Lightest, SM-like Z mass always fixed

[charlie]

Hi,

In a model with gauge group SU(2)R x SU(2)L x U1(X) I am struggling to get the variations of the W and Z SM-like masses in terms of the new gauge coupling gR and the vev vR of a bidoublet scalar that breaks both SU(2)s.

I can reproduce the SPheno output with the SARAH analytical eigenvalues for W' and Z', which both vary in the (gR,vR) plane, however the masses of W and Z always stay fixed at the values 80.385 and 91.1876 even if I explicitly state

Mass -> LesHouches or Mass -> Automatic

in particles.m. Is SPheno forcing the SM-like gauge boson masses to be those derived from the numbers in the SMINPUTS block? What is the strategy to get the lightest MZ and MW, does it require to trade the set of free parameters (alpha,GF,MZ) for an equivalent set where MZ is free?

[FStaub]

Hi,

the SPheno output contains for the known SM particles the measured pole masses. That means, the calculated masses are overwritten. The simple reason is that SPheno doesn't provide the necessary higher-order corrections to the SM gauge bosons (two-loop and higher) to obtain values which are in agreement with the experimental values. Thus, to prevent confusion, the measured values are printed.
If you need the calculated values, you need to do some hacking. For instance, by commenting out these lines in LoopMasses_MODEL.f90

! Set pole masses
MVWm = mW
MVWm2 = mW2
MVZ = mZ
MVZ2 = mZ2
MFe(1:3) = mf_l
MFe2(1:3) = mf_l**2
MFu(1:3) = mf_u
MFu2(1:3) = mf_u**2
MFd(1:3) = mf_d
MFd2(1:3) = mf_d**2

Cheers,
Florian

[charlie]

Your suggestion is very helpful. Thanks Florian