The Matter-Antimatter Asymmetry and New Interactions

Transcription

1 The Matter-Antimatter Asymmetry and New Interactions The baryon (matter) asymmetry The Sakharov conditions Possible mechanisms A new very weak interaction

2 Recent Reviews M. Trodden, Electroweak baryogenesis, Rev. Mod. Phys. 71, 1463 (1999) [arxiv:hep-ph/ ]. W. Bernreuther, CP violation and baryogenesis, Lect. Notes Phys. 591, 237 (2002) [arxiv:hep-ph/ ]. M. Dine and A. Kusenko, The origin of the matter-antimatter asymmetry, arxiv:hep-ph/ A. D. Dolgov, Cosmological matter antimatter asymmetry and antimatter in the universe, arxiv:hep-ph/

3 The baryon (matter) asymmetry The baryon asymmetry: Matter and antimatter are (almost) symmetric, but our part of the universe involves matter only n B nγ (Big Bang Nucleosynthesis (BBN)), 6.14 ± (WMAP) n B 0 (small amounts consistent with secondary production)

4 BBN: ν e n e p and e + n ν e p keep n n /n p in equilibrium as long as it is rapid enough Freezeout at T 1 MeV, when Γ weak H n n n p = e (m n m p +µ ν e )/T 4 He (µ ν e ν e ν e asymmetry) 4 He mass fraction: Y p = 4n 4 He n H depends strongly on ξ e µ νe /T, weakly on η n B nγ Y 2 = D H depends on η (baryometer) n B nγ

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6 Independent determination of η from CMB n B nγ 6.14 ±

7 Angular Scale TT Cross Power Spectrum l(l+1)cl/2π (µk 2 ) Λ - CDM All Data WMAP CBI ACBAR Reionization TE Cross Power Spectrum (l+1)cl/2π (µk 2 ) Multipole moment (l)

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9 n B 0 (small amounts consistent with secondary production) For T > GeV, had n B n B n γ ; most B B pairs annihilated, leaving small baryon excess (Otherwise, n B = n B n γ ) Hence, need n B n B n γ for T > GeV Neutrality: n e n B ; n e + 0 (up to secondary production) Large neutrino-antineutrino asymmetry possible (important for BBN), but unlikely

10 (Barger, Kneller, Marfatia, PL, Steigman)

11 Origin: Where did the asymmetry come from? Prexisting asymmetry? Only if no inflation Domains of matter and antimatter? Absence of annihilation radiation implies separation > 10 Mpc (probably much stronger by CMB) Separation of symmetric plasma? No known mechanism. Causality constraints imply regions contain less than 10 6 M Domains by spontaneous CP breaking possible, but hard to avoid domain wall difficulties Baryogenesis: dynamical generation of asymmetry from initially symmetric conditions

12 The Sakharov conditions Basic ideas worked out by Sakharov in 1967, but no concrete model 1. Baryon number violation 2. CP violation: to distinguish baryons from antibaryons 3. Nonequilibrium of B-violating processes

13 1. Baryon number violation Processes involving black holes Standard model: tunneling between vacua with different B (Rate at T = 0 is e 4πsin2 θ W /α !) Grand unification (GUT): new interactions lead to proton decay

14 2. CP violation: to distinguish baryons from antibaryons Complex phases introduced by mass terms or interactions with spin-0 Need interference of two amplitudes Active programs in neutrino physics and heavy (b) quark decays to further explore CP violation

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16 3. Nonequilibrium of B-violating processes (or CPT violation due to expanding universe) Out of equilibrium decays of heavy particles (n e m/t ) Phase transitions Classical field dynamics (e.g., inflaton)

17 Grand Unification Pati-Salam, 73; Georgi-Glashow, 74 Strong, weak, electromagnetic unified at Q > M X M Z Simple group G M X SU(3) SU(2) U(1) Gravity not included (perhaps not ambitious enough) Couplings meet at M X GeV (w/o SUSY) (works much better with SUSY M X GeV)

18 q X = 4 3 q Y = 1 3 q, q, l, l unified (in same multiplets) Charge quantization (no U(1) factors) Proton decay mediated by new gauge bosons, e.g. p e + π 0 (other modes in SUSY GUTS) τ p M 4 X α 2 m 5 p 1030 yr for M X GeV (10 38 yr in SUSY, but faster p νk + )

