It is actually called "decay width".maximdogger said:thanks ..I will look up mass width.
The mass of an "unstable particle" (or more accurately a resonance) is a well-defined number. It's given by the complex pole of its Green's function in (four-)momentum space, i.e., the real part of this pole is the mass and the imaginary part is its decay width, i.e., the inverse mean lifetime.malawi_glenn said:No idea what "when viewed" means.
There is however a concept of mass width in QFT for unstable particles.
Yup.vanhees71 said:The mass of an "unstable particle" (or more accurately a resonance) is a well-defined number. It's given by the complex pole of its Green's function in (four-)momentum space, i.e., the real part of this pole is the mass and the imaginary part is its decay width, i.e., the inverse mean lifetime.
I used that paper when I was starting my phd heheDemystifier said:No, but the mass of "unparticle" fluctuates.
https://arxiv.org/abs/0801.4471
No, a particle's rest mass is considered an intrinsic property and does not fluctuate over time. However, the effective mass can appear to change under different conditions, such as when particles are in motion or interacting with fields.
The effective mass of a particle refers to its mass as it appears in a specific context, such as within a material or under the influence of a field. This can differ from the particle's rest mass due to interactions with its environment.
Quantum fluctuations do not change a particle's rest mass. However, they can influence the energy levels and properties of particles in a way that might seem like mass fluctuation in certain scenarios, such as in virtual particles in quantum field theory.
In special relativity, the mass of a particle increases with its velocity. This is often referred to as relativistic mass. However, the rest mass, which is the mass of the particle when it is at rest, remains constant.
Interactions with fields, such as the Higgs field, can give particles mass. However, once a particle has acquired mass through such interactions, its rest mass remains constant unless it undergoes a fundamental change in its properties or identity.