Fermion Definition and 112 Threads

Things I don't understand: What do they mean by "two spin-1/2 doublets and a spin-3/2 quadruplet"? Why do they use the two flavours "+2/3e and -1/3e" ?

Say I have a scalar field which decays into to a fermion - anti fermion pair which then interact in a closed loop to produce two photons. How would I evaluate this? Can I just follow the loop backwards from any of the two photon vertices and just write vertex factor, propogator, vertex factor...

hi fellas, I have been working on Chandrashekhar limit, and I found a mass-radius relationship for the nonrelativistic fermi gases using this formula and i got the graph of this R=((18pi)^(2/3))/10 *H^2/(GmM^(1/3) ) (0.5/n)^(5/3) where H=(6.63*10^-34)/2pi G=6.67*10^-11 m=9.11*10^-31...

If we have two fermion operators with a known anti-commutator AB+BA, what do we do if we find ourselves with AB-BA in an equation? Does this automatically vanish for fermions? if not, is there anything we can say about in general?

For bosons we define states as eg. ln> = l1 0 1 ... > where the numbers denote how many particles belong to the j'th orbital. And similarly for fermions. We then define creation and anihillation operators which raise and lower the number of particles in the j'th orbital: c_j...

Can we have a coherent state between a fermion and a photon! I mean can there ever be a fermionic polariton?

My understanding of how one fermion changes the energy of another is something like: fermion x approaches fermion y and x emits bosons which are absorbed by y. But why does one billiard ball transfer a lot of its energy to another billiard ball on contact? Say billiard ball x approaches...

http://www.eurekalert.org/pub_releases/2013-06/vu-stm061013.php http://arxiv.org/abs/1211.0503 Anapole Dark Matter Chiu Man Ho, Robert J. Scherrer (Submitted on 2 Nov 2012) We consider dark matter (DM) that interacts with ordinary matter exclusively through an electromagnetic anapole, which...

I was taking a look at the SM particle table and I noticed that the up/down quarks seem to be "reversed" from the usual structure. Neglecting those two quarks, the "up" family is the most massive, then the "down" family, then the "electron" family, then the "neutrino" family. However for some...

Hi there, Just a quick question which I'm sure I'm over complicating in my head.:confused: I've read that Helium 4 is a Boson because it has 0 spin and that Helium 3 is a Fermion because it has 1/2 spin. Is this right? I don't see how whole atoms can be associated with fundamental particle...

Homework Statement Fermions and bosons combine through the reaction F + F + ΔE = B (so the creation of a single boson requires 2 fermions and some positive energy). What is the ratio of fermions to bosons at T = 0? Homework Equations 2[nF]/[nB] = K(T), where [nF] is the...

I am trying to understand the measurement of spin, in order to understand Bell's paper on the Einstein-Podolsky-Rosen paradox. When we measure the spin of a fermion in the direction of unit vector a, will the result be: 1. a value of either +0.5 or -0.5, and upon measurement, the fermion...

In the textbook, usually the fermion mass renormalization is introduced as follows: the mass shift \delta m must vanish when m_0=0. The mass shift must therefore be proportional to m_0. By dimensional analysis, it can only depend logarithmically on \Lambda (the ultraviolet cutoff): \delta m \sim...

Hi! I have a little problem. Consider a 4-fermion interaction (neglecting constant factors) of the form \overline{\psi_{a \mathrm{L}}} \gamma^{\lambda} \psi_{b \mathrm{L}} \overline{\psi_{c \mathrm{L}}} \gamma_{\lambda} \psi_{d \mathrm{L}} . I want to average this interaction over a...

In many papers about hep theory, I can find the concept, vectorlike fermion. But, I cannot get the exact meaning of vectorlike fermion. I would like you guys to explain vectorlike fermion. Thank you.

Could a Fermion be Entangled with a Boson ?

Hi. I've been thinking about this proof for over a day now and have reached the point where I can't come up with any new approaches! I'm trying to prove equation (5.15) in these notes: http://www.damtp.cam.ac.uk/user/tong/qft/qft.pdf Just above eqn (5.15) we are told that the proof...

