alpha\beta}u_{\beta} Weak-field: ds^{2}= - (1+2\phi)dt^{2}+(1-2\phi)(dx^{2}+dy^{2}+dz^{2}) Magnetic field, B is set to be zero. I want to find electric field, E, but don't know where to start, so...

If you need to cross a bridge and you have reason to worry about its load-bearing capacity, do you choose to drive across it fast, or slow, or does it not matter? What are the considerations?

Hi people: I keep reading one day that weak isospin is exactly conserved by all interactions; other days that sometimes weak isospin is *not* conserved. Can anyone clear this one up?!

What are the weak and strong forces? I'm trying to understand what are the strong and weak forces and more importantly what is its role (if any) on the architecture of the atoms. Thanks!

Hi guys, Could someone with a better understanding of the standard model answer a question about the weak force? In a class I'm teaching, a question in the textbook asks if photons feel the weak force. My first thought was that it's fermions that feel the weak force and therefore the...

Hello! I have a question that has been bothering me for some time, and I thought this would be a good place to ask. This is my first posting on PF as well, so I hope this is well placed. There are force laws for the coulomb attraction and gravity. Are there similar force laws that can be...

After talking with students from other schools and looking around at "typical" physics curricula, I can't help but wonder whether mine is a bit weak... I go to a large state school with a relatively tiny physics department and part of me thinks they have condensed the workload in order to...

Hi; In chapter 9 of Solid state physics of Ashcroft&Mermin(Electrons in a weak periodic potential), there is a General Approch to the Schrodinger Equation when the Potential is Weak. i can't understand what is meant by the term DEGENERACY? or what does "nearly degenerate free electron...

The leptons and hadrons carry the weak isospin charge. What allows the weak bosons do carry the charge? Is it because they have a mass?

Hi, I don't know very much about the weak force, but gravity, EM and the strong force all seem to apply an actual F = ma type of force (at least, I think the strong force does). But my limited knowledge of the weak force is just that it is involved in radioactive decay. Maybe this is why some...

Anyone have an idea when/where there might be accessible draft of the paper, or want to share any insights beyond the press: http://www.scientificamerican.com/article.cfm?id=first-proof-that-infinite-many-prime-numbers-come-in-pairs Terry Tao has an initial comment...

Hello. I am a high school level student and I had a question about weak acids/bases and why they wouldn't work as a buffer on its own. If the dissociation of a weak acid is HA \rightleftharpoons H^{+} + A^{-}, then when we add OH^{-}, it will react with the H^{+} to form water. Because the...

Homework Statement Find the pH in 50.0 mL of 1.00M HCl + 50.0 mL of 1.00M HF Homework Equations None to speak of really... The Attempt at a Solution I figured out [HCl] and [HF] in the solution: they're both 0.5M. I have absolutely no idea what to do at this point... Thanks.

In Deep Down Things, an excellent book of B Schumm, at page 288, he explains that the weak force is short range because the Weak quanta have a large mass. Using de Broglie wavelength relation: Lamda = h / p, he gets a wavelength of 10 ** -18 m, and he concludes that this is the W quanta range...

The W couples to left-handed particles only. What about the Z? Is it the same? Thanks in advance!