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Sven Heinemeyer - EWPO and BSM
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main idea: take precision data and compare with theory (SM, BSM, EFT)
test of theory at quantum level: sensitivity to loop corrections
need very accurate measurements and theory predictions: only models ready are SM, MSSM, and maybe pure Higgs extensions
classical EWPO:
mW
hadronic cross sections
Z width
ratio of leptonic channels
ration of b, c channels
AFB
ALR
mixing angle
more possible EWPO:
anomalous magnetic moment of muon
Higgs boson mass (if it is not a free parameter!)
new SM and BSM couplings
evaluation of classical EWPO
mW: evaluate loop corrections from mu decay (Ayres world expert in these calculations)
one-loop results in SM: remaining term containing Higgs component
effective mixing angle
EWPO in BSM
note: best worked out model is SM
table with experimental and intrinsic uncertainties
intrinsic uncertainties << experimental uncertainties only in SM
question is: which BSM sufficiently worked out? i.e., which satisfy:
several/all EWPO available at full one-loop
at best: leading 2-loop
uncertainty estimate available
MSSM: rough uncertainty available; all EWPO at full 1-loop, some at 2-loop
NMSSML no uncertainty estimate
xSM (SM w/ 1 singlet extension): only S, T, U at 1-loop, no uncertainty
2HDM: S, T, U only at 1 loop, T at 2-loop, no uncertainty
pure Higgs sector extensions: S, T, U probably sufficient (new physics comes in only in boson propagator); no uncertainties?
better overview necessary! (LOI submitted)
what BSM have been worked out and to what extent?
uncertainty estimates?
what possible predictions on other parts of BSM spectrum?
are there patterns arising?
EWPO in MSSM
(urge to repeat exercise on favorite BSM theory)
differences in MSSM vs SM:
new contributions from SUSY particles (e.g., loops)
CPV effects via new CPV phases
large Yukawa corrections
large corrections from b/sb sector
non-decoupling SUSY effects
corrections to many observables can be approximated via rho parameter: relative strength between neutral current and charged current interactions
delta-rho is difference between Z and W current w/ 0 momentum transfer divided by EWK boson mass square
delta-rho gives main contribution to correction to EW observables
SM results: full 1-, 2-loop, 3- and 4-loop leading via delta-rho
MSSM: full 1-loop, 2-loop via delta-rho
note: delta-rho does not contain effects from sleptons, charginos, neutralinos
there are examples of non-negligible non-delta-rho 1-loop effects (in other words, rho does not contain all effects)
example: prediction for mW and effective mixing angle in SM and MSSM
one example MSSM scenario
look at plot of mW vs mtop, show effects not captured by rho and delta-rho, must do explicit calculation
see area allowed by LHC searches and compatible with MSSM
example: effects of stop
example: another MSSM scenario
assume light stop, and precise mW measurement
see that one can constrain spectrum by measuring precisely mW (need <5MeV precision here)
one can get limits on stop and sbottom with this
why not just look at EFT?
shortcomings:
- all BSM assumed to be very heavy, out of direct reach of current and future colliders
- if one finds large effects in EFT predictions, not clear whether it can be reproduced by any real model
- EFTs leave unclear what is underlying real model to which each effects correspond
let us assume we see deviations from SM
need to compare with _predicted_ deviations in _concrete_ models
need a mapping from concrete models to EFT
for this, need sufficiently precise predictions in BSM models, including uncertainty estimations
ideally: would like analysis of patterns of deviations
conclusion:
EWPO powerful tool: top and Higgs masses predicted correctly within SM
current predictions of EWPO in SM under control, not so much in BSM: better overview needed for Snowmass 2021
MSSM used as showcase in presentation: sufficiently worked out, possible clear patterns, but delta-rho not enough to cover all possible effects
assuming we will see effects, need mapping from EFT to models
Tania: did calculation on mW in 2HDM, very strong constraint obtained; also in xSM, no strong constraints derived; did not try uncertainty estimation
(https://arxiv.org/abs/1406.1043)
Ayres: for 2HDM there are also other corrections
about criticism on EFT: true needed model-by-model matching; calculation of observables is much more work
experimentalists can fit data with EFT, once and for all
theorist comes up with new model which solves some more deviations, then one can check Wilson coefficients (at hand, at that point)
moving out of S, T, U era,
A: EFT great, but if interested in underlying physics, must do mapping
renormalization then problem: it is there for EWPO in SM, need to check w/ BSM
Ayres: are there regions in parameter space in which EFT fails?
particles with 100GeV mass in loops, EFT works
for EWPO and Higgs, if one has 100GeV particle in masses, EFT works (threshold is 200GeV)
could have uncertainty of 20% for not including HO operators, but ok for comparison with measurements
at LHC, need to worry about unitarity breakdown
A: if want to see how things play together
need to demonstrate in concrete model that EFT breaks down in parameter space that LHC can reach
this would be important, to do for a few example models
would be important to make a concrete statement
A: LHC can cover 500-600GeV mass range, important for precision measurements (that can be done there?)
g-2 result important in this regime
Junping: slide 17/18: required precision on mW is 5MeV; how much below really required? future colliders may get in that ball park
A: ILC talking about 2-3MeV; FCC-ee go below... 5MeV was reported, in those days, as possible LHC result
current experimental is 12MeV, and theory 4MeV
manpower quite limited! could get down to 1MeV, but not enough people (now: Janos and Ayres!)
Junping: parametric uncertainty from top large, indication that important to have future e+e- colliders with ECM>= 350 GeV...
A: indeed, need e+e- precision to lock top mass
Junping: planning to organize LOI on mapping EFT to concrete models?
A: hope to get better overview, others experts in 2HDM, xSM... look for patterns is important
Tania: think I heard talk about how well EFT fits concrete models, probably in Higgs, but not in context of EWPO
people are looking at this mapping (https://arxiv.org/abs/2007.01296)
William Sheperd: really need 1-loop for EFT
Rg effects are important
Tania: https://arxiv.org/abs/1211.0311
this is singlet (first) and 2hdm
for the 2 real singlet i have it as well (the code), and we also did an uncertainty estimate... i have it somewhere in my private notes