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Status of the Standard Model and Beyond

LNF Spring School, May ’03. Status of the Standard Model and Beyond. G. Altarelli CERN/Roma Tre. The Standard Model. }. }. Electroweak. Strong. SU(3) colour symmetry is exact!. The EW symmetry is spont. broken down to U(1) Q. Higgs sector (???). Gauge Bosons. 8 gluons g A.

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Status of the Standard Model and Beyond

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  1. LNF Spring School, May ’03 Status of the Standard Model and Beyond G. Altarelli CERN/Roma Tre

  2. The Standard Model } } Electroweak Strong SU(3) colour symmetry is exact! The EW symmetry is spont. broken down to U(1)Q Higgs sector (???) Gauge Bosons 8 gluons gA W±, Z, g Matter fields: 3 generations of quarks (coloured) and leptons + 2 more replicas (???) mW, mZ~GF-1/2Fermi scale of mass(???)

  3. The EW theory: L = Lsymm + LHiggs A chiral theory: - with Lsymm: well tested (LEP, SLC, Tevatron…), LHiggs: ~ untested Rad. corr's -> mH≤193 GeV but no Higgs seen: mH>114.4 GeV; (mH=115 GeV ?) Only hint mW=mZcosqWdoublet Higgs LEP: 2.1s

  4. Overall the EW precision tests support the SM and a light Higgs. The c2 is reasonable but not perfect: 2/ndof=25.5/15 (4.4%) Note: includes NuTeV and APV [not (g-2)m Without NuTeV: (th. error questionable) 2/ndof=16.7/14 (27.3%) NuTeV APV

  5. [copied from Grunewald, Amsterdam ‘02 talk]

  6. [copied from Grunewald, Amsterdam ‘02 talk]

  7. My opinion: the NuTeV anomaly could simply arise from a large underestimation of the theoretical error •The QCD LO parton analysis is too crude to match the required accuracy •A small asymmetry in the momentum carried by s-s could have a large effect They claim to have measured this asymmetry from dimuons. But a LO analysis of s-s makes no sense and cannot be directly transplanted here (as*valence corrections are large and process dependent) •A tiny violation of isospin symmetry in parton distrib’s can also be important. S. Davidson, S. Forte, P. Gambino, N. Rius, A. Strumia

  8. Atomic Parity Violation (APV) •QW is an idealised pseudo-observable corresponding to the naïve value for a N neutron-Z proton nucleus •The theoretical ”best fit” value from ZFITTER is (QW)th = -72.880±0.003 •The “experimental” value contains a variety of QED and nuclear effects that keep changing all the time: Since the 2002 LEP EWWG fit (showing a 1.52s deviation) a new evaluation of the QED corrections led to Kuchiev, Flambaum ’02 Milstein et al ‘02 (QW)exp = -72.83±0.49 So in this very moment (winter ‘03) APV is OK!

  9. (g-2)m ~3s discrepancy shown by the BNL’02 data EW ~ 15.2±0.4 LO hadr ~ 683.1±6.2 NLO hadr ~ -10±0.6 Light-by-Light ~ 8±4 (was ~ -8.5±2.5) These units hadr. L by L

  10. Question Marks on EW Precision Tests •The measured values of sin2qeff from leptonic (ALR) and from hadronic (AbFB) asymmetries are ~3s away •The measured value of mW is somewhat high •The central value of mH (mH=83+50-33 GeV) from the fit is below the direct lower limit (mH≥114.4 GeV at 95%) [more so if sin2qeff is close to that from leptonic (ALR) asymm. mH < ~110 GeV] Chanowitz; GA, F. Caravaglios, G. Giudice, P. Gambino, G. Ridolfi Hints of new physics effects??

  11. [copied from Grunewald, Amsterdam ‘02 talk]

  12. Plot sin2qeff vs mH Exp. values are plotted at the mH point that better fits given mtexp

  13. Question Marks on EW Precision Tests •The measured values of sin2qeff from leptonic (ALR) and from hadronic (AbFB) asymmetries are ~3s away •The measured value of mW is somewhat high •The central value of mH (mH=83+50-33 GeV) from the fit is below the direct lower limit (mH≥114.4 GeV at 95%) [more so if sin2qeff is close to that from leptonic (ALR) asymm. mH < ~110 GeV] Chanowitz; GA, F. Caravaglios, G. Giudice, P. Gambino, G. Ridolfi Hints of new physics effects??

