1、Big-Bang Cosmology,Hitoshi Murayama 129A F2002 Semester,Introduction,Brief review of standard cosmology Big-Bang Nucleosynthesis Observational evidence for Dark Matter Observational evidence for Dark Energy Particle-physics implications Baryon Asymmetry,Brief review of standard cosmology,The Isotrop
2、ic Universe,The Cosmological Principle,Universe highly isotropic CMBR anisotropy O(105) Unless we occupy the “center of the Universe,” it must also be homogenous Isotropy and Homogeneity maximally symmetric space Flat Euclidean space R3 Closed three-sphere S3=SO(4)/SO(3) Open three-hyperbola SO(3,1)
3、/SO(3),Friedman Equation,Equation that governs expansion of the Universe k=1 (closed), k=1 (open), k=0 (flat) energy density r First law of thermodynamics: For flat Universe: Matter-dominated Universe Radiation-dominated Universe Vacuum-dominated Universe Temperature TR1,Energy budget of Universe,St
4、ars and galaxies are only 0.5% Neutrinos are 0.310% Rest of ordinary matter (electrons and protons) are 5% Dark Matter 30% Dark Energy 65% Anti-Matter 0% Higgs condensate 1062%?,Cosmic Microwave Background,Fossils of Hot Big Bang,When the temperature of Universe was higher than about 3000K, all atom
5、s (mostly hydrogen and helium) were ionized. Photons scatter off unbound electrons and could not stream freely: “opaque Universe.” Photons, atoms, electrons in thermal equilibrium. Once the temperature drops below 3000K, electrons are bound to atoms and photons travel freely, “recombination.” CMBR p
6、hotons from this era simply stretched by expansion R,Density Fluctuation,Completely homogeneous Universe would remain homogeneous no structure Need “seed” density fluctuation From observation, it must be nearly scale-invariant (constant in k space) Atoms also fall into gravitational potential due to
7、 the fluctuation and hence affects CMBR From COBE, we know dr/r105,Structure Formation,Jeans instability of self-gravitating system causes structure to form (there is no anti-gravity to stop it!) Needs initial seed density fluctuation Density fluctuation grows little in radiation- or vacuum-dominate
8、d Universe Density fluctuation grows linearly in matter-dominated Universe If only matter=baryons, had only time for 103 growth from 105: not enough time by now!,CMBR Anisotropy Probe to Cosmology,Evolution of the anisotropy in CMBR depends on the cosmological parameters: Wmatter, Wbaryon, WL, geome
9、try of Universe Evolution: acoustic oscillation between photon and baryon fluid Characteristic distance scale due to the causal contact Yard stick at the last rescattering surface Angular scale determines geometry,Acoustic Peaks Probe Cosmology,Wayne Hu,Max Tegmark,Polarization,Compton scattering po
10、larizes the photon in the polarization plane,Big-Bang Nucleosynthesis,Thermo-Nuclear Fusion in Early Universe,Best tested theory of Early Universe Baryon-to-photon ratio hnB/ng only parameter Neutron decay-anti-decay equilibrium ends when T1MeV, they decay until they are captured in deuterium Deuter
11、ium eventually form 3He, 4He, 7Li, etc Most of neutrons end up in 4He Astronomical observations may suffer from further chemical processing in stars,Data,“Crisis” the past few years Thuan-Izotov reevaluation of 4He abundance Sangalia D abundance probably false Now concordanceWBh2=0.0170.004(Thuan, I
12、zotov) CMB+LSS now consistentWB=0.020.037 (Tegmark, Zaldarriaga. Hamilton),Cosmic Microwave Background,Observational evidence for Dark Matter,Theoretical Arguments for Dark Matter,Spiral galaxies made of bulge+disk: unstable as a self-gravitating system need a (near) spherical halo With only baryons
13、 as matter, structure starts forming too late: we wont exist Matter-radiation equality too late Baryon density fluctuation doesnt grow until decoupling Need electrically neutral component,Galactic Dark Matter,Observe galaxy rotation curve using Doppler shifts in 21 cm line from hyperfine splitting,G
14、alactic Dark Matter,Luminous matter (stars)Wlumh=0.0020.006 Non-luminous matterWgal0.020.05 Only lower bound because we dont quite know how far the galaxy halos extend Could in principle be baryons Jupiters? Brown dwarfs?,MAssive Compact Halo Objects (MACHOs),Search for microlensing towards LMC, SMC
