Is SUSY alive and well?

Transcription

1 Alessandro Strumia, talk at Is SUSY alive and well? No Madrid, September 29, 2016.

2 Was SUSY alive and well? Yes SM B, L SUSY Natural Beauty g 1 = g 2 = g 3 Dark Matter Superstring TOE

3 And for a good reason

4 R. Barbieri, G.F. Giudice / Supersymmetric particle masses lt*o0, II GeV L I~ II :,\ ----r-"._ 1988: naturalness bounds on sparticles,oooii/i,! ii -of}'!i '\ /i' Barbieri was grilling a kidney without enough fire, a student was going around excited like a stock operator, telling chargino 200! gluino 400! 700~I uevi 300 a] : I~ I~ I~ 25O m lxo) m Ix') \. 200 X.~. \ TM b) Mt, p (GeV) Fig_2. Upper bounds for A = 10 (fine ttmings of at most one order of magnitude), as functi M t "; ( I f 2 / g ) M w Y t, on the masses of: (a) gluino (g), scalar partner of the fight-handed up quark scalar partner of the right-handed electron(~r); (b) tightest neutralino (X ), tightest chargino (X Rattazzi expressed doubts but Barbieri said bischero this a delicacy, eat it. So it tasted weird, but my advisor thought it was gourmet, I ate it. dimension of mass and A, B dimensionless. These parameters play the role of t introduced in the previous section.

5 1990: LEP1 data speak Neutralino was synonymous of Dark Matter

6 1998: SK, LEP and cosmology speak SUSY needs Z 2,3 and universal m to get B, L, L i that come for free in the SM. Even so, if m M Z, p decay at dimension 5 is problematic in minimal SU(5). LEP2 experiments pose a serious naturalness problem for supersymmetric models. [hep-ph/ ]. About 95% of CMSSM parameter space is excluded i.e. [hep-ph/ ] p(no SUSY at LEP CMSSM) = 5% FT = Bayesian probability of numerical accidents. The well known naturalness problem of the Fermi scale has gained a pure low energy aspect. The cosmological constant poses another serious unsolved problem, also related to power divergences. [hep-ph/ ]

7 The CMSSM Use dimension-less ratios as parameters and fix the SUSY scale from M 3 MZ 2 0.2m M 3 2 2µ2 = (91 GeV) 2 ( 110 GeV )2 + β = = /μ = / /μ = Main worry: so many sparticles at LHC that disentangling them will be hard.

8 2010: LHC data speak % σ / gluino mass in GeV allowed excluded by LHC excluded by LEP 30 10

9 The CMSSM β = = = /μ / /μ = Survives only only close to the critical line v = 0 Even one loop stop corrections start to be unnaturally big.

10 LHC data speak badly about SUSY (Same message to workers on naturalness, diphoton...)

11 Dark Matter? Thermal abundance: ΩDMh2 σv = pb The CMSSM bulk region where σv e4/4π m 2 needs m 150 GeV. Excluded in the CMSSM. Dissecting the spherical cow, what remains is fine-tuned tails σ β - β - ℓ - - ν - and Minimal Dark Matter limit: higgsino at 1.1 TeV, wino at 2.5 TeV...

12 Higgs at 125 GeV? The MSSM prediction for λ i.e. M h can now be computed in a simpler way: 1) Weak scale: SM at 2 loops; 2) 3 loop RGE running up to m; 3) λ = 8 1 g2 c 2 2β loop SUSY. Sparticle corrections to y t, g 3 can be neglected. Higgs mass in GeV Quasi natural SUSY, tanβ 20 SUSY thresholds at 2 QCD loops SUSY thresholds at 1 loop Maximal stop mixing exp Minimal stop mixing Result: predicted M h gets lower 115 and more precise, δm h 1 GeV Multi-TeV stop, huger tuning Degenerate SUSY scale in TeV

13 Options: USUSY or USUSY U Ugly Unnatural m TeV TeV Naturalness Bad No Higgs mass Bad Good Dark Matter Bad Good Unification Bad Good Flavour Bad Good Models Bad Good TeV signals Yes No Makes sense? Bah An***pic? Higgs mass m h in GeV tanβ 50 tanβ 4 tanβ 2 tanβ 1 Split SUSY High Scale SUSY Experimentally favored For example mini-split: m 4πM 1,2,3 with H or W as Minimal DM.

14 Does Unnatural SUSY make sense? Does the anthropic multiverse justify Unnatural SUSY? m p M Pl allows systems with N M 3 Pl /m3 p 1 particles. y d v α em Λ QCD allows chemistry. But natural solutions exist, difficult to argue that multiverse avoids them. If we live in a multiverse with many low-energy SUSY vacua, the likely outcome is again natural SUSY with m M Z (e.g. mini-split SUSY with M 3 m p ). If we live in a multiverse with many Planck-scale SUSY vacua, the likely lowenergy physics is an anthropically acceptable alternative to the SM that does not involve an unnaturally light Higgs scalar; or (even within the Standard Model) a smaller y or a smaller M Pl. To argue differently one needs to add ad hoc counting or DM restrictions. Keep searching alternatives to anthropic nirvana

15 Subtle is the Lord What is going on? We are confused but nature is surely following some logic

16 Data speak and tell Standardissimo Model We now have all SM parameters, let s assume SM and see what happens y t g 3 Facts: 1: SM can be extrapolated above M Pl. 2: λ(m Pl ) 0 at 2σ. 3: β(λ) vanishes around M Pl. SM couplings y b g 2 g 1 m in TeV Λ

17 Scalarphobic vs scalarfriendly Scalarphobic theorists believe that scalars are unnatural because δm h g SM Λ. But power divergences give no physical effect. In quantum mechanics it s better to stick to observables, without adding realism. Maybe scalarphobic theorists over-interpret equations, as happened with the æther: wave medium. Scalarfriendly theorists can try new roads: Finite naturalness. Upper bounds on new physics from naturalness of physical corrections: δm h g new M new at 1/2/3 loops. Allows SM + DM + neutrino masses + baryogenesis + inflation + axions. No GUT, no string. Dynamical generation of the weak scale. de E = 0 if physics is dimensionless. Simple models where a vev (λ < 0) or a condensate (g ) generates M h and DM. Even models with 0 new parameters: predict m 2 h < 0, M DM, Ω DM. Gravity: δm h E 2 /M Pl : natural at E < Mh M Pl. New physics there could be the spin 2 negative-norm (?) graviton of agravity = dimension-less renormalizable gravity, where δm h g 2 gravity M Pl. Dynamical generation of the Planck scale.

18 Inflation. Dimension-less theories allow super- Planckian vevs and give quasi-flat potentials: ɛ, η β, P R M h / M Pl. Total Asymptotic Freedom. Theories valid up to infinite energy with all couplings g, y, λ flowing to zero. No cut-off, predictions, e.g. g Y = 0, M t = 186 GeV, M τ = 0 in the SM. Weak-scale extensions of the SM into SU(3) 3. Fundamental models of composite Higgs Tensor scalar ratio r Predictions of agravity inflation Ξ S 0.1,1,10 N 50 N 60 Spectral index n s 68,95 C.L. Tony Gherghetta said: Wow! Better than Trump! But: cosmological constant? U(3) 5 U(1) B,Li suggests some unification.

19 Is SUSY well? No Giving up naturalness maybe better than giving up the rest SM B, L, flavour λ, β λ 0 around M Pl Data SUSY Beauty g 1 = g 2 = g 3 Minimal Dark Matter Multiverse TOA?

20 Is SUSY popular? Yes

21 Is SUSY alive? Ibis redibis non morieris in bello