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## MOTIVAZIONI PER COLLIDER ADRONICI DOPO L’LHC: DALL’SLHC AL VLHC

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**MOTIVAZIONI PER COLLIDER ADRONICI DOPO L’LHC: DALL’SLHC**AL VLHC Padova, 19 Nov 2003 G.F. Giudice CERN R. Brock (EXP Fermilab) C. Hill (TH Fermilab) P. Sphicas (EXP Cern) G. Giudice (TH Cern)**LHC**Well-motivated energy range • Find the Higgs • Find the physics ultimately responsible for EW breaking**~ 2 GCHF**300-450 MCHF (incluso 70 MCHF di Linac4, ma senza rivelatori); 500 MCHF per SPL**Stage-2 VLHC Conclusions**• The Stage 2 VLHC can reach 200 TeV and 2x1034 or more in the 233 km tunnel. • A large-circumference ring is a great advantage for the high-energy Stage-2 collider. A small-circumference high-energy VLHC may not be realistic. • There is the need for magnet and vacuum R&D to demonstrate feasibility and to reduce cost. • This R&D will not be easy, will not be quick, and will not be cheap.**Underground Construction**• Three orientations chosen to get representative geological samples of sites near Fermilab. • South site samples many geologic strata and the Sandwich fault. • One north site is flat and goes through many strata. • Other north site is tipped to stay entirely within the Galena-Platteville dolomite, and is very deep. • These are not selected sites – merely representative. • Cost of other sites can be built from data gained in these sites.**Desert, e.g. conventional susy need for precision**m < TeV measurements after LHC Multi-TeV linear collider? NEW THEORY New thresholds around 10 TeV need for energy increase to make next step of discoveries VLHC ? LHC is the machine to study the scale of EW breaking VLHC not meant to push new-physics limits by an order of magnitude, but to explore a well-motivated (after some LHC discoveries) energy region**DESERT**• Connection with GUT, strings, quantum gravity • Gauge-coupling unification • Neutrino masses • Suppression of proton decay and flavour violations • Setup for cosmology (inflation, baryogenesis) • NON DESERT • Low-scale string theory,… • Accelerated running, different sin2qW • nR in bulk • Different location of quarks and leptons in bulk • Low-scale inflation, EW baryogenesis**NON-DESERT SCENARIOS offer good motivations for explorations**with a √s ~ 100 TeV hadron collider • Need to test the theory well above the EW breaking scale • Existence of new thresholds in the 10 TeV region Not a systematic review, but some examples relevant to VLHC**Any short-distance scale < LSM-1 explained by geometry**GRAVITY IN EXTRA DIMENSIONS Fundamental scale at LSM FLAT Arkani Hamed-Dimopoulos-Dvali WARPED Randall-Sundrum**QUANTUM GRAVITY AT LHC**G.G.- Rattazzi - Wells Missing energy (flat) Resonances (warped) Graviton emission Contact interactions (loop dominates over tree if gravity is strong) G.G. - Strumia Higgs-radion mixing H**These processes are based on linearized gravity valid at**√s <<MD ~TeV • Suitable for LHC • VLHC can extend limits, but the motivations are weak VLHC can probe the region √s >>MD~TeV (only marginal at LHC) independent test, crucial to verify gravitational nature of new physics**TRANSPLANCKIAN REGIME**Planck length quantum-gravity scale classical gravity Schwarzschild radius same regime**b > RS**Non-perturbative, but calculable for b>>RS (weak gravitational field) Gravitational scattering: two-jet signal at hadron colliders G.G.-Rattazzi-Wells**At b<RS, no longer calculable**Strong indications for black-hole formation Giddings-Thomas, Dimopoulos-Landsberg b < RS At the LHC, limited space for transplanckian region and quantum-gravity pollution At the VLHC, perfect conditions**2-jets with large Minv and Dh Black holes**VLHC Semi-classical approximation Transplanckian QUANTUM GRAVITY Linearized gravity Cisplanckian LHC Jets + missing ET 2-leptons**- +**LEP1 Bounds on LLH LLH> 5-10TeV LEP2 MFV INVESTIGATING THE THEORY OF ELECTROWEAK BREAKING**LSM<1 TeV, LLH>5-10 TeV**“Little” hierarchy between LSM and LLH a • New physics at LSM is weakly interacting • No (sizable) tree-level contributions from new physics at LSM • Strongly-interacting physics can only occur at scales larger than LLH**t**~ t dmH2 = + H H PROBLEMA DELLA GERARCHIA controllo delle divergenze quadratiche alla massa dell’Higgs SUPERSIMMETRIA:**HIGGS AS PSEUDOGOLDSTONE BOSON**Gauge, Yukawa and self-interaction are large non-derivative couplings _ Violate global symmetry and introduce quadratic div.**ℒ1**ℒ1 ℒ2 H ℒ2 Arkani Hamed-Cohen-Georgi LITTLE HIGGS A less ambitious programme: Explain only little hierarchy At LSM new physics cancels one-loop power divergences “Collective breaking”: many (approximate) global symmetries preserve massless Goldstone boson**Realistic models are rather elaborate**Effectively, new particles at the scale f ~ LSM canceling (same-spin) SM one-loop divergences with couplings related by symmetry Typical spectrum: Vectorlike charge 2/3 quark Arkani Hamed-Cohen-Georgi-Katz-Nelson-Gregoire-Wacker-Low-Skiba-Smith-Kaplan-Schmaltz-Terning… Gauge bosons EW triplet + singlet Scalars (triplets ?)**Higgs/gauge unification as graviton/photon unification in**Kaluza-Klein gauge Higgs HIGGS AS EXTRA-DIM COMPONENT OF GAUGE FIELD AM = (Am,A5), A5g A5 +∂5L forbids m2A52 Correct Higgs quantum numbers by projecting out unwanted states with orbifold Yukawa couplings, quartic couplings without reintroducing quadratic divergences Csaki-Grojean-Murayama Burdman-Nomura Scrucca-Serone-Silvestrini Csaki-Grojean-Murayama-Pilo-Terning EW BROKEN BY BOUNDARY CONDITIONS?**Calculable description of EW breaking with strong dynamics**at 5-10 TeV New realizations of technicolour theories with new elements (extra dimensions, AdS/CFT correspondence) allowing some calculability “Little hierarchy” is satisfied LHC will discover weak physics at LSM New strong-dynamics thresholds at LLH within the reach of VLHC**P. Limon**• The most important requirement for the survival of HEP is worldwide cooperation resulting in a global strategy based on a visionary science roadmap. • Sell the science, not the instruments • Learn from the NASA strategy, in which the goals are truly large and visionary, and the instruments are missions along the way. • The parameters and schedule for a VLHC will depend on the timing and location of all other large facilities. The global plan should recognize these couplings. • If we ever want to build a VLHC, or any other very large facility, we need to have a vigorous R&D program now. • The R&D is very challenging, and the penalty for failure will be severe.**CONCLUSIONI**• Anni futuri cruciali per i nuovi progetti di alte energie • La fisica fondamentale puo’ difendere con orgoglio la sua missione • EXP • Un grande progetto negli USA necessario per la fisica delle particelle • R&D sui vari fronti deve proseguire • TH • Nuove strategie per capire la fisica della rottura EW • In scenari “non-desert”, forti motivazioni per una nuova scala a ~ 10 TeV VLHC