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  1. Q

    Mathematica , a simple question.

    I have a very simple issue with Mathematica, but I can't seem to find an answer for it. I solved an equation with DSolve, and I got a result as an array of the following type: Solution = { A11 -> Function[ {t} , expression1] , A22 ->Function[ {t}, expression 2] , etc } Now I want to define...
  2. Q

    Solving a matrix differential equation in Mathematica

    Now it seems to be working. Thank you very much Bill. :)
  3. Q

    Solving a matrix differential equation in Mathematica

    Hmm, if I use this one, I only get one vector listing all 9 equations, but it does not solve them. The real problem would be too big to write here, that is why I posted just a simple example.
  4. Q

    Solving a matrix differential equation in Mathematica

    Thanks Bill, it seems to work. I just have to extend the code you've given to suit something like: A={{A00,A01,A02},{A10,A11,A12},{A20,A21,A22}} and B={{cA11-dA22 , eA01, fA02},{gA10, hA11+jA22, kA12},{lA20,mA21,nA11-oA22}} where a,b,c,d... are simple coefficients and A00,A01... are the 9...
  5. Q

    Solving a matrix differential equation in Mathematica

    I want to solve a differential equation of the form d/dt (R) = B(t) where R and B are two complex matrices, with time dependent functions as their coefficients. I want to solve these 3x3 differential equations (ones on the diagonal are actually coupled) and to obtain a matrix form for R. So...
  6. Q

    Mathematica 5.0 notebook does not work in Mathematica 9.0

    1. I have managed to find the following notebook that would prove useful for me in calculating the concurrence of a 2-qubit state. http://library.wolfram.com/infocenter/MathSource/6227/ 2. The problem is that the code is for Mathematica 5.0, and try as I may, I could not make it...
  7. Q

    Switching the position of matrix elements in Mathematica

    Say I have the following matrix, written in Mathematica A := {{a11, a12, a13, a14}, {a21, a22, a23, a24}, {a31, a32, a33, a34}, {a41, a42, a43, a44}} I want to exchange the positions of a12 and a21, a14 and a23, a32 and a41 , a34 and a43. Any ideas? Thanks.
  8. Q

    A question about kaon masses and decay widths

    Dauto, I know they represent the masses of the short and long lived states. The problem is I cannot find their numerical values anywhere, only their difference. Does anyone know what are the specific values of ms and ml? L.E. Ok , so I managed to solve it and it works. Topic can be closed.
  9. Q

    A question about kaon masses and decay widths

    I need to parametrize these values in order to verify a bell inequality, and the result that I get is not ok. This was my question, how can I parametrize these 4 values with the information above, because it seems that only the mL-mS difference is measured, but I haven't found mS and mL themselves.
  10. Q

    A question about kaon masses and decay widths

    Homework Statement Ok, so I need to make a software that will simulate a neutral kaon system, and I only have the following data about the masses and decay widths: gammaS = 580*gammaL {S = short lived state, L = long lived state} mS - mL = 0.477*gammaS Homework Equations How...
  11. Q

    Decay Width

    What is the Decay Width of a particle and how is it related to the particle's lifetime ?
  12. Q

    Defining variables in mathematica

    I need to define some "general" variables in Mathematica 8, and I wonder if this can be done the following way. Say ta[n] and tb[m] are my variables, in turn depending on n and m. I want to define a function, for example E[ta[n]_ , tb[m]_ ] := Cos[ ta[n] ] + Sin [tb[m] ] (just a simple...
  13. Q

    Change of basis

    So considering I have two bases (a,b) and (a', b'), with a' = 1/sqr(2) ( a + b) b' = 1/sqr(2) (a - b) am I correct in saying that the unitary transformation between them is U = 1/sqr(2) ## \left( \begin{array}{cc} 1 & 1 \\ 1 & -1 \\ \end{array} \right) ##. ? and then Then ##...
  14. Q

    Change of basis

    I have two possible bases (a,b) and (a',b'). If I also have the transformation matrix P, such that P(a,b)=(a',b'), am I correct in assuming that I can change an operator A, from the (a,b) basis to the (a',b') basis by applying A' = P_transposed * A * P ?
  15. Q

