Electroweak Baryogenesis in the LHC era

Transcription

1 Electroweak Baryogenesis in the LHC era Sean Tulin (Caltech) In collaboration with: Michael Ramsey-Musolf Dan Chung Christopher Lee Vincenzo Cirigliano Bjorn Gabrecht Shin ichiro ichiro Ando Stefano Profumo

2 Summary of this talk 1. Review the basic picture of electroweak baryogenesis (EWB) 2. EWB doesn t t work in the Standard Model 3. EWB in the MSSM is almost ruled out likely to be excluded at LHC and next gen EDM searches 4. What next? Next-to to-minimal supersymmetric standard model (It may be ugly/messy, but at least its testable.)

3 Supersymmetry is super-great! The minimal supersymmetric standard model (MSSM): + +

4 What is electroweak baryogenesis and how does it work?

5 Electroweak Baryogenesis Picture We want to explain 95% C.L. PDG Dunkley et al [WMAP5] based on dynamics during the electroweak phase transition. Sakharov conditions: 1. Baryon number violation Electroweak sphalerons 2. C- and CP-violation 3. Departure from thermal equilibrium complex phases 1st order phase transition

6 Electroweak Baryogenesis Picture First order electroweak phase transition during the early universe V( ) Higgs potential T > T c T = T c T =0 High T: EW symmetry restored from thermal corrections to Higgs potential Low T: EW symmetry broken At critical temp T c, degenerate minima. Just below T c, quantum tunneling from to bubble nucleation!

7 Electroweak Baryogenesis Picture Cohen, Kaplan, Nelson, ; Huet, Nelson, 1996 CP moving bubble wall diffusion Three Steps: 1. Nucleation and expansion of bubbles of broken EW symmetry 2. CP-violating interactions at bubble wall induces charge density, diffusing outside bubble 3. Sphalerons convert LH asymmetry into B asymmetry Quark number density electroweak sphaleron

8 Electroweak Baryogenesis Picture Cohen, Kaplan, Nelson, ; Huet, Nelson, 1996 CP moving bubble wall Three Steps: 1. Nucleation and expansion of bubbles of broken EW symmetry 2. CP-violating interactions at bubble wall induces charge density, diffusing outside bubble 4. Baryon asymmetry captured by expanding 3. Sphalerons bubble convert LH asymmetry into B asymmetry diffusion Quark number density electroweak sphaleron

9 Requirements for electroweak baryogenesis to work Given a model of electroweak symmetry breaking (e.g. the standard model), what is required? Two requirements: 1. A strong first-order electroweak phase transition 2. Sufficient CP-violation to explain observed n B Not satisfied in the SM May be satisfied in the MSSM, but only in one, small, very special region of parameter space

10 electroweak baryogenesis requirements Requirement #1: a strong 1st-order phase transition Need EW sphalerons to be quenched after electroweak symmetry breaking, or else have wash out of n B

11 electroweak baryogenesis requirements Quark number density

12 Wash out (i.e. what we don t t want to happen) Quark number density Wash out If EW sphalerons still active after symmetry breaking

13 electroweak baryogenesis requirements Requirement #1: a strong 1st-order phase transition Need EW sphalerons to be quenched after electroweak symmetry breaking, or else have wash out of n B Weak sphaleron rate: Unbroken EW symmetry Broken EW symmetry

14 electroweak baryogenesis requirements Requirement #1: a strong 1st-order phase transition Higgs potential V( ) T > T c T = T c T =0 Calculate finite T effective potential No wash-out of n B requires

15 Standard Model electroweak baryogenesis Requirement #1: a strong 1st-order phase transition In the SM, for m h > 114 GeV A strong, first-order EW phase transition does not occur in the SM

16 MSSM electroweak baryogenesis Requirement #1: a strong 1st-order phase transition Need new light bosons with large coupling to Higgs: top squarks!

17 MSSM electroweak baryogenesis Requirement #1: a strong 1st-order phase transition Carena, Nardini, Quiros, Wagner, 2008 LH stop m=500 TeV LH stop m=8000 TeV Parameter space consistent with 1. Experimental searches for stop/higgs 2. No spontaneous breaking of SU(3) color 3. Strong 1 st order EW phase transition

18 MSSM electroweak baryogenesis Cost of this parameter window: Carena, Nardini, Quiros, Wagner, Large hierarchy in MSSM spectrum RH stop < 125 GeV, charginos, neutralinos m < 300 GeV All other squarks and sleptons very heavy (m > 6.5 TeV) 2. The EW vacuum is metastable EW vacuum Color-breaking (CB) vacuum tunneling? Universe nucleates to EW vacuum before CB vacuum We are safe from decay through quantum tunneling

19 MSSM electroweak baryogenesis Light RH stop at the LHC Observation of direct decay difficult: Missing energy + low energy QCD

20 MSSM electroweak baryogenesis Light RH stop at the LHC Indirect detection: Menon, Morrissey Light RH stop modifies Higgs production and decay rates 2 BR( ) Constructive: σ enhanced for light RH stop 2 Destructive: BR suppressed for light RH stop

