Arnold Neumaier

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Dec
3
 reviewed Approve suggested edit on Stiffness tensor
Dec
3
 answered Why the Hamiltonian and the Lagrangian are used interchangeably in QFT perturbation calculations
Dec
3
 answered Time evolution of a reduced density matrix
Dec
3
 awarded  Nice Question
Dec
3
 reviewed Approve suggested edit on Change in time period of pendulum
Dec
3
 reviewed Reject suggested edit on How does a comet form?
Dec
3
 reviewed Edit suggested edit on momentum four vector and dirac matrices
Dec
3
 revised momentum four vector and dirac matrices
I corrected your brackets.
Dec
3
 comment Relativistic Hamiltonian Formulations
I only claimed that it does not reproduce the standard results.
Dec
3
 comment Is the momentum operator well-defined in the basis of standing waves?
The Hilbert space of states for the square well problem only consists of the L^2 wave functions that vanish at the boundary (and outside).
Dec
3
 comment Is the momentum operator well-defined in the basis of standing waves?
I had meant: Thus $(\hat p\psi)(x)$ is generally nonzero. Thus $\hat p$ does not preserve the boundary condition.
Dec
3
 comment Is the momentum operator well-defined in the basis of standing waves?
@VladimirKalitvianski: I expressed it globally rather than locally; momentum is infinitesimal translation. if $psi(x)=0$ it doesnt always imply that $\psi'(x)=0$. Thus $\hat p(x)$ is generally nonzero at the boundary.
Dec
3
 comment Relativistic Hamiltonian Formulations
@juanrga: e.g., hep-th/9601021 ''calculate certain elementary processes, including Compton scattering and Moeller scattering. These calculations lead to qualitative deviations from the usual scattering cross-sections''
Dec
3
 comment Is the momentum operator well-defined in the basis of standing waves?
@VladimirKalitvianski: There are two walls. If you translate to the right, the right boundary condition will be violated.
Dec
3
 answered What makes an equation an 'equation of motion'?
Dec
2
 revised What is the meaning of the word “particle” in particle physics?
added 16 characters in body
Dec
2
 revised Is the momentum operator well-defined in the basis of standing waves?
added remark on the lack of proerties of the momentum operator.
Dec
2
 comment What is the meaning of the word “particle” in particle physics?
... just completed.
Dec
2
 answered What is the meaning of the word “particle” in particle physics?
Dec
2
 comment What is the meaning of the word “particle” in particle physics?
I read the article, and now understand how he is using the terminology. It is quite uncommon to phrase things the way he does, but with the proper interpretation, what he says corresponds to something correct. I'll write my own answer explaining this.
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