Higgs Maxwell Workshop Current Status and Future Prospects

Higgs Maxwell Workshop: Current Status and Future Prospects “Theory Forward Look” James Stirling Cambridge University Higgs-Maxwell 2009 1

• current issues and challenges • looking forwards to 2020 • … and briefly backwards to 1999 Note: only a brief and highly subjective survey! Higgs-Maxwell 2009 2

Standard Model ~10 -18 m D=4 6 quarks* (u, d, s, c, b, t) 6 leptons (e, , , e, , ) gauge bosons ( , W , Z, g) Higgs boson + supersymmetry? particle sparticle dark matter? bottom up + string, brane theory? M-Theory? top down *quarks and gluons confined in hadrons: baryons (p, n), mesons ( ) ~10 -35 m D=11? Higgs-Maxwell 2009 “Theory of Everything”? 3

particle physics the key questions • • What is the origin of mass? Is it the Higgs boson? – What is the origin of the matter-antimatter asymmetry in the universe? – • the good news: the answer is likely to be at or below the 1 Te. V scale CKM by itself cannot explain the cosmological asymmetry, therefore need to look for flavour , CP violation beyond the SM Is there unification of particles and forces including gravity? – ~1016 Ge. V, in simplest models, this will be at measurements at lower energies give hints mass and coupling LHC • What is the dark matter? And the dark energy? – LSP or axion or …? • What is the quantum theory of gravity? – • best candidate is (super)string theory, with extra dimensions and supersymmetry, but at what scale? What are the properties of neutrinos? – may also be a window on unification, matter asymmetry, … Higgs-Maxwell 2009 expts. 4

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the 3 pillars of the Standard Model MW = cos w MZ [ 1 + α F(mt, MH, SUSY, . . )+ …] I – CKM II – EW Higgs-Maxwell 2009 6

the 3 pillars of the Standard Model I – CKM II – EW Higgs-Maxwell 2009 7

III – QCD thrust@NNLO DGLAP HERASFWG S S(MZ)=0. 118± 0. 002 Gehrmann. De Ridder Gehrmann Glover Heinrich PDG 2008 Higgs-Maxwell 2009 8

(SM) Higgs production at LHC ar. Xiv: 0803. 1154 [hep-ph] small print! Higgs-Maxwell 2009 9

direct Higgs searches Tevatron excludes at 95% C. L. the production of a 170 Ge. V SM Higgs boson! Higgs-Maxwell 2009 10

supersymmetry The argument for Te. V scale supersymmetry: • • solves naturalness/hierarchy problem allows coupling constant unification predicts light Higgs mass provides candidate (LSP) for dark matter Problem: to say anything more quantitative requires model assumptions, e. g. masses, SUSY breaking mechanism, … and even the most general MSSM has > 100 free parameters! Hence phenomenological studies focus on “constrained, minimal” models etc. Higgs-Maxwell 2009 11

e. g. CMSSM five parameters: • tan = v 2/v 1 • m 0, the common scalar mass • m 1/2, the common gaugino mass • A 0, the common trilinear coupling • sign( ) = ± 1, Higgs potential parameter … at MGUT, then radiative corrections accelerator and non-accelerator experiments already provide reasonably strong constraints on models like CMSSM Higgs-Maxwell 2009 12

A 0=0 allowed by g - 2 WMAP cosmological constraint from DMh 2 excluded by b→s LSP = charged stau excluded by LEP Ellis Olive Santoso Spanos Higgs-Maxwell 2009 13

SUSY prospects for sparticle discovery at LHC Higgs-Maxwell 2009 14

alternatives to SUSY? Challenges for alternative theories for non-SUSY Te. V scale physics: • • • if based on strong dynamics, issues of theoretical consistency and predictivity strong EW precision constraints from experiment, need to avoid large corrections which would spoil agreement no compelling single obvious alternative different models can have similar phenomenology in general complexity of models fine-tuning of parameters Higgs-Maxwell 2009 15

