20,273 reputation
3975
bio website mat.univie.ac.at/~neum
location Vienna, Austria
age
visits member for 3 years, 6 months
seen 44 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


  • Jul
    11
    revised What is $\phi(x)|0\rangle$?
    added remark of electromagnetic field
    Jul
    11
    comment What is $\phi(x)|0\rangle$?
    Position is never fixed, always uncertain with an uncertainty of the Compton length. This reconciles the different points of view. Note that probabilities are associated with observations, which always happen in the eigenframe of the observer. What you describe is a simplified version of the Unruh effect, which even says that the notion of particle is frame dependent.
    Jul
    11
    comment Mathematician learning theoretical physics
    I answered this at physicsoverflow.org/32400
    Jul
    11
    answered What is $\phi(x)|0\rangle$?
    Jul
    11
    comment How to understand the QED, QCD and standard model Lagrangians?
    There is an answer at physicsoverflow.org/5191
    Jul
    11
    comment Projector and delta function on a cycle $\Sigma$ of a manifold $\mathcal{M}_6$
    There is an answer at physicsoverflow.org/31997
    Jul
    11
    comment Super Lie-infinity algebra of closed superstring field theory?
    There is an answer at physicsoverflow.org/4978
    Jun
    28
    comment Choice of framing in Gravitational Chern-Simons
    There is an answer at physicsoverflow.org/32208
    Jun
    20
    comment Anomalous magnetic moment of electron
    @MarkWayne: Of course; g=1 also violates experimental results directly. I was just pointing out that without invoking the Dirac equation one has a 1-parameter family of Hamiltonians parameterized by g, so that choosing one needs experimental input, while the Dirac equation fixes g=2, close to the the experimental value of g.
    Jun
    18
    comment Anomalous magnetic moment of electron
    @MarkWayne: H_0=(p^2+(σ⋅p)(σ⋅p))/(4m) should give g=1.
    Jun
    17
    comment Anomalous magnetic moment of electron
    @MarkWayne: interesting. By writing H_0 in other quadratic patterns before doing the minimal substitution one can probably get an arbitrary value of g.
    Jun
    16
    comment If a symmetry operator S in a QFT annihilates the vacuum, why does S preserve the space of 1-particle states?
    More answers (among them mine) together with an extensive discussion can be found at physicsoverflow.org/30822
    Jun
    11
    awarded  Nice Answer
    Jun
    10
    comment Question regarding moduli space of a Calabi-Yau manifold
    another answer is at physicsoverflow.org/31683
    Jun
    9
    awarded  Enthusiast
    Jun
    7
    comment Symplectic leaves, tori and Poisson manifolds
    Qmechanic's suggestion to remove the nambu part is sensible - you can pose the removed part as a new question. It is never good to ask too much and too disparate things in one question.
    Jun
    5
    revised Symplectic leaves, tori and Poisson manifolds
    grammar corrected
    Jun
    5
    comment Symplectic leaves, tori and Poisson manifolds
    @JanetthePhysicist: The relation to the Dirac bracket is complicated - it amounts to giving a more explicit description of the centralizer.
    Jun
    4
    revised Symplectic leaves, tori and Poisson manifolds
    added detail
    Jun
    4
    answered Symplectic leaves, tori and Poisson manifolds