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May
26
comment Can elementary particles be rightfully considered quasiparticles?
In S-matrix formalism (which I think is limited for unstable particles) particle=state and the states have a specific (on-shell) four momentum from it I may compute mass (and width). Is this what you mean?
May
26
awarded  Commentator
May
26
comment Can elementary particles be rightfully considered quasiparticles?
@CuriousOne I tried to explain that I am not thinking of balls of some sort.
May
25
comment Can elementary particles be rightfully considered quasiparticles?
@CuriousOne I think that mass and width are as well to be considered properties of an elementary particle. As I pointed out, their values can only be approximate in a renormalized theory (they become momentum dependent). I am not sure if size matters. In a kinetic description in particle approximation the size will be set to zero in any case. I do not insinuate that elementary particles are composite, even though technically quantum-loops can contribute in their propagation.
May
25
comment Can elementary particles be rightfully considered quasiparticles?
@ACuriousMind Probably there is no exact definition (at least I don't know one). I would invent: A localized (in the limits of quantum mechanics) excitation which allows for a simplified effective particle description of properties of many-body systems.
May
25
awarded  Scholar
May
25
accepted Can bosons have anti-particles?
May
25
asked Can elementary particles be rightfully considered quasiparticles?
May
25
revised What processes contribute to non-relativistic proton-antiproton collsions (annihilation)
fixed grammar
May
25
asked What processes contribute to non-relativistic proton-antiproton collsions (annihilation)
May
16
awarded  Curious
May
15
awarded  Editor
May
15
revised Can bosons have anti-particles?
added 130 characters in body
May
15
comment Can bosons have anti-particles?
For me, it is the C/CP-conjugate of the corresponding particle state. Of course, C and CP are not exact symmetries of the Standard Model but, if this is an issue, I would set the corresponding CP-violating phases to zero for that matter. Which other definition would be sensible?
May
15
asked Can bosons have anti-particles?
Jul
28
comment Renormalization, symmetries and freedom to choose counterterms
My problem is probably to see how 'symmetries' are respected in arbitrary Greens functions if I 'absorb' the counterterm rules in that for the basic Lagrangian. Surely my questions are very basic, but I might be a bit irritated because these concerns are largely irrelevant for the simple models treated in the literature.
Jul
28
comment Renormalization, symmetries and freedom to choose counterterms
Yes, I understand this. What I meant here is that the set of basic Feynman graphs (propagators and vertices) is taken to be the same as for the bare theory. This is because, as you say, the structure of the Lagrangian stays the same. Obviously the rules (analytic expressions) for the Feynman graphs are different, such that perturbative results computed based on the new rules are the same (possibly up to higher orders), as if I would take the rules for the basic Lagrangian plus that for the counterterms.
Jul
28
asked Renormalization, symmetries and freedom to choose counterterms
Apr
4
asked CP-symmetry and Ward identities and finite temperature
Nov
18
comment Unstable particles and quantum field theory
Concerning physical interpretations I think of modified decay laws, Quantum Zeno effect and so on. Things which are usually discussed for individual particles. How may such effects be extracted from the statistical Kadanoff-Baym description or how can I understand it in terms of ordinary relativistic quantum mechanics.