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bio website motls.blogspot.com
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Hi, I am a string theorist and a publicist.


Feb
7
comment Where does the $\gamma_5$ here come from?
Hi, I am confident that the equations you wrote down - if nothing is added - can't lead to any inconsistency. If you can derive an inconsistency from the equations in the book only, it's bad. But if you add any extra guesses about $\psi_L$ etc. that I mentioned, there may be (independent) signs everywhere so you must be careful what's the correct sign at each place. But even if there are real sign errors in the book, you should still be able to "do the same thing right", i.e. write a similar self-consistent set of equations without errors.
Feb
7
comment Why are atoms of the same element exactly the same?
You may use approximate Hamiltonians or treatments where the perfect antisymmetry or perfect symmetry is violated but they're always at most approximations or fudges. The exact treatment doesn't allow any deviation from the perfect symmetry or antisymmetry.
Feb
7
comment Why are atoms of the same element exactly the same?
Dear @BjornW, all electrons in the Universe - those in atoms and those outside atoms - are perfectly interchangeable, identical, and the wave function is totally antisymmetric in them. Similarly for protons. For helium nuclei, they are identical bosons. It's not going "far". It's what the principle about the indistinguishability says. If it weren't true, the principle would be (completely) wrong.
Feb
7
comment Where does the $\gamma_5$ here come from?
Excellent. There are many reasons where such a wrong sign could come from. My definition of $\psi_L$ and independently $\psi_R$ may have wrong signs, and so on. The overall sign may also be absorbed to the normalization of $T_a$ or $\epsilon$, and so on. You should be able to derive what the thing is. But even if you don't, I think that you should trust that there is a fix of the sign, you should consider those equations as "essentially proven", and you should respect your book's conventions, and not mine, because they are those you will need.
Feb
7
comment Where does the $\gamma_5$ here come from?
$\psi_L$ is just defined as $(1+\gamma_5)/2 \cdot \psi$, and similarly with the minus sign in the middle and $R$, maybe the signs are reversed. They are the chiral pieces of the Dirac spinor. Then, $\psi=\psi_L+\psi_R$ and because $\psi_L$ and $\psi_R$ appear on the right hand side as well, you must express them in terms of the Dirac spinor $\psi$ and you need $\gamma_5$ for that because of the relations that started this comment.
Feb
7
comment Who (and Why) started the “electrons are negative, protons are positive” convention?
Your "correction" of the "positively charged carriers" is wrong. This correct triplet of word may also be said as "positive-charge carriers" but not "positive charge-carriers" because carriers in general cannot be positive or negative. It is the charge that is positive or negative, and that's why the adjective or adverb "positive" or "positively" is linked to the word "charge". ... It is also completely untrue that holes can't travel by themselves. Holes may travel perfectly - they behave exactly as positive-charge particles.
Feb
7
comment Who (and Why) started the “electrons are negative, protons are positive” convention?
Sorry, @Glance, but I must assure you that the velocity has a sign and may be positive or negative. In 3 dimensions, velocity is a vector which can have any direction. In 1 dimension of a wire, it is a 1-dimensional vector which is equivalent to a real number including the sign that may be either plus or minus, and it's always possible to say whether the velocity and the current have the same or opposite sign.
Feb
7
answered Why are atoms of the same element exactly the same?
Feb
6
comment Charged particle close to a charged black hole - what happens?
Sorry, cosmic censorship surely wasn't alive and kicking in 2011. It's been excluded - in general models of quantum gravity - for many years.
Feb
5
awarded  Necromancer
Feb
4
comment Particle in infinite potential well which is doubled in size at $t_0$
Hi @user44816, it's the first point of this calculation (and first sentence in my answer) that the expectation value (not just value!!!) of the Hamiltonian stays constant after the change because the two Hamiltonians only differ by the potential energy at places where the particle was 100% guaranteed to be absent. A general change of the Hamiltonian changes its expectation value in a general state by a general amount - but in this particular problem, my argument clearly shows that the amount is zero.
Feb
3
awarded  Nice Answer
Jan
29
awarded  Enlightened
Jan
29
awarded  Nice Answer
Jan
28
comment If the moon was rapid enough would it be able to orbit the earth from a close distance?
A good point if it's right.
Jan
23
answered How do I solve this Gaussian path integral?
Jan
19
comment Why are Majorana fields usually used to introduce gravity in the Rarita-Schwinger Lagrangian?
By the "real one-half of the Dirac spinor", I mean one-half of the degrees of freedom that are present in the Dirac spinor, a spinor with 4 complex components transforming as a spin-1/2 representation of the Lorentz group, and the one-half is obtained by demanding a reality condition so that the 4 complex components become 4 real components. If you understand that the word "Majorana field" in that explanation may mean a field with any $j\in Z+1/2$ and a real condition, then it's just fine, but then I don't understand too well why you don't understand the original text.
Jan
19
answered How does QFT interpret the Negative probability problem of the real scalar fields' Klein-Gordon equation?
Jan
19
answered Why are Majorana fields usually used to introduce gravity in the Rarita-Schwinger Lagrangian?
Jan
19
reviewed Reject Why does maximal entropy imply equilibrium?