Baryogenesis - Wikipedia, the free encyclopedia - The Diigo Meta page

• 02 Jul 12
  

  void void
  • The CPT Theorem guarantees that a particle and its antiparticle have exactly the same mass and lifetime, and exactly opposite charge. Given this symmetry, it is puzzling that the universe does not have equal amounts of matter and antimatter.
  • There are two main interpretations for this disparity: either the universe began with a small preference for matter (total baryonic number of the universe different from zero), or the universe was originally perfectly symmetric, but somehow a set of phenomena contributed to a small imbalance in favour of matter over time. The second point of view is preferred, although there is no clear experimental evidence indicating either of them to be the correct one. The preference is based on the following point of view:
  • if the universe encompasses everything (time, space, and matter), nothing exists outside of it and therefore nothing existed before it, leading to a total baryonic number of 0. From a more scientific point of view, there are reasons to expect that any initial asymmetry would be wiped out to zero during the early history of the universe.^{[citation needed]} One challenge then is to explain how the total baryonic number is not conserved.

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• 19 Jul 11
  

  dgaskey
• 04 Dec 08
  

  innovate T
  • Indeed, there is no experimental evidence that there are any significant concentrations of antimatter in the observable universe.
  • There are two main interpretations for this disparity: either when the universe began there was already a small preference for matter, with the total baryonic number of the universe different from zero (); or, the universe was originally perfectly symmetric (), but somehow a set of phenomena contributed to a small imbalance. The second point of view is preferred, although there is no clear experimental evidence indicating either of them to be the correct one.
  • From a more scientific point-of-view, there are reasons to expect that any initial asymmetry would be wiped out to zero during the early history of the universe.
  • However, the Standard Model is known to violate the conservation of baryon number non-perturbatively:
  • The challenges to the physics theories are then to explain how to produce this preference of matter over antimatter, and also the magnitude of this asymmetry. An important quantifier is the asymmetry parameter,

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• 07 Aug 08
  

  dmjacobs

  The photon density at equilibrium temperature T, per cubic kelvin and per cubic centimeter, is given by
  
  n_\gamma = \frac{1}{\pi^2} {\left(\frac{k_B T}{\hbar c}\right)}^3 \int_0^\infty \frac{x^2}{\exp(x) - 1} dx \simeq 20.3 T^3 ,

  photon density

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