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Register a new userThe new MUON G-2 Result and Supersymmetry
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The electroweak (EW) sector of the Minimal Supersymmetric Standard Model (MSSM), with the lightest neutralino as Dark Matter (DM) candidate, can account for a variety of experimental data. This includes the DM content of the universe, DM direct detection limits, EW SUSY searches at the LHC and in particular the so far persistent $3-4,sigma$ discrepancy between the experimental result for the anomalous magnetic moment of the muon, $(g-2)_mu$, and its Standard Model (SM) prediction. The recently published ``MUON G-2 result is within $0.8,sigma$ in agreement with the older BNL result on $(g-2)_mu$. The combination of the two results was given as $a_mu^{rm exp} = (11 659206.1 pm 4.1c) times 10^{-10}$, yielding a new deviation from the SM prediction of $Delta a_mu = (25.1 pm 5.9) times 10^{-10}$, corresponding to $4.2,sigma$. Using this improved bound we update the results presented in [1] and set new upper limits on the allowed parameters space of the EW sector of the MSSM. We find that with the new $(g-2)_mu$ result the upper limits on the (next-to-) lightest SUSY particle are in the same ballpark as previously, yielding updated upper limits on these masses of $sim 600$ GeV. In this way, a clear target is confirmed for future (HL-)LHC EW searches, as well as for future high-energy $e^+e^-$ colliders, such as the ILC or CLIC.
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A new measurement of the muon anomalous magnetic moment has been recently reported by the Fermilab Muon g-2 collaboration and shows a $4.2,sigma$ departure from the most precise and reliable calculation of this quantity in the Standard Model. Assuming that this discrepancy is due to new physics, we consider its relation with other potential anomalies, especially in the muon sector, as well as clues from the early universe. We comment on new physics solutions discussed extensively in the literature in the past decades, to finally concentrate on a simple supersymmetric model that also provides a dark matter explanation. We show results for an interesting region of supersymmetric parameter space that can be probed at the high luminosity LHC and future colliders, while leading to values of ($g_mu-2$) consistent with the Fermilab and Brookhaven ($g_mu-2$) measurements. Such a parameter region can simultaneously realize a Bino-like dark matter candidate compatible with direct detection constraints for small to moderate values of the Higgsino mass parameter $|mu|$.
The inverse seesaw mechanism has been claimed to be consistent with existing bounds while accommodating the muon anomalous magnetic moment (g-2). We revisit this idea and review the importance of nonunitarity bounds over the inverse seesaw mechanism, either in the canonical version or when it is embedded in extended gauge theories. We show that, when nonunitarity constraints are brought into place, the inverse seesaw mechanism fails to accommodate the g-2 anomaly.
After a brief review of the muon g-2 status, we discuss hypothetical errors in the Standard Model prediction that could explain the present discrepancy with the experimental value. None of them looks likely. In particular, an hypothetical increase of the hadroproduction cross section in low-energy e^+e^- collisions could bridge the muon g-2 discrepancy, but is shown to be unlikely in view of current experimental error estimates. If, nonetheless, this turns out to be the explanation of the discrepancy, then the 95% CL upper bound on the Higgs boson mass is reduced to about 130 GeV which, in conjunction with the experimental 114.4 GeV 95% CL lower bound, leaves a narrow window for the mass of this fundamental particle.
Using the approach based on Bogoliubov compensation principle is applied to calculation of a contribution to the muon $g-2$. Using the previous results on spontaneous generation of the effective anomalous three-boson interaction we calculate the contribution, which proves to agree with the well-known discrepancy. The calculated quantity contains no adjusting parameters but the experimental values for the muon and the W-boson masses. The result can be considered as a confirmation of the approach.
Precision measurements of fundamental quantities have played a key role in pointing the way forward in developing our understanding of the universe. Though the enormously successful Standard Model (SM) describes the breadth of both historical and modern experimental particle physics data, it is necessarily incomplete. The muon $g-2$ experiment executed at Brookhaven concluded in 2001 and measured a discrepancy of more than three standard deviations compared to the Standard Model calculation. Arguably, this remains the strongest hint of physics beyond the SM. A new initiative at Fermilab is under construction to improve the experimental accuracy four-fold. The current status is presented here.
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