From introductory QM class, my understanding is that one can consider any number of "fundamental" particles as a composite system and pretend it is a particle. When 2 fermions are considered as a single composite system/particle, it becomes a boson. When 1 fermion and 1 boson are considered...

Sometime I read that the helium atoms can be considered as boson, but I don't understand why. I know that its nucleous has a spin of 2 (integer) and that its 2 electrons gives the atom a total spin of 3, an integer. But then why isn't hydrogen considered also as a boson? I think it's considered...

Homework Statement Hello, I'm studying for my final exam on statistical physics, and I found an exercise of which I think it is really easy but I'm unsure of how to do it! So now I wonder if I actually don't understand what I'm doing at all! The question is as follows: Calculate for...

Homework Statement Given the current: J^{\epsilon}_{0} (t,x) = \overline{\psi_{L}}(t,x + \epsilon) \gamma^{0} \psi_{L}(t,x - \epsilon) = \psi_{L}^{\dagger} (x + \epsilon) \psi_{L}(x - \epsilon) with \psi_{L} = \frac{1}{2} (1 - \gamma^{5}) \psi_{D}. Use the canonical equal time...

It is interesting that our elementary fermions have 1/2 spin, meaning it takes a full 720 degree rotation to bring them back to their original state and these fermions constitute ordinary matter, eg. quarks, and electrons. Classical nature, however, does not have a 720 degree symmetry, but...

http://science.slashdot.org/story/12/04/13/1547242/scientists-find-long-sought-majorana-particle Is this legitimate? I tried reading the original paper but my physics skills weren't quite enough to keep up with it.

This ought to be simple, I think. But I haven't found a consistent way to think about things yet. Is it as simple as adding up all the spins of the elementary particles in the particle and checking whether the total has inter or half-integer spin? Homework Statement State whether the...

Is there any evidence for quantum fermi-dirac distributions among neutrinos, besides the obvious fact about their spin? I was wondering how Pauli exclusion principle would work with a neutrino 'gas', and what kind of quantum numbers they could have. It has been expected that if we ever did...

Is it possible to put a Boson and Fermion in superposition? If not possible, why not?

It is known to all that the Hamiltonin H=p^2/m+x^2 can describe the boson and fermion particle, but how can embody the fermion properties when a fermion oscillator interacted with a boson oscillator? what is their interaction form?

Consider a fermion gas of N electrons in volume V. Using the density of momentum states , show that the Fermi energy can be written as (h^2)/(2m (subscript e)) ((3N)/(8pi V))^(3/2) Homework Equations g(p)=(V/h^3) (4pi) p^2 The Attempt at a Solution N=integral from 0 to k(subsript...

I still don't understand antisymmetry and fermions. Is the proton wavefunction equal to this: |\psi_p>=\frac{1}{\sqrt{6}}\left(2|u\uparrow u\uparrow d \downarrow \rangle - |u\uparrow u\downarrow d \uparrow \rangle - |u\downarrow u\uparrow d \uparrow \rangle \right) or this...

Please take a moment to help enlighten a poor ignorant layperson. My understanding is that every known boson and fermion has a corresponding anti-particle, with the only exception being the photon. If true, can anyone explain WHY that that is?

In calculations of weak interaction processes in the Fermi-theory, there are some amplitudes of the form: \bar{a}(\gamma_{\alpha} + \lambda \gamma_{\alpha}\gamma_{5}) b \bar{c}(\gamma^{\alpha} + \gamma^{\alpha}\gamma_5)d where a,b,c,d are Dirac-spinors. Now, if this is a Lorentz-scalar. In that...

I'm studying particle physics now and am confused with all these terminologies.

why? i can see the link between spin value and the statistics in quantum mechanics

Homework Statement prove , using appropriate commutation relations that the number operator yields the values 0 and 1 for fermions , and any non - negative values for bosons. Homework Equations the commutation relations for bosons and fermions. The Attempt at a Solutionthe boson...