15、 When a “Jupiter” passes the line of sight, the background star brightens MACHO & EROS collab. Joint limit astro-ph/9803082 Need non-baryonic dark matter in halo Primordial BH of M ?,Dark Matter in Galaxy Clusters,Galaxies form clusters bound in a gravitational well Hydrogen gas in the well get heat
16、ed, emit X-ray Can determine baryon fraction of the clusterfBh3/2=0.0560.014 Combine with the BBNWmatterh1/2=0.380.07 Agrees with SZ, virial,Particle-physics implications,Neutrino Dark Matter?,Now that we seem to know neutrinos are massive, cant they be dark matter?Problem: neutrinos dont clump!,Col
17、d Dark Matter,Cold Dark Matter is not moving much Gets attracted by gravity,Neutrino Free Streaming,Neutrinos, on the other hand, move fast and tend to wipe out the density contrast.,Particle Dark Matter,Suppose an elementary particle is the Dark Matter WIMP (Weakly Interacting Massive Particle) Sta
18、ble heavy particle produced in early Universe, left-over from near-complete annihilationElectroweak scale the correct energy scale! We may produce Dark Matter in collider experiments.,Particle Dark Matter,Stable, TeV-scale particle, electrically neutral, only weakly interacting No such candidate in
19、the Standard Model Supersymmetry: (LSP) Lightest Supersymmetric Particle is a superpartner of a gauge boson in most models: “bino” a perfect candidate for WIMP But there are many other possibilities (techni-baryons, gravitino, axino, invisible axion, WIMPZILLAS, etc),Detection of Dark Matter,Direct
20、detection CDMS-II, Edelweiss, DAMA, GENIUS, etc,Indirect detection SuperK, AMANDA, ICECUBE, Antares, etc,complementary techniques are getting into the interesting region of parameter space,Particle Dark Matter,Stable, TeV-scale particle, electrically neutral, only weakly interacting No such candidat
21、e in the Standard Model Lightest Supersymmetric Particle (LSP): superpartner of a gauge boson in most models LSP a perfect candidate for WIMP,Detect Dark Matter to see it is there. Produce Dark Matter in accelerator experiments to see what it is.,CDMS-II,Observational evidence for Dark Energy,Type-I
22、A Supernovae,As bright as the host galaxy,Type-IA Supernovae,Type-IA Supernovae “standard candles” Brightness not quite standard, but correlated with the duration of the brightness curve Apparent brightness how far (“time”) Know redshift expansion since then,Type-IA Supernovae,Clear indication for “
23、cosmological constant” Can in principle be something else with negative pressure With w=p/r, Generically called “Dark Energy”,Cosmic Concordance,CMBR: flat UniverseW1 Cluster data etc: Wmatter0.3 SNIA:(WL2Wmatter)0.1 Good concordance among three,Constraint on Dark Energy,Data consistent with cosmolo
24、gical constant w=1,Dark Energy is an energy that doesnt thin much as the Universe expands!,Embarrassment with Dark Energy,A nave estimate of the cosmological constant in Quantum Field Theory: rLMPl410120 times observation The worst prediction in theoretical physics! People had argued that there must
25、 be some mechanism to set it zero But now it seems finite?,Quintessense?,Assume that there is a mechanism to set the cosmological constant exactly zero. The reason for a seemingly finite value is that we havent gotten there yet A scalar field is slowly rolling down the potential towards zero energy
26、But it has to be extremely light: 1042 GeV. Can we protect such a small mass against radiative corrections? It shouldnt mediate a “fifth force” either.,Cosmic Coincidence Problem,Why do we see matter and cosmological constant almost equal in amount? “Why Now” problem Actually a triple coincidence pr
27、oblem including the radiation If there is a fundamental reason for rL(TeV)2/MPl)4, coincidence natural,Arkani-Hamed, Hall, Kolda, HM,Amusing coincidence?,The dark energy density rL(2meV)4 The Large Angle MSW solution Dm2(510meV)2 Any deep reason behind it? Again, if there is a fundamental reason for
28、 rL(TeV)2/MPl)4, and using seesaw mechanism mn(TeV)2/MPl , coincidence may not be an accident,What is the Dark Energy?,We have to measure w For example with a dedicated satellite experiment,SNAP,Baryogenesis,Baryon Asymmetry Early Universe,They basically have all annihilated away except a tiny diffe
29、rence between them,10,000,000,001,10,000,000,000,Baryon Asymmetry Current Universe,They basically have all annihilated away except a tiny difference between them,1,us,Sakharovs Conditions for Baryogenesis,Necessary requirements for baryogenesis: Baryon number violation CP violation Non-equilibrium G
