Scattering is a general term for several physical processes in which radiation of some sort changes direction due to an interaction with a particle. Scattering can be classified by the type of radiation (ie, electromagnetic, x-ray, neutron), or by the relative sizes of the wave and the particle (ie, ...
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1answer
91 views
Is the Møller wave operators $\Omega_\pm$ related to $\lim_{t\rightarrow\infty}U(t)$ of field theory?
When we want to compute correlation functions $\langle\Omega|\,T\hat{\phi}(x_1)\ldots|\Omega\rangle$ in an interacting quantum field theory, we relate it to the free-field objects $|0\rangle$ and ...
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0answers
27 views
Impurity scattering [duplicate]
Possible Duplicate:
Impurity scattering temperature dependence
Is there any temperature dependence of relaxation time in impurity scattering of conducting electrons? It seems to me that ...
2
votes
2answers
252 views
Scalar Field Redefinition and Scattering Amplitude
Consider a field redefinition
$$
\phi \rightarrow \phi' = \phi+\lambda \phi^2
$$
Find the Feynman rules for this theory and work out the $2\rightarrow 2$ scattering amplitude at tree level (The result ...
8
votes
2answers
415 views
What is the physical interpretation of the S-matrix in QFT?
A few closely related questions regarding the physical interpretation of the S-matrix in QFT: I am interested in both heuristic and mathematically precise answers.
Given a quantum field theory when ...
4
votes
1answer
142 views
Scattering states of Hydrogen atom in non-relativistic perturbation theory
In doing second order time-independent perturbation theory in non-relativistic quantum mechanics one has to calculate the overlap between states
$$E^{(2)}_n ~=~ \sum_{m \neq n}\frac{|\langle m | H' ...
1
vote
1answer
428 views
Plane wave expansion in cylindrical coordinates
I am trying to solve scattering problem in 2D and got to expand the wave function in cylindrical system which comes out to be Hankel function. Can you tell me how to expand the plane wave $\exp(i ...
14
votes
2answers
461 views
Does the exact string theory $S$-matrix describe all physics there is?
Suppose someone manages to evaluate the string theory $S$-matrix to all orders for any and all vertex operator insertions including non-perturbative contributions from world-sheet instantons and ...
1
vote
1answer
73 views
Definition of scattered particle?
Compare the number of scattered particles:
$N_s=Fa\int\sigma(\theta)d\Omega$
With the total number of incident particles:
$N_{in}=Fa$
Here, F is the flux of incoming beam, a the area. sigma the ...
2
votes
2answers
82 views
particles scattering on fluids: breakdown of the effective continuum description
When does the macroscopic continuum description of a medium like a fluid break down?
Say I'm interested in a scattering process of some particles with momentum p and energy E off a fluid of ...
7
votes
1answer
253 views
When we define the S-matrix, what are “in” and “out” states?
I have seen the scattering matrix defined using initial ("in") and final ("out") eigenstates of the free hamiltonian, with
$$\left| \vec{p}_1 \cdots \vec{p}_n \; \text{out} \right\rangle
=
S^{-1}
...
0
votes
2answers
145 views
Why is the sky blue? [duplicate]
Possible Duplicate:
Why does the sky change color?
Basically what the title says. What mechanisms are significant and how do they contribute to make the sky blue. Also when the sky is not ...
1
vote
1answer
306 views
Electron Incident On A Finite Potential Barrier
This is problem 2.8.3 from Miller's Quantum Mechanics For Scientists And Engineers. I'm getting stuck when I try to figure out the wave equation on the right-hand side of the barrier. The original ...
2
votes
3answers
908 views
What is the difference between Raman scattering and fluorescence?
What is the difference between Raman scattering and fluorescence?
Both phenomena involve the emission of photons shifted in frequency relative to the incident light, because of some energetic ...
6
votes
1answer
412 views
Proof of Yang's theorem
Yang's theorem states that a massive spin-1 particle cannot decay into a pair of identical massless spin-1 particles. The proof starts by going to the rest frame of the decaying particle, and relies ...
2
votes
1answer
98 views
scattering singularity
In QFT when one works out the cross section between two colliding electrons one gets a formula which is proportional to $\theta^{-4}$ where $\theta$ is the scattering angle which is due to a nearly ...
0
votes
1answer
81 views
Light in the absence of colloids?