19 Possible mechanisms for generating the asymmetry GUT baryogenesis (Yoshimura, 1979) Out of equilibrium decay of heavy (M > GeV) colored spin-0 particle H (grand unification partner of Higgs boson): Equal total rates (CPT conservation) but unequal partial rates (CP violation) Large enough asymmetry generated (for nonminimal model) B L conserved B = L H q q or ql; H qq or q l

20 Hard to combine with inflation unless very high reheating T Electroweak baryon number unsuppressed at T > 100 GeV (electroweak scale); wipes out asymmetry with B = L

21 Seesaw model of neutrino mass: mixing between light and heavy neutrino 10 0 KARMEN2 LS m light m2 D m heavy m D where m D is similar to quark or charged lepton mass, and m heavy GeV m 2 [ev 2 ] SMA Leptogenesis: (Fukugita, Yanagida) Successful for neutrino mass scales, but mixings problematic

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23 Out of equilibrium decays of N heavy l + Higgs N heavy l + Higgs created a lepton asymmetry Electroweak tunneling (actually thermal fluctucation) then converts some of the lepton asymmetry into a baryon asymmetry! Difficulties in supersymmetric version: gravitino problem suggests reheating temperature too low (unless N heavy produced nonthermally)

24 Electroweak baryogenesis Utilize the electroweak (B-violating) tunneling to generate the asymmetry at time of electroweak phase transition (Kuzmin, Rubakov, Shaposhnikov) Off the wall scenario (Cohen, Kaplan, Nelson) Strong first order phase transition from electroweak symmetry unbroken (massless W, Z, fermions) to broken phase (massive W, Z, fermions) proceeds by nucleation and 0 expansion of bubbles φ crit φ (Figures: W. Bernreuther, hep-ph/ ) V eff T = T 2 > T C T = T C T = T 1 < T C

25 CP violation by asymmetric reflection/transmission of quarks and leptons from the wall (e.g. quarks transmitted, antiquarks reflected) Electroweak B violation in unbroken phase outside wall Scenario requires strong first order transition, v(t c )/T c > and adequate CP violation in expanding bubble wall v Wall q q broken phase φ = 0 becomes our world unbroken phase q q CP Sph Γ B + L _~ 0 CP _ q _ q _ q _ q Sph Γ B + L >> H

26 Implementation of off the wall Standard model: no strong first order for M h violation too small > GeV; CP Minimal supersymmetric extension (MSSM): small parameter space for light Higgs and stop NMSSM (extension to include extra Higgs fields): can have strong first order but cosmological domain walls

27 A new very weak interaction? Extended gauge symmetry: (extra Z boson with mass TeV) (M. Cvetič, PL, et al; J. Erler, PL, T. Li) Expected in many string theories, grand unification, dynamical symmetry breaking Solves supersymmetric mass (µ) problem

28 Implications Exotics FCNC (especially in string models) rare B decays Non-standard Higgs masses, couplings (doublet-singlet mixing) Non-standard sparticle spectrum Neutrino mass, BBN, structure Enhanced possibility of EW baryogenesis

29 (Alberto Sirlin et al, 1987)

30 Typically M Z > GeV (Tevatron, LEP 2, WNC), θ Z Z < few 10 3 (Z-pole) (PL, Jens Erler) (cf., M W 80 GeV, M Z 91 GeV)

31 Electroweak Baryogenesis with an extra U(1) Generates adequate baryon asymmetry (J. Kang, PL, T. Li, T. Liu) First phase transition breaks extended gauge symmetry, second breaks SU(2) U(1) Strong first order phase transition Tree level CP breaking in Higgs sector Spontaneous CP breaking in Higgs sector for unbroken SU(2) U(1) New contributions to electric dipole moments very small

32 Transition at T c = 122 GeV, v(t c )/T c = 2.02

33 Conclusions The matter-antimatter asymmetry is one of the most important issues in particle physics and cosmology Several possible mechanisms: leptogenesis, electroweak baryogenesis, Affleck-Dine (decay of coherent (classical) scalar quark fields in supersymmetry) Heavy Z? Very well motivated in grand unification, strings, dynamical symmetry breaking Many new features, including enhanced possibility of electroweak baryogenesis, non-standard Higgs, contributions to rare B decays Should be observable at LHC, linear collider, possibily Tevatron if it exists