Muon g-2 and Dark Matter inthe MSSM
Peter CoxKavli IPMU
In collaboration with Chengcheng Han, Tsutomu T. Yanagida
arXiv:1805.02802

Muon g-2
➢Long standing discrepancy in the g-2 of the muon:[E821][Keshavarzi et. al. arXiv:1802.02995]

3.7𝜎(discrepancy of order EW contributions)➢

Factor of 4 improvement in precision expected with new experiments
at Fermilab and J-PARC

Peter Cox – Kavli IPMU

Beyond the BSM – Oct 20182g-2 in the MSSM➢

One-loop contributions from chargino-sneutrino and smuonneutralino loopsAssuming degenerate spectrum:

Need relatively light EW superpartners➢

Bino-smuon contribution enhancedby L-R smuon mixing∝ 𝜇 tan 𝛽➢

Leading 2-loop effects reduce by ~10%
Peter Cox – Kavli IPMU

Beyond the BSM – Oct 20183

Dark Matter in the MSSMWith R-parity, neutralino LSP provides a natural DM candidate

But… generic ‘well-tempered’ neutralino strongly constrained by direct detection➢Possible ways out:
• “Blind-spot” regions• Z/h/A funnel regions• h/H destructive interference➢෩ or pure 𝑊෩Other possibilities are (almost) pure 𝐻
but masses required for thermal relic density too large for g-2

Strong bounds from direct detection motivate a bino-like LSP!

Peter Cox – Kavli IPMU

Beyond the BSM – Oct 2018

4

Bino-like LSP

co-annihilation• Bino-like DM generally over abundantco-annihilations can be used to obtain correct relic abundance• LHC already suggests squarks, gluino need to be relatively heavy.
assume they play no role for DM

Leaves two scenarios to consider:➢෩ co-annihilation𝐵෨ − 𝑊➢𝐵෨ − 𝑙ሚ co-annihilation

Peter Cox – Kavli IPMU

Beyond the BSM – Oct 20185෩ co-annihilation𝐵෨ − 𝑊[Harigaya et. al. arXiv:1403.0715]•Requires small mass-splitting 𝑂(10) GeV•

Avoids DM direct/indirect detection•Dedicated LHC searches for this kind of spectrum, but bounds are weak(also indirect probes at HL-LHC, ILC)
Peter Cox – Kavli IPMU

Beyond the BSM – Oct 20186෩ co-annihilation𝐵෨ − 𝑊𝑚𝑒ǁ 𝐿,𝑅 = 𝑚𝜇෥𝐿,𝑅 [GeV]

𝑴𝟐 − 𝑴𝟏 =15 GeV

Significant regions of parameter space can be probed at (HL)-LHCPeter Cox – Kavli IPMU

Beyond the BSM – Oct 20187෩ co-annihilation𝐵෨ − 𝑊𝑚𝑒ǁ 𝐿,𝑅 = 𝑚𝜇෥𝐿,𝑅 [GeV]

𝑴𝟐 − 𝑴𝟏 =15 GeVWhat about large𝜇 tan 𝛽 ?

Significant regions of parameter space can be probed at (HL)-LHC
Peter Cox – Kavli IPMU

Beyond the BSM – Oct 20188

Large 𝜇 tan 𝛽•

Bino-smuon contribution to g-2 proportional to 𝜇 tan 𝛽•

In principle, can explain g-2 with very large smuon masses!
(eventually saturates when higher order effects included)•But, large L-R slepton mixing leads to problems with EW vacuum stability:
Upper bound on smuon mass:[Endo et. al. arXiv:1309.3065]

g-2 @ 1𝜎, 2𝜎Peter Cox – Kavli IPMU

Beyond the BSM – Oct 20189𝐵෨ − 𝑙ሚ co-annihilation•Often expect 𝜏ǁ to be NLSP, but 𝜏ǁ instability highly constrains parameter
space for g-2
I will focus on co-annihilation with 1st/2nd generation sleptons•Requires even smaller mass-splitting ≲ 10 GeV•

Very challenging spectrum to test at the LHC•

For realistic mass-splitting, bestlimits still from LEP

Peter Cox – Kavli IPMU

Beyond the BSM – Oct 201810

𝐵෨ − 𝑙ሚ co-annihilation
𝜈෤ 𝑁𝐿𝑆𝑃𝑚𝑒ǁ 𝐿,𝑅 = 𝑚𝜇෥𝐿,𝑅 [GeV]

𝑀2 = 3 TeV, 𝑀1 fixed by relic density𝜇෤ 𝑁𝐿𝑆𝑃

Most of the parameter space can be probed by direct detection (for large tan 𝛽)Peter Cox – Kavli IPMU

Beyond the BSM – Oct 201811

𝐵෨ − 𝑙ሚ co-annihilation𝑚𝑒ǁ 𝐿,𝑅 = 𝑚𝜇෥𝐿,𝑅 [GeV]

𝑀2 = 3 TeV, 𝑀1 fixed by relic density

Requires slepton masses ≲ 350 GeV
potentially within reach of a future lepton collider
Peter Cox – Kavli IPMU

Beyond the BSM – Oct 201812

High-scale models?
➢So far, only focused on low-energy MSSM…

➢Are there high-scale models that can realise the required spectra?

Peter Cox – Kavli IPMU

Beyond the BSM – Oct 201813

High-scale models?
➢So far, only focused on low-energy MSSM…

➢

Are there high-scale models that can realise the required spectra?

An example: non-universal gaugino mediation
At GUT scale: 𝑀1 , 𝑀2 , 𝑀3 , tan 𝛽, sgn(𝜇)But, issues with tachyonic slepton masses…
Introduce additional universal scalar soft mass 𝑚0( proxy for effects of B-L gaugino mediation? )Peter Cox – Kavli IPMU

Beyond the BSM – Oct 201814

Non-universal gaugino mediation
𝑀3 = 4 TeV, tan 𝛽=15[PC, Han, Yanagida, Yokozaki, preliminary]𝐵෨ − 𝜏ǁ co-annihilation

෩ co-annihilation𝐵෨ − 𝑊𝜏ǁ instabilityPeter Cox – Kavli IPMU

Beyond the BSM – Oct 201815

Non-universal gaugino mediation
𝑀3 = 4 TeV, tan 𝛽=15[PC, Han, Yanagida, Yokozaki, preliminary]
LHC slepton search𝐵෨ − 𝜏ǁ co-annihilation

෩ co-annihilation𝐵෨ − 𝑊𝜏ǁ instability

Better to consider scenarios that split the 3rd gen. sleptons
Peter Cox – Kavli IPMU

Beyond the BSM – Oct 2018

Higgs mediation?
16Summary➢

SUSY remains a well-motivated framework and can simultaneously
account for the DM density and observed discrepancy in the muon g-2➢Strong direct detection constraints motivate a bino-like LSP, with relicdensity obtained via co-annihilations➢෩ : much of the parameter space can be probed at (HL)-LHC, but𝐵෨ − 𝑊
in extreme case sleptons as heavy as 1.4 TeV➢𝐵෨ − 𝑙ሚ : significant regions will be probed by direct detection; relicdensity requires light sleptons ≲ 350 GeV, potentially within reach of afuture linear collider➢

Necessary spectrum can be obtained in high-scale models, but ideallywant to split 3rd generation sfermionsfurther model buildingPeter Cox – Kavli IPMU

Beyond the BSM – Oct 201817