Loss of precision in SQME
Affects | Status | Importance | Assigned to | Milestone | |
---|---|---|---|---|---|
CalcHEP |
New
|
Undecided
|
Unassigned |
Bug Description
I'm encountering an error message while running n_calchep for a very simple model in which a Z' couples to first generation leptons (with purely vectorial couplings) and to a dirac dark matter candidate (with purely vectorial couplings). When the ratio of the dark matter coupling to standard model coupling is large (ie one has a dark sector-like model), and when the Z' mass is less than about 2 \times 10^3 M_{dark matter} (for example, take the dark matter mass of 3 TeV, the Z' mass of 0.1 GeV, dark matter couplings of 1, and SM couplings of 0.1), I find an error in the calculation of the cross section, with the error message reading 'Lost of precision in SQME'. I've tried adjusting things like the precision of the calculation, and I've tested this with 3 different model files (written by 3 different individuals).
Have you encountered a problem like this before, and if so is there an easy fix?
Thank you!
Dear Sam Witte.
Thank you for your mail.
I'll try to use your example to generate error message in next version
of micrOMEGAs.
I guess the problem is caused by unitary gauge of Z' vector field. We
have lost of precision because diagram cancellation.
Because your Z' interacts only with conserved current, you can treat it
in Feynman gauge without auxiliary ghosts. Just write symbol G in
'aux' field in particle table. and call 'make' before next launch of
micrOMEGAs main.
Other solution which increases energy limit is the usage of other
types of real numbers.
You can open file CalcHEP_ src/include/ nTypes. h and comment out one of
lines
//#define _LONG_ to use long double type in numerical calculations
//#define _QUAD16_ to use quadrouple precision for icc compiler.
In the second case you will need icc compiler. Use "make clean" and
"make" for all micrOMEGAs package after correction of nTypes.h.
But this solutions are temporal. At larger rate Mcd/mZ' you again will
meet a problem with precision. The best way is to declare Z' as a gouge
particle.
Best
Alexander Pukhov
On 03.03.2019 13:12, Sam Witte wrote:
> Public bug reported:
>
> I'm encountering an error message while running n_calchep for a very
> simple model in which a Z' couples to first generation leptons (with
> purely vectorial couplings) and to a dirac dark matter candidate (with
> purely vectorial couplings). When the ratio of the dark matter coupling
> to standard model coupling is large (ie one has a dark sector-like
> model), and when the Z' mass is less than about 2 \times 10^3 M_{dark
> matter} (for example, take the dark matter mass of 3 TeV, the Z' mass of
> 0.1 GeV, dark matter couplings of 1, and SM couplings of 0.1), I find an
> error in the calculation of the cross section, with the error message
> reading 'Lost of precision in SQME'. I've tried adjusting things like
> the precision of the calculation, and I've tested this with 3 different
> model files (written by 3 different individuals).
>
> Have you encountered a problem like this before, and if so is there an
> easy fix?
>
> Thank you!
>
> ** Affects: calchep
> Importance: Undecided
> Status: New
>