19,275 reputation
3670
bio website mat.univie.ac.at/~neum
location Vienna, Austria
age
visits member for 3 years, 2 months
seen 34 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


  • May
    20
    comment Realistic interacting QFT construction
    @AbdelmalekAbdesselam: What do you think of Klauder's construction attempts, e.g., in arxiv.org/abs/1405.0332 ? Has anyone checked whether this would satisfy the Wightman axioms? Or proved that it does not?
    May
    19
    comment Spin-statistics theorem on spaces with non-integer dimensions
    There is an answer at physicsoverflow.org/21964
    May
    13
    comment Haag's theorem and practical QFT computations
    @jjcale: This link is broken.
    May
    13
    comment Realistic interacting QFT construction
    Note: observable local fields = gauge invariant local fields. These are sums of products of local fields at the same point with all gauge indices and spinor indices contracted, and products regularized by subtracting the singular part of the operator product expansion.
    May
    13
    comment Realistic interacting QFT construction
    @user41508: All conditions in the Wightman axioms with exception of the uniqueness of the vacuum are essential for any meaningful Hilbert space interpretation of a relativistic QFT. They express very basic properties of unitarity, causality and covariance of observable local fields. They are known to be inadequate for unobservable fields such as gauge fields - but even in the presence of gauge fields, the observable local fields such as currents and squared curvature must satisfy the axioms; see my review at physicsoverflow.org/21846
    May
    13
    comment About the definition of the Møller operator
    The second operator is just the adjoint of the first.
    May
    13
    comment Dynamical map of open quantum system
    Every monoid is a semigroup, so the terminology is correct, though not comprehensive.
    May
    13
    comment Realistic interacting QFT construction
    @AbdelmalekAbdesselam: Doesn't the Aizenman-Froehlich result only exclude a certain typpe of constructions for a $\phi^4$ theory in $>4$ dimensions? It does not prove that a scalar Wightman QFT satisfying a renormalized quartic field equations does not exist.
    May
    13
    answered Realistic interacting QFT construction
    May
    8
    awarded  Nice Answer
    May
    3
    answered Does the time ordering operator have a rigorous definition?
    May
    1
    comment Is the Hilbert space spanned by both bound and continuous hydrogen atom eigenfunctions?
    @wondering: The claim of of ACuriousMind that ''the bound states are, as eigenvectors of a self-adjoint operator, a full basis'' is valid only if there is no continuous spectrum. Hence this is wrong in case of hydrogen! See my answer at physicsoverflow.org/30657
    May
    1
    comment Canonical or microcanonical ensemble?
    The most natural ensemble is the grand canonical ensemble. This corresponds to thermodynamic boundary conditions that are relatively easy to satisfy in practice.
    May
    1
    comment Ground state for interacting field thoeries
    @Yesterday: Perturbatively, one cannot see the differences between the unitarily inequivalent representations. But perturbation theory only works without problems in 2 dimensions. In 4 dimensions, one needs mass and field renormalizations, and these destroy the naive relations. It is simply meaningless to try to express the vacuum state in an interacting theory in 3 or 4 dimensions in terms of a Fock space.
    May
    1
    comment About states, observables and the wave functional interpretation in QFT with gauge fields
    I gave a very detailed answer at physicsoverflow.org/30642
    Apr
    29
    answered Good layman definition of the critical point(phases) and supercriticality
    Apr
    26
    comment Dilemma: Fusion space from a direct sum of anyons or NOT
    I answered this at physicsoverflow.org/30478
    Apr
    25
    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.