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Supersymmetry, the Baryon Asymmetyry and the Origin of Mass

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Supersymmetry, the Baryon Asymmetyry and the Origin of Mass BaryogenesisBaryogenesis andand NewNew PhysicsPhysics atat thethe WeakWeak ScaleScale C.E.M. Wagner Argonne National Laboratory EFI, University of Chicago SLAC Summer Institute, SLAC, August 11, 2004 TheThe PuzzlePuzzle ofof thethe MatterMatter--AntimatterAntimatter asymmetryasymmetry Anti-matter is governed by the same interactions as matter. Observable Universe is composed of matter. Anti-matter is only seen in cosmic rays and particle physics accelerators The rate observed in cosmic rays consistent with secondary emission of antiprotons n P ≈ 10 − 4 n P BaryonBaryon--AntibaryonAntibaryon asymmetryasymmetry Baryon Number abundance is only a tiny fraction of other relativistic species n B ≈ 6 10−10 nγ But in early universe baryons, antibaryons and photons were equally abundant. What explains the above ratio ? Explanation: Baryons and Antibaryons annihilated very efficiently. No net baryon number if B would be conserved at all times. What generated the small observed baryon-antibaryon asymmetry ? ElectroweakElectroweak BaryogenesisBaryogenesis ElectroweakElectroweak BaryogenesisBaryogenesis inin thethe StandardStandard ModelModel SM fufills the Sakharov conditions: Baryon number violation: Anomalous Processes CP violation: Quark CKM mixing Non-equilibrium: Possible at the electroweak phase transition. BaryonBaryon NumberNumber ViolationViolation atat finitefinite TT At zero T baryon number violating processes highly suppressed At finite T, only Boltzman suppression ⎛ E ⎞ 8π v ⎜ sph ⎟ E ∝ Γ(∆B≠0)∝AT exp⎜− ⎟ sph g ⎝ T ⎠ Baryon Number violating processes unsuppressed at high temperatures, but suppressed at temperatures below the electroweak phase transition. Anomalous processes violate both baryon and lepton number, but preserve B – L. Relevant for the explanation of the Universe baryon asymmetry. BaryonBaryon NumberNumber GenerationGeneration From weak scale mass particle decay: Difficult, since non-equilibrium condition is satisfied for small couplings, for which CP- violating effects become small (example: resonant leptogenesis). Baryon number violating processes out of equilibrium in the broken phase if phase transition is sufficiently strongly first order : Baryon asymmetry generation at the electroweak phase transition (Electroweak Baryogenesis). BaryonBaryon AsymmetryAsymmetry PreservationPreservation If Baryon number generated at the electroweak phase transition, n n (T ) ⎛ 1016 ⎛ E (T )⎞ ⎞ B B c ⎜ ⎜ sph c ⎟ ⎟ = exp ⎜ − exp ⎜ − ⎟ ⎟ s s ⎝ Tc (GeV) ⎝ Tc ⎠ ⎠ Baryon number erased unless the baryon number violating processes are out of equilibrium in the broken phase. Therefore, to preserve the baryon asymmetry, a strongly first order phase transition is necessary: v(T ) c > 1 Tc ElectroweakElectroweak PhasePhase TransitionTransition Higgs Potential Evolution in the case of a first order Phase Transition v(Tc ) FiniteFinite TemperatureTemperature HiggsHiggs PotentialPotential D receives contributions at one-loop proportional to the sum of the couplings of all bosons and fermions squared, and is responsible for the phenomenon of symmetry restoration E receives contributions proportional to the sum of the cube of all light boson particle couplings m2 v(Tc ) E H ≈ , with λ ∝ 2 Tc λ v Since in the SM the only bosons are the gauge bosons, and the quartic coupling is proportional to the square of the Higgs mass, v(Tc ) > 1 implies mH < 40 GeV. Tc If the Higgs Boson is created , it will decay rapidly into other particles At LEP energies mainly into pairs of b quarks One detects the decay products of the Higgs and the Z bosons LEP Run is over • No Higgs seen with a mass below 114 GeV • But, tantalizing hint of a Higgs with mass about 115 -- 116 GeV (just at the edge of LEP reach) Electroweak Baryogenesis in the SM is ruled out ElectroweakElectroweak BaryogenesisBaryogenesis andand NewNew PhysicsPhysics atat thethe WeakWeak ScaleScale Supersymmetry fermionsfermions bosonsbosons electronelectron sselectronelectron quarkquark ssquarkquark photphotinoino photonphoton gravitgravitinoino gravitongraviton Photino, Zino and Neutral Higgsino: Neutralinos Charged Wino, charged Higgsino: Charginos Particles and Sparticles share the same couplings to the Higgs. Two superpartners of the two quarks (one for each chirality) couple strongly to the Higgs with a Yukawa coupling of order one (same as the top-quark Yukawa coupling) WhyWhy SupersymmetrySupersymmetry ?? Helps to stabilize the weak scale—Planck scale hierarchy Supersymmetry algebra contains the generator of space-time translations. Necessary ingredient of theory of quantum gravity. Minimal supersymmetric extension of the SM : Leads to Unification of gauge couplings. Starting from positive masses at high energies, electroweak symmetry breaking is induced radiatively. 