What Is The Strong CP Problem
1
The Strong CP Problem Johar M. Ashfaque The SU (3) gauge theory allows a CP-violating interaction of the form L CP = θα s 32π 2 ˜ G μν G μν to be added to the QCD Lagrangian which contributes to the neutron electric dipole moment (nEDM). Note. G μν is the gluon field strength and ˜ G μν is its dual. Note. θ ≡ θ QCD + arg det Y u Y d is the strong CP phase with Y u,d being the up and down yukawas respectively. The idea behind axions is to add fields to the Standard Model so that there is a new anomalous U (1) symmetry which is known as a Peccei-Quinn symmetry. If this U (1) PQ is spontaneously broken, it will generate a new Goldstone boson, the pseudo-Goldstone boson, a. The current bound on the neutron EDM is |d N | < 2.9 × 10 -26 e cm so that | θ| < 10 -10 which is a strikingly small value for a dimensionless natural constant given that the CP violating phase in the CKM matrix is of order one. This smallness of θ despite the large amount of CP violation in the weak sector is known as the strong CP problem. 1
-
Upload
johar-m-ashfaque -
Category
Documents
-
view
14 -
download
5
Transcript of What Is The Strong CP Problem
The Strong CP Problem
Johar M. Ashfaque
The SU(3) gauge theory allows a CP-violating interaction of the form
LCP =θαs
32π2G̃µνG
µν
to be added to the QCD Lagrangian which contributes to the neutron electric dipole moment (nEDM).
Note. Gµν is the gluon field strength and G̃µν is its dual.
Note.
θ ≡ θQCD + arg detYuYd
is the strong CP phase with Yu,d being the up and down yukawas respectively.
The idea behind axions is to add fields to the Standard Model so that there is a new anomalous U(1)symmetry which is known as a Peccei-Quinn symmetry. If this U(1)PQ is spontaneously broken, it willgenerate a new Goldstone boson, the pseudo-Goldstone boson, a.
The current bound on the neutron EDM is
|dN | < 2.9× 10−26e cm
so that|θ| < 10−10
which is a strikingly small value for a dimensionless natural constant given that the CP violating phasein the CKM matrix is of order one. This smallness of θ despite the large amount of CP violation in theweak sector is known as the strong CP problem.
1