    Mathematica indices as variables

    Thanks for that DrClaude, it worked :) PS: Why won't Mathematica allow me to write: (R[p_] := {{p/2, 0, 0, p/2}, {0, 1 - p, 0, 0}, {0, 0, 0, 0}, {p/2, 0, 0, p/2}}) // MatrixForm It gives the error:
  16. Q

    Mathematica indices as variables

    1. I'll post here a simplified version of my problem Say you have a matrix A, and you want all its components to be functions, for example: A11 = Sin(a_n) A12 = Cos(a_n) A21 = Sin(b_n) A22 = Cos(b_n) And I want to be able to do this in mathematica so as to have the matrix A a...
  17. Q

    Yang-Mills Theory

    What exactly is a Yang-Mills Theory? Is it a general theory, based on SU(N) symmetry, which can then be applied for particular cases (ElectroWeak, Chromodynamics) ? Is it like a general mathematical model of gauge theory ?
  18. Q

    How do theoretical physicists know so much?

    Yeah, but I mean... it's freakin' awsome reading them and seeing how they solve one problem in QFT using GR or Statistical Physics arguments, and so on. Another question, related to the first...after you finish studying something, do you remember how to do the derivations? For example, could you...
  19. Q

    How do theoretical physicists know so much?

    I'm a PhD student in theoretical physics, and I am just amazed by how much physicists working in my field actually know. I am currently studying QFT and plan on going a bit deeper into General Relativity afterwards, but look at people like Rovelli or Susskind (just two names that came to my...
  20. Q

    A problem in deriving the interaction field equation for photons

    Well, I was doing a problem the other day, inserting the complete interaction QED Lagrangian into the Euler-Lagrange equations, in order to obtain the field equation governing the interacting electromagnetic field, with the Dirac field. The problem is that, by doing so, I got the equation, but...
  21. Q

    Haag's Theorem in QFT

    Ok, so what is Infrared cutoff / UV cutoff, specifically, what is a cutoff ? An upper/lower bound placed on the energy / frequency spectra? If so, by an infinite volume cutoff, do you mean the volume that appears in all field equation solutions of QFT (Klein-Gordon, Dirac, Vector) is imposed as...
  22. Q

    What does QM hint about time-space?

    Standard QM and QFT use space-time as a background, I don't think they give any hint at the structure or properties of space-time. Maybe symmetries are the only thing touching on the subject, but other than that...it's really difficult to define a time operator (as an observable), but I could be...
  23. Q

    Time ordering in QFT

    aaaa202 , a cristal clear explanation of the time ordering operator, and Wick's theorem (among most fundamental concepts of QFT) is given in R. Klauber's book https://www.amazon.com/dp/0984513922/?tag=pfamazon01-20&tag=pfamazon01-20 This and Mandl&Shaw are what you must start out with.
  24. Q

    A Naive Question

    When you switch from Classical to Quantum Physics, as an undergraduate, there is one more thing you lose, after certainty....you lose intuitive understanding. Ok, we can obtain probability amplitudes for this or that, but is there any chance we will ever know HOW it happens? Could we have a...
  25. Q

    Haag's Theorem in QFT

    First of all, what is an "asymptotically free theory" ? Second, I don't know how you apply a lattice to QFT. From what wikipedia says, "Every lattice in ℝ^n can be generated from a basis for the vector space by forming all linear combinations with integer coefficients." So taking linear...
  26. Q

    Haag's Theorem in QFT

    So I'm currently studying QFT, and I got to the point where I realized that the S operator, initially assumed to be unitary, is not unitary anymore, since it is assumed to act between t0 = - infinity and tf = infinity. The author of the book I'm using says this is due to Haag's Theorem, so I...
  27. Q

    How do you take notes?

    Well, it works, but it's a hell of a lot of work. The thing is that I don't understand the topic if I don't do all the intermediary calculations, and some books skip a whole lot of detail, so you can find yourself going over 2 or 3 pages per day... and if you're unlucky, you can even get stuck...
  28. Q

    How do you take notes?

    Well, my style is relatively simple. I read each subchapter, write in my notebook everything, by doing all intermediary calculations, and then , after I finish the whole chapter, re-read all my notes and do the problems. Sometimes I create a chart, where I put the most important results, in a...
  29. Q

    How do you take notes?

    Interesting...is there any reason why you don't keep your notes?
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