  14. Plot mW vs mH mW points to a light Higgs Like [sin2qeff]l

  15. New developments (winter ‘03) mW went down (ALEPH: -79 MeV). Still the central value points to mH~50 GeV Now: 80.426±0.034 Was: 80.449±0.034

  16. Question Marks on EW Precision Tests •The measured values of sin2qeff from leptonic (ALR) and from hadronic (AbFB) asymmetries are ~3s away •The measured value of mW is somewhat high •The central value of mH (mH=83+50-33 GeV) from the fit is below the direct lower limit (mH≥114.4 GeV at 95%) [more so if sin2qeff is close to that from leptonic (ALR) asymm. mH < ~110 GeV] Chanowitz; GA, F. Caravaglios, G. Giudice, P. Gambino, G. Ridolfi Hints of new physics effects??

  17. Sensitivities to mH The central value of mH would be even lower if not for AbFB One problem helpes the other: AbFB vs ALR cures the problem of ALR, mW clashing with mH>114.4 GeV AbFB ALR mW

  18. Some indicative fits Most important observables: mt, mW, Gl, Rb, as(mZ), a, sin2qeff Note: here 2001 data Taking sin2qeff from leptonic or hadronic asymmetries as separate inputs, [sin2qeff]l and [sin2qeff]h, with a-1QED=128.936±0.049 (BP’01) we obtain: c2/ndof=18.4/4, CL=0.001; mHcentral=100 GeV, mH≤ 212 GeV at 95% Taking sin2qeff from only hadronic asymm. [sin2qeff]h c2/ndof=15.3/3, CL=0.0016; Taking sin2qeff from only leptonic asymm. [sin2qeff]l c2/ndof=2.5/3, CL=0.33; mHcentral=42 GeV, mH≤ 109 GeV at 95% Much better c2 but clash with direct limit!

  19. •It is not simple to explain the difference [sin2q]l vs [sin2q]h in terms of new physics. A modification of the Z->bb vertex (but Rb and Ab(SLD) look ~normal)? •Probably it arises from an experimental problem •Then it is very unfortunate because [sin2q]l vs [sin2q]h makes the interpretation of precision tests ambigous Choose [sin2q]h: bad c2 (clashes with mW, …) Choose [sin2q]l: good c2, but mH clashes with direct limit •In the last case, SUSY effects from light s-leptons, charginos and neutralinos, with moderately large tanb solve the mH problem and lead to a better fit of the data GA, F. Caravaglios, G. Giudice, P. Gambino, G. Ridolfi

  20. AbFB vs [sin2q]lept:New physics in Zbb vertex? Unlikely!!(but not impossible->) For b: From AbFB=0.0995±0.0017, using [sin2q]lept =0.23113±0.00020 or Ae=0.1501±0.0016, one obtains Ab=0.884±0.018 (Ab)SM - Ab = 0.052 ± 0.018 -> 2.9 s A large dgR needed (by about 30%!) But note: (Ab)SLD = 0.922±0.020, Rb=0.21644±0.00065 (RbSM~0.2157)

  21. Choudhury, Tait, Wagner dgR Ab(from AbSLD and AbFB) 0.992 gL(SM), 1.26 gR(SM) Rb SM dgL A possible model involves mixing of the b quark with a vectorlike doublet (w,c) with charges (-1/3, -4/3)

  22. •It is not simple to explain the difference [sin2q]l vs [sin2q]h in terms of new physics. A modification of the Z->bb vertex (but Rb and Ab(SLD) look ~normal)? •Probably it arises from an experimental problem •Then it is very unfortunate because [sin2q]l vs [sin2q]h makes the interpretation of precision tests ambigous Choose [sin2q]h: bad c2 (clashes with mW, …) Choose [sin2q]l: good c2, but mH clashes with direct limit •In the last case, SUSY effects from light s-leptons, charginos and neutralinos, with moderately large tanb solve the mH problem and lead to a better fit of the data GA, F. Caravaglios, G. Giudice, P. Gambino, G. Ridolfi

  23. EW DATA and New Physics For an analysis of the data beyond the SM we use the  formalism GA, R.Barbieri, F.Caravaglios, S. Jadach One introduces     such that: •Focus on pure weak rad. correct’s, i.e. vanish in limit of tree level SM + pure QED and/or QCD correct’s [a good first approximation to the data] Z,W •Are sensitive to vacuum pol. and Z->bb vertex corr.s (but also include non oblique terms)    b Z  b •Can be measured from the data with no reference to mt and mH (as opposed to S, T, U)

  24. One starts from a set of defining observables: Oi = mW/mZ, Gm, AmFB, Rb e1 e3 e2 eb Oi[ek] = Oi”Born”[1 + Aik ek + …] Oi”Born” includes pure QED and/or QCD corr’s. Aik is independent of mt and mH Assuming lepton universality: Gm, AmFB --> G, AFB To test lepton-hadron universality one can add GZ, sh, Rl to Gl etc.