Higgs or no Higgs… Randall-Sundrum I Holographic PNGB Higgsless Technicolour Little Higgs ? ? ? See for example, “Little Higgs, Non-standard Higgs, No Higgs and All That”, Hsin-Chia Cheng, ar. Xiv: 0710. 3407 [hep-ph] Higgs-Maxwell 2009 16

a Theory of Everything? String Theory: everything we want in one consistent framework… • Quantum Mechanics • Standard Model-like gauge theory • General Relativity • Cosmology (inflation) Bonus: new theoretical toolbox with applications Higgs-Maxwell 2009 to e. g. perturbative QCD calculations, …. 17

too much of a good thing? • consistent string theories require N=10 dimensions • but string unification is easier if one of these dimensions is • smaller than the GUT scale → ‘large extra dimension’ scenarios possibility of signatures at LHC: • • Kaluza-Klein excitations of gravitons missing energy leaking into extra dimensions microscopic short-lived black hole production … • but there appear to be an enormous number of models with SM-like behaviour → estimated 10500 4 D vacua! Higgs-Maxwell 2009 18

In fact, the 5 possible string theories are all thought to be related as different aspects of a single theory: M-theory Higgs-Maxwell 2009 19

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string model-building • classify all possible compactifications/constructions that give rise to a low-energy theory resembling as much as possible the SM or MSSM • if completely realistic models are found, this proves that string theory may be a unified theory of all particles and interactions • identify general patterns (e. g. symmetries, extra particle content etc. ) which could be present in large classes of realistic vacua • obtain, if possible, predictions that could be tested experimentally (e. g. SUSY-breaking MSSM soft terms, dark matter, . . ) • what information on possible string compactifications may be extracted from LHC data? • if only very few classes (if any) of compactifications were able to fit all experimental data, what other new testable predictions could be derived from these? ─ a formidable task! Higgs-Maxwell 2009 21

Luis Ibanez, ATM 08 Higgs-Maxwell 2009 22

Luis Ibanez, ATM 08 Higgs-Maxwell 2009 23

progress in theory calculations • driven by high-precision measurements at the LEP, SLC, Tevatron, HERA, … colliders, theorists have made corresponding progress in refining theoretical predictions • in practice – – gg→ttbb background only at LO, difficult to distinguish from signal precision electroweak precision p. QCD …and including BSM etc contributions in loops Higgs-Maxwell 2009 precision np. QCD on the lattice: key tool in e. g. flavour physics 24

precision p. QCD in the LHC era fine-tuned event simulation MCs, interfaced with NLO hard scattering ^ LO for any n-particle hard scattering final state few % precision on pdfs up to NNLO, ‘good enough’ in most cases NLO for a wide range of processes, esp. with multijets, interfaced with parton shower MCs NNLO for a restricted range of ‘quasi -inclusive’ processes supplemented by Nn. LL improvements, EW corrections, … Higgs-Maxwell 2009 25

recent progress… • on-shell LO tree-amplitudes, arbitrary # of external legs: automated brute force (MADGRAPH, …) or recursion (MHV-BCFW, . . ) – rough estimates of multiparticle scattering cross … sections, e. g. p + p →n jets + X • two-loops (NNLO), 4 legs – high-precision for Z, H, … inclusive cross sections at LHC etc. • one-loop (NLO), 5 legs – precision multiparticle scattering cross sections, especially LHC backgrounds involving W, Z, jets, top, … Higgs-Maxwell 2009 26

the impact of NNLO … Anastasiou, Dixon, Melnikov, Petriello, 2004 Higgs-Maxwell 2009 27

progress in one-loop calculations • ~1948 (Schwinger) electron anomalous magnetic moment • ~2008 (Bern, Dixon, Kosower; Dixon, Kunszt, Signer; Campbell, Ellis; Febres, Cordero, Reina , Wackeroth) Higgs-Maxwell 2009 28

feynman diagrams complexity… consider Passarino-Veltmann reduction Higgs-Maxwell 2009 ! 29

5 legs generally OK > 5 legs ? ? ? Higgs-Maxwell 2009 30

recent one-loop progress…* • pp→ WW + 2 j via VBF Jager, Oleari, Zeppenfeld, Bozzi • pp→ WW + 1 j Campbell, Ellis, Zanderighi; Dittmaier, Kallweit, Uwer • pp → H + 2 j Campbell, Ellis, Zanderighi; Ciccolini, Denner, Dittmaier • pp → ZZZ Lazopoulos, Petriello, Melnikov • pp → WWZ Hankele, Zeppenfeld • pp → VVV Binoth, Ossola, Papadopoulos, Pittau • pp → tt. H, tt. Z Lazopoulos, Petriello, Melnikov, Mc. Elmurry • pp → Wbb, Zbb Febres Cordero, Reina, Wackeroth • pp → t t + 1 j Dittmaier, Uwer, Weinzierl • pp → t t + bb (qqbar only) Denner, Bredenstein, Dittmaier, Pozzorini • uu~ → ss~cc~ Binoth, Heinrich et al *relevant for LHC Higgs-Maxwell 2009 31

