19,200 reputation
3669
bio website mat.univie.ac.at/~neum
location Vienna, Austria
age
visits member for 3 years, 1 month
seen 55 mins ago

I am currently primarily active on Physics Overflow. Here I mainly respond to comments on my old postings, sometimes upon request by email, and sometimes because I happen to see an interesting question for which I know a quick but useful answer. Occasionally I also post purely mathematical questions.

Some physics material I wrote:

  • A theoretical physics FAQ
  • Classical and Quantum Mechanics via Lie algebras
  • Renormalization without infinities - an elementary tutorial
  • Classical and quantum field aspects of light
  • Optical models for quantum mechanics
  • Molecular modeling of proteins and mathematical prediction of protein structure


  • 1h
    comment Dilemma: Fusion space from a direct sum of anyons or NOT
    I answered this at physicsoverflow.org/30478
    1d
    comment Constructing dual gravity theory from general CFT
    There is an answer at physicsoverflow.org/30169
    Apr
    22
    comment EM wave function & photon wavefunction
    @JiaYiyang: Useful interactions can be found in Weinberg's 1964 paper on massless fields.
    Apr
    22
    comment EM wave function & photon wavefunction
    @JiaYiyang: The relevant formula is ⟨α|F(x)|α⟩=α(x), where F(x) is the operator version of the silberstein vector, α is a solution of the homogeneous Maxwell equations in Silberstein form and |α⟩ is the corresponding coherent state.
    Apr
    22
    comment History of QFT after 1973
    See the answers at physicsoverflow.org/25199
    Apr
    22
    comment Indices of a Pauli matrix transformed in the Lorentz representation
    More detailed answers are at physicsoverflow.org/30233
    Apr
    22
    comment More than one time dimension
    @BenCrowell: The concept of hyperbolicity is by definition tied to the Lorentzian metric! Curling up the second time direction does not change the signature of the metric. Thus even a curled up 2D time makes the distinction between spacelike and timelike impossible.
    Apr
    17
    comment Susceptibilities and response functions
    For a pure chemical system, the Helmholtz free energy is a function of temperature and volume, and the conjugate observables are entropy and pressure. Alternatively, the Gibbs free energy is a function of temperature and pressure, and the conjugate observables are entropy and volume.
    Apr
    17
    comment Susceptibilities and response functions
    @user929304: There are different kinds of free energy, each one depending on a distinguished set of variables. The first derivatives of a free energy are the observables conjugate to those with respect to one the derivatives are taken. Which pairs of observables are meaningful depends on the system under study. For a magnetic system, the free energy is a function of temperature and magnetic field, and the conjugate observables are entropy and magnetization. Their changes gives three different susceptibilities.
    Apr
    14
    answered Susceptibilities and response functions
    Apr
    13
    comment What is the physical interpretation of the automorphism on bounded operators induced by an S matrix?
    scholar.google.at/… gives a number of possibly relevant references.
    Apr
    13
    comment What is the physical interpretation of the automorphism on bounded operators induced by an S matrix?
    link.springer.com/chapter/10.1007/978-3-642-97306-2_12#page-1 has a comment in the top paragraph that seems related.
    Apr
    6
    comment Landau poles in dimension <4?
    E.R. Speer, Analytic renormalization using many space-time dimensions, projecteuclid.org/euclid.cmp/1103859813
    Apr
    6
    comment Landau poles in dimension <4?
    E.R. Speer, Analytic Renormalization, scitation.aip.org/content/aip/journal/jmp/9/9/10.1063/1.1664729
    Apr
    6
    revised Landau poles in dimension <4?
    added 38 characters in body
    Apr
    5
    awarded  Necromancer
    Apr
    3
    comment An inconsistency in Hamiltonian formulation for non-local Lagrangian: what am I doing wrong?
    I don't understand. What do you substitute where to get which (E)? (You use (E) once in your question and once in your comment, although the content is different.)
    Apr
    2
    comment An inconsistency in Hamiltonian formulation for non-local Lagrangian: what am I doing wrong?
    rather one has $v(1-t)v(u)$. You must replace the function name and the arguments.
    Apr
    1
    comment An inconsistency in Hamiltonian formulation for non-local Lagrangian: what am I doing wrong?
    $\tau$ is only a dummy variable, which means when you vary $q(t-\tau)$ you need to replace it by $q(t-\tau)+\delta q(t-\tau)$, and similar for all other terms. After expansion, you need to make a variable transformation to bring it to a form where you can collect all required terms. Just as when you derive the equation of motion. I suggest you replace your current answer by a full derivation of the equation of motion; then it is easier to comment on mistakes and on the relation to the Hamiltonian version.
    Apr
    1
    comment Quantum anharmonic ocscillator $E_0(\lambda)$ curve or table
    @LarryHarson: I link to an answer on PO only if it is longer than a few lines.