3B+L+2S If discrete symmetry, P = (-1) is imposed, lightest SUSY particle neutral and stable: Excellent candidate for cold Dark Matter. Supersymmetry at colliders Gluino production and decay: Missing Energy Signature Supersymmetric Particles tend to be heavier if they ~χ 0 carry color charges. 1 Particles with large Yukawas tend to be lighter. ~χ 0 Charge-less particles 1 tend to be the lightest ones. ¾ Lightest supersymmetric particle = Excellent Cold dark matter candidate. PreservationPreservation ofof thethe BaryonBaryon AsymmetryAsymmetry EW Baryogenesis requires new boson degrees of freedom with strong couplings to the Higgs. Supersymmetry provides a natural framework for this scenario. Relevant SUSY particle: Superpartner of the top Each stop has six degrees of freedom (3 of color, two of charge) and coupling of order one to the Higgs g 3 h 3 E = w + t ≈ 8 E SUSY 4π 2π SM m2 v(Tc ) E H Since ≈ , with λ ∝ 2 Tc λ v Higgs masses up to 120 GeV may be accomodated ConstraintsConstraints onon thethe StopStop SectorSector The top quark has two supersymmetric partners, one for each chirality (left and right). One of the stops has to be light, in order to make the phase transitioin strongly first order Second stop needs to be heavier than about 1 TeV in order to make the Higgs mass larger than the current bound, of about 114 GeV. Upper bound on the Higgs imposed by the requirement of the preservation of the baryon asymmetry. LightLight Stops:Stops: MotivationMotivation In low energy supersymmetry models, light stops are induced as a consequence of large mixing or large negative radiative effects. They are required for the realization of the mechanism of electroweak baryogenesis in the MSSM Signatures of a light stop at the Tevatron collider depend strongly on the chargino and neutralino spectrum as well as on the nature of supersymmetry breaking StopStop massmass matrixmatrix Radiative corrections affect mostly the hierarchy of diagonal masses in stop mass matrix 2 2 ⎡mQ + mt mt (At − µ cotanβ )⎤ M 2 = ⎢ ⎥ 2 2 ⎣⎢mt (At − µ cotanβ ) mU + mt ⎦⎥ Stop mixing induced by off-diagonal elements in stop mass matrix In supersymmetric theories, two Higgs doublet superfields necessary to cancel anomalies and give masses to all fermions v 2 tanβ = with v i the v..e v.of the twoHiggsfields v1 HiggsHiggs andand StopStop MassesMasses MSSM: Limits on the Stop and Higgs Masses to preserve the baryon asymmetry Suficciently strong first order phase transition to preserve generated baryon asymmetry: • Higgs masses up to 120 GeV • The lightest stop must have a mass below the top quark mass. Moderate values of tanβ, tanβ ≥ 5 preferred in order to raise the Higgs LEP Excluded boson mass. M. Carena, M. Quiros, C.W. ExperimentalExperimental TestsTests ofof ElectroweakElectroweak BaryogenesisBaryogenesis inin thethe MSSMMSSM Experimental Tests of Electroweak Baryogenesis and Dark Matter • Higgs searches beyond LEP: 1. Tevatron collider may test this possibility: 3 sigma evidence with about 4 fb−1 Discovery quite challenging, detecting a signal will mean that the Higgs has relevant strong (SM-like) couplings to W and Z Maximal mixing scenario 2. A definitive test of this scenario will come at the LHC with the first 30 fb − 1 of data qq → qqV*V* → qqh with h →τ +τ − TevatronTevatron StopStop ReachReach whenwhen twotwo bodybody decaydecay channelchannel isis dominantdominant Main signature: 2 or more jets plus missing energy 2 or more Jets with ET > 15 GeV Missing ET > 35 GeV Demina, Lykken, Matchev,Nomerotsky ‘99 StopStop--NeutralinoNeutralino MassMass Difference:Difference: InformationInformation fromfrom thethe CosmosCosmos If the neutralino provides the observed dark matter relic density, then it must be stable and lighter than the light stop. Relic density is inversely proportional to the neutralino annihilation cross section. If only stops, charginos and neutralinos are light, there are three main annihilation channels: 1. Coannihilation of neutralino with light stop or charginos: Small mass differences. 2. s-channel annihilation via light CP-even Higgs boson 3. s-channel annihilation via heavy CP-even Higgs boson and CP-odd Higgs boson Relic density is inversely proportional to the thermally averaged ~ 0 ~ 0 χ χ annihilation cross section σ v ~ 0 χ f h,H,A,Z χ~ 0 f If any other SUSY particle has mass close to the neutralino LSP, it may substantially affect the relic density via co-annihilation χ~ 0 χ~0 w w if stops NLSP t χ~ + neutralino-stop ~ t b ~ co-annihilation t b RelicRelic DensityDensity valuesvalues (WMAP)(WMAP) hh=0.71=0.71±±0.040.04 2 ΩΩMhh =0.135=0.135±±0.0090.009 2 ΩΩBhh =0.0224=0.0224±±0.00090.0009 ΩΩtot=1.02=1.02±±0.020.02 DarkDark MatterMatter andand ElectroweakElectroweak BaryogenesisBaryogenesis
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