Perhaps the most important recent development has been the appearance of automated programmes for one-loop, multi-leg amplitudes, either based on • traditional or numerical Feynman approaches (Golem 95, …) • on-shell methods based on unitarity method + on-shell recursion (Black. Hat, Cut. Tools, Rocket, …) real hope of addressing all the experimenters’ wishlist! See for example the “NLO multileg working group: summary report” at the Workshop "Physics at Te. V Colliders", Les Houches, 2007, ar. Xiv: 0803. 0494 [hep-ph] with contributors: Bern, Bernicot, Binoth, Boudjema, Britto, Campbell, Czakon, Denner, Dissertori, Dittmaier, Dixon, Duplancic, Ellis, Frederix, Gehrmann-De Ridder, Giele, Glover, Guillet, Heinrich, Kallweit, Karg, Kauer, Kosower, Krauss, Kunszt, Le, Mastrolia, Mitov, Moch, Odaka, Ossola, Papadopoulos, Pilon, Pittau, Reiter, Sanguinetti, Schumann, Schwinn, Skands, Soper, Stenzel, Uwer, Weinzierl, Zanderighi (Durham-Edinburgh-Glasgow in red) Higgs-Maxwellcontributors 2009 32

interfacing Nn. LO and parton showers + MC@NLO POWHEG … Benefits of both: Nn. LO PS correct overall rate, hard scattering kinematics, reduced scale dep. complete event picture, correct treatment of collinear logs to all orders Example: MC@NLO Frixione, Webber www. hep. phy. cam. ac. uk/theory/webber/MCat. NLO/ processes include: pp WW, WZ, ZZ, bb, tt, t, t. W, H, W, Z/ , HW/Z Higgs-Maxwell 2009 p. T distribution of tt at Tevatron 33

pdfs @ LHC • most new physics samples pdfs in a region of x where they are already well known • low-mass forward production (e. g. Drell-Yan) might provide new information on small-x partons SUSY, Higgs, W, Z, … * Higgs-Maxwell 2009 see e. g. Martin 34 et al, ar. Xiv: 0901. 002 [hep-ph]

back in 1999 … Burton Richter, summarising the 1999 Lepton-Photon Conference: • • • experimenters (and phenomenologists) need to be more concerned about systematic errors and the tails on errordistribution functions experimenters should learn more theory all theorists should have a required course in statistics before receiving their Ph. D we all hope for new things from LEP 2 and the Tevatron, although the chances seem small we have big hopes for B-factories – the SM’s CPviolation is not enough and new directions may become clear from the factories neutrino physics is in ferment: more data should help make things clear but it will take 4 -5 years Higgs-Maxwell 2009 35

• • • LHC starts up in 2005 and we all hope to find out what is beyond our SM an e+e- collider of 0. 5 --1 Te. V is a necessary companion to the LHC; it will only come about if we all get behind it and push it as an international and regional program non-accelerator experiments in space and on the ground will be of increasing importance; the HEP community should not be too parochial string theorists are doing great things – I hope they justify or eliminate supersymmetry and think up an experimental test there is an exciting future: the work will be difficult, expensive and rewarding… the young generation, with support from governments, can and will do it. Higgs-Maxwell 2009 36

looking forward to 2020… • what will we be working on? ! WJS 2009 Higgs-Maxwell 2009 37

decreasing likelihood looking forward to 2020… • • • the UK theory community will be strong and active there will be a significant improvement in our ability to perform hard calculations in perturbative field theory the LHC will have collected a large amount of data at 14 Te. V the Higgs boson will be discovered at the LHC supersymmetry will be discovered at the LHC … and we will know the origin of the dark matter we will understand the matter-antimatter asymmetry in the Universe we will understand the origin of the “dark energy” string theory will constrain the many parameters of the SM and SUSY large extra dimensions will be discovered at the LHC will discover something completely unexpected Higgs-Maxwell 2009 38

c b W, Z 1970 1980 t 1990 H, SUSY, ED, …? 2000 2010 2020 The End! Higgs-Maxwell 2009 39