If Earth had no colloids (Don't take LIFE into account) or any kind of scattering medium (like atmosphere) that promote to Tyndall effect, how would we able to receive the sun's rays? In the other ...
1
vote
3answers
141 views
Why is a nucleus isotropic?
I believe in Neutron Scattering the neutrons after hitting a nucleus can bounce in any of 360*3 dimensions -> 1080 degrees?
Why is this so? Shouldn't it only bounce "off" the neutron in approximately ...
1
vote
0answers
340 views
Scattering on delta function potential
Suppose a particle has energy $E>V(+/-\infty)=0$, then the solutions to the Schrodinger equation outside of the potential will be $\psi(x)=Ae^{i k x}+Be^{-i k x}$.
How can one show or explain that ...
0
votes
1answer
180 views
Scattering problem: Finding the speed of the scatterer after collision
A particle of mass $M$ moving in a straight line with speed $v$ collides with a stationary particle of the same mass. In the center of mass coordinate system, the first particle is deflected by 90 ...
1
vote
1answer
421 views
Scattering problem: Converting the two-body lab frame problem into a one-body center-of-mass frame problem
I'm reading the section on scattering in Goldstein's Classical Mechanics, and I have a rather basic question about this.
It says that scattering in the laboratory is a two-body problem because of ...
0
votes
1answer
72 views
Finding the number of particles scattered by a certain angle
I'm trying to do the problem below, but it seems like there is incomplete information.
PROBLEM STATEMENT:
In a scattering experiment, $10^6$ $\alpha$ particles are scattered at an angle of ...
2
votes
1answer
180 views
Meaning of $d\Omega$ in basic scattering theory?
In basic scattering theory, $d\Omega$ is supposed to be an element of solid angle in the direction $\Omega$. Therefore, I assume that $\Omega$ is an angle, but what is this angle measured with respect ...
1
vote
0answers
197 views
What is the relationship between Luminosity, Intensity, and Flux?
I am always confused by the terminology:
In high energy particle scattering, and in particular, in the context of collider physics, what is the relationship between luminosity, intensity and flux? ...
0
votes
1answer
109 views
Scattering problem: Expression for angular momentum of particle
I'm reading Goldstein's Classical Mechanics, the part on "Scattering" in the "Central Force" chapter.
In relation to the figure below, he says that angular momentum, $l$, is given by $$l=mv_0s$$ ...
5
votes
2answers
411 views
How do we distinguish between virtual particle exchange and particle decay?
The difference between virtual particles and unstable particles is discussed at length in this question (namely, virtual particles correspond to internal lines in Feynman diagrams and are not ...
1
vote
1answer
292 views
Quark Radius Upper Bound
If quarks had internal structure (contradicting current beliefs), what is the lowest
upper bound on their "radius" based on current experimental results?
If possible, I'd prefer to only consider ...
1
vote
2answers
288 views
Compton scattering angle
Say a photon hits a free electron at rest. I understand that there is a formula for the Compton scattering when the photon is scattered with an angle $\theta$, but I don't understand what determines ...
1
vote
0answers
40 views
scattering theory quantization condition
where and how is found the scattering quatniztion condition
$ det (1-zS)= 0 $ so the energies or bounded states of scattering come out from this
here $ S=S(k)=e^{2i\delta (k)} $ where could i find ...
1
vote
2answers
156 views
Compton scattering multiple wavelengths?
The formula given for compton scattering shows that when x-ray of one specific wavelength hits carbon or some materials, emitted x-ray will be of one new specific wavelength.
However, according to ...
2
votes
1answer
81 views
When does the “norm of quasi-eigenvectors” matter in calculations? For which physical results are these even used?
Which physical system in nonrelativistic quantum mechanics is actually described by a model, where the norm of the "position eigenstate" (i.e. the delta distribution as limit of vectors in the ...
1
vote
1answer
135 views
How do particle scattering cross sections scale with energy in colliders?
How do particle scattering cross sections scale with energy in colliders?
Particularly photons, electrons, protons, and gold or lead nucleii?
(If necessary, break this into four separate questions.)
...
2
votes
2answers
168 views
Understanding Dynamic light scattering
I'd like to understand the physics of dynamic light scattering experiment. In particular I want to understand the basic relation between relaxation time $\tau_q$ and the diffusion coefficient $D$:
...
2
votes
1answer
778 views
Does the Breit Wigner formula apply to intermediate virtual particles?