30、(DB0) G(DB0) Possible new consequences in Proton decay CP violation,Original GUT Baryogenesis,GUT necessarily breaks B. A GUT-scale particle X decays out-of-equilibrium with direct CP violationNow direct CP violation observed: e!But keeps BL0 “anomaly washout”,Out-of-Equilibrium Decay,When in therma
31、l equilibrium, the number density of a given particle is nem/T But once a particle is produced, they “hang out” until they decay net/t,Therefore, a long-lived particle (tMPl/m2) decay out of equilibrium,thermal,actual,T=m,t=t,Anomaly washout,Actually, SM violates B (but not BL). In Early Universe (T
32、 200GeV), W/Z are massless and fluctuate in W/Z plasma Energy levels for left-handed quarks/leptons fluctuate correspon-dingly,DL=DQ=DQ=DQ=DB=1 B=L=0,Two Main Directions,BL0 gets washed out at TTEW174GeV Electroweak Baryogenesis (Kuzmin, Rubakov, Shaposhnikov) Start with B=L=0 First-order phase tran
33、sition non-equilibrium Try to create BL0 Leptogenesis (Fukugita, Yanagida) Create L0 somehow from L-violation Anomaly partially converts L to B,Electroweak Baryogenesis,Electroweak Baryogenesis,Two big problems in the Standard Model First order phase transition requires mH60GeV Need new source of CP
34、 violation becauseJ detMu Mu, Md Md/TEW12 1020 1010 Minimal Supersymmetric Standard Model First order phase transition possible if New CP violating phasee.g., (Carena, Quiros, Wagner), (Cline, Joyce, Kainulainen),scenario,First order phase transition Different reflection probabilities for chargino s
35、pecies Chargino interaction with thermal bath produces an asymmetry in top quark Left-handed top quark asymmetry partially converted to lepton asymmetry via anomaly Remaining top quark asymmetry becomes baryon asymmetry,parameters,Chargino mass matrixRelative phaseunphysical if tanb Need fully mixed
36、 charginos M2(Cline, Joyce, Kainulainen),mass spectrum,Need with severe EDM constraints from e, n, Hg 1st, 2nd generation scalars 10 TeV To avoid LEP limit on lightest Higgs boson, need left-handed scalar top TeV Light right-handed scalar top, charginos cf. Carena, Quiros, Wagner claim enough EDM co
37、nstraint is weaker, but rest of phenomenology similar,Signals of Electroweak Baryogenesis,O(1) enhancements to Dmd, Dms with the same phase as in the SM Bs mixing vs lattice fBs2BBs Bd mixing vs Vtd from Vub and angles Find Higgs, stop, charginos (Tevatron?) Eventually need to measure the phase in t
38、he chargino sector at LC to establish it(HM, Pierce),Leptogenesis,60,Seesaw Mechanism Prerequisite for Leptogenesis,Why is neutrino mass so small? Need right-handed neutrinos to generate neutrino mass, but nR SM neutral,To obtain m3(Dm2atm)1/2, mDmt, M31015GeV (GUT!) Majorana neutrinos: violate lept
39、on number,Leptogenesis,You generate Lepton Asymmetry first. L gets converted to B via EW anomaly Fukugita-Yanagida: generate L from the direct CP violation in right-handed neutrino decay,Leptogenesis,Two generations enough for CP violation because of Majorana nature (choose 1 Pilaftsis) M11010 GeV O
40、K want supersymmetry,Can we prove it experimentally?,We studied this question at Snowmass2001 (Ellis, Gavela, Kayser, HM, Chang) Unfortunately, no: it is difficult to reconstruct relevant CP-violating phases from neutrino data But: we will probably believe it if 0nbb found CP violation found in neut
41、rino oscillation EW baryogenesis ruled out,CP Violation in Neutrino Oscillation,Plans to shoot neutrino beams over thousands of kilometers to see this,CP-violation may be observed in neutrino oscillation,Conclusions,Mounting evidence that non-baryonic Dark Matter and Dark Energy exist Immediately im
42、ply physics beyond the SM Dark Matter likely to be TeV-scale physics Search for Dark Matter via Collider experiment Direct Search (e.g., CDMS-II) Indirect Search via neutrinos (e.g., SuperK, ICECUBE) Dark Energy best probed by SNAP (LSST?),Conclusions (cont),The origin of matter anti-matter asymmetry has two major directions: Electroweak baryogenesis leptogenesis Leptogenesis definitely gaining momentum May not be able to prove it definitively, but we hope to have enough circumstantial evidences: 0nbb , CP violation in neutrino oscillation,
