SFB 676 selected theory issues (with a broad brush)

Transcription

1 SFB 676 selected theory issues (with a broad brush) Leszek Motyka Hamburg University, Hamburg & Jagellonian University, Krakow Physics of HERA and goals of the Large Hadron Collider The Higgs boson Supersymmetry what why and how? Supersymmetry and cosmology

2 The Standard Model Matter: fermions - 3 families (generations) Interactions: bosons Electroweak part: photon, W, Z Strong interactions: gluons Missing particle: Higgs boson giving mass to all particles

3 DIS at HERA Electron proton scattering at large energies and large angles: Large momentum transfer Q - plays the role of the resolution scale Observed: cross sections e± (k) 27.5 GeV s = 318 GeV Proton (P) 920 GeV

4 Asymptotic freedom Due to quantum corrections the strong coupling decreases with increasing resolution: partons The other side: confinement of color

5 Parton distributions Partons change with resolution scale according to evolution equations. Important: gluons do self-mutliply Data + evolution equations permit for precise determinations and extrapolation of parton densities

6 The new collider experiment: LHC pp collisions at 14 TeV Goal: discovery of the Higgs boson and physics beyond SM Dynamics driven by strong interactions Quantum Chromodynamics Production of particles computable from theory

7 Factorisation in hard processes Cross section for production of heavy particles factorizes into measured proton structure (parton densities) and calculable hard subprocess cross section The simple factorized picture holds for inclusive cross sections Full description of events requires much more complex framework, e.g. description of jets and multiple interactions is necessary

8 SM Higgs boson mass Manifestations of Higgs boson presence: Direct production - mass resonance with suitable quantum numbers (LEP exclusion M > 114 GeV) or via quantum corrections then one relies on assumptions about couplings

9 Higgs boson at the LHC Cross sections for Higgs boson production at the LHC are know with good accuracy and large enough (cross section of 1pb should give more than 10k events / year) Problem: large background from other (strong) processes without Higgs boson production need for experimental cuts

10 Higgs boson signal Standard Model Higgs boson discovery at the LHC guaranteed... but not easy

11 Exclusive Higgs boson production Idea: reduce the background by choosing exclusive channel Problem: signal supressed by 10000, still OK Theory - challenging magneti c fi el d mai n det ect or be am si l i con detector 420 m di ffracti ve prot on

12 Shortcomings of the SM Surprising mass spread (0.1 ev GeV) Does not lead to Grand Unification Theory Problems with light Higgs boson Too many free parameters Possible resolution: Supersymmetry Fundamental symmetry between bosons and fermions Solves most problems of the SM and may be found at the LHC

13 Supersymmetry and GUT SUSY greatly improves unification of couplings SUSY provides natural solution of the hierarchy problem (that is the light Higgs boson) due to partial cancellation of quantum corrections

14 Minimal Superzoo

15 What do we know about SUSY? Constraints on sparticles from: symmetry connecting them with standard particles Direct searches and precision observables Cosmology and GUTs Decays of sparticles lead to striking experimental signatures Good chances to produce and observe sparticles at the LHC

16 Detour into Cosmology Consistent cosmological models require presence of so called dark matter to be distinguished from visible baryonic matter Dark matter interacts weakly on short scales but carries a lot of mass

17 Supernovea and Microwaves Supernovea standard candles tell that expansion of the Universe accelerates Correlations of CMB the Universe is flat

18 Strong evidence for dark matter and dark energy

19 Sparticles as dark matter Massive Stable (R-parity) or very long-lived Neutral Weakly interacting Candidates: neutralino, sneutrino, gravitino Constraints from leptogenesis and Big Bang nucleosynthesis Hopefully some insight will come from direct measurements at the LHC

20 Further questions Origin of the dark energy or of the cosmological constant? GUT theory and its relation to gravity? Quantum theory of space and time? Superstring theory?