Breit Wigner Formula describes the cross section for interactions that proceed dominantly via a intermediate particle (O*) A+B → O* → C + D:
$$σ = \frac{2\Pi}{k^{2}}\frac{Γ_{i}Γ_{f}}{(E-E_{o})^{2} + ...
3
votes
2answers
156 views
Radiative Corrections and Bremsstrahlung
I am having trouble understanding why it is consistent to include "Breamsstrahlung" diagrams in computations of scattering amplitudes.
For example, consider the scattering of two electrons to two ...
2
votes
2answers
955 views
If blue light has a higher energy than red light, why does it scatter more?
As $E=hf=\frac{hc}{\lambda}$, blue light - with a smaller wavelength - should have a higher energy. However, it is the case that blue light scatters the most. Why is it that higher energy rays scatter ...
-2
votes
2answers
148 views
Angle of deflection of an atomic nucleus [closed]
when firing a proton (for example) to an atomic nucleus, from a distance $D$, the deflection angle of the proton $\alpha $ to the type of changes atomic nuclei? or always constant?
0
votes
1answer
141 views
Why does the d-spacing of a polymer decrease as its crystallinity increases?
I am currently investigating the annealing of a polymer (Parylene-C). In my reading I have found that when the polymer is annealed, there is a decrease in thickness of the film which results from a ...
4
votes
1answer
201 views
A certain gluon scattering amplitude
I am stuck with this process of calculating the tree-level scattering amplitude of two positive helicity (+) gluons of momentum say $p_1$ and $p_2$ scattering into two gluons of negative (-) helicity ...
3
votes
1answer
206 views
Spinor integration
I am learning on-shell methods for one loop integrals from this paper: Loop amplitudes in gauge theory: modern analytic approaches by Britto. Starting with formula (18) spinor integration is ...
3
votes
1answer
183 views
Differential cross section in momentum space?
Suppose I have a spherically symmetric potential and I can find its cross section in configuration space (i.e position-space), $d\sigma / d\theta$. Now I need to find its distribution $d^2\sigma / ...
2
votes
2answers
252 views
At what angle does a single atom “reflect” a single photon?
Does this question make sense in the quantum world?
Imagining a single photon (wave packet?) interacting with a single atom (its electrons etc) how do we currently describe/define the emitted photon ...
6
votes
1answer
89 views
Some more questions about the BCFW reduction
This question is a continuation of this previous question of mine and I am continuing with the same notation.
One claims that one can actually split this $n$-gluon amplitude such that there is just ...
5
votes
2answers
906 views
Why are scattering matrices unitary?
In Griffith's QM book, he introduces scattering matrices as an end-of-the-chapter problem.
For a Dirac-Delta potential $V(x) = \alpha \delta (x - x_0)$, I've derived the scattering matrix and ...
5
votes
1answer
107 views
Some questions about the BCFW reduction
I am trying to give a fast sketch of what the BCFW reduction does and embed within it some questions at the steps which I don't seem to understand clearly. The first bullet point is sort of a very ...
4
votes
3answers
355 views
Unitarity of S-matrix in QFT
I am a beginner in QFT, and my question is probably very basic.
As far as I understand, usually in QFT, in particular in QED, one postulates existence of IN and OUT states. Unitarity of the S-matrix ...
5
votes
0answers
74 views
$WW\to t\bar{t}$ growth
I was told recently that "it is well known that processes like $WW\to t\bar{t}$ ($t$ being a top, or any massive fermion) grows linearly with the energy in the absence of an Higgs boson." Does anyone ...
7
votes
3answers
814 views
Why is it necessary for an object to have a bigger size than the wavelength of light in order for us to see it?
I keep hearing this rule that an object must have a bigger size than the wavelength of light in order for us to see it, and though I don't have any professional relationship with physics, I want to ...
7
votes
4answers
209 views
Different kinds of S-matrices?
It seems to me that the notion of an "S-matrix" refers to several different objects
One construction you can find in the literature is allowing the coupling constant to adiabatically approach 0 in ...
2
votes
1answer
222 views
How does physics scattering experiments relate to real life? And what does the scientist gain from such experiments?
How does physics scattering experiments relate to real life? And what does the scientist gain from such experiments? I am having a hard time figuring the answer out. Please help.
2
votes
2answers
294 views
Physical interpretation of infinite total cross section
What does it tell us about a process, say A+B->C+D, if the calculated total cross section is infinite?