  25. a: mW, Gl, Rb, [sin2q]l b: mW, Gl, Rb, GZ, sh, Rl, [sin2q]l c: mW, Gl, Rb, GZ, sh, Rl, [sin2q]l+[sin2q]h Note: 1s ellipses (39% cl)      OK, (mW), depends on sin2q for [sin2q]l (mH)

  26. MSSM: me-L = 96-300 GeV, mc-= 105-300 GeV, m = (-1)-(+1) TeV, tgb = 10, mh = 113 GeV, mA = me-R = mq =1 TeV ~ ~ ~

  27. s-leptons and s-n’s plus gauginos must be as light as possible given the present exp. bounds! ~ ~ In general in MSSM: m2e-=m2n+m2W|cos2b|

  28. Light charginos also help by making 2 corr’s larger than those of e3

  29. The sign of  is irrelevant here. But crucial for (g-2)m This model can also fit (g-2)m Approx. at large tgb: Exp. ~300 ~ am ~ 130 10-11(100 GeV/m)2 tgb

  30. tanb=40, A=0, sign(m)>0 Djouadi, Kneur, Moultaka m0 b->s-g (g-2)m m1/2

  31. The Standard Model works very well So, why not find the Higgs and declare particle physics solved? First, you have to find it! LHC Because of both: Conceptual problems • Quantum gravity • The hierarchy problem ••••• and experimental clues: • Coupling unification • Neutrino masses • Baryogenesis • Dark matter • Vacuum energy •••••

  32. Conceptual problems of the SM • No quantum gravity (MPl ~ 1019 GeV) Most clearly: • But a direct extrapolation of the SM leads directly to GUT's (MGUT ~ 1016 GeV) MGUT close to MPl • suggests unification with gravity as in superstring theories • poses the problem of the relation mW vs MGUT- MPl The hierarchy problem Can the SM be valid up to MGUT- MPl?? Not only it looks very unlikely, but the new physics must be near the weak scale!

  33. Indeed in SM mh, mW... are linear in L! e.g. the top loop (the most pressing): mh2=m2bare+dmh2 t h h The hierarchy problem demands new physics near the weak scale L~o(1TeV) L: scale of new physics beyond the SM • L>>mZ: the SM is so good at LEP • L~ few times GF-1/2 ~ o(1TeV) for a natural explanation of mh or mW Barbieri, Strumia The LEP Paradox: mh light, new physics must be so close but its effects are not directly visible

  34. Examples: SUSY • Supersymmetry: boson-fermion symm. exact (unrealistic): cancellation of dm2 approximate (possible): L ~ mSUSY-mord The most widely accepted • The Higgs is a yy condensate. No fund. scalars. But needs new very strong binding force: Lnew~103LQCD (technicolor). Strongly disfavoured by LEP • Large extra spacetime dimensions that bring MPl down to o(1TeV) Elegant and exciting. Does it work? • Models where extra symmetries allow mh only at 2 loops and non pert. regime starts at L~10 TeV "Little Higgs" models. Now extremely popular around Boston. Does it work?

  35. SUSY at the Fermi scale •Many theorists consider SUSY as established at MPl (superstring theory). •Why not try to use it also at low energy to fix some important SM problems. •Possible viable models exists: MSSM softly broken with gravity mediation or with gauge messengers or with anomaly mediation ••• • •Maximally rewarding for theorists • Degrees of freedom identified • Hamiltonian specified • Theory formulated, finite and computable up to MPl Unique! Fully compatible with, actually supported by GUT’s

  36. •Coupling unification:Precise matching of gauge couplings at MGUT fails in SM and is well compatible in SUSY SUSY fits with GUT's From aQED(mZ), sin2qW measured at LEP predict as(mZ) for unification (assuming desert) Non SUSY GUT's as(mZ)=0.073±0.002 SUSY GUT's as(mZ)=0.130±0.010 EXP: as(mZ)=0.119±0.003 Present world average Langacker, Polonski Dominant error: thresholds near MGUT • Proton decay:Far too fast without SUSY • MGUT ~ 1015GeV non SUSY ->1016GeV SUSY • Dominant decay: Higgsino exchange While GUT's and SUSY very well match, (best phenomenological hint for SUSY!) in technicolor , large extra dimensions, little higgs etc., there is no ground for GUT's

  37. GUT's Effective couplings depend on scale M a3(M) The log running is computable from spectrum a2(M) a1(M) MPl mW MGUT logM The large scale structure of particle physics: • SU(3) SU(2) U(1) unify at MGUT • at MPl: quantum gravity Superstring theory: a 10-dimensional non-local, unified theory of all interact’s x x r~10-33 cm The really fundamental level

  38. By now GUT's are part of our culture in particle physics • Unity of forces: unification of couplings • Unity of quarks and leptons different "directions" in G • B and L non conservation ->p-decay, baryogenesis, n masses • Family Q-numbers e.g. in SO(10) a whole family in 16 • Charge quantisation: Qd= -1/3-> -1/Ncolour • • • • • Most of us believe that Grand Unification must be a feature of the final theory!

