Tuesday, November 15, 2022

The State Of Viable Supersymmetry Parameter Spaces

There are still plenty of high energy physics theorists clinging to supersymmetry theories (a.k.a. SUSY), in part because many theorists believe that SUSY theories are necessarily the low energy approximations of all string theory vacua. In other words, if SUSY is falsified, so is string theory in the eyes of many theorists. An abstract of a report from a group of physicists trying to make the case for the continued viability of SUSY is below.

A few observations:

1. The new anomalous CDF W boson mass measurement is disfavored even in a SUSY context. Also, like most physicists advancing BSM theories, the analysis ignores the fact that the new CDF W boson mass measurement is far out of step with all of the prior W boson mass measurements around the world which also have to be explained by any theory. The only plausible explanation is that the anomalous CDF W boson mass recalculation is wrong.

A new global electroweak fit, likewise, confirms that the anomalous CDF W boson mass recalculation is completely inconsistent with all other data.

2. SUSY needs the muon g-2 anomaly to fit the data in any low energy parameter space. But, if the BMW calculations of the Standard Model value of muon g-2 and alternative calculations of the hadronic light by light contribution to muon g-2 are correct, as is increasingly appears to be the case, while the Theory Initiative "data driven" hybrid calculations of the Standard Model value of muon g-2 are wrong, then low energy SUSY simply can't be fit to the experimental data. This strongly suggests that SUSY is not "just around the corner" waiting to be discovered at a next generation higher energy particle collider.

3. Needless to say, there is no direct experimental evidence of any SUSY particles to date at the LHC or anywhere else which means that any SUSY particles have to have masses above the electroweak mass scale it was designed to address. Direct exclusions of SUSY push its particles close to and beyond the TeV scale. No version of SUSY with parameters consistent with experimental constraints solves the hierarchy "problem" that it was original devised to address.

4. A thermal freeze out scenario for SUSY dark matter candidates can produce the right amount of dark matter inferred in the universe in a dark matter particle paradigm. 

But the authors conveniently ignore that direct dark matter detection tests that basically rule out a lightest neutralino dark matter candidate, because the cross-sections of interaction with ordinary matter are weaker than they should be in a SUSY theory. The cross-section of interaction of the lightest neutralino can be calculated precisely from theory in SUSY theories and should be comparable to the cross-section of interaction of ordinary neutrinos. The direct dark matter detection experiments place constraints on the cross-section of interaction which are many orders of magnitude smaller over a very large mass range. 

Other constraints disfavor heavy thermal freeze out SUSY WIMP dark matter particle candidates, which would, among other things, lead to more galaxy scale structure in the universe than we observe.
This is a brief overview on the low energy supersymmetry in light of current experiments including the LHC searches, the dark matter (DM) detections, the muon g-2 and the CDF II measurement of the W-boson mass. We focus on the minimal framework of supersymmetry, namely the minimal supersymmetric model (MSSM), and obtain the following conclusions: (i) The MSSM can survive all current experiments, albeit suffering from the little hierarchy problem due to the heavy stops pushed up by the LHC searches; (ii) The DM relic density can be readily achieved by the thermal freeze-out of the lightest neutralino and the null results of DM direct detections are typically driving the parameter space to the bino-like lightest neutralino region; (iii) The muon g-2 anomaly reported by FNAL and BNL can be explained at 2-sigma level, which indicates light sleptons and electroweakinos possibly accessible at the HL-LHC; (iv) The CDF II measurement of the W-boson mass can be marginally explained, but requires light stops near TeV which may soon be covered by the LHC searches.
Jin Min Yang, Pengxuan Zhu, Rui Zhu, "A brief survey of low energy supersymmetry under current experiments" arXiv:2211.06686 (November 12, 2022) (Proceedings of the LHCP 2022 conference).


neo said...

what do you think is the most likely BSM particles with in the next 20 years

andrew said...


A spin-2, zero rest mass, graviton that couples proportionately to mass-energy with a coupling constant strength that is a function of Newton's constant.

neo said...

how will this be verified before 2040

andrew said...

There are a variety of proposed observational ways to identify quantum gravity which would imply a graviton mostly via premature decoherence of other otherwise quantum character interactions in stronger gravitational fields.