![]() © Claude Paris (2008) |
Laurent LellouchCNRS Research DirectorCentre de Physique
Théorique Ph: +33/0 491 26 95 17 |
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Ab initio calculation of the neutron-proton mass difference |
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This
figure shows how the neutron-proton
mass difference depends on two combinations of fundamental parameters.
On the horizontal axis, the fine structure constant, proportional to
the square of the elementary unit of charge is varied from zero to
twice its measured value. Along the vertical axis, it is the difference
in mass between down and up quarks that is varied. The blue cross
indicates the point corresponding to our universe. The black curves
correspond to contours of constant neutron-proton mass difference. Each
has a label indicating the value of the neutron-proton mass
difference to which it corresponds. Any point in the blue region
corresponds to a very different universe from ours, in which the proton
could decay into a neutron through the weak interaction. Units are
mega-electron-volts (MeV). The mass of a hydrogen atom is approximately
1000 MeV. |