Particle creation, energy density and the Compton wavelength

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SUMMARY

The Compton wavelength of a particle is defined by the equation $$\lambda=\frac{h}{mc}$$, which leads to the energy density expression $$\rho = \frac{m^4 c^5}{h^3}$$. This discussion explores the implications of this energy density, particularly regarding the spontaneous creation of particles as the Universe cools. It clarifies that while higher energy densities increase the likelihood of pair creation, particles do not spontaneously appear; rather, conditions must be favorable for such processes to occur. The discussion also highlights that the expression primarily applies to fermions, as it assumes a single particle or particle-antiparticle pair per volume of $$\lambda^3$$.

PREREQUISITES
  • Understanding of Compton wavelength and its formula
  • Familiarity with energy density concepts in particle physics
  • Knowledge of particle-antiparticle pair creation
  • Basic principles of quantum mechanics and fermions
NEXT STEPS
  • Research the implications of energy density on particle creation in quantum field theory
  • Study the role of pressure in particle-antiparticle pair production
  • Explore the relationship between mass, energy density, and the formation of massless particles like photons
  • Examine the conditions under which fermions and bosons behave differently in particle physics
USEFUL FOR

Physicists, cosmologists, and students of quantum mechanics interested in the fundamental principles of particle creation and energy density in the context of the Universe's evolution.

jcap
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The Compton wavelength of a particle is given by
$$\lambda=\frac{h}{mc}.$$
One can construct an expression for the energy density ##\rho## of a particle of mass ##m## given by
$$\rho = \frac{mc^2}{\lambda^3}=\frac{m^4 c^5}{h^3}.$$
What is the physical significance of the mass scale ##m## in the above expression?

Does it mean that particles of mass ##m## will spontaneously appear when the energy density ##\rho## reaches the relevant level as the Universe cools?

Is the expression only correct for fermions as it assumes only one particle (or more correctly one particle/antiparticle pair) per ##\lambda^3## volume?

Once the energy density ##\rho## cools to a level such that ##m## is less than the mass of any particle would one then get massless particles such as photons spontaneously produced with an energy ##h\nu=mc^2## ?
 
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jcap said:
Does it mean that particles of mass ##m## will spontaneously appear when the energy density ##\rho## reaches the relevant level as the Universe cools?
Things cannot spontaneously appear. There can be pair creation, and in general it gets more likely with higher pressure. It doesn't necessarily mean it has to happen. If we plug in 1 eV as an upper bound on neutrino masses we get 0.08 Pa, that is a good vacuum, with no process that would produce any relevant number of neutrinos if the pressure comes from air.
 

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