[Jlab-seminars] Theory Center Seminar

[Mary Fox]

Theory Center Seminar
Mon., Feb. 11, 2013
1:00 p.m. (coffee at 12:45 p.m.)
CEBAF Center, Room F113


Andre Walker-Loud
University of Washington, Seattle

*M_n - M_p *

Our understanding of the formation of light nuclei in the early 
universe, known as Big Bang Nucleosynthesis, is now a precision science. 
For example, given the baryon to photon ratio determined from the Cosmic 
Microwave Background, the mass fraction of He(4) in the early universe 
is predicted with 0.1% precision. The predicted abundances of the 
primordial nuclei match well with astrophysical observations in all 
cases except Li(7). The resulting picture is highly constraining on 
possible physics beyond the Standard Model, one such example being the 
time-variation of fundamental constants.

Big Bang Nucleosynthesis is most sensitive to the neutron-proton mass 
splitting as this quantity controls the initial ratio of neutrons to 
protons and also impacts the neutron lifetime. There are two sources of 
isospin violation in the Standard Model which give rise to the 
neutron-proton mass spitting: the masses of the up and down quarks and 
their electromagnetic couplings. The electromagnetic correction can be 
determined via contour integrals and the experimentally measured elastic 
and inelastic structure functions of the nucleons. The contribution from 
the down-quark up-quark mass splitting can only be determined with 
lattice QCD. I will describe in detail our understanding of these two 
contributions and summarize with implied constraints from primordial 
nucleosynthesis.
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