21 MSSM electroweak baryogenesis Light RH stop at the LHC Indirect detection: Menon, Morrissey Light RH stop modifies Higgs production and decay rates Total rate: gg -> h -> γγ X BR( ) 10-20% uncertainty on rate with 300 fb -1 Zeppenfeld 2002

22 electroweak baryogenesis requirements Requirement #2: sufficient CP-violation Need to have sufficient CP-violation to produce the observed baryon asymmetry 1. Take V eff and solve for bubble solutions : the space-time dependent Higgs vev during phase transition 2. Derive and solve Boltzmann equations for dynamics of particles in presence of bubbles 3. Calculate total # left-handed quarks and leptons General rule of thumb: CP-violating phases in a sector whose particles have large couplings to Higgs bosons

23 Boltzmann equations CP-violating source CP-violating scattering of particles with bubble wall. Particles with largest couplings to Higgs give largest source S. Received most theoretical effort, but much discrepency Riotto, 1998 Lee et al, 2004 Carena et al 2000, 2002 Cline et al, 2001 Konstandin et al 2005, 2006

24 Boltzmann equations Diffusion Number density diffuses outside the bubble (Also diffuses inside the bubble, but gets quickly washed out) Cohen, et al Joyce, et al.

25 Boltzmann equations Interactions Particles interact with one another Scattering, absorption, decay, etc. Huet & Nelson, 1996 Joyce et al. Lee et al, 2006

26 Boltzmann equations Interactions Fast interactions: Γ X is large, enforces chemical equilibrium: Slow interactions: Γ X is small, can neglect from Boltzmann equations (Bjorn Garbrecht s talk tomorrow)

27 Boltzmann equations in MSSM Lee et al, 2006 Same phase gives rise to EDMs

28 MSSM electroweak baryogenesis Requirement #2: sufficient CP-violation Different EDMs are complementary in general For electroweak baryogenesis, electron EDM is most important Pospelov, Ritz, 2006 Can observed n B be generated by and be consistent with EDM searches? Yes, but just barely.

29 MSSM electroweak baryogenesis Requirement #2: sufficient CP-violation Need to make as large as possible. Need μ ~M 2, m A light. φ μ needed for observed n B Irreducible 2-loop EDM Lee et al, 2006

30 MSSM electroweak baryogenesis Requirement #2: sufficient CP-violation Need to make as large as possible. Need μ ~M 2, m A light. φ μ needed for observed n B φ μ > 1/40 Chung et al, 2008 Irreducible 2-loop EDM Lee et al, 2006 Caveat: φ μ ~ O(1) allowed if m A >> TeV. Still, Irr. 2-loop EDM with lightest Higgs will rule out this scenario for O(10) improvement in eedm. Carena, Nardini, Quiros, Wagner, 2008

31 MSSM electroweak baryogenesis Future eedm measurements can rule out EWB in the MSSM (even for our optimistic n B estimates)

32 MSSM baryogenesis conclusions Still viable, but only within very specific region of parameter space. 1. Lightest Higgs and RH stop masses: m < 125 GeV 2. Non-zero eedm within factor 10 of current limit

33 Electroweak baryogenesis beyond the MSSM

34 Suppose we have SUSY at the LHC, but MSSM baryogenesis ruled out. What next? Consider electroweak baryogenesis in extensions of the MSSM.

35 Next-to to-minimal supersymmetric standard model MSSM + gauge singlet field + + +

36 Next-to to-minimal supersymmetric standard model Why consider an extra singlet? 1. Solution to the μ problem in the MSSM EW symmetry breaking: } Higgs potential

37 Next-to to-minimal supersymmetric standard model Why consider an extra singlet? 2. Why not? Minimal=elegant=true bias for the MSSM may be based a selection principle. Nature may not be minimal (at least at the EW scale) e.g. the SM. All the fundamental particles discovered so far do not have bare masses because of symmetries of SM Extra singlet is a toy model for additional SUSY degree of freedom

38 Next-to-minimal supersymmetric standard model Superpotential NMSSM nmssm or MNSSM

39 Next-to-minimal supersymmetric standard model Superpotential Keep most general theory, see what is allowed for baryogenesis, and THEN try to solve the μ problem Huber, Schmidt, 2000 Ando, Ramsey-Musolf, ST

40 Requirements for electroweak baryogenesis to work Can they work in the NMSSM? Yes, pretty easy Two requirements: 1. A strong first-order electroweak phase transition 2. Sufficient CP-violation to explain observed n B O(10) new CP-violating phases, not strongly constrained by EDMs

41 Baryogenesis in the NMSSM For me, a work in progress (also see Thomas Konstandin s talk Wed) Two underappreciated points: 1. The important role of oblique parameters 2. Additional CP-violating sources that have not been considered

42 electroweak baryogenesis requirements Requirement #1: a strong 1st-order phase transition Huber, Schmidt, 2000 Singlet mass (NOT the NMSSM) SM + real singlet EW precision observables can have a HUGE impact on allowed parameter regions Profumo, Ramsey-Musolf, Shaughnessy Doublet mass

43 electroweak baryogenesis requirements Requirement #2: Sufficient CP-violation to explain observed n B

44 Conclusions Electroweak baryogenesis is almost ruled out in the MSSM Consider extended models