Dark Matter and Electroweak Baryogenesis

DarkDark MatterMatter andand ElectroweakElectroweak BaryogenesisBaryogenesis

Rencontres de Moriond: Electroweak Interactions and Unified Theories

March 21-28, 2004

Marcela Carena

Fermilab Theoretical Physics Department Open questions in the Standard Model

• Source of Mass of fundamental particles.

• Origin of the observed asymmetry between particles and antiparticles (Baryon Asymmetry).

• Nature of the Dark Matter, contributing to most of the matter energy of the Universe.

• Quantum Gravity and Unified Interactions. Evidence for Dark Matter:

Visible stars do not account for enough mass to explain the rotation curves of galaxies v2 M(r) 1 Gravity prediction: =G ⇒ v2 ∝ r N r 2 r

Strong evidence for additional, non-luminous, source of matter:

Dark Matter

Zwicky , 1930s Cosmic Microwave Background WMAP measures the CMB and determines

Ω 2 Ω 2 M h = 0.135 ± 0.009 B h = 0.0224 ± 0.0009 h = 0.71 ± 0.04 Ω 2 = ± 0.0161 difference gives CDM energy density: CDM h 0.1126 0.0181

Possible origin of Dark Matter • Weakly interacting particles (WIMPS), with masses and interaction cross sections of order of the electroweak scale most compelling alternative • Supersymmetry, with R parity conservation naturally provides a stable, neutral, dark matter candidate: χ~0 Relic density is inversely proportional to the thermally averaged χ~ 0 χ~ 0 σ annihilation cross section v

= n s

~ 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 The Puzzle of the Matter-Antimatter asymmetry • Anti-matter is governed by the same interactions as matter. >> • Observable Universe is mostly made of matter: N B NB

• Anti-matter only seen in cosmic rays and particle physics accelerators The rate observed in cosmic rays consistent with secondary emission of antiprotons N ≈ 10 − 4 N P P Ω B Information on the baryon abundance:

• Abundance of primordial elements combined with predictions from Big Bang Nucleosynthesis: n B 421 η = γ , n γ = n cm 3 • CMBR: ρρ B ≡Ω ρ ≈ −5 2 GeV B , c 10 h 3 c cm ρ B Baryon-Antibaryon asymmetry • Baryon Number abundance is only a tiny fraction of other relativistic species η = n B = −8 Ω 2 ≈ −10 2.68 10 Bh 6 10 nγ

• In early universe B, B and γ 's were equally abundant. B, B annihilated very efficiently. No net baryon number if B would be conserved at all times. What generated the small observed baryon antibaryon asymmetry ?

Sakharov’s Requirements: = Baryon Number Violation (any B conserving process: N B N B ) ≠ C and CP Violation: (NB )L,R (NB )L,R

Departure from thermal equilibrium

All three requirements fulfilled in the SM In the SM Baryon Number conserved at classical level but violated at quantum level : ∆ B = ∆ L

Anomalous processes violate both B and L number, but preserve B-L. (Important for leptogenesis idea)

• At T = 0, Baryon number violating processes exponentially suppressed Γ ≅ π α ∆B≠0 exp(-2 / W )

• At very high temperatures they are highly unsuppressed, Γ ∝ ∆B≠0 T

• At Finite Temperature, instead, only Boltzman suppressed Γ ≅ β ∆B≠0 0 T exp(-Esph (T) /T ) ≅ π with Esph 8 v(T) / g and v(T) the Higgs v.e.v. Baryogenesis at the Electroweak Phase transition • Start with B=L=0 at T>Tc • CP violating phases create chiral baryon-antibaryon asymmetry in the symmetric phase. Sphaleron processes create net baryon asymmetry. • Net Baryon Number diffuse in the broken phase = if n B 0 at T > Tc, independently of the source of baryon asymmetry  16  E ()T  nB nB (Tc )  10  sph c  = exp− exp−  s s  Tc (GeV)  Tc  To preserve the generated baryon asymmetry:

strong first order phase transiton: > v (T c ) / T c 1 Baryon number violating processes out of equilibrium in the broken phase SM Electroweak Baryogenesis fufills the Sakharov conditions • SM Baryon number violation: Anomalous Processes • CP violation: Quark CKM mixing • Non-equilibrium: Possible at the electroweak phase transition.

Finite Temperature Higgs Potential = 2 − 2 2 + 3 +λ 4 V D(T T0 ) H ET H H E receives contributions proportional to the sum of the cube of all light boson particle couplings λ m2 v(Tc )≈ E λ ∝ H , with 2 Tc 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 ruled out! Tc • Independent Problem: not enough CP violation

Electroweak Baryogenesis in the SM is ruled out In the MSSM: • New bosonic degrees of freedom: superpartners of the top quark, ⇒ ≈ with strong couplings to the Higgs: E SUSY 8 E SM 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.

LEP Excluded

M.C, Quiros, Wagner Dark Matter and Electroweak Baryogenesis

• light right handed stop: m ~ ≈ 0 • heavy left handed stop: m~ ≥ 1 TeV U3 Q3

• values of stop mixing compatibleµ with Higgs mass constraints and with a strong first order phase transition: = β − = − X t / tan At 0.3 0.5 m ~ Q3 • the rest of the squarks, sleptons and gluinos order TeV and ≅ M2 2M1 = β = mA 500 GeV tan 10 three interesting regions with neutralino σ = 1 E - 07 σ = 1 E - 08 si si relic density compatible with WMAP obs. < Ω 2 < (green areas) 0.095 CDMh 0.129

1. neutralino-stop co-annihilation: = m 0 160 GeV χ~ mass difference about 20-30 GeV 1 140 3 120 2. s-channel neutralino annihilation via lightest CP-even Higgs = m~t 164 GeV 169 174 3. annihilation via Z boson exchange 2 µ small and M1 Balazs, MC, Wagner 04 Heavy Higgs mass Effects A,H contribute to annihilation cross section vis s-channel: m = 300 GeV •A main effect for values of neutralino mass close to stop mass, , allowed region moves away from co-annihilation to lower neutralino masses = •mA 200 GeV new resonant region due to A,H s-channel (much wider band than for h due to tan β enhanced bb couplings). Stop co-annihilation region reappears.

σ = σ = si 1 E - 07 si 1 E - 07 σ = si 1 E - 08

σ = si 1 E - 08

tan β =10 = = mA 300 GeV mA 200 GeV

• larger neutralino-proton scattering cross sections! Balazs, MC, Wagner Experimental Tests of Electroweak Baryogenesis and Dark Matter • Higgs searches: Higgs associated with electroweak symmetry breaking: SM-like. Higgs mass below 120 GeV required − 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 − Searches for a light stop at the Tevatron

Light-stop models with neutralino LSP dark matter E T signal ~ ∆ ~ ~ if t   → c χ decay mode dominant and m t χ~ < 30 GeV: trigger on E T crucial < ≤ ∆ ≥ m ~0 100 GeV and m~ 180 GeV at reach if 30 GeV χ t m~t χ~ Balazs, MC, Wagner’ ≥ ~ 04 m χ~0 120 GeV then m t out of reach

−1 • co-annihilation region not at Tevatron reach 20 fb • away from it strong dependence on the neutralino mass 4 fb−1

if m ~ > m χ ~ + m + m (3-body decay) t W b 2 fb −1 this always happens for ≈ mh m 0 (h-resonance) χ ~ 2 ~ ≥ and m t 140 GeV no reach l. c (can search for charginos in trilepton channel) x e P E L LHC: good for chargino/neutralino searches but also difficulties for stops in co-annihilation region Direct Dark Matter Detection at colliders important evidence of DM candidate, E T but, stability of LSP on DM time scales cannot be chekced at colliders

Neutralino DM is searched for in neutralino-nucleon scattering exp. detecting elastic recoil off nuclei EDELWEISS 03

CDMS L E ZEPLIN upper bounds on ~P Spin independent cross sections t excl.

σ ≈ −8 XENON Next few years: SI 10 pb σ ≈ −10 (Fiorucci’s talk) Ultimate goal: SI 10 pb

σ µ small si for large : co-annihilation and h-resonant regions Balazs, MC, Wagner ’04 Conclusions < • Supersymmetry with a light stop m stop m top and < a SM-like Higgs with mh 120 GeV opens the window for electroweak baryogenesis and allows for a new region of SUSY parameter space compatible with Dark Matter also Gaugino and higssino masses of order of the electroweak scale and moderate CP-odd Higgs mass preferred

EWBG and DM in the MSSM interesting experimental framework stop-neutralino co-annihilation challenging for hadron colliders

Tevatron: good prospects in searching for a light stop χ ± LHC: will add to these searches and explore the relevant ~ 0 / χ~ spectra Stop co-annihilation region provides motivation to search in the small ∆ regime ~ m tχ~ ∆ LC: important role in testing this scenario: small ~ and nature and m tχ~ composition of light gauginos and stop

Direct Dark Matter detection: nicely complementary to collider searches