Hi. If c and c^\dagger are fermion annihilation and creation operators, respectively, we know that cc^\dagger+c^\dagger c=1 and cc=0 and c^\dagger c^\dagger=0. I can use this to show the following [c^\dagger c,c]=c^\dagger cc-c c^\dagger c=-cc^\dagger c=-c(1-cc^\dagger)=-c But on the...

The action for a fermion in curved spacetime is S = -\int d^4 x \sqrt{- \det(\eta^{ab} e_{a\mu}e_{b\nu})} \left[ i\overline{\psi} e^\mu_a \gamma^a D_\mu \psi + i m \overline{\psi}\psi \right] where g_{\mu\nu} = \eta^{ab} e_{a\mu} e_{b\nu} and the derivative operator acting on fermions is...

Is it possible to express fermion annihilation operator as a function of position and momentum? I've seen on Wikipedia the formula for boson annihilation operator: \begin{matrix} a &=& \sqrt{m\omega \over 2\hbar} \left(x + {i \over m \omega} p \right) \\ a^{\dagger} &=& \sqrt{m \omega...

Homework Statement Consider the collapse of the Sun into a white dwarf. For the Sun, M = 2 \times 10^{30} kg, R = 7 \times 10^{8}m, V = 1.4 \times 10^{27}m^{3} . (c) What is the average speed of the electrons in the fermion gas? (d) What is the density of the electron gas? Compare it...

Homework Statement (a) If you had a particle of mass 9.1*10^-31 kg, plot its most likely speed versus temperature, in a range from 0 to 6000 K, assuming it behaved as a classical particle. (b) repeat part (a) if the particle behaved as a fermion. Homework Equations The Attempt at...

Homework Statement For free electrons in a metal, the depth of a potential well can be determined by observing that the work function is the energy required to remove an electron at the top of the occupied states from the metal; an electron in this state has the Fermi energy. Assuming...

Hey all! Just a very short question: May I interpret the Lorenz invariant quantity \bar\psi\psi as being the probability density of a fermion field? Thanks! Blue2script

Ok my understanding of the Fermion, Boson difference is this: Identical Particles carry a representation of the permutation group. Since we have not found any para statistics, this representation must be one dimensional. And there are only two one dimensional irreducible representations of...

Hi all! Just a short question I am wondering about. Take a bound state with some valence and sea level. The momentum distribution of the valence quarks and antiquarks has a very direct interpretation. But what about the fermion density? Say the fermion number of the valence quarks is 4 and for...

Old quantum adage: Anything not forbidden, will occur. So why not more fermion generations - on the cheap, in regards to energy? Look for higher mass charged leptons. Tau has mass of ~1.7 GEV. A number of accelerators could search for such charged leptons.

...like in Photon-Photon-scattering. I know this doesn't make sense physically but the value for the diagram should still be computeable. If I want to put the expression for the matrix element together, I get a matrix, but it should be a scalar, right? Since the spinor bi-product is missing...

It is often said that fermions are protected from large mass corrections by chiral symmetry. My question is does the axial anomaly generate corrections to fermion masses, and if so, doesn't this ruin the protection afforded by chiral symmetry to some extent? Thanks, Ben

I've been analysing the following toy theory which I've called psi^4 theory for want of a better name. \mathcal{L} = :i\bar{\psi}\gamma^\mu\partial_\mu \psi - m\bar{\psi}\psi + \lambda (\bar{\psi}\psi)^2:. Ie a fermion with quartic self-interaction. This interaction can describe contact...

Suppose I couple a fermion field to a scalar field using \mathrm{i} g \bar{\psi}\psi \varphi and \mathrm{i} g \bar{\psi}\gamma_5\psi\varphi. I'm trying to understand what would be the physical difference between these interactions. I know that (1/2)(1\pm \gamma_5) approximately projects out...

i have a little doubt about the nature of the cooper pair that carries the super current if it is bosons or fermions? and why?

Good morning everyone! :smile: What do people think of the Higgs fermion candidate reportedly being studied at the Albanian reactor at Loöf Lirpana? … :confused: http://en.wikipedia.org/wiki/Higgs_boson#LoofLirpana