  39. Neutrino masses point to MGUT, well fit into the SUSY picture and in GUT’s and have added considerable support to this idea.

  40. Solid evidence for n oscillations (+LSND unclear) Dm2atm ~ 3 10-3 eV2, Dm2sol ~ 7 10-5 eV2 (Dm2LSND ~ 1 eV2)

  41. First results from KamLAND •Solar oscill.’s confirmed on earth •Large angle sol. established Dm2~7.10-5 eV2, sin22q =1 •ne from reactors behave as ne from sun: Constraint on CPT models Best fit

  42. In summary for solar n's: After Kamland Before Kamland Dm2 (eV2) J. Bahcall et al Note the change of scale

  43. n Oscillations: Summary of Exp. Facts Homestake, Gallex, Sage, (Super)Kamiokande, Macro... GNO,K2K,.. New: after SNO, KAMLAND Atmospheric: Solar: Dm2atm ~ 3.10-3 eV2 sin22q23>0.92  solution selected Dm2~ 7 10-5 eV2, sin22q12~ 0.8 nm->ntdominant nm-> ne small (Chooz |U13|<~0.2) nm-> nsterile small ne->nm,ntdominant ne-> nsterile small Solar: true or false? MINIBOONE Solar:Sola LSND: nm-> ne,nsterile Dm2~ 1 eV2, sin22q~small CPT violation?

  44. n oscillations measureDm2. What is m? Dm2atm ~ 3 10-3 eV2; Dm2sun< Dm2atm •Direct limits (PDG '02) End-point tritium b decay(Mainz) m"ne" < 2.8 eV m"nm" < 170 KeV m"nt" < 18.2 MeV •Cosmology Wn h2~ Simi /94eV (h2~1/2) NEW!! WMAP Simi ≤ ~0.69 eV (95%) [Wn ≤ ~0.014] Any n mass ≤ 0.23-1eV Why n's so much lighter than quarks and leptons?

  45. New powerful cosmological limit Wnh2<0.076 mn<0.23 eV 3 degenerate n’s All i on the  scale  mass is very important! Combined WMAP+ 2dFGRS+ ACBAR+ CBI.. Finding 0nbb would also prove Majorana n’s

  46. Neutrino masses are really special! Log10m/eV t 10 b t c mt/(Dm2atm)1/2~1012 s 8  d u Massless n’s? • no nR • L conserved 6 e 4 2 Small nmasses? •nR very heavy • L not conserved  0 Upper limit on mn (Dm2atm)1/2 (D m2sol)1/2 -2 KamLAND

  47. A very natural and appealing explanation: n's are nearly massless because they are Majorana particles and get masses through L non conserving interactions suppressed by a large scale M ~ MGUT m2 m ≤ mt ~ v ~ 200 GeV M: scale of L non cons. mn ~ M Note: mn ~ (Dm2atm)1/2~ 0.05 eV m ~ v ~ 200 GeV M ~ 1015 GeV Neutrino masses are a probe of physics at MGUT !

  48. B and L conservation in SM: "Accidental" symmetries: in SM there is no dim.≤4 gauge invariant operator that violates B and/or L (if no nR, otherwise M nTR nR is dim-3 |DL|=2) The same is true in SUSY with R-parity cons. u + u -> e+ + d e. g. for the DB=DL= -1 transition all good quantum numbers are conserved: e.g. colour u~3, d~3 and 3x3 = 6+3 but l dcGu ecGu dim-6 M2 SU(5): p-> e+p0 Once nR is introduced (Dirac mass) large Majorana mass is naturally induced see-saw

  49. Baryogenesis nB/ng~10-10, nB <<nB Conditions for baryogenesis:(Sacharov '67) • B non conservation (obvious) • C, CP non conserv'n (B-B odd under C, CP) • No thermal equilib'm (n=exp[m-E/kT]; mB=mB, mB=mB by CPT If several phases of BG exist at different scales the asymm. created by one out-of-equilib'm phase could be erased in later equilib'm phases:BG at lowest scale best Possible epochs and mechanisms for BG: • At the weak scale in the SM Excluded • At the weak scale in the MSSM Disfavoured • Near the GUT scale via Leptogenesis Very attractive

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