What is a particle in quantum mechanics?

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In quantum mechanics, a particle can be viewed as an entity detected by particle detectors, often appearing as a dot on a screen. It is defined as a discrete excitation of a quantum field, characterized by eigenvalues of conserved operators such as charge, mass, and spin. Particles are typically well-localized in space, though this is not always the case. A more formal definition describes a particle as a quantum state in the rigged Hilbert space, representing an irreducible representation of the universal covering group of the restricted Poincare group. This multifaceted understanding highlights the complexity of particle definitions in quantum theory.
arupel
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I would imagine that there are different viewpoints of what a particle is in quantum mechanics. Is it possible to get a summary of what they are?
 
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Something that is detected by a particle detector, i.e. something that shows up as a dot on a screen, or some such.
 
A discrete excitation of a quantum field which is characterized by the eigenvalues of some set of conserved operators (e.g. charge, mass, and spin). They are often, but not necessarily, well-localized in space.
 
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The definition in post#3 reminds me of the famous one by E.P. Wigner which can be recast as: A particle is a quantum state in the (rigged) Hilbert space which carries an irreducible representation of the universal covering group of the restricted Poincare group.
 

Thread 'Two equivalent statements of time reversal symmetric Hamiltonian'

Time reversal invariant Hamiltonians must satisfy ##[H,\Theta]=0## where ##\Theta## is time reversal operator. However, in some texts (for example see Many-body Quantum Theory in Condensed Matter Physics an introduction, HENRIK BRUUS and KARSTEN FLENSBERG, Corrected version: 14 January 2016, section 7.1.4) the time reversal invariant condition is introduced as ##H=H^*##. How these two